Earthquake Report: Sumatra!

There were two interesting earthquakes near the northern tip of the Island of Sumatra whilst I was off on a field trip with some HSU geology students. So, I think it prudent to review these earthquakes now.

These earthquakes happened along the convergent plate boundary that is formed by the oblique subduction of the India-Australia plate beneath the Sunda plate (part of Eurasia). The India-Australia plate has numerous north-south striking fracture zones that are reactivated as normal faults when they reach the subduction trench (where the subducting plate flexes, causing bending and extension in the upper part of the plate). These fracture zones are initially strike-slip (or transform) faults.

In 2004 there was a Great megathrust earthquake (M =9.0)that triggered a catastrophic and deadly trans-oceanic tsunami. Three months later, in 2005, there was a triggered Great earthquake (M = 8.6), which also caused a tsunami, but a much smaller one for various reasons. The 2004 M 9.2 earthquake provided some ground breaking (sorry for the pun) advancements in our knowledge of the earth. One new observation is that this earthquake ruptured into the mantle, previously thought to behave in a ductile manner, so not capable of brittle failure during an earthquake. Earthquake reports for some of the earthquakes discussed on this page are listed at the bottom of the page.

In 2012, there was a series of Great earthquakes to the west of these 2004 & 2005 subduction zone earthquakes in a region that experienced increased strain following the 2004/2005 earthquakes. These two earthquakes initially appeared to have ocurred on one of these fracture zone faults. However, upon further investigations (including various analyses and aftershock analysis), these two earthquakes were actually along faults ~orthogonal to the fracture zones. They were also very very deep, also probably occurring in the mantle! But, the crust is really thick here (possibly the thickest oceanic crust in the world, associated with the ninetyeast ridge. The 90E ridge is thickened because the I-A plate floated over a hotspot, causing it to be thicker). The larger of the two had a magnitude of M = 8.6, which is currently the largest strike-slip earthquake ever recorded on modern seismometers. Later, on 2016.03.02, there was another strike-slip fault in the I-A plate. Assistant Professor Wei Shengi (Earth Observatory of Singapore) derived some slip models for this earthquake and chose a slip model based on an East-West fault, making it a right lateral strike-slip earthquake (EOS, 2016).

    Here are the USGS websites for these two earthquakes.

  • 2017.03.17 02:51 UTC M 6.0
  • 2017.03.17 13:13 UTC M 5.5

There was an earthquake with a magnitude of M 6.0 that is just west of the tip of the megathrust fault, so is clearly in the India plate west of the subduction zone. This earthquake occurred on a strike-slip fault and is oriented similar to the 2012 and 2016 earthquakes. Like the 2016 earthquake, I am not sure which nodal plane is the fault plane and which is the auxiliary fault plane.

About 10 hours later, there was an M 5.5 earthquake that has a hypocentral depth of 41.2 km. This depth is fully consistent with the depth of the subduction zone megathrust fault here (Hayes et al., 2012). The moment tensor is consistent with a thrust fault and the fault plane is probably the northeast shallowly dipping nodal plane.

Below is my interpretive poster for this earthquake.

I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include the USGS moment tensors from these earthquakes.

  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. The moment tensor for the M 6.0 compares well with other Wharton Basin earthquakes from the past (e.g. 2012 & 2016). The triggered M 5.5 earthquake was instead possibly a subduction zone earthquake.
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I include the slab contours plotted (Hayes et al., 2012), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault. The hypocentral depth of the M 5.5 plots this close to the location of the fault as mapped by Hayes et al. (2012).

    I include some inset figures in the poster.

  • In the upper right corner I include a map showing the plate tectonics of the region as well as earthquake rupture regions for historic subduction zone earthquakes. Bathymetry and topography data come from the Smith and Sandwell (1997) Space Shuttle Radar Topography (SRTM) data set. The India-Australia plate subducts northeastward beneath the Sunda plate (part of Eurasia; sz–subduction zone). Orange vectors plot India plate movement relative to Sunda, and black vectors plot Australia relative to Sunda (global positioning system velocity based on Nuvel-1A; Bock et al., 2003; Subarya et al., 2006). Historic ruptures (Bilham, 2005; Malik et al., 2011) are plotted in grey, calendar years are in white. The 2004 and 2005 slip contours are shown orange and green, respectively (Chlieh et al., 2007, fig. 11 therein; Chlieh et al., 2008, figure 20 therein). Bengal and Nicobar fans cover structures of the India-Australia plate in the northern part of the map; are dashed black lines delimit their southern boundaries (Stow et al., 1990). The 2004 and 2005 earthquake focal mechanisms are plotted.
  • In the lower right corner is a Time Space plot of seismicity from this region for the period of 1973-2012 (Hayes et al., 2013). Great earthquakes are represented by yellow stars on the map time-space plot. The epicenters from the 2012 earthquakes are plotted on this map, so the figure caption is incorrect in their publication (can’t be perfect). Note how the rate of seismicity (prior to 2004 and 2010) at and north of the latitude of the 2007-09-12 M 8.4 subduction zone earthquake (4° S) is lower than south of this latitude. Of particular interest is that there is a slightly higher rate of seismicity between 4° and 8°. Could this inform us about whether or not there will be a Great earthquake in this region of the subduction zone?
  • In the upper left corner is a map that has the same earthquake patches as in the plate tectonic map. The base map is the Magnetic Anomaly data (Maus et al., 2009). These magnetic data is a compilation of data from ships, satellites, and airborne platforms. The first order patterns of dark and light gray represents the change in magnetic polarity through time. These show up on the map as horizontal/East-West bars in the oceanic crust west of Sumatra. These horizontal bars are also offset along North-South fracture zones (strike slip faults). Ninetyeast Ridge and the Investigator fracture zone are labeled. The Wharton Ridge is a spreading center that went inactive ~45 million years ago, which is part of the diffuse plate boundary between the India and Australia plates.
  • Below that map is a tectonic map of the Wharton Basin from Earth Observatory of Singapore (EOS, 2012). The Wharton Basin is the ocean basin east of the Ninetyeast Ridge west of the Sunda Megathrust. This map shows some earthquake rupture areas and the plate boundary faults (including the forearc sliver fault, the Sumatra fault), and North-South fracture zones in the Wharton Basin. The 2012 earthquakes and earthquake fault ruptures are shown in red stars and red dashed lines. Aftershocks are plotted as red oranges. Note how these help us define the faults that ruptured.
  • In the lower left corner are two maps that show seismicity from the 2012 earthquakes. On the left is a map showing the Satellite Gravity Anomaly. Variations in gravity anomaly data represent variations in earth material properties (things that change the spatial distribution of gravitational force). On the right is a map that shows the Magnetic Anomaly (like my map above). Epicenters and moment tensors for these earthquakes are plotted on both maps. The upper-right panel shows how the authors interpret how the faults slipped.


    Sumatra-Wharton Basin Eartquakes

  • Here is an interpretive map that shows the early 21st century Great Earthquakes in the Sumatra-Wharton Basin region. More interpretive maps can be found here.

Some of the Poster Figures

  • This is the magnetic anomaly map.

  • This is the historic earthquake map.

  • This is the EOS 2012 earthquake map.

  • Tectonic setting of the April 11, 2012 earthquake. Seafloor fault information from Dyment et al. (2007) and Jacob et al. (2009), Satish et al. (2011), Deplus et al. (1998).

  • This is the main figure from Hayes et al. (2013) from the Seismicity of the Earth series. There is a map with the slab contours and seismicity both colored vs. depth. There are also some cross sections of seismicity plotted, with locations shown on the map.

  • This is the map and Time-Space plot (Hayes et al. (2013).

  • These are the gravity and magnetic anomaly maps (Duputel et al., 2012). I include the figure caption below as a blockquote.

  • The 2012 Sumatra great earthquake sequence.(a) Map of the 2012 Sumatra great earthquake region. The 11 April 2012 mainshock can be decomposed into two subevents separated by about 200 km (green mechanisms and circles labeled I and II). The W phase and Global CMT (GCMT solution available in July 2012; Ekstrom et al.,2012.) single-point-source solutions for the mainshock (inset green mechanisms), the W phase solutions for the 10 January foreshock (blue mechanism), for the Mw 8.2 aftershock (yellow mechanism) and for the 5.8 < Mw < 8.2 aftershocks (red mechanisms) are shown. Yellow circles indicate the earthquake epicenters and magnitudes from the National Earthquake Information Center (NEIC)catalog between 1 January 1973 and 10 April 2012. Red circles show the events since the Mw 8.6 11 April 2012 earthquake through May 2012. White arrows indicate the direction of motion of the Australian plate relative to the Indian plate at about 13 mm/yr (De Mets et al.,2010). The red triangles on the globe indicate the locations of broadband stations RER and BFO. b) W phase waveforms recorded at station RER (epicentral distance delta = 43, azimuth phi = 235) and BFO(delta = 84, phi = 317) during the 11 Mw 8.6 April 2012 Sumatra earthquake. In each figure, the black trace is the vertical broad-band displacement data and the red trace is the very-long- period displacement data filtered in the 200–1000 s pass band. The W phase, body wave arrivals (P,PP, S,SS) and the Rayleigh wavetrain (R) are indicated.

  • These are the gravity and magnetic anomaly maps (Meng et al., 2012). I include the figure caption below as a blockquote.

  • Spatiotemporal distribution of HF radiation imaged by the (left) European and (right) Japanese networks. Colored circles and squares indicate the positions of primary and secondary peak HF radiation (from movies S1 and S2, respectively). Their size is scaled by beamforming amplitude, and their color indicates timing relative to hypocentral time (color scale in center). The secondary peaks of the MUSIC pseudo-spectrum are those at least 50% as large as the main peak in the same frame. The brown shaded circles in the right figure are the HF radiation peaks from the Mw 8.2 aftershock observed from Japan. The colored contours in the Sumatra subduction zone (left) represent the slip model of the 2004 Mw 9.1 Sumatra earthquake (28). The figure background is colored by the satellite gravity anomaly (left) in milligalileos (mgals) (color scale on bottom left) and the magnetic anomaly (right) in nanoteslas (color scale on bottom right). Black dots are the epicenters of the first day of aftershocks from the U.S. National Earthquake Information Center catalog. The big and small white stars indicate the hypocenter of the mainshock and Mw 8.2 aftershock. The moment tensors of the Mw 8.6 mainshock, Mw 8.2 aftershock, and double CMT solutions of the mainshock are shown as colored pink, yellow, red, and blue beach balls. The red line in the top left inset shows the boundary between the India (IN) and Sundaland (SU) plates (29). The patterned pink area is the diffuse deformation zone between the India and Australia plate. The red rectangular zone indicates the study area. The top right inset shows the interpreted fault planes (gray dashed lines) and rupture directions (colored arrows).

References:

