Earthquake Report: Ecuador

Earlier today there was a moderate sized earthquake (M 6.0) along coast of Ecuador. This earthquake happened in the region of the 2016.04.16 M 7.8 subduction zone earthquake. Based upon the depth and our knowledge of this region, this earthquake may also be on the megathrust. However, the depth is poorly resolved (initially depth ~ 7 km, but now set at 10 km, the default depth). Here is the USGS website for this earthquake.
More information about this earthquake can be found here at earthquake report dot com.

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.
  • 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 lower left corner I include a clipping of the map and cross section from the USGS Open File Report for the historic seismicity of this region (Rhea et al., 2010). I include the seismicity cross section in the upper left corner. This cross section shows earthquakes related to the downgoing Nazca plate.
  • Between the map and cross section, I include the MMI intensity maps for both the M 7.8 earthquake and this M 6.0 earthquake.
  • In the upper right corner, I include a map that shows the regional tectonics as published by Gutscher et al. (1999). These authors pose that the Carnegie Ridge exerts a control for the segmentation of the subduction zone.
  • In the lower right corner, I include a figure from Chlieh et al. (2014) that shows their coupling model. This model informs us about how strongly the subduction zone fault is seismogenically “locked” and how this varies spatially. They also plot historical earthquake locations and their “moment rate deficit” calculation (i.e. how much the plate motion rate has been accumulated as tectonic strain, which would presumably lead to earthquake slip). I include blue stars in the general location of these two earthquakes. The M 7.8 lies within the seismic gap hypothesized by Chlieh et al. (2014).


  • Here is the same poster but only with the seismicity from the past month and the MMI contours from the 2016 M 7.8 earthquake. (wait for now to get this done… need to restart software)

  • Here are my two interpretive posters for the 2016 M 7.8 earthquake. Here is my initial report. Here is my update.
  • First is the initial interpretive poster.

  • Here is the updated interpretive poster.

  • Below is the tectonic setting map from Gutscher et al. (1999). I include their figure caption as a blockquote.

  • Tectonic setting of the study area showing major faults, relative plate motions according to GPS data [7] and the NUVEL-1 global kinematic model [8], magnetic anomalies [13] and active volcanoes [50]. Here and in Fig. 4, the locations of the 1906 (Mw D 8:8, very large open circle) and from south to north, the 1953, 1901, 1942, 1958 and 1979 (M  7:8, large open circles) earthquakes are shown. GG D Gulf of Guayaquil; DGM D Dolores–Guayaquil Megashear.

  • Below is a low angle oblique view of the structures in the downgoing Nazca plate, from Gutscher et al. (1999). I include their figure caption as a blockquote.

  • 3-D view of the two-tear model for the Carnegie Ridge collision featuring: a steep ESE-dipping slab beneath central Colombia; a steep NE-dipping slab from 1ºS to 2ºS; the Peru flat slab segment south of 2ºS; a northern tear along the prolongation of the Malpelo fossil spreading center; a southern tear along the Grijalva FZ; a proposed Carnegie flat slab segment (C.F.S.) supported by the prolongation of Carnegie Ridge.

  • The 2016 M 7.8 earthquake is near two historic earthquakes with similar magnitudes. Below I plot a map showing the seismicity from 1900-2016 for earthquakes with magnitudes greater than or equal to M 6.0. Here is the USGS query that I used to make this map.
    • 1906.01.31 M 8.3 occurred ~100 km to the northeast.
    • 1942.05.14 M 7.8 occurred <50 km to the southwest.


  • Here are a couple maps from Chlieh et al. (2014). I include their figure captions below. Chlieh et al. (2014) use GPS data to infer the spatial variation and degree to which the subduction zone megathrust is seismogenically coupled. They consider plate motion rates and estimate the moment (earthquake energy) deficit along this fault (how much strain that plate convergence has imparted upon the fault over time). Then they compare this moment deficit to regions of the fault that have slipped historically.
  • Tectonics and GPS motion rates.

  • Seismotectonic setting of the oceanic Nazca plate, South America Craton (SoAm) and two slivers: the North Andean Sliver (NAS) and the Inca Sliver (IS). The relative Nazca/SoAm plate convergence rate in Ecuador is about 55mm/yr (Kendrick et al., 2003). Black arrows indicate the diverging forearc slivers motions relative to stable SoAm are computed from the pole solutions of Nocquet et al.(2014). The NAS indicates a northeastward long-term rigid motion of about 8.5 ±1mm/yr. The ellipse indicates the approximate rupture of the great 1906 Mw=8.8 Colombia–Ecuador megathrust earthquake. The Carnegie Ridge intersects the trench in central Ecuador and coincides with the southern limit of the great 1906 event. Plate limits (thick red lines) are from Bird(2003). DGFZ =Dolores–Guayaquil Fault Zone; GG =Gulf of Guayaquil; GR =Grijalva Ridge; AR =Alvarado Ridge; SR =Sarmiento Ridge. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

  • GPS velocities along with historic earthquake patches.

  • Interseismic GPS velocity field in the North Andean Sliver reference frame. The relative Nazca/NAS convergence rate is 46 mm/yr. The highest GPS velocity of 26 mm/yr is found on La Plata Island that is the closest point to the trench axis. The GPS network adequately covers the rupture areas of the 1998 Mw=7.1, 1942 Mw=7.8and 1958 Mw=7.7 earthquakes but only 1/4th of the 1979 Mw=8.2 and 2/3rd of the great 1906 Mw=8.8 rupture area. The black star is the epicenter of the great 1906 event and white stars are the epicenters of the Mw>7.01942–1998 seismic sequence. Grey shaded ellipses are the high slip region of the 1942, 1958, 1979 and 1998 seismic sources (Beck and Ruff, 1984;Segovia, 2001; Swenson and Beck, 1996). Red dashed contours are the relocated aftershocks areas of the 1942, 1958 and 1979 events (Mendoza and Dewey, 1984). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

  • Moment deficit along strike and historic earthquake locations (Chlieh et al., 2014). The 2016 M 7.8 earthquake may have occurred in the region marked “gap” in these figures.

  • (A) Along-strike variations of the annual moment deficit for all the interseismic models shown in Fig.5. (B)Maximum ISC model and (C)Minimum ISC model. (A)The blue, green and red lines correspond to the along-strike variation of the annual moment deficit rate respectively for models with smoothing coefficient λ1 =1.0, 0.25 and 0.1. (B) Smoother solution of Fig.5 ith a maximum moment deficit rate of 4.5 ×1018N m/yr. (C)Rougher solution of Fig.5 with a minimum moment deficit rate of 2.5 ×1018N m/yr. Yellow stars are the epicenters of subduction earthquakes with magnitude Mw>6.0 from the last 400 yr catalogue