  • Abercrombie, R.E., Antolik, M., Ekstrom, G., 2003. The June 2000 Mw 7.9 earthquakes south of Sumatra: Deformation in the India–Australia Plate. Journal of Geophysical Research 108, 16.
  • Bassin, C., Laske, G. and Masters, G., The Current Limits of Resolution for Surface Wave Tomography in North America, EOS Trans AGU, 81, F897, 2000.
  • Bock, Y., Prawirodirdjo, L., Genrich, J.F., Stevens, C.W., McCaffrey, R., Subarya, C., Puntodewo, S.S.O., Calais, E., 2003. Crustal motion in Indonesia from Global Positioning System measurements: Journal of Geophysical Research, v. 108, no. B8, 2367, doi: 10.1029/2001JB000324.
  • Bothara, J., Beetham, R.D., Brunston, D., Stannard, M., Brown, R., Hyland, C., Lewis, W., Miller, S., Sanders, R., Sulistio, Y., 2010. General observations of effects of the 30th September 2009 Padang earthquake, Indonesia. Bulletin of the New Zealand Society for Earthquake Engineering 43, 143-173.
  • Chlieh, M., Avouac, J.-P., Hjorleifsdottir, V., Song, T.-R.A., Ji, C., Sieh, K., Sladen, A., Hebert, H., Prawirodirdjo, L., Bock, Y., Galetzka, J., 2007. Coseismic Slip and Afterslip of the Great (Mw 9.15) Sumatra-Andaman Earthquake of 2004. Bulletin of the Seismological Society of America 97, S152-S173.
  • Chlieh, M., Avouac, J.P., Sieh, K., Natawidjaja, D.H., Galetzka, J., 2008. Heterogeneous coupling of the Sumatran megathrust constrained by geodetic and paleogeodetic measurements: Journal of Geophysical Research, v. 113, B05305, doi: 10.1029/2007JB004981.
  • DEPLUS, C. et al., 1998 – Direct evidence of active derormation in the eastern Indian oceanic plate, Geology.
  • DYMENT, J., CANDE, S.C. & SINGH, S., 2007 – Oceanic lithosphere subducting beneath the Sunda Trench: the Wharton Basin revisited. European Geosciences Union General Assembly, Vienna, 15-20/05.
  • Hayes, G. P., Wald, D. J., and Johnson, R. L., 2012. Slab1.0: A three-dimensional model of global subduction zone geometries in J. Geophys. Res., 117, B01302, doi:10.1029/2011JB008524.
  • Hayes, G.P., Bernardino, Melissa, Dannemann, Fransiska, Smoczyk, Gregory, Briggs, Richard, Benz, H.M., Furlong, K.P., and Villaseñor, Antonio, 2013. Seismicity of the Earth 1900–2012 Sumatra and vicinity: U.S. Geological Survey Open-File Report 2010–1083-L, scale 1:6,000,000, https://pubs.usgs.gov/of/2010/1083/l/.
  • JACOB, J., DYMENT, J., YATHEESH, V. & BHATTACHARYA, G.C., 2009 – Marine magnetic anomalies in the NE Indian Ocean: the Wharton and Central Indian basins revisited. European Geosciences Union General Assembly, Vienna, 19-24/04.
  • Ji, C., D.J. Wald, and D.V. Helmberger, Source description of the 1999 Hector Mine, California earthquake; Part I: Wavelet domain inversion theory and resolution analysis, Bull. Seism. Soc. Am., Vol 92, No. 4. pp. 1192-1207, 2002.
  • Ishii, M., Shearer, P.M., Houston, H., Vidale, J.E., 2005. Extent, duration and speed of the 2004 Sumatra-Andaman earthquake imaged by the Hi-Net array. Nature 435, 933.
  • Kanamori, H., Rivera, L., Lee, W.H.K., 2010. Historical seismograms for unravelling a mysterious earthquake: The 1907 Sumatra Earthquake. Geophysical Journal International 183, 358-374.
  • Konca, A.O., Avouac, J., Sladen, A., Meltzner, A.J., Sieh, K., Fang, P., Li, Z., Galetzka, J., Genrich, J., Chlieh, M., Natawidjaja, D.H., Bock, Y., Fielding, E.J., Ji, C., Helmberger, D., 2008. Partial Rupture of a Locked Patch of the Sumatra Megathrust During the 2007 Earthquake Sequence. Nature 456, 631-635.
  • Maus, S., et al., 2009. EMAG2: A 2–arc min resolution Earth Magnetic Anomaly Grid compiled from satellite, airborne, and marine magnetic measurements, Geochem. Geophys. Geosyst., 10, Q08005, doi:10.1029/2009GC002471.
  • Malik, J.N., Shishikura, M., Echigo, T., Ikeda, Y., Satake, K., Kayanne, H., Sawai, Y., Murty, C.V.R., Dikshit, D., 2011. Geologic evidence for two pre-2004 earthquakes during recent centuries near Port Blair, South Andaman Island, India: Geology, v. 39, p. 559-562.
  • Meltzner, A.J., Sieh, K., Chiang, H., Shen, C., Suwargadi, B.W., Natawidjaja, D.H., Philobosian, B., Briggs, R.W., Galetzka, J., 2010. Coral evidence for earthquake recurrence and an A.D. 1390–1455 cluster at the south end of the 2004 Aceh–Andaman rupture. Journal of Geophysical Research 115, 1-46.
  • Meng, L., Ampuero, J.-P., Stock, J., Duputel, Z., Luo, Y., and Tsai, V.C., 2012. Earthquake in a Maze: Compressional Rupture Branching During the 2012 Mw 8.6 Sumatra Earthquake in Science, v. 337, p. 724-726.
  • Natawidjaja, D.H., Sieh, K., Chlieh, M., Galetzka, J., Suwargadi, B., Cheng, H., Edwards, R.L., Avouac, J., Ward, S.N., 2006. Source parameters of the great Sumatran megathrust earthquakes of 1797 and 1833 inferred from coral microatolls. Journal of Geophysical Research 111, 37.
  • Newcomb, K.R., McCann, W.R., 1987. Seismic History and Seismotectonics of the Sunda Arc. Journal of Geophysical Research 92, 421-439.
  • Philibosian, B., Sieh, K., Natawidjaja, D.H., Chiang, H., Shen, C., Suwargadi, B., Hill, E.M., Edwards, R.L., 2012. An ancient shallow slip event on the Mentawai segment of the Sunda megathrust, Sumatra. Journal of Geophysical Research 117, 12.
  • Prawirodirdjo, P., McCaffrey,R., Chadwell, D., Bock, Y, and Subarya, C., 2010. Geodetic observations of an earthquake cycle at the Sumatra subduction zone: Role of interseismic strain segmentation, JOURNAL OF GEOPHYSICAL RESEARCH, v. 115, B03414, doi:10.1029/2008JB006139
  • Rivera, L., Sieh, K., Helmberger, D., Natawidjaja, D.H., 2002. A Comparative Study of the Sumatran Subduction-Zone Earthquakes of 1935 and 1984. BSSA 92, 1721-1736.
  • Shearer, P., and Burgmann, R., 2010. Lessons Learned from the 2004 Sumatra-Andaman Megathrust Rupture, Annu. Rev. Earth Planet. Sci. v. 38, pp. 103–31
  • SATISH C. S, CARTON H, CHAUHAN A.S., et al., 2011 – Extremely thin crust in the Indian Ocean possibly resulting from Plume-Ridge Interaction, Geophysical Journal International.
  • Sieh, K., Natawidjaja, D.H., Meltzner, A.J., Shen, C., Cheng, H., Li, K., Suwargadi, B.W., Galetzka, J., Philobosian, B., Edwards, R.L., 2008. Earthquake Supercycles Inferred from Sea-Level Changes Recorded in the Corals of West Sumatra. Science 322, 1674-1678.
  • Singh, S.C., Carton, H.L., Tapponnier, P, Hananto, N.D., Chauhan, A.P.S., Hartoyo, D., Bayly, M., Moeljopranoto, S., Bunting, T., Christie, P., Lubis, H., and Martin, J., 2008. Seismic evidence for broken oceanic crust in the 2004 Sumatra earthquake epicentral region, Nature Geoscience, v. 1, pp. 5.
  • Smith, W.H.F., Sandwell, D.T., 1997. Global seafloor topography from satellite altimetry and ship depth soundings: Science, v. 277, p. 1,957-1,962.
  • Sorensen, M.B., Atakan, K., Pulido, N., 2007. Simulated Strong Ground Motions for the Great M 9.3 Sumatra–Andaman Earthquake of 26 December 2004. BSSA 97, S139-S151.
  • Subarya, C., Chlieh, M., Prawirodirdjo, L., Avouac, J., Bock, Y., Sieh, K., Meltzner, A.J., Natawidjaja, D.H., McCaffrey, R., 2006. Plate-boundary deformation associated with the great Sumatra–Andaman earthquake: Nature, v. 440, p. 46-51.
  • Tolstoy, M., Bohnenstiehl, D.R., 2006. Hydroacoustic contributions to understanding the December 26th 2004 great Sumatra–Andaman Earthquake. Survey of Geophysics 27, 633-646.
  • Zhu, Lupei, and Donald V. Helmberger. “Advancement in source estimation techniques using broadband regional seismograms.” Bulletin of the Seismological Society of America 86.5 (1996): 1634-1641.

Posted in earthquake, sumatra, Transform

Earthquake Report: Cape Mendocino Region

We just had an interesting earthquake in the region of the Mendocino triple junction. Recent earthquakes in this region show different fault plane solutions, owing to complexity of this area.

In 1983 there was an earthquake ~10 km to the west of today’s earthquake which had a right-lateral oblique compressional focal mechanism. In 2015, there was an earthquake ~15 km to the east of today’s earthquake that also had a right-lateral strike-slip moment tensor. If today’s earthquake was oblique, it would be left-lateral extensional. Today’s earthquake is quite interesting. I will need to think about it further.

Below is my interpretive poster for this earthquake.

I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend).

  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. The moment tensor shows northwest-southeast compression. This is very strange. I initially thought it was a compressional earthquake (slightly oblique), but now interpret this as an extensional earthquake. I am struggling to explain this.
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I include the slab contours plotted (Hayes et al., 2012), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault.

    I include some inset figures in the poster.

  • In the upper right corner is a map of the Cascadia subduction zone (CSZ) and regional tectonic plate boundary faults. This is modified from several sources (Chaytor et al., 2004; Nelson et al., 2004)
  • Below the CSZ map is an illustration modified from Plafker (1972). This figure shows how a subduction zone deforms between (interseismic) and during (coseismic) earthquakes. Today’s earthquake did not occur along the CSZ, so did not produce crustal deformation like this. However, it is useful to know this when studying the CSZ.
  • In the upper left corner is a figure from Rollins and Stein (2010). In their paper they discuss how static coulomb stress changes from earthquakes may impart (or remove) stress from adjacent crust/faults. I also present their figure where they present seismic observations for the 1983.08.24 M 5.5 earthquake (Rollins and Stein list M 6.3).
  • In the lower left corner is a figure from Dengler et al. (1995) that shows focal mechanisms from earthquakes in this region, along the Mendocino fault. Today’s earthquake is near the 1994 earthquake.


  • Here is a map from Rollins and Stein, showing their interpretations of different historic earthquakes in the region. This was published in response to the January 2010 Gorda plate earthquake. The faults are from Chaytor et al. (2004). The 1980, 1992, 1994, 2005, and 2010 earthquakes are plotted and labeled. I did not mention the 2010 earthquake, but it most likely was just like 1980 and 2005, a left-lateral strike-slip earthquake on a northeast striking fault.

  • Tectonic configuration of the Gorda deformation zone and locations and source models for 1976–2010 M ≥ 5.9 earthquakes. Letters designate chronological order of earthquakes (Table 1 and Appendix A). Plate motion vectors relative to the Pacific Plate (gray arrows in main diagram) are from Wilson [1989], with Cande and Kent’s [1995] timescale correction.

  • Here is a large scale map of the 1983 earthquake. The mainshock epicenter is a black star and epicenters are denoted as white circles. This earthquake is interpreted to be strike slip oblique (compression).

  • Source models for earthquakes A and B, 26 November 1976, Mw = 6.7, and 8 November 1980, Mw = 7.3; C, 24 August 1983, Mw = 6.1 (poorly constrained); D, 10 September 1984, Mw = 6.6 (no model made); E, 31 July 1987, Mw = 6.0, “WS2008” refers to Waldhauser and Schaff ’s [2008] double‐difference catalog; F, 13 July 1991, Mw = 6.8 (poorly constrained); G, 16 August 1991 (2226 UTC), Mw = 6.3 (no model made), open circles are NCSN locations for 16 August 1991 (2226 UTC) to 17 August 1991 (2216 UTC); H, 17 August 1991 (1929 UTC),Mw = 6.1; I, 17 August 1991 (2217 UTC), Mw = 7.1 (no model made); J, 25 April 1992, Mw = 6.9, open circles are from Waldhauser and Schaff ’s [2008] earthquake locations for 25 April 1992 (1806 UTC) to 26 April 1992 (0741 UTC); K and L, 26 April 1992 (0741 UTC), Mw = 6.5 and 26 April 1992 (1118 UTC), Mw = 6.6 (both poorly constrained), seismicity shallower than 15 km was excluded so that shallow aftershocks of (J) do not crowd figure; M, 1 September 1994, Mw = 7.0; N and O, 19 February 1995, Mw = 6.6, and 16 March 2000, Mw = 5.9; P, Q, and R, 15 June 2005, Mw = 7.2, 17 June 2005, Mw = 6.6 (poorly constrained), and 28 November 2008, Mw = 5.9 (poorly constrained); S and T, 10 January 2010, M = 6.5, and 4 February 2010, Mw = 5.9; Z, 18 April 1906, M = 7.8.

  • In this map below, I label a number of other significant earthquakes in this Mendocino triple junction region. Another historic right-lateral earthquake on the Mendocino fault system was in 1994. There was a series of earthquakes possibly along the easternmost section of the Mendocino fault system in late January 2015, here is my post about that earthquake series.

There are three types of earthquakes, strike-slip, compressional (reverse or thrust, depending upon the dip of the fault), and extensional (normal). Here is are some animations of these three types of earthquake faults. Many of the earthquakes people are familiar with in the Mendocino triple junction region are either compressional or strike slip. The following three animations are from IRIS.

Strike Slip:

Compressional:

Extensional:

Here is a primer that helps people learn how to interpret focal mechanisms and moment tensors. Moment tensors are calculated differently from focal mechanisms, but the interpretation of their graphical solution is similar. This is from the USGS.

For more on the graphical representation of moment tensors and focal mechnisms, check this IRIS video out:

This figure shows what a transform plate boundary fault is. Looking down from outer space, the crust on either side of the fault moves side-by-side. When one is standing on the ground, on one side of the fault, looking across the fault as it moves… If the crust on the other side of the fault moves to the right, the fault is a “right lateral” strike slip fault. The Mendocino and San Andreas faults are right-lateral (dextral) strike-slip faults.

Here is an IRIS animation showing a transform plate boundary fault as it relates to spreading ridges.

    References

  • Atwater, B.F., Musumi-Rokkaku, S., Satake, K., Tsuju, Y., Eueda, K., and Yamaguchi, D.K., 2005. The Orphan Tsunami of 1700—Japanese Clues to a Parent Earthquake in North America, USGS Professional Paper 1707, USGS, Reston, VA, 144 pp.
  • Chaytor, J.D., Goldfinger, C., Dziak, R.P., and Fox, C.G., 2004. Active deformation of the Gorda plate: Constraining deformation models with new geophysical data: Geology v. 32, p. 353-356.
  • Dengler, L.A., Moley, K.M., McPherson, R.C., Pasyanos, M., Dewey, J.W., and Murray, M., 1995. The September 1, 1994 Mendocino Fault Earthquake, California Geology, Marc/April 1995, p. 43-53.
  • Geist, E.L. and Andrews D.J., 2000. Slip rates on San Francisco Bay area faults from anelastic deformation of the continental lithosphere, Journal of Geophysical Research, v. 105, no. B11, p. 25,543-25,552.
  • Irwin, W.P., 1990. Quaternary deformation, in Wallace, R.E. (ed.), 1990, The San Andreas Fault system, California: U.S. Geological Survey Professional Paper 1515, online at: http://pubs.usgs.gov/pp/1990/1515/
  • McLaughlin, R.J., Sarna-Wojcicki, A.M., Wagner, D.L., Fleck, R.J., Langenheim, V.E., Jachens, R.C., Clahan, K., and Allen, J.R., 2012. Evolution of the Rodgers Creek–Maacama right-lateral fault system and associated basins east of the northward-migrating Mendocino Triple Junction, northern California in Geosphere, v. 8, no. 2., p. 342-373.
  • Nelson, A.R., Asquith, A.C., and Grant, W.C., 2004. Great Earthquakes and Tsunamis of the Past 2000 Years at the Salmon River Estuary, Central Oregon Coast, USA: Bulletin of the Seismological Society of America, Vol. 94, No. 4, pp. 1276–1292
  • Rollins, J.C. and Stein, R.S., 2010. Coulomb stress interactions among M ≥ 5.9 earthquakes in the Gorda deformation zone and on the Mendocino Fault Zone, Cascadia subduction zone, and northern San Andreas Fault: Journal of Geophysical Research, v. 115, B12306, doi:10.1029/2009JB007117, 2010.
  • Stoffer, P.W., 2006, Where’s the San Andreas Fault? A guidebook to tracing the fault on public lands in the San Francisco Bay region: U.S. Geological Survey General Interest Publication 16, 123 p., online at http://pubs.usgs.gov/gip/2006/16/
  • Wallace, Robert E., ed., 1990, The San Andreas fault system, California: U.S. Geological Survey Professional Paper 1515, 283 p. [http://pubs.usgs.gov/pp/1988/1434/].

Posted in Uncategorized

Earthquake Report: New Britain

We just had an earthquake with a USGS magnitude of M 6.5 along the subduction zone formed by the convergence of the Solomon Sea plate on the south and the South Bismarck plate on the north.

Here is the USGS website for this M 6.5 earthquake.

Below is my interpretive poster for this earthquake.

I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I also include seismicity from 1917-2017 for earthquakes with magnitudes M ≥ 7.0. I include the USGS moment tensor from this earthquake.

  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. The moment tensor shows northeast-southwest compression, perpendicular to the convergence at this plate boundary.
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I include the slab contours plotted (Hayes et al., 2012), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault. The hypocentral depth plots this close to the location of the fault as mapped by Hayes et al. (2012). This earthquake appears to be in the upper plate based upon the hypocentral depth of <30 km and the slab contour of 60 km at this location, though this is unclear.

    I include some inset figures in the poster.

  • At the top of the poster are two figures from Oregon State University, which are based upon Hamilton (1979). “Tectonic microplates of the Melanesian region. Arrows show net plate motion relative to the Australian Plate.” To the right of the map is a cross section showing how the Solomon Sea plate is subducting beneath New Britain. This is from Johnson, 1976.
  • In the upper right corner are two figures from Holm and Richards (2013). Their paper discusses the back-arc spreading in the Bismarck Sea. They use hypocenter data to construct this 3-D model of the slab. On the right is a forecast of how the slab will be consumed along these subduction zones in the future.
  • In the lower right corner is a cross sectional view of the New Britain subduction zone for the past 10 million years (Holm and Richards, 2013). The approximate location of for this cross section is designated by an orange dashed line on the main map, with N and S labels.
  • In the upper left corner is a figure from Baldwin et al. (2012). This figure shows a series of cross sections along this convergent plate boundary from the Solomon Islands in the east to Papua New Guinea in the west. Cross section ‘C’ is the most representative for the earthquake today. I place the general location of the C-C’ section on the main map as an orange dashed line. I present the map and this figure again below, with their original captions.
  • In the lower left corner is the map from Baldwin et al. (2012) that goes along with the cross sections above.


Here is a map that adds epicenters from earthquakes that occurred between 1917 and 2017 for earthquakes of magnitudes M ≥ 7.0. Here is the kml that I used to make this map.


  • This is a map showing the seismicity of this region since 2000 A.D.

  • Earlier, I discussed seismicity from 2000-2015 here. The seismicity on the west of this region appears aligned with north-south shortening along the New Britain trench, while seismicity on the east of this region appears aligned with more east-west shortening. Here is a map that I put together where I show these two tectonic domains with the seismicity from this time period (today’s earthquakes are not plotted on this map, but one may see where they might plot).

  • Here is the generalized tectonic map of the region from Holm et al., 2015. I include the figure caption below as a blockquote.

  • Tectonic setting and mineral deposits of eastern Papua New Guinea and Solomon Islands. The modern arc setting related to formation of the mineral deposits comprises, from west to east, the West Bismarck arc, the New Britain arc, the Tabar-Lihir-Tanga-Feni Chain and the Solomon arc, associated with north-dipping subduction/underthrusting at the Ramu-Markham fault zone, New Britain trench and San Cristobal trench respectively. Arrows denote plate motion direction of the Australian and Pacific plates. Filled triangles denote active subduction. Outlined triangles denote slow or extinct subduction. NBP: North Bismarck plate; SBP: South Bismarck plate; AT: Adelbert Terrane; FT: Finisterre Terrane; RMF: Ramu-Markham fault zone; NBT: New Britain trench.

  • Here is the slab interpretation for the New Britain region from Holm and Richards, 2013. I include the figure caption below as a blockquote.

  • 3-D model of the Solomon slab comprising the subducted Solomon Sea plate, and associated crust of the Woodlark Basin and Australian plate subducted at the New Britain and San Cristobal trenches. Depth is in kilometres; the top surface of the slab is contoured at 20 km intervals from the Earth’s surface (black) to termination of slabrelated seismicity at approximately 550 km depth (light brown). Red line indicates the locations of the Ramu-Markham Fault (RMF)–New Britain trench (NBT)–San Cristobal trench (SCT); other major structures are removed for clarity; NB, New Britain; NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; TLTF, Tabar–Lihir–Tanga–Feni arc. See text for details.

  • Here are the forward models for the slab in the New Britain region from Holm and Richards, 2013. I include the figure caption below as a blockquote.

  • Forward tectonic reconstruction of progressive arc collision and accretion of New Britain to the Papua New Guinea margin. (a) Schematic forward reconstruction of New Britain relative to Papua New Guinea assuming continued northward motion of the Australian plate and clockwise rotation of the South Bismarck plate. (b) Cross-sections illustrate a conceptual interpretation of collision between New Britain and Papua New Guinea.

  • This map shows plate velocities and euler poles for different blocks. Note the counterclockwise motion of the plate that underlies the Solomon Sea (Baldwin et al., 2012). I include the figure caption below as a blockquote.

  • Tectonic maps of the New Guinea region. (a) Seismicity, volcanoes, and plate motion vectors. Plate motion vectors relative to the Australian plate are surface velocity models based on GPS data, fault slip rates, and earthquake focal mechanisms (UNAVCO, http://jules.unavco.org/Voyager/Earth). Earthquake data are sourced from the International Seismological Center EHB Bulletin (http://www.isc.ac.uk); data represent events from January 1994 through January 2009 with constrained focal depths. Background image is generated from http://www.geomapapp.org. Abbreviations: AB, Arafura Basin; AT, Aure Trough; AyT, Ayu Trough; BA, Banda arc; BSSL, Bismarck Sea seismic lineation; BH, Bird’s Head; BT, Banda Trench; BTFZ, Bewani-Torricelli fault zone; DD, Dayman Dome; DEI, D’Entrecasteaux Islands; FP, Fly Platform; GOP, Gulf of Papua; HP, Huon peninsula; LA, Louisiade Archipelago; LFZ, Lowlands fault zone; MaT, Manus Trench; ML, Mt. Lamington; MT, Mt. Trafalgar; MuT, Mussau Trough; MV, Mt. Victory; MTB, Mamberamo thrust belt; MVF, Managalase Plateau volcanic field; NBT, New Britain Trench; NBA, New Britain arc; NF, Nubara fault; NGT, New Guinea Trench; OJP, Ontong Java Plateau; OSF, Owen Stanley fault zone; PFTB, Papuan fold-and-thrust belt; PP, Papuan peninsula; PRi, Pocklington Rise; PT, Pocklington Trough; RMF, Ramu-Markham fault; SST, South Solomons Trench; SA, Solomon arc; SFZ, Sorong fault zone; ST, Seram Trench; TFZ, Tarera-Aiduna fault zone; TJ, AUS-WDKPAC triple junction; TL, Tasman line; TT, Trobriand Trough;WD, Weber Deep;WB, Woodlark Basin;WFTB, Western (Irian) fold-and-thrust belt; WR,Woodlark Rift; WRi, Woodlark Rise; WTB, Weyland thrust; YFZ, Yapen fault zone.White box indicates the location shown in Figure 3. (b) Map of plates, microplates, and tectonic blocks and elements of the New Guinea region. Tectonic elements modified after Hill & Hall (2003). Abbreviations: ADB, Adelbert block; AOB, April ultramafics; AUS, Australian plate; BHB, Bird’s Head block; CM, Cyclops Mountains; CWB, Cendrawasih block; CAR, Caroline microplate; EMD, Ertsberg Mining District; FA, Finisterre arc; IOB, Irian ophiolite belt; KBB, Kubor & Bena blocks (including Bena Bena terrane); LFTB, Lengguru fold-and-thrust belt; MA, Mapenduma anticline; MB, Mamberamo Basin block; MO, Marum ophiolite belt; MHS, Manus hotspot; NBS, North Bismarck plate; NGH, New Guinea highlands block; NNG, Northern New Guinea block; OKT, Ok Tedi mining district; PAC, Pacific plate; PIC, Porgera intrusive complex; PSP, Philippine Sea plate; PUB, Papuan Ultramafic Belt ophiolite; SB, Sepik Basin block; SDB, Sunda block; SBS, South Bismarck plate; SIB, Solomon Islands block; WP, Wandamen peninsula; WDK, Woodlark microplate; YQ, Yeleme quarries.

  • This figure incorporates cross sections and map views of various parts of the regional tectonics (Baldwin et al., 2012). The New Britain region is in the map near the A and B sections. I include the figure caption below as a blockquote.

  • Oblique block diagram of New Guinea from the northeast with schematic cross sections showing the present-day plate tectonic setting. Digital elevation model was generated from http://www.geomapapp.org. Oceanic crust in tectonic cross sections is shown by thick black-and-white hatched lines, with arrows indicating active subduction; thick gray-and-white hatched lines indicate uncertain former subduction. Continental crust, transitional continental crust, and arc-related crust are shown without pattern. Representative geologic cross sections across parts of slices C and D are marked with transparent red ovals and within slices B and E are shown by dotted lines. (i ) Cross section of the Papuan peninsula and D’Entrecasteaux Islands modified from Little et al. (2011), showing the obducted ophiolite belt due to collision of the Australian (AUS) plate with an arc in the Paleogene, with later Pliocene extension and exhumation to form the D’Entrecasteaux Islands. (ii ) Cross section of the Papuan peninsula after Davies & Jaques (1984) shows the Papuan ophiolite thrust over metamorphic rocks of AUS margin affinity. (iii ) Across the Papuan mainland, the cross section after Crowhurst et al. (1996) shows the obducted Marum ophiolite and complex folding and thrusting due to collision of the Melanesian arc (the Adelbert, Finisterre, and Huon blocks) in the Late Miocene to recent. (iv) Across the Bird’s Head, the cross section after Bailly et al. (2009) illustrates deformation in the Lengguru fold-and-thrust belt as a result of Late Miocene–Early Pliocene northeast-southwest shortening, followed by Late Pliocene–Quaternary extension. Abbreviations as in Figure 2, in addition to NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; (U)HP, (ultra)high-pressure.

References:

Posted in earthquake, education, geology, HSU, pacific, plate tectonics, subduction, tsunami

Earthquake Report: Banda Sea

Earlier this week there was a moderate earthquake along a strike-slip fault that appears to adjoin the Banda/Timor/Java Arc with New Guinea. This strike-slip fault appears to cross oblique to the subduction zone that forms the Timor Trench to the south and the Seram Trench to the north. Various researchers portray the faulting in this region differently. Given earthquake moment tensor and focal mechanism from the USGS, this earthquake supports the interpretation that this fault system is left-lateral (synistral) strike-slip. A focal mechanism from an earthquake in 1938 (magnitude M 8.5) provides evidence that is a little more confusing. But, this region is a complicated region.

UPDATE: 2017.03.05 (23:00 local time): Interesting, I was reading my tweet after Lila Lisle noticed a mistake. I fixed that, but later realized that the possible fault in the downgoing plate is not the Sorog fault, but a fault that might intersect with the Sorong fault. I did not delete the tweet since this mistake is a topic of conversation and not really a key part of the story.

Here is the USGS earthquake website for this M 5.5 earthquake.

Here are the USGS websites for the major earthquakes in this region from the past century.

Below is my interpretive poster for this earthquake.

I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I also include seismicity from 1917-2017 for earthquakes with magnitudes M ≥ 7.0. I show the fault plane solutions for some of these earthquakes.

  • moment tensors for 2005, 2012, and 2017 (USGS)
  • focal mechanisms for 1987 (USGS) and 1938 (Okal and Reymond, 2003)
  • The fault plane solutions for the 1963, 1987, 2005, and 2012 earthquakes are all very similar to the 2017 M 5.5. However, these earthquakes are form two depth “populations.” The 1963 and 1987 earthquakes are at ~65 km depth, while the 2005, 2012, and 2017 are between 150-200 km. There are some earthquakes that are much shallower depth eastward along this possibly strike-slip fault. Near where this fault comes on land at the base of the Bird’s Head in New Guinea, there are some earthquakes from the past couple of decades that also have strike-slip fault–plane solutions. The earthquake depths along this Sorong fault (Hall, 2011) appear to show that the Sorong fault is active beneath the Sunda plate. The 1938 earthquake may be the result of some form of strain partitioned faulting(?). Alternatively, these earthquakes may be unrelated to the Sorong fault. There may be some internal structure in the Australia plate that is interacting with the subduction zones or other faults (some preexisting structure that is optimally oriented to reactivate with the .
  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I include the slab contours plotted (Hayes et al., 2012), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault. The hypocentral depth plots this close to the location of the fault as mapped by Hayes et al. (2012).

    I include some inset figures in the poster.

  • In the upper left corner is a general tectonic map for this part of the world. I placed a green star in the location of this M 5.5 earthquake (Zahirovic et al., 2014).
  • In the upper right corner is a low-angle oblique view of the plate boundaries in the northern part of this region (Hall, 2011). The upper part of the diagram shows the opposing vergent subduction zones along that strike north-south along the Molucca Strait (Halmahera, Philippines). The lower panel shows the downgoing Australia plate along the Timor Trench and Seram Trench. Note the location of the Bird’s Head, the northwestern part of New Guinea. I have also labeled this region in the main map for comparison. The strike-slip fault at the northern boundary of New Guinea is the Sorong fault and this is labeled in this Hall (2011) figure.
  • Below the Hall (2011) figure is a figure from Baldwin et al. (2012) that shows the regional seismicity and faulting as they are related to different geologic types in New Guinea. I placed a green star in the location of this M 5.5 earthquake.
  • In the lower right corner is a part of the USGS Poster that reviews the seismicity of this region for the past century or so (Benz et a., 2011). The map shows seismicity with depth, along with some cross section locations. I place a green star at the location of this M 5.5 earthquake. I present three of the cross sections from this poster, A-A’, B-B’, and C-C.’ Of particular interest is the section B-B’ because this is placed near the M 5.5 earthquake. I have placed a green star that represents the hypocentral location on cross section B-B.’ The hypocentral depth suggests this M 5.5 earthquake is in the downgoing Australia plate slab.
  • In the lower left corner is a diagram showing the subducting Australia plate at the Java Trench (Yves Descatoire).
  • To the right of the Java Trench figure presents a detailed view of the faulting along the eastern Java and western Timor trenches (Hangesh and Whitney, 2016). They present evidence for oblique motion along the Timor trough. And present evidence for a backthrust on the northern side of Timor and the Indonesia islands east of Java.


  • Here is the map from Baldwin et al. (2012)

  • Tectonic maps of the New Guinea region. (a) Seismicity, volcanoes, and plate motion vectors. Plate motion vectors relative to the Australian plate are surface velocity models based on GPS data, fault slip rates, and earthquake focal mechanisms (UNAVCO, http://jules.unavco.org/Voyager/Earth). Earthquake data are sourced from the International Seismological Center EHB Bulletin (http://www.isc.ac.uk); data represent events from January 1994 through January 2009 with constrained focal depths. Background image is generated from http://www.geomapapp.org. Abbreviations: AB, Arafura Basin; AT, Aure Trough; AyT, Ayu Trough; BA, Banda arc; BSSL, Bismarck Sea seismic lineation; BH, Bird’s Head; BT, Banda Trench; BTFZ, Bewani-Torricelli fault zone; DD, Dayman Dome; DEI, D’Entrecasteaux Islands; FP, Fly Platform; GOP, Gulf of Papua; HP, Huon peninsula; LA, Louisiade Archipelago; LFZ, Lowlands fault zone; MaT, Manus Trench; ML, Mt. Lamington; MT, Mt. Trafalgar; MuT, Mussau Trough; MV, Mt. Victory; MTB, Mamberamo thrust belt; MVF, Managalase Plateau volcanic field; NBT, New Britain Trench; NBA, New Britain arc; NF, Nubara fault; NGT, New Guinea Trench; OJP, Ontong Java Plateau; OSF, Owen Stanley fault zone; PFTB, Papuan fold-and-thrust belt; PP, Papuan peninsula; PRi, Pocklington Rise; PT, Pocklington Trough; RMF, Ramu-Markham fault; SST, South Solomons Trench; SA, Solomon arc; SFZ, Sorong fault zone; ST, Seram Trench; TFZ, Tarera-Aiduna fault zone; TJ, AUS-WDKPAC triple junction; TL, Tasman line; TT, Trobriand Trough;WD, Weber Deep;WB, Woodlark Basin;WFTB, Western (Irian) fold-and-thrust belt; WR,Woodlark Rift; WRi, Woodlark Rise; WTB, Weyland thrust; YFZ, Yapen fault zone.White box indicates the location shown in Figure 3. (b) Map of plates, microplates, and tectonic blocks and elements of the New Guinea region. Tectonic elements modified after Hill & Hall (2003). Abbreviations: ADB, Adelbert block; AOB, April ultramafics; AUS, Australian plate; BHB, Bird’s Head block; CM, Cyclops Mountains; CWB, Cendrawasih block; CAR, Caroline microplate; EMD, Ertsberg Mining District; FA, Finisterre arc; IOB, Irian ophiolite belt; KBB, Kubor & Bena blocks (including Bena Bena terrane); LFTB, Lengguru fold-and-thrust belt; MA, Mapenduma anticline; MB, Mamberamo Basin block; MO, Marum ophiolite belt; MHS, Manus hotspot; NBS, North Bismarck plate; NGH, New Guinea highlands block; NNG, Northern New Guinea block; OKT, Ok Tedi mining district; PAC, Pacific plate; PIC, Porgera intrusive complex; PSP, Philippine Sea plate; PUB, Papuan Ultramafic Belt phiolite; SB, Sepik Basin block; SDB, Sunda block; SBS, South Bismarck plate; SIB, Solomon Islands block; WP, Wandamen p ninsula; WDK, Woodlark microplate; YQ, Yeleme quarries.

  • Here is the tectonic map from Hangesh and Whitney (2016)

  • Illustration of major tectonic elements in triple junction geometry: tectonic features labeled per Figure 1; seismicity from ISC-GEM catalog [Storchak et al., 2013]; faults in Savu basin from Rigg and Hall [2011] and Harris et al. [2009]. Purple line is edge of Australian continental basement and fore arc [Rigg and Hall, 2011]. Abbreviations: AR = Ashmore Reef; SR = Scott Reef; RS = Rowley Shoals; TCZ = Timor Collision Zone; ST = Savu thrust; SB = Savu Basin; TT = Timor thrust; WT =Wetar thrust; WASZ = Western Australia Shear Zone. Open arrows indicate relative direction of motion; solid arrows direction of vergence.

  • Here is the Audley (2011) cross section showing how the backthrust relates to the subduction zone beneath Timor. I include their figure caption in blockquote below.

  • Cartoon cross section of Timor today, (cf. Richardson & Blundell 1996, their BIRPS figs 3b, 4b & 7; and their fig. 6 gravity model 2 after Woodside et al. 1989; and Snyder et al. 1996 their fig. 6a). Dimensions of the filled 40 km deep present-day Timor Tectonic Collision Zone are based on BIRPS seismic, earthquake seismicity and gravity data all re-interpreted here from Richardson & Blundell (1996) and from Snyder et al. (1996). NB. The Bobonaro Melange, its broken formation and other facies are not indicated, but they are included with the Gondwana mega-sequence. Note defunct Banda Trench, now the Timor TCZ, filled with Australian continental crust and Asian nappes that occupy all space between Wetar Suture and the 2–3 km deep deformation front north of the axis of the Timor Trough. Note the much younger decollement D5 used exactly the same part of the Jurassic lithology of the Gondwana mega-sequence in the older D1 decollement that produced what appears to be much stronger deformation.

  • Here is a figure showing the regional geodetic motions (Bock et al., 2003). I include their figure caption below as a blockquote.

  • Topographic and tectonic map of the Indonesian archipelago and surrounding region. Labeled, shaded arrows show motion (NUVEL-1A model) of the first-named tectonic plate relative to the second. Solid arrows are velocity vectors derived from GPS surveys from 1991 through 2001, in ITRF2000. For clarity, only a few of the vectors for Sumatra are included. The detailed velocity field for Sumatra is shown in Figure 5. Velocity vector ellipses indicate 2-D 95% confidence levels based on the formal (white noise only) uncertainty estimates. NGT, New Guinea Trench; NST, North Sulawesi Trench; SF, Sumatran Fault; TAF, Tarera-Aiduna Fault. Bathymetry [Smith and Sandwell, 1997] in this and all subsequent figures contoured at 2 km intervals.

References:

  • Audley-Charles, M.G., 1986. Rates of Neogene and Quaternary tectonic movements in the Southern Banda Arc based on micropalaeontology in: Journal of fhe Geological Society, London, Vol. 143, 1986, pp. 161-175.
  • Audley-Charles, M.G., 2011. Tectonic post-collision processes in Timor, Hall, R., Cottam, M. A. &Wilson, M. E. J. (eds) The SE Asian Gateway: History and Tectonics of the Australia–Asia Collision. Geological Society, London, Special Publications, 355, 241–266.
  • Baldwin, S.L., Fitzgerald, P.G., and Webb, L.E., 2012. Tectonics of the New Guinea Region in Annu. Rev. Earth Planet. Sci., v. 41, p. 485-520.
  • Benz, H.M., Herman, Matthew, Tarr, A.C., Hayes, G.P., Furlong, K.P., Villaseñor, Antonio, Dart, R.L., and Rhea, Susan, 2011. Seismicity of the Earth 1900–2010 New Guinea and vicinity: U.S. Geological Survey Open-File Report 2010–1083-H, scale 1:8,000,000.
  • Hall, R., 2011. Australia-SE Asia collision: plate tectonics and crustal flow in Geological Society, London, Special Publications 2011; v. 355; p. 75-109 doi: 10.1144/SP355.5
  • Hangesh, J. and Whitney, B., 2014. Quaternary Reactivation of Australia’s Western Passive Margin: Inception of a New Plate Boundary? in: 5th International INQUA Meeting on Paleoseismology, Active Tectonics and Archeoseismology (PATA), 21-27 September 2014, Busan, Korea, 4 pp.
  • Hayes, G.P., Wald, D.J., and Johnson, R.L., 2012. Slab1.0: A three-dimensional model of global subduction zone geometries in, J. Geophys. Res., 117, B01302, doi:10.1029/2011JB008524
  • Hayes, G.P., Smoczyk, G.M., Benz, H.M., Villaseñor, Antonio, and Furlong, K.P., 2015. Seismicity of the Earth 1900–2013, Seismotectonics of South America (Nazca Plate Region): U.S. Geological Survey Open-File Report 2015–1031–E, 1 sheet, scale 1:14,000,000, http://dx.doi.org/10.3133/ofr20151031E.
  • Okal, E. A., & Reymond, D., 2003. The mechanism of great Banda Sea earthquake of 1 February 1938: applying the method of preliminary determination of focal mechanism to a historical event in EPSL, v. 216, p. 1-15.
  • Zahirovic, S., Seton, M., and Müller, R.D., 2014. The Cretaceous and Cenozoic tectonic evolution of Southeast Asia in Solid Earth, v. 5, p. 227-273, doi:10.5194/se-5-227-2014

Posted in asia, australia, earthquake, education, geology, HSU, Indonesia, pacific, plate tectonics, strike-slip, subduction

Earthquake Report: Alaska

We had an earthquake a few days ago along the Cook Strait west of Anchorage, Alaska. This earthquake happened nearby a couple earthquakes from the past 2 years that have similar senses of motion along faults that seem to be oriented the same. Here is my report for the 2016 M 7.1 earthquake.

    The USGS websites for the three large earthquakes with moment tensors plotted on the poster are here

  • 2015.07.29 M 6.3
  • 2016.01.24 M 7.1
  • 2017.03.02 M 5.5

Below is my interpretive poster for this earthquake.

I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I also include seismicity from 2015-2017 for earthquakes with magnitudes M ≥ 4.0.

  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. The moment tensors for all three of these earthquakes are very similar.
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I include the slab contours plotted (Hayes et al., 2012), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault. The hypocentral depth plots this close to the location of the fault as mapped by Hayes et al. (2012). All three earthquakes listed above plot clearly within the downgoing Pacific plate slab.

    I include some inset figures in the poster.

  • In the upper right corner is a map produced by Dr. Peter Haeussler from the USGS Alaska Science Center (pheuslr at usgs.gov) that shows the historic earthquakes along the Aleutian-Alaska subduction zone.
  • In the upper left corner I include an inset map from the USGS Seismicity History poster for this region (Benz et al., 2010). There is one seismicity cross section with its locations plotted on the map. The USGS plot these hypocenters along this cross section and I include that below (with the legend). I placed orange circles on the map and cross section showing the general location of the M 7.1 and M 5.5 earthquakes. The M 6.3 earthquake would plot almost in the same location as the M 7.1.
  • To the right of the Benz et al. (2010) figures is a map showing seismicity plotted as dots colored vs. depth. This map is from the Alaska Earthquake Center as presented by IRIS.
  • In the lower right corner are the MMI intensity maps for the two earthquakes listed above: 2015 M 6.3, 2016 M 7.1, and 2017 M 5.5. These figures were created by the USGS, but were made at different sizes, so they don’t match perfectly (don’t ask me why they keep changing the sizes of their figures and maps, I don’t know the answer). Below each map are plotted the reports from the Did You Feel It? USGS website for each earthquake. These reports are plotted as green dots with intensity on the vertical axes and distance on the horizontal axes. There are comparisons with Ground Motion Prediction Equation (attenuation relations) results (the orange model uses empirical data from central and eastern US earthquakes; the green model uses empirical data from earthquakes in California). Neither model seems appropriate given the DYFI results, though the California model works slightly better for the M 5.5 earthquake.


Here is the same poster with only seismicity from the past 30 days plotted.


  • Dr. Peter Haeussler produced a cross section for this region, as prepared for the 2016 M 7.1 earthquake. Below is his description of this figure.

  • I made up a quick diagram (thanks Alaska Earthquake Center tools) showing the tectonic setting of the earthquake. This was a “Benioff zone” event, which means that the earthquake is related to bending of the subducting Pacific Plate as it slides into the mantle.

  • Here is a map for the earthquakes of magnitude greater than or equal to M 7.0 between 1900 and 2016. This is the USGS query that I used to make this map. One may locate the USGS web pages for all the earthquakes on this map by following that link.

    • Here is a cross section showing the differences of vertical deformation between the coseismic (during the earthquake) and interseismic (between earthquakes).

    • Here is a figure recently published in the 5th International Conference of IGCP 588 by the Division of Geological and Geophysical Surveys, Dept. of Natural Resources, State of Alaska (State of Alaska, 2015). This is derived from a figure published originally by Plafker (1969). There is a cross section included that shows how the slip was distributed along upper plate faults (e.g. the Patton Bay and Middleton Island faults).

    • Here is an animation that shows earthquakes of magnitude > 6.5 for the period from 1900-2016. Above is a map showing the region and below is the animation. This is the URL for the USGS query that I used to make this animation in Google Earth.

    • Here is a link to the file for the embedded video below (5 MB mp4)

    References:

  • Posted in alaska, earthquake, education, geology, HSU, pacific, plate tectonics, strike-slip, subduction

    Earthquake Report: EOTD Chile M 8.8 2010.02.27

    Earthquake of the Day: 2010.02.27 M 8.8 Maule, Chile.

    There was an earthquake with a magnitude of M 8.8 on this day in 2010. I have prepared an interpretive poster that shows the extent of ground shaking modeled for this earthquake. The attenuation relations (how the ground shaking diminishes with distance from the rutpure) generally match the ground shaking reports on the USGS “Did You Feel It?” web page.

    I also include other material on the poster, including information about the 1960 M 9.5 Chile earthquake, which is the largest that we have ever recorded on modern seismologic instruments. Below are the USGS web pages for these two earthquakes. Here is the kml file for these earthquakes.

    Below is my interpretive poster for this earthquake.


    I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I also include seismicity from 1917-2017 for earthquakes with magnitudes M ≥ 8.0.

    • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. The moment tensor shows northeast-southwest compression, perpendicular to the convergence at this plate boundary. Most of the recent seismicity in this region is associated with convergence along the New Britain trench or the South Solomon trench.
    • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
    • I include the slab contours plotted (Hayes et al., 2012), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault. The hypocentral depth plots this close to the location of the fault as mapped by Hayes et al. (2012).

      I include some inset figures in the poster.

    • In the upper right corner, I include a time-space diagram from Moernaut et al. (2010).
    • In the upper left corner I include an inset map from the USGS Seismicity History poster for this region (Rhea et al., 2010). There is one seismicity cross section with its locations plotted on the map. The USGS plot these hypocenters along this cross section and I include that below (with the legend).
    • In the lower right corner are the MMI intensity maps for the two earthquakes listed above: 1960 M 9.5 & 2010 M 8.8. Note these are at different map scales.


    Here is a version that includes the MMI contours for the 1960 earthquake as well.


    • Here is a great figure from Lin et al. (2013) that shows the tectonic context of the 2010 Maule earthquake. On the map are plotted extents of historic earthquakes along this convergent plate margin. On the right is a large scale map showing the active magmatic arc volcanoes associated with this subduction zone. Finally, there is a cross section showing where the coseismic slip and postseismic slip occurred. I include the figure captions as blockquote.

    • (a) Regional tectonic map showing slab isodepth contours (blue lines) [Cahill and Isacks, 1992], M>=4 earthquakes from the National Earthquake Information Center catalog between 1976 and 2011 (yellow circles for depths less than 50 km, and blue circles for depths greater than 50 km), active volcanoes (red triangles), and the approximate extent of large megathrust earthquakes during the past hundred years (red ellipses) modified from Campos et al. [2002]. The large white vector represents the direction of Nazca Plate with respect to stable South America [Kendrick et al., 2003]. (b) Simplified seismo-tectonic map of the study area. Major Quaternary faults are modified after Melnick et al. [2009] (black lines). The Neogene Deformation Front is modified from Folguera et al. [2004]. The west-vergent thrust fault that bounds the west of the Andes between 32 and 38S is modified from Melnick et al. [2009]. (c) Schematic cross-section along line A–A0 (Figure 1b), modified from Folguera and Ramos [2009]. The upper bound of the coseismic slip coincides with the boundary between the frontal accretionary prism and the paleo-accretionary prism [Contreras-Reyes et al., 2010], whereas the contact between the coseismic and postseismic patch is from this study. The thick solid red line and dashed red line on top of the slab represent the approximate coseismic and postseismic plus interseismic slip section of the subduction interface. The thin red and grey lines within the overriding plate are active and inactive structures in the retroarc, modified from Folguera and Ramos [2009]. The red dashed line underneath the Andean Block represents the regional décollement. Background seismicity is from the TIPTEQ catalog, recorded between November 2004 and October 2005 [Rietbrock et al., 2005; Haberland et al., 2009].

    • Below are some figures from Moreno et al. (2011) that show estimates of locking along the plate interface in this region. I include the figure captions as blockquote.
    • The first figure shows how the region of today’s earthquake is in an area of higher locking.

    • a) Optimal distribution of locking rate in the plate interface. Predicted interseismic velocities and GPS vectors corrected by the postseismic signals are shown by green and blue arrows, respectively. b) Tradeoff curve for a broad range of the smoothing parameter (β). The optimal value for β is 0.0095 located at the inflection of the curve.

    • This second figure shows the moment released during historic earthquakes and the moment accumulated due to seismogenic locking along the megathrust.

    • a) Latitudinal distribution of the coseismic moment (Mc) released by the 1960 Valdivia (Moreno et al., 2009) (red line) and 2010 Maule (Tong et al., 2010) (blue line) earthquakes, and of accumulated deficit of moment (Md) due to interseismic locking of the plate interface 50 (orange line) and 300 (gray line) years after the 1960 earthquake, respectively. The range of errors of the Md rate is depicted by dashed lines. High rate of Md was found in the earthquake rupture boundary, where slip deficit accumulated since 1835 seems to be not completely released by the 2010 Maule earthquake. b) Schematic map showing the deformation processes that control the observed deformation in the southern Andes and the similarity between coseismic and locking patches. Blue and red contours denote the coseismic slip for the 2010 Maule (Tong et al., 2010) and 1960 Valdivia (Moreno et al., 2009) earthquakes, respectively. Patches with locking degree over 0.75 are shown by brown shaded areas. The 1960 earthquake (red star) nucleated in the segment boundary, area that appears to be highly locked at present. The 2011 Mw 7.1 aftershock (gray) may indicate that stress has been transmitted to the southern limit of the Arauco peninsula.

    • Here is a figure from Moreno et al. (2010) that shows the seismogenic locking for the region that includes the 2010 earthquake (shown with a focal mechanism from the M 8.8 earthquake. The figure caption is included below in blockquote.

    • Tectonic setting of the study area, data, observations and results. a, Shaded relief map of the Andean subduction zone in South- Central Chile. Earthquake segmentation along the margin is indicated by ellipses that enclose the approximate rupture areas of historic earthquakes (updated from refs 4–6). The inset shows the location of panel a (rectangle) relative to the South American continent. b, Compilation of GPS-observed surface velocities (1996–2008) with respect to stable South America before the 2010 Maule earthquake (for references see online-only Methods). Ellipses attached to the arrows represent 95% confidence limits. c, GPS 1 FEM modelled interface locking (fraction of plate convergence) distribution along the Andean subduction zone megathrust in the decade before the 2010 Maule earthquake. The epicentre (white star, USGS NEIC) and focal mechanism (beach ball, GCMT, http://www.globalcmt.org) of the 2010 Maule earthquake are shown in panels a and c.

    • This is also from Moreno et al. (2010) and shows the relations between different parts of the earthquake cycle. Recall these parts are the interseismic (between earthquakes), coseismic (during the earthquake), preseismic (before the earthquake), and postseismic (after the earthquake). The postseismic phase can last days to decades.

    • Relationship [sic] between pre, co- and postseismic deformation patterns. a, Coseismic slip distribution during the 2010 (blue contours; USGS slip model26) and 1960 (green contours; from ref. 30) earthquakes overlain onto pre-seismic locking pattern (red shading $0.75), as well as early (during the first 48 h post-shock) M$5 aftershock locations (the grey circle sizes scale with magnitude; GEOFON data29). b, Histograms of early (first 48 h; total number of events, 80) and late (first 3 months; total number of events, 168) aftershock density along a north–south profile (GEOFON data29, M$5). c, Residual slip deficits since 1835 as observed after the 2010 earthquake along a north–south profile (left column, based on the USGS slip model26). The middle and right columns show the effects on slip deficit of overlapping twentieth-century earthquakes (the black lines are polynomial fits to the data). Coloured data points and dates indicate earthquakes by year of occurrence.

    • This figure shows the results of analyses from Lin et al. (2013) where they estimate the spatial variation in postseismic slip associated with the 201 M 8.8 Maule earthquake. They used GPS observations along the upper plate to estimate how the fault continued to slip after the main earthquake.

    • Comparison of the postseismic slip model between the 1st and 488th day constrained by (a) horizontal GPS observations only, (b) all three components of GPS observations, and (c) three component GPS observations plus InSAR data. The coseismic slip model is of 2.5 m contour intervals (gray lines). (d) The same afterslip model as Figure 9c. Red dots are aftershocks [Rietbrock et al., 2012]. Black triangles represent the location of GPS stations. A is the afterslip downdip of the coseismic slip patch, with the black arrows indicating the along-strike extent. B and C correspond to two regions of afterslip that bound the southern and northern end of the coseismic slip patch. D is a deep slip patch that may reflect some tropospheric errors in the Andes.

    • Here is the space-time diagram from Moernaut et al., 2010. I include their figure caption below in blockquote.

    • Fig.: Setting and historical earthquakes in South-Central Chile. Data derived from Barrientos (2007); Campos et al. (2002); Melnick et al.(2009)

    • Here is the cross section of the subduction zone just to the south of the Sept/Nov 2015 swarm (Melnick et al., 2006). Below I include the text from the Melnick et al. (2006) figure caption as block text.

    • (A) Seismotectonic segments, rupture zones of historical subduction earthquakes, and main tectonic features of the south-central Andean convergent margin. Earthquakes were compiled from Lomnitz (1970, 2004), Kelleher (1972), Comte et al. (1986), Cifuentes (1989), Beck et al. (1998 ), and Campos et al. (2002). Nazca plate and trench are from Bangs and Cande (1997) and Tebbens and Cande (1997). Maximum extension of glaciers is from Rabassa and Clapperton (1990). F.Z.—fracture zone. (B) Regional morphotectonic units, Quaternary faults, and location of the study area. Trench and slope have been interpreted from multibeam bathymetry and seismic-reflection profiles (Reichert et al., 2002). (C) Profile of the offshore Chile margin at ~37°S, indicated by thick stippled line on the map and based on seismic-reflection profiles SO161-24 and ENAP-017. Integrated Seismological experiment in the Southern Andes (ISSA) local network seismicity (Bohm et al., 2002) is shown by dots; focal mechanism is from Bruhn (2003). Updip limit of seismogenic coupling zone from heat-fl ow measurements (Grevemeyer et al., 2003). Basal accretion of trench sediments from sandbox models (Lohrmann, 2002; Glodny et al., 2005). Convergence parameters from Somoza (1998 ).

    • In September through November of 2015, there was a M 8.3 earthquake further to the north. Below is my interpretive poster for that earthquake and here is my report, where I discuss the relations between the 2010, 2015, and other historic earthquakes in this region. Here is my report from September.

    • Here is a space time diagram from Beck et al. (1998 ). The 2015 earthquake occurs in the region of the 1943 and 1880 earthquakes. I updated this figure to show the latitudinal extent of the 2010 and 2015 earthquakes.

    References:

    Posted in education, geology, HSU, pacific, plate tectonics, subduction, tsunami

    Earthquake Report: Makran subduction zone (Pakistan)!

    There was a good sized earthquake along the Makran subduction zone. This subduction zone is a convergent plate boundary where the Arabia plate subducts (goes beneath) northwards under the Eurasia plate. There has been one aftershock reported by the USGS. These earthquakes are in the region of an earthquake with a magnitude of M 8.1 from 1945, which generated a large tsunami in the region. There are some reports of damage. There was an aftershock to the 1945 earthquake in 1947, when there was an earthquake with a magnitude of M 6.8 occurred in almost the same location as this 2017 earthquake. However, the 2017 M 6.3 is much deeper. There is some indication that there may be underplated sediment (sediment that is scraped off of the downgoing plate and attached to the upper plate). Perhaps the 1945 and 1947 earthquakes are on a shallower fault. Perhaps their locations are poorly resolved due to poor seismometer instrument coverage at that time.

    This is also a region that experienced some effects from an earthquake further to the north in 2013. On 2013.09.24 there was an earthquake with a magnitude of M 7.7 that caused ground shaking throughout the region, as well as an interesting feature that arose from the seafloor along the continental shelf (what this feature is called is in debate; some called it a mud volcano). Here is my brief report on the 2013 earthquake.

      Here are the USGS websites for these earthquakes.

    • 2017.02.07 22:03 (UTC) M 6.3
    • 2017.02.08 11:02 (UTC) M 5.2
    • 2013.09.24 11:29 (UTC) M 7.7
    • 1945.11.27 21:56 (UTC) M 8.1

    Below I present my interpretive poster for this M 6.3 earthquake. I include epicenters for earthquakes from the past century with magnitudes M ≥ 6.0. Here is the kml I created from the USGS earthquakes website.

  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. The moment tensor shows north-south compression, perpendicular to the convergence at this plate boundary. I interpret this 2017 M 6.3 earthquake to be along a fault that dips to the north. Read my discussion below about the inset figure in the upper right corner.
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I include some inset figures in the poster below.

    • In the upper right corner I include a map that shows historic earthquakes in the region (Smith et al., 2013). The authors plot focal mechanisms for selected earthquakes. These earthquakes all have similar solutions as this 2017 M 6.3 earthquake. Given the low angle of subduction along this fault system, and that all these fault plane solutions have either a shallow fault or a steep fault, I suspect that these earthquakes are all occurring on a shallowly dipping fault that is southward vergent. Vergence refers to which direction the fault is oriented in the up-dip direction. The Makran subduction zone fault dips down to the north, so is southward vergent.
    • In the lower right corner I include a line drawing of the faults and plate boundaries in this region (Kukowski et al., 2000). I like this figure because it is simple yet includes some details of the complexity of the faulting in this region (especially the Murray Ridge, which is a series of enechelon east-west striking spreading ridges offset by north-east striking strike-slip faults, forming Dalyrimple Trough). This detail is missing on the USGS plate boundary fault (the red line in the main interpretive poster, as plotted in Google Earth). The paper from which this is taken is a paper where they document the northwest striking Sonne fault that crosses oblique to the fold and thrust belt of the Makran margin.
    • In the lower left corner is are two figures from Kopp et al. (2000). The upper panel shows a low angle oblique view of the bathymetry for the Makran margin in this region. The lower panel shows their interpretation of seismic reflection data that they presented in that paper. This profile is located on the upper panel, as well as on the interpretive poster as a green dashed line labeled A-A.’ These earthquakes occurred to the east of the northernmost extent of this seismic profile, but this profile gives us a good idea about the general configuration of the accretionary prism here.
    • In the upper left corner is a figure from Jaiswal et al. (2009) that shows some regions where large subduction zone tsunamigenic earthquakes have happened. There has been much work done on the 1945 tsunami (modeling, interviewing of observers, etc.).


      Here are some of the figures that I included in the poster, as well as some additional related figures. I include their original figure captions as blockquotes beneath the figures.
    • Here is the Smith et al. (2013) figure showing the historic earthquakes and their focal mechanisms.

    • Location map of the Makran Subduction Zone. Earthquakes from post-1960 (and pre-1960 with assigned magnitudes) from the EHB Catalog [Engdahl et al., 1998] are illustrated by circles. Those from pre-1960 with no assigned magnitude are small black dots. Significant possible plate boundary events with focal mechanisms from Byrne et al. [1992] and the Global CMT Catalog (magnitudes in inset table). Bathymetry is from the GEBCO_08 Grid [Smith and Sandwell, 1997]. Strike lengths of three rupture scenarios for magnitude calculations are indicated by shaded bars. The thermal modeling profile is marked as a black line. Triangles are volcanoes.

    • Here are two figures from Kukowski et al. (2000) showing the faults and their interpretations of this large strike-slip fault that cuts oblique to the margin.

    • A: Plate tectonic sketch indicating position and framework of newly identified Ormara plate. ONF is Ornach Nal fault; OFZ is Owen Fracture Zone;TJ is triple junction. For symbols see Figure 1 and text. B:Velocity diagram for triple junction among Arabian, Ormara, and Indian plates.


      A:Three-dimensional perspective, shaded bathymetric image of Makran accretionary wedge, showing Sonne strike-slip fault and erosive canyons crossing wedge. B:Tectonic interpretation showing offset of accretionary ridges and extensional jog of Sonne fault, which may result from some rotation of Ormara plate.

    • Here are a series of figures from Kopp et al. (2000). The upper figure is the low angle oblique view of the region that they studied. The lower figure includes the seismic data and their interpretation (that led to their interpretation presented in the interpretive poster above).

    • Bathymetric map of the MAKRAN accretionary wedge with profile and OBH locations. The labelled lines/OBH are discussed in the text.


      Prestack depth migration and interpretation of CAM30. The migration was calculated with velocities derived from depth-focusing (cdp 0±3200) and semblance (cdp 3200±4800) analysis. A post-migration radon filter was applied to reduce residual multiples. The interpretation is based on the distinct seismic signature of sedimentary reflectors in the abyssal plain and within the ®rst two thrusts (Fruehn et al., 1997).

    • There was a semi-recent paper where some important discoveries were made regarding the sediment routing along this margin (Bourget et al., 2011). This paper includes material that may eventually lead to an earthquake history for this margin. I include a few of their figures below.
    • This figure shows the geomorphology of the Makran continental margin and how the authors interpret there to be different sedimentary pathways.

    • Slope map of the Makran turbidite system, showing the seven canyon systems (yellow), their main pathway (red) and the main architectural elements in the abyssal plain. Longitudinal depth profiles of these canyon pathways are shown in Fig. 4. The cross-section (below) shows a general longitudinal profile of the Makran margin from the upper slope (Canyon 5) to the Oman abyssal plain, with main slope changes.

    • This is a illustration showing how some turbidity currents may interact with the submarine landforms.

    • Interpretative cartoon showing the sedimentary processes within the plunge pools at the deformation front.

    • This figure links the offshore sediment routing systems with the onshore sources of sediment.

    • (A) 3D onshore topography (SRTM data) and offshore bathymetry (MARABIE and CHAMAK cruises merged with the ETOPO 1 database) of the Makran accretionary prism, showing the structural organization of the margin. Significant streams/rivers and submarine canyons are drawn. Note the shallowing of the deformation front depth (red line) towards the east, joining the western edge of the India plate in the triple-junction area (simplified after Ellouz-Zimmermann et al., 2007b; Mouchot, 2009). (B) Along-strike evolution of the depth of the deformation front (black dashed line) and the length of the Makran submarine canyons (red continuous line). (C) Along-strike evolution of the Makran watersheds size (km2). Note that the largest watersheds are confined in the eastern Makran and Kirthar range, corresponding to the triple-junction area where the higher reliefs are observed.

    • This is their summary illustration showing their interpretation of the factors controlling sedimentation along this margin.

    • Summary of the impact of the variability of the forcing parameters (tectonics and fluvial input) on the theoretical ‘equilibrium’ conditions of the Makran canyons, and its implication for sediment distribution and turbidite system architecture at large (continental slope) and small (architectural elements in the abyssal plain) scales of observation.

    • Here are some photos of some damage from the town of Pasni in Gwadar. These were posted on social media by Faiz Baluch.



    M 7.7 Earthquake Observations

    • The 2013 M 7.7 Pakistan earthquake produced some interesting effects along the coast. Here are some photos of the island that formed as a result of this earthquake.
    • Here is an aerial image of the island published by RT as acquired by NASA.

    • Here is a satellite image of before and after shots as prepared by Danielle Madugo.

    • Here are three photos taken from people who visited the island.



    • This is a fascinating observation. Following the 1945 M 8.1 earthquake, a similar island formed in this region. Schluter et al. (2002) published a paper where they put forth their interpretations for the formation of these mud volcanoes.

    References:

    • Kopp, C., Fruehn, J., Flueh, E.R., Reichart, C., Kukoski, N., Bialas, J., and Klaeschen, D., 2000. Structure of the Makran subduction zone from wide-angle and reflection seismic data in Tectonophysics, p. 171-191
    • Kukowski, N., Schilhorn, T., Flueh, E.R., and Huhn, K., 2000. Newly identified strike-slip plate boundary in the northeastern Arabian Sea in Geology, v. 28, no. 4, p. 355-358.
    • Schluter, H.U., Prexl, A., Gaedicke, C., Roseser, H. , Reichert, C., Meyer, H., and von Daniels, C., 2002. The Makran accretionary wedge: sediment thicknesses and ages and the Origin of mud volcanoes in Marine Geology, v. 185, p. 219-232.
    • Smith, G.L., McNeill, L.C., WEang, K., He, J., Henstock, T., 2013. Thermal structure and megathrust seismogenic potential of the Makran subduction zone in GRL v. 40, p. 1528-1533, doi:10.1002/grl.50374

    Posted in asia, geology, Indian Ocean, plate tectonics, subduction, tsunami

    Radio Show Material: KHUM with Lyndsey Battle

    Radio Show KHUM with Lyndsey Battle

    Reinterpretation of a classic by Dana Gould.


    Strawman Questions

    What is a fact?

    How can we decipher facts from “alternative facts?”

    • Scientific Method?
      • What do we want? Evidence based science
      • When do we want it? After peer review
    • What does the peer review process look like?

    I addressed these questions during the radio show, but did not document this before the show. Please listen to the show to hear more about this.

    How does culture shape science?


    In a broadly stroking nutshell, culture is a broad range of things that relates people to their existence and their belief systems. So, in that sense, changes in our belief systems have affected how science is practiced and how people believe in science. In times past, people based their beliefs mostly on religious principles put forth by some religious authority. Through centuries of struggle, science responded to this by developing and forming based on a belief that there is a natural-systems-explanation for all observable phenomena.

    How does science shape policy?


    Policy is often based on the rule of law and how organizations want to implement those laws. So, policy is often in the realm of the attorney at law and how actions using these policies satisfy the laws. Often science is used by law makers when they write bills to be considered.

    Some policies are based more on how best to accomplish a certain task. For example, managing rivers to reduce flood hazards or protecting public land for recreation value.

    Science can inform both legal and other policy development. For example,

    1. Studying river flows for decades to centuries gives us the facts with which to define flood hazard zones.
      1. Affects county building codes (policy)
      2. Affects insurance rates (side effect)
    2. USGS National Seismic Hazard Map is based upon 3 & 4
      1. Affects county building codes (policy)
      2. Affects insurance rates (side effect)
    3. Studying earthquake recurrence of the past to help inform us of the likelihood of a future earthquake
    4. tudying how subduction zone faults slip and how that might affect
      1. ground shaking
      2. landslides
      3. tsunami

    Example of Local Policy influenced by facts:

    • Dissect policy to facts
    • Replace facts w/alt-facts
    • Rebuild policy with alt facts and talk about how they differ?
    • What is the potential impact on society of new alt-fact based policy?

    1. Fact Based Policy: Tsunami Evacuation Zones (very generally)
      • Step 1: develop numerical model for tsunami inundation
      • Step 2: for evacuation zones, extend inundation limits to easy to identify geographic features
        • i.e. easier to identify a road than a position out in a cow pasture with no landmarks
      • Step 3: prepare maps and place signs
      • Step 4: develop county/city/community response plans and community evacuation routes
      • Step 5: rehearse these plans and have tsunami drills
    2. Alt-Fact Based Policy: Building in the Flood Zone
      • FEMA Flood Zones are based upon:
        • scientific analyses of river flows and
        • statistical estimates of likelihood (probabilities)
        • numerical modeling of river flows
      • Imagine adopting alt-facts that suggest floods would be different than FEMA Flood Hazard Maps.
      • Change county development policy (e.g. General Plan Update or other modification)
      • Build large residential development in flood plain prior to a major flood. The flood destroys some percent of the development. Alt-Fact policy can be expensive.

    Can we talk about the idea of arguing (or creating policy) from evidence vs. ideology?

    • In my opinion, are evidence based facts powerful enough tools to counter an approach of irrational bombardment?
      • This is a very interesting question. There are some varying opinions on this.
        • Atul Gawande (New Yorker, 2016) suggests avoid arguing with people about their skewed views, but to help them develop their own critical skills. e.g. “Rebutting bad science may not be effective, but asserting the true facts of good science is. And including the narrative that explains them is even better.”
        • If I focus on the facts instead of bashing the Alt-Facts, I am probably more successful. Of course, I am not perfect at this. Sometimes I do spend time trying to help someone change their mind.
    • How do we better ground ourselves in a reality based on facts in a world where it becoming hard to recognize facts based from science?
      • This is very challenging. It takes time to evaluate information and sometimes it requires a certain level of expertise. For example, it takes a hydrologist and an engineer to estimate what the flood hazards would be for a certain region.
      • If we are not experts, we need to develop some other way to evaluate the credibility of a source of information. This is a somewhat indirect way to assess how factual something is. Everyone should develop their own rules. Here are some that I have developed for evaluating an article online or in a journal, in no particular order (there are other lists online elsewhere).
        1. References – what are the sources of information? Are these from peer reviewed literature? Are there lots of references (like a meta-analysis like the IPCC Assessment Reports)? Does the article only refer to other articles with the same URL (web address) as the main article? (climate change denier websites do this, as do websites for extremist organizations)
        2. Contrasting Views – are there alternate hypotheses discussed?
        3. Publisher – is the article published by a peer review journal publisher (like Elsevier, Nature, Science, etc.)? Is the article from a newspaper that has an editorial board? Newspapers have a lower credibility than a peer review journal, but more credibility than an op-ed in the same newspaper. Is the article in a blog? Blogs can be OK, but they generally don’t have the same level of review as other sources. Blogs can be terrible sources of information too.
        4. Primary Source – is the article the primary source for this information or does the entire article exist as an article from some other publisher. The primary source of the article is the most credible. Beware of articles that are copied word-for-word between different websites. This is a strategy to artificially increase the apparent credibility of an article. I initially noticed this strategy on early climate change denier websites.

    Strawman Discussion

    • I prepared this document as a strawman discussion for the radio show on KHUM. I had a conversation with Lyndsey Battle on 2/4/17 at noon. Here I discuss facts, science, and scientific philosophy. My discussion is outlined generally like this:
      1. Facts
      2. Scientific Method
      3. Facts vs. Alt-Facts
      4. Scientific Philosophy
      5. Resources

    Facts

    Facts are things that have actually occurred or correct. If these things did not occur or are incorrect are not facts. How can we tell if something is a fact? Facts are verifiable based upon empirical observation (see scientific method below), as opposed to theoretical statements.

    Opinions are statements or viewpoints. Opinions can be based upon facts. Opinions can be based upon ideas that people have, often theoretical positions. Fact-based opinions generally are more “real” than theoretical-based opinions because they are based upon real and verifiable observations. Anyone and everyone can have opinions, but we need to evaluate opinions based on their credibility. If someone has an opinion that is theoretical but in opposition to a fact, their opinion loses credibility. Likewise, if someone has an opinion that is based upon a fact, their opinion gains credibility. As Scotty (the engineer) on the Star Trek the original series said, “Everyone is entitled to an opinion,” those stating their opinions may be incorrect if they are not based upon fact.

    Here is a video about facts and the anthropogenic forcing of climate change

    Scientific Method

    I start every single science class that I teach with a review of the scientific method as all science is based on this process. There are no hard rules about these steps as when one asks 5 scientists what the steps are, one will get 5 or more answers. Here are the steps that I propose to students.

    1. Make an/some observation(s)
    2. Form an/some hypothesis/hypotheses to explain the observation(s)
    3. Formulate an/some experiment(s) to test the hypothesis
    4. Conduct the test
    5. Evaluate and analyze the results to accept, reject, or modify the hypothesis/hypotheses.

    I use a part of the story from Star Trek Nemesis, a film with the cast from The Next Generation television series. In short, the Enterprise crew finds the prototype artificial person for Data on a planet. Geordi, the engineer, downloads all of Data’s “memories” into the prototype (named “Before,” heheh). Data hypothesized that “Before” would be as perfect as he is after he knew all that Data knows. After Data’s memories are downloaded and “Before” is disconnected from Data, Data asks “Before” where he is. They are in the Engineering section of the Enterprise and if everything worked correctly “Before” should know this. Before answers to Data, “I am in a room with lights.” Data’s test failed, but the reason I use this story is to help students know that they all have the basic skills required to be a scientist, the skills of observation. Before made the basic observations that he was in a room and that there were lights on. It is ironic that the scene also represents an example of the entire scientific method, in addition to being an easy to remember analogy about simple observational skills. Also, this can empower students to realize that they are capable of being scientists and all they need to do is rely on their basic senses. I remind students that when they are confronted with challenges to understand things, if they rely on these basic senses, they can reason through these challenges.

    Here is a great overview video about the scientific method as shared on social media by Dr. David Bazard, Dean of the Department of Science at the College of the Redwoods. Here is the YT link to the embedded video below.

    Facts vs. Alt-Facts

    This is one of the simplest principles of all. Alt-Facts are not facts because they violate the definition of what a fact is. They are not based upon real observations. They are not based upon verifiable tests. Alt-Facts are not real. Alt-facts are an imaginary representation.

    To present an Alt-Fact as a fact is a dishonest representation of reality. Recently I heard an interview on NPR (while listening to KHSU public radio) of a journalist. They were asked why they did not state that the comments from a particular political entity was a lie. The journalist claimed that because they had not been able to establish intent [to be dishonest], they could not call it a lie. However, the difference between being dishonest and telling a lie is not that much different, in my opinion.

    My friend, Stephen Tillinghast, likes to use the phrase “post-factual” society to describe our culture. This makes me think about what my professors used to say when I was a younger student in the early 1990s. My professors would discuss how they would need to lower their standards and level of academic scholarship each year because the students were sequentially lesser prepared. They would discuss how entering students would be covering material that used to be covered in High School. I came up with the term “the dumbing down of America.” I am sure I did not coin this phrase, but it was my first observation of this phenomena as presented to me by professors and mentors who had decades of observations prior to my coming on the scene. Now that I have been teaching introductory science courses for 5 years, I have found that, in large part, the observations from my mentors of decades past are cogent and applicable today. Considering the recent political cycle and the formation of a political group called the alt-right, I coined a term “Alt-Fact.” Of course, I learned shortly after that David Frum had coined the term a day or two before I did. I am sure there are probably others who also used this term.

    Why are people so fooled to believe Alt-Facts? There are probably many reasons ranging from exposure or lack of exposure to television, books, science classes, video games, social media, etc. Perhaps the largest factor may be the overstimulation from information presented online. With the plethora of information online, it is challenging to evaluate the credibility of all this information. It is time consuming and requires a certain amount of expertise in a certain subject matter. I first started developing my skills to distinguish fact from alt-fact when I was taking an atmospheric science class at Oregon State University. I started evaluating websites that discussed the anthropogenic forcing of climate change. Some websites promoted a climate change denial perspective. I learned that there was a wide range of strategies that websites like these used to promote misinformation as fact based reasoning. I soon realized that I could quickly evaluate the credibility of a source of information based upon some simple rules. These rules were based upon my observation of the climate change denier websites. I discuss this below when I talk about my website about the radiation from the Fukushima-Daiichi Nuclear Power Plant.

    There are many aspects of websites that reveal that they are not credible sources of information and I reveal these aspects as I evaluate each source of information about Fukushima radiation on that webpage. I put together a similar page for modern climate change websites.

    Scientific Philosophy

    I present some great quotes from an editorial presented by Atul Gawande on 6/10/2016. This article came to my social media feed as tweeted by Rich Boone, the Dean of the College of Natural Resources and Sciences. Below are some cogent observations by Gawande, interspersed with some observations of my own.

    Quotes From “THE MISTRUST OF SCIENCE” Other quotes are also below in blockquote.

    “The great physicist Edwin Hubble, speaking at Caltech’s commencement in 1938, said a scientist has “a healthy skepticism, suspended judgement, and disciplined imagination”—not only about other people’s ideas but also about his or her own. The scientist has an experimental mind, not a litigious one.”

    “Ultimately, you hope to observe the world with an open mind, gathering facts and testing your predictions and expectations against them. Then you make up your mind and either affirm or reject the ideas at hand. But you also hope to accept that nothing is ever completely settled, that all knowledge is just probable knowledge. A contradictory piece of evidence can always emerge. Hubble said it best when he said, “The scientist explains the world by successive approximations.” “

    “People are prone to resist scientific claims when they clash with intuitive beliefs.”

    This reminds me of a book I read for one of my anthropology courses about women who lived in Cairo, “Baladi Women of Cairo: Playing With an Egg and a Stone.” https://www.rienner.com/title/Baladi_Women_of_Cairo_Playing_with_an_Egg_and_a_Stone

    I was growing up in a world (in the 1990s) that was dominated by allopathic medicine while I was surrounded by naturopaths and herbalists, who certainly bring value to our health. The stories in the book rang true with me because they told of how the Baladi Women (women living in an urban setting) in Cairo were also living in a juxtaposition of sometimes competing health care techniques. When confronted with healthcare choices, they challenged themselves to consider either western medicine or traditional medicine. There were values from using either modality. This ethnology is a work of cultural anthropology in that it seeks an understanding of others based upon their beliefs and how these become developed often as a learned perspective.

    The sociologist Gordon Gauchat studied U.S. survey data from 1974 to 2010 and found some deeply alarming trends. Despite increasing education levels, the public’s trust in the scientific community has been decreasing.

    Today, we have multiple factions putting themselves forward as what Gauchat describes as their own cultural domains, “generating their own knowledge base that is often in conflict with the cultural authority of the scientific community.”

    They [the groups] all harbor sacred beliefs that they do not consider open to question.

    Science’s defenders have identified five hallmark moves of pseudoscientists. They argue that the scientific consensus emerges from a conspiracy to suppress dissenting views. They produce fake experts, who have views contrary to established knowledge but do not actually have a credible scientific track record. They cherry-pick the data and papers that challenge the dominant view as a means of discrediting an entire field. They deploy false analogies and other logical fallacies. And they set impossible expectations of research: when scientists produce one level of certainty, the pseudoscientists insist they achieve another.

    I have found some of these practices on a variety of websites that promote alt-fact views about chemtrails, climate change, and radiation from Fukashima. The first major effort I used my website for was to help people develop their own critical skills to distinguish between more and less credible sources of information regarding the dangers of radiation from the terrible and continuing disaster at the Fukashima-Daiichi Nuclear Power Plant following the 2011 Tohoko-oki magnitude M 9.0 earthquake and tsunami. Many of my friends on social media are not scientists and they were sharing these conspiracy theory websites like globalresearch.ca. I found myself spending too much time explaining my rationale to everyone individually. Therefore, I put together a web page where I model how to form ways to distinguish more and less credible information. I did not want to tell people what to think, but what skills they can use to distinguish these information sources on their own. I created three categories of decreasing credibility and placed every source on the subject matter into one of these categories.

    Turns out it was a good strategy, to avoid arguing with people about their skewed views, but to help them develop their own critical skills. As Gawande mentions, “Describing facts that contradict an unscientific belief actually spreads familiarity with the belief and strengthens the conviction of believers. That’s just the way the brain operates; misinformation sticks, in part because it gets incorporated into a person’s mental model of how the world works. Stripping out the misinformation therefore fails, because it threatens to leave a painful gap in that mental model—or no model at all.” But more importantly, “Rebutting bad science may not be effective, but asserting the true facts of good science is. And including the narrative that explains them is even better.” In my Fukashima radiation page, I explain why I place each sources of information into each category.

    It is difficult to tell the difference between fact and opinion these days, especially with the tremendous amount of information on the internet. It is almost impossible, in many cases, to be able to completely review a subject if one is not an expert in that subject. Even individual scientists, who are subject matter experts, cannot do this. As Gawande mentions, “Few working scientists can give a ground-up explanation of the phenomenon they study; they rely on information and techniques borrowed from other scientists. Knowledge and the virtues of the scientific orientation live far more in the community than the individual.”

    For people live in a world of belief. And modern science is founded on this, the belief that there is a natural systems explanation for observable phenomena. Modern Science arose as a response to the dark ages when religious philosophy dominated our belief systems. Science sure existed before that, but modern science was a rebirth of older practices.
    Some quotes I like to use that reflect how people incorporate science into their belief systems, some more successfully than others.

    • “correlation is not causation”
    • This is possibly the most common mistake that people make.

      Determining causality is one of the most important parts of science because understanding causality allows us to form policy and make smart decisions.
      For example,

      • Someone sees a plane fly overhead, they get sick, and blame the airplane. Maybe they got sick because they were losing sleep worrying about planes that might cause them to get sick.
      • Someone measures differences in radiation between a parking lot and the beach and conclude Fukushima radiation has reached California. The higher radiation at the beach is actually from the feldspar being moved around by the waves.
    • “the absence of evidence is not evidence of absence”
    • In other words, it is possible that there is evidence to support or reject an hypothesis, but we have not (1) observed it or (2) been able to observe it. This is related to the next quote:

    • “we cannot test hypotheses about phenomena for which we cannot yet observe”
    • In other words, one needs to be able to (1) observe phenomena and (2) measure those phenomena before these phenomena can be evaluated with science. Prior to our ability to measure the presence and abundance of different isotopes of Carbon, we could not use radiocarbon dating to evaluate the time when something died. Or, prior to the development of lenses and microscopes, we could not evaluate the existence nor function of cells and subcellular structures.

      The development of new abilities to make observations (and to causal linkages between observations) is the key to scientific discovery. It is extremely unlikely that we know everything that there is to know. For example, recently there was a discovery of a new organ in our body, the mesentery. Scientists needed to be able to measure its structure and function.

      http://www.thelancet.com/journals/langas/article/PIIS2468-1253(16)30026-7/abstract

    Scientific Discovery requires imagination. One needs to think outside of the box in order to create new discoveries. I love using the word create in my science classes.

    Gawande concludes with some thoughts on truth that I fully agree with. That there is no truth, but that scientists (all of us) are truth-seekers. The scientific method is a cycle with ongoing improvements in methods, observation techniques, and inventions (creativity). There is no end.

    The mistake, then, is to believe that the educational credentials you get today give you any special authority on truth. What you have gained is far more important: an understanding of what real truth-seeking looks like. It is the effort not of a single person but of a group of people—the bigger the better—pursuing ideas with curiosity, inquisitiveness, openness, and discipline. As scientists, in other words.

    I guess the cliché that goes along with this is, “the more one knows, the more they know that they don’t know.” Like life, the seeking of scientific facts in a journey, not a destination.

    Resources

    Chemtrails Easily Debunked

    Posted in Uncategorized

    Earthquake Report: 1700 Cascadia subduction zone 317 year commemoration

    Today (possibly tonight at about 9 PM) is the birthday of the last known Cascadia subduction zone (CSZ) earthquake. There is some evidence that there have been more recent CSZ earthquakes (e.g. late 19th century in southern OR / northern CA), but they were not near full margin ruptures (where the entire fault, or most of it, slipped during the earthquake).

    I have been posting material about the CSZ for the past couple of years here and below are some prior Anniversary posts, as well as Earthquake Reports sorted according to their region along the CSZ. Below I present some of the material included in those prior reports (to help bring it all together), but I have prepared a new map for today’s report as well.


    On this evening, 317 years ago, the Cascadia subduction zone fault ruptured as a margin wide earthquake. I here commemorate this birthday with some figures that are in two USGS open source professional papers. The Atwater et al. (2005) paper discusses how we came to the conclusion that this last full margin earthquake happened on January 26, 1700 at about 9 PM (there may have been other large magnitude earthquakes in Cascadia in the 19th century). The Goldfinger et al. (2012) paper discusses how we have concluded that the records from terrestrial paleoseismology are correlable and how we think that the margin may have ruptured in the past (rupture patch sizes and timing). The reference list is extensive and this is but a tiny snapshot of what we have learned about Cascadia subduction zone earthquakes. Brian Atwater and his colleagues have updated the Orphan Tsunami and produced a second edition available here for download and here for hard copy purchase (I have a hard copy).

    Here is a map of the Cascadia subduction zone, modified from Nelson et al. (2006). The Juan de Fuca and Gorda plates subduct northeastwardly beneath the North America plate at rates ranging from 29- to 45-mm/yr. Sites where evidence of past earthquakes (paleoseismology) are denoted by white dots. Where there is also evidence for past CSZ tsunami, there are black dots. These paleoseismology sites are labeled (e.g. Humboldt Bay). Some submarine paleoseismology core sites are also shown as grey dots. The two main spreading ridges are not labeled, but the northern one is the Juan de Fuca ridge (where oceanic crust is formed for the Juan de Fuca plate) and the southern one is the Gorda rise (where the oceanic crust is formed for the Gorda plate).


    Today I prepared this new map showing the results of shakemap scenario model prepared by the USGS. I prepared this map using data that can be downloaded from the USGS website here. Shakemaps show what we think might happen during an earthquake, specifically showing how strongly the ground might shake. There are different measures of this, which include Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), and Modified Mercalli Intensity (MMI). More background information about the shakemap program at the USGS can be found here. One thing that all of these measures share is that they show that there is a diminishing of ground shaking with distance from the earthquake. This means that the further from the earthquake, the less strongly the shaking will be felt. This can be seen on the maps below. The USGS prepares shakemaps for all earthquakes with sufficiently large magnitudes (i.e. we don’t need shakemaps for earthquakes of magnitude M = 1.5). An archive of these USGS shakemaps can be found here. All the scenario USGS shakemaps can be found here.

    I chose to use the MMI representation of ground shaking because it is most easily comparable for people to understand. This is because MMI scale is designed based upon relations between ground shaking intensity and observations that people are able to make (e.g. how strongly they felt the earthquake, how much objects in their residences or places of business responded, how much buildings were damaged, etc.).

    The MMI ground motion model is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. More on the MMI scale can be found here and here.


    Here is the USGS version of this map. The outline of the fault that was used to generate the ground motions that these maps are based upon is outlined in black.


    I prepared an end of the year summary for earthquakes along the CSZ. Below is my map from this Earthquake Report.

    • Here is the map where I show the epicenters as circles with colors designating the age. I also plot the USGS moment tensors for each earthquake, with arrows showing the sense of motion for each earthquake.
    • I placed a moment tensor / focal mechanism legend in the lower left corner of the map. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.
    • In some cases, I am able to interpret the sense of motion for strike-slip earthquakes. In other cases, I do not know enough to be able to make this interpretation (so I plot both solutions).

      I include some inset figures in the poster.

    • In the upper left corner is a map of the Cascadia subduction zone (CSZ) and regional tectonic plate boundary faults. This is modified from several sources (Chaytor et al., 2004; Nelson et al., 2004)
    • Below the CSZ map is an illustration modified from Plafker (1972). This figure shows how a subduction zone deforms between (interseismic) and during (coseismic) earthquakes. Today’s earthquake did not occur along the CSZ, so did not produce crustal deformation like this. However, it is useful to know this when studying the CSZ.
    • To the lower right of the Cascadia map and cross section is a map showing the latest version of the Uniform California Earthquake Rupture Forecast (UCERF). Let it be known that this is not really a forecast, and this name was poorly chosen. People cannot forecast earthquakes. However, it is still useful. The faults are colored vs. their likelihood of rupturing. More can be found about UCERF here. Note that the San Andreas fault, and her two sister faults (Maacama and Bartlett Springs), are orange-red.
    • To the upper right of the Cascadia map and cross section is a map showing the shaking intensities based upon the USGS Shakemap model. Earthquake Scenarios describe the expected ground motions and effects of specific hypothetical large earthquakes. The color scale is the same as found on many of my #EarthquakeReport interpretive posters, the Modified Mercalli Intensity Scale (MMI). The latest version of this map is here.
    • In the upper right corner I include generalized fault map of northern California from Wallace (1990).
    • To the left of the Wallace (1990) map is a figure that shows the evolution of the San Andreas fault system since 30 million years ago (Ma). This is a figure from the USGS here.
    • In the lower right corner I include the Earthquake Shaking Potential map from the state of California. This is a probabilistic seismic hazard map, basically a map that shows the likelihood that there will be shaking of a given amount over a period of time. More can be found from the California Geological Survey here. I place a yellow star in the approximate location of today’s earthquake.


    This figure shows how a subduction zone deforms between (interseismic) and during (coseismic) earthquakes. We also can see how a subduction zone generates a tsunami. Atwater et al., 2005.


    Here is a version of the CSZ cross section alone (Plafker, 1972).


    Here is an animation produced by the folks at Cal Tech following the 2004 Sumatra-Andaman subduction zone earthquake. I have several posts about that earthquake here and here. One may learn more about this animation, as well as download this animation here.

    Here is a graphic showing the sediment-stratigraphic evidence of earthquakes in Cascadia. Atwater et al., 2005. There are 3 panels on the left, showing times of (1) prior to earthquake, (2) several years following the earthquake, and (3) centuries after the earthquake. Before the earthquake, the ground is sufficiently above sea level that trees can grow without fear of being inundated with salt water. During the earthquake, the ground subsides (lowers) so that the area is now inundated during high tides. The salt water kills the trees and other plants. Tidal sediment (like mud) starts to be deposited above the pre-earthquake ground surface. This sediment has organisms within it that reflect the tidal environment. Eventually, the sediment builds up and the crust deforms interseismically until the ground surface is again above sea level. Now plants that can survive in this environment start growing again. There are stumps and tree snags that were rooted in the pre-earthquake soil that can be used to estimate the age of the earthquake using radiocarbon age determinations. The tree snags form “ghost forests.


    Here is a photo of the ghost forest, created from coseismic subsidence during the Jan. 26, 1700 Cascadia subduction zone earthquake. Atwater et al., 2005.


    Here is a photo I took in Alaska, where there was a subduction zone earthquake in 1964. These tree snags were living trees prior to the earthquake and remain to remind us of the earthquake hazards along subduction zones.


    This shows how a tsunami deposit may be preserved in the sediment stratigraphy following a subduction zone earthquake, like in Cascadia. Atwater et al., 2005. If there is a source of sediment to be transported by a tsunami, it will come along for the ride and possibly be deposited upon the pre-earthquake ground surface. Following the earthquake, tidal sediment is deposited above the tsunami transported sediment. Sometimes plants that were growing prior to the earthquake get entombed within the tsunami deposit.


    The NOAA/NWS/Pacific Tsunami Warning Center has updated their animation of the simulation of the 1700 “Orphan Tsunami.”

    Source: Nathan C. Becker, Ph.D. nathan.becker at noaa.gov


    Below are some links and embedded videos.

    • Here is the yt link for the embedded video below.
    • Here is the mp4 link for the embedded video below. (2160p 145 mb mp4)
    • Here is the mp4 link for the embedded video below. (1080p 145 mb mp4)
    • Here is the text associated with this animation:

      Just before midnight on January 27, 1700 a tsunami struck the coasts of Japan without warning since no one in Japan felt the earthquake that must have caused it. Nearly 300 years later scientists and historians in Japan and the United States solved the mystery of what caused this “orphan tsunami” through careful analysis of historical records in Japan as well as oral histories of Native Americans, sediment deposits, and ghost forests of drowned trees in the Pacific Northwest of North America, a region also known as Cascadia. They learned that this geologically active region, the Cascadia Subduction Zone, not only hosts erupting volcanoes but also produces megathrust earthquakes capable of generating devastating, ocean-crossing tsunamis. By comparing the tree rings of dead trees with those still living they could tell when the last of these great earthquakes struck the region. The trees all died in the winter of 1699-1700 when the coasts of northern California, Oregon, and Washington suddenly dropped 1-2 m (3-6 ft.), flooding them with seawater. That much motion over such a large area requires a very large earthquake to explain it—perhaps as large as 9.2 magnitude, comparable to the Great Alaska Earthquake of 1964. Such an earthquake would have ruptured the earth along the entire length of the 1000 km (600 mi) -long fault of the Cascadia Subduction Zone and severe shaking could have lasted for 5 minutes or longer. Its tsunami would cross the Pacific Ocean and reach Japan in about 9 hours, so the earthquake must have occurred around 9 o’clock at night in Cascadia on January 26, 1700 (05:00 January 27 UTC).

      The Pacific Tsunami Warning Center (PTWC) can create an animation of a historical tsunami like this one using the same too that they use for determining tsunami hazard in real time for any tsunami today: the Real-Time Forecasting of Tsunamis (RIFT) forecast model. The RIFT model takes earthquake information as input and calculates how the waves move through the world’s oceans, predicting their speed, wavelength, and amplitude. This animation shows these values through the simulated motion of the waves and as they race around the globe one can also see the distance between successive wave crests (wavelength) as well as their height (half-amplitude) indicated by their color. More importantly, the model also shows what happens when these tsunami waves strike land, the very information that PTWC needs to issue tsunami hazard guidance for impacted coastlines. From the beginning the animation shows all coastlines covered by colored points. These are initially a blue color like the undisturbed ocean to indicate normal sea level, but as the tsunami waves reach them they will change color to represent the height of the waves coming ashore, and often these values are higher than they were in the deeper waters offshore. The color scheme is based on PTWC’s warning criteria, with blue-to-green representing no hazard (less than 30 cm or ~1 ft.), yellow-to-orange indicating low hazard with a stay-off-the-beach recommendation (30 to 100 cm or ~1 to 3 ft.), light red-to-bright red indicating significant hazard requiring evacuation (1 to 3 m or ~3 to 10 ft.), and dark red indicating a severe hazard possibly requiring a second-tier evacuation (greater than 3 m or ~10 ft.).

      Toward the end of this simulated 24-hours of activity the wave animation will transition to the “energy map” of a mathematical surface representing the maximum rise in sea-level on the open ocean caused by the tsunami, a pattern that indicates that the kinetic energy of the tsunami was not distributed evenly across the oceans but instead forms a highly directional “beam” such that the tsunami was far more severe in the middle of the “beam” of energy than on its sides. This pattern also generally correlates to the coastal impacts; note how those coastlines directly in the “beam” have a much higher impact than those to either side of it.

      Offshore, Goldfinger and others (from the 1960’s into the 21st Century, see references in Goldfinger et al., 2012) collected cores in the deep sea. These cores contain submarine landslide deposits (called turbidites). These turbidites are thought to have been deposited as a result of strong ground shaking from large magnitude earthquakes. Goldfinger et al. (2012) compile their research in the USGS professional paper. This map shows where the cores are located.


      Here is an example of how these “seismoturbidites” have been correlated. The correlations are the basis for the interpretation that these submarine landslides were triggered by Cascadia subduction zone earthquakes. This correlation figure demonstrates how well these turbidites have been correlated. Goldfinger et al., 2012.


      This map shows the various possible prehistoric earthquake rupture regions (patches) for the past 10,000 years. Goldfinger et al., 2012. These rupture scenarios have been adopted by the USGS hazards team that determines the seismic hazards for the USA.


      Here is an update of this plot given new correlations from recent work (Goldfinger et al., 2016).


      Here is a plot showing the earthquakes in a linear timescale.


      I combined the plot above into another figure that includes all the recurrence intervals and segment lengths in a single figure. This is modified from Goldfinger et al. (2012).


      http://earthquake.usgs.gov/earthquakes/shakemap/global/shake/casc9.0_expanded_peak_se/

    Posted in cascadia, earthquake, education, geology, gorda, HSU, humboldt, oregon, pacific, plate tectonics, San Andreas, subduction, Transform, tsunami, washington

    Earthquake Report: Bougainville! (western equatorial Pacific)

    Last night (my time) we had a large earthquake along a plate boundary that is one of the most tectonically active regions in the world. There was an earthquake with a magntude of M 7.9 along the San Cristobal Trench (north of the South Solomon Trench). Here is the USGS website for this M 7.9 earthquake. This earthquake seems to be related to a series of earthquakes that started (at least) in December of 2016. This M 7.9 has a similar depth as the 12/17 M 7.9 further to the north. However, today’s earthquake is about 40+- km deeper than the subduction zone fault as suggested by Hayes et al. (2012).

    Below is my interpretive poster for this earthquake.


    I plot the seismicity from the past year, with color representing depth and diameter representing magnitude (see legend).

    • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. The moment tensor shows northeast-southwest compression, perpendicular to the convergence at this plate boundary. Most of the recent seismicity in this region is associated with convergence along the San Cristobal trench or the South Solomon trench.
    • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
    • I include the slab contours plotted (Hayes et al., 2012), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault. The hypocentral depth plots this deeper that the fault as mapped by Hayes et al. (2012).
    • I include some inset figures.

    • In the lower left corner is a generalized tectonic map of the region from Holm et al., 2015. This map shows the major plate boundary faults including the New Britain trench (NBT), one of the main culprits for recent seismicity of this region.
    • In the upper left corner a figure from Oregon State University, which are based upon Hamilton (1979). “Tectonic microplates of the Melanesian region. Arrows show net plate motion relative to the Australian Plate.” This is from Johnson, 1976. There is a plate tectonic map and a cross section showing the subduction of the Solomon Sea plate.
    • In the upper right corner is a figure from Baldwin et al. (2012). This figure shows a series of cross sections along this convergent plate boundary from the Solomon Islands in the east to Papua New Guinea in the west. Cross section ‘C’ is the most representative for the earthquake today. I present the map and this figure again below, with their original captions.
    • In the lower right corner is the USGS fault plane solution plotted in place on a map. This figure shows their model results with color representing the spatial variation in earthquake fault slip for this M 7.8 earthquake. This model is calibrated using seismologic observations. I include the fault plane solution from the 12/17 M 7.9 earthquake to the north for comparison.


    • There have been several observations of tsunami in the region. This table comes from the Pacific Tsunami Warning Center. There was no likelihood for a tsunami to hit the west coast of the continental USA.

    • In earlier earthquake reports, I discussed seismicity from 2000-2015 here. The seismicity on the west of this region appears aligned with north-south shortening along the New Britain trench, while seismicity on the east of this region appears aligned with more east-west shortening. Here is a map that I put together where I show these two tectonic domains with the seismicity from this time period (today’s earthquakes are not plotted on this map, but one may see where they might plot).


    Background Figures

    • Here is the generalized tectonic map of the region from Holm et al., 2015. I include the figure caption below as a blockquote. Compare this figure with the map above where I present the tectonic domains associated with the New Britain and San Cristobal trenches.

    • Tectonic setting and mineral deposits of eastern Papua New Guinea and Solomon Islands. The modern arc setting related to formation of the mineral deposits comprises, from west to east, the West Bismarck arc, the New Britain arc, the Tabar-Lihir-Tanga-Feni Chain and the Solomon arc, associated with north-dipping subduction/underthrusting at the Ramu-Markham fault zone, New Britain trench and San Cristobal trench respectively. Arrows denote plate motion direction of the Australian and Pacific plates. Filled triangles denote active subduction. Outlined triangles denote slow or extinct subduction. NBP: North Bismarck plate; SBP: South Bismarck plate; AT: Adelbert Terrane; FT: Finisterre Terrane; RMF: Ramu-Markham fault zone; NBT: New Britain trench.

    • Here is the slab interpretation for the New Britain region from Holm and Richards, 2013. Note the tear in the slab where the New Britain and South Solomon trenches intersect. This feeds into the tectonic domains discussed in my map above and also here. I include the figure caption below as a blockquote.

    • 3-D model of the Solomon slab comprising the subducted Solomon Sea plate, and associated crust of the Woodlark Basin and Australian plate subducted at the New Britain and San Cristobal trenches. Depth is in kilometres; the top surface of the slab is contoured at 20 km intervals from the Earth’s surface (black) to termination of slabrelated seismicity at approximately 550 km depth (light brown). Red line indicates the locations of the Ramu-Markham Fault (RMF)–New Britain trench (NBT)–San Cristobal trench (SCT); other major structures are removed for clarity; NB, New Britain; NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; TLTF, Tabar–Lihir–Tanga–Feni arc. See text for details.

    • This map shows plate velocities and euler poles for different blocks. Note the counterclockwise motion of the plate that underlies the Solomon Sea (Baldwin et al., 2012). I include the figure caption below as a blockquote.

    • Tectonic maps of the New Guinea region. (a) Seismicity, volcanoes, and plate motion vectors. Plate motion vectors relative to the Australian plate are surface velocity models based on GPS data, fault slip rates, and earthquake focal mechanisms (UNAVCO, http://jules.unavco.org/Voyager/Earth). Earthquake data are sourced from the International Seismological Center EHB Bulletin (http://www.isc.ac.uk); data represent events from January 1994 through January 2009 with constrained focal depths. Background image is generated from http://www.geomapapp.org. Abbreviations: AB, Arafura Basin; AT, Aure Trough; AyT, Ayu Trough; BA, Banda arc; BSSL, Bismarck Sea seismic lineation; BH, Bird’s Head; BT, Banda Trench; BTFZ, Bewani-Torricelli fault zone; DD, Dayman Dome; DEI, D’Entrecasteaux Islands; FP, Fly Platform; GOP, Gulf of Papua; HP, Huon peninsula; LA, Louisiade Archipelago; LFZ, Lowlands fault zone; MaT, Manus Trench; ML, Mt. Lamington; MT, Mt. Trafalgar; MuT, Mussau Trough; MV, Mt. Victory; MTB, Mamberamo thrust belt; MVF, Managalase Plateau volcanic field; NBT, New Britain Trench; NBA, New Britain arc; NF, Nubara fault; NGT, New Guinea Trench; OJP, Ontong Java Plateau; OSF, Owen Stanley fault zone; PFTB, Papuan fold-and-thrust belt; PP, Papuan peninsula; PRi, Pocklington Rise; PT, Pocklington Trough; RMF, Ramu-Markham fault; SST, South Solomons Trench; SA, Solomon arc; SFZ, Sorong fault zone; ST, Seram Trench; TFZ, Tarera-Aiduna fault zone; TJ, AUS-WDKPAC triple junction; TL, Tasman line; TT, Trobriand Trough;WD, Weber Deep;WB, Woodlark Basin;WFTB, Western (Irian) fold-and-thrust belt; WR,Woodlark Rift; WRi, Woodlark Rise; WTB, Weyland thrust; YFZ, Yapen fault zone.White box indicates the location shown in Figure 3. (b) Map of plates, microplates, and tectonic blocks and elements of the New Guinea region. Tectonic elements modified after Hill & Hall (2003). Abbreviations: ADB, Adelbert block; AOB, April ultramafics; AUS, Australian plate; BHB, Bird’s Head block; CM, Cyclops Mountains; CWB, Cendrawasih block; CAR, Caroline microplate; EMD, Ertsberg Mining District; FA, Finisterre arc; IOB, Irian ophiolite belt; KBB, Kubor & Bena blocks (including Bena Bena terrane); LFTB, Lengguru fold-and-thrust belt; MA, Mapenduma anticline; MB, Mamberamo Basin block; MO, Marum ophiolite belt; MHS, Manus hotspot; NBS, North Bismarck plate; NGH, New Guinea highlands block; NNG, Northern New Guinea block; OKT, Ok Tedi mining district; PAC, Pacific plate; PIC, Porgera intrusive complex; PSP, Philippine Sea plate; PUB, Papuan Ultramafic Belt ophiolite; SB, Sepik Basin block; SDB, Sunda block; SBS, South Bismarck plate; SIB, Solomon Islands block; WP, Wandamen peninsula; WDK, Woodlark microplate; YQ, Yeleme quarries.

    • This figure incorporates cross sections and map views of various parts of the regional tectonics (Baldwin et al., 2012). The New Britain region is in the map near the A and B sections. I include the figure caption below as a blockquote.

    • Oblique block diagram of New Guinea from the northeast with schematic cross sections showing the present-day plate tectonic setting. Digital elevation model was generated from http://www.geomapapp.org. Oceanic crust in tectonic cross sections is shown by thick black-and-white hatched lines, with arrows indicating active subduction; thick gray-and-white hatched lines indicate uncertain former subduction. Continental crust, transitional continental crust, and arc-related crust are shown without pattern. Representative geologic cross sections across parts of slices C and D are marked with transparent red ovals and within slices B and E are shown by dotted lines. (i ) Cross section of the Papuan peninsula and D’Entrecasteaux Islands modified from Little et al. (2011), showing the obducted ophiolite belt due to collision of the Australian (AUS) plate with an arc in the Paleogene, with later Pliocene extension and exhumation to form the D’Entrecasteaux Islands. (ii ) Cross section of the Papuan peninsula after Davies & Jaques (1984) shows the Papuan ophiolite thrust over metamorphic rocks of AUS margin affinity. (iii ) Across the Papuan mainland, the cross section after Crowhurst et al. (1996) shows the obducted Marum ophiolite and complex folding and thrusting due to collision of the Melanesian arc (the Adelbert, Finisterre, and Huon blocks) in the Late Miocene to recent. (iv) Across the Bird’s Head, the cross section after Bailly et al. (2009) illustrates deformation in the Lengguru fold-and-thrust belt as a result of Late Miocene–Early Pliocene northeast-southwest shortening, followed by Late Pliocene–Quaternary extension. Abbreviations as in Figure 2, in addition to NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; (U)HP, (ultra)high-pressure.


    Background Videos

    • Here is an educational video (from IRIS) for this part of the western Pacific. There are many plate boundaries and these margins are very active. This is a link to the embedded video below (10.4 MB mp4)
    • I put together an animation that shows the seismicity for this region from 1900-2016 for earthquakes with magnitude of M ≥ 6.5. Here is the USGS query I used to search for these data used in this animation. I show the location of the Benz et al. (2011) cross section E-E’ as a yellow line on the main map.
    • In this animation, I include some figures from the interpretive poster above. I also include a tectonic map based upon Hamilton (1979). Music is from copyright free music online and is entitled “Sub Strut.” Above the video I present a map showing all the earthquakes presented in the video.
    • Here is a link to the embedded video below (5 MB mp4)

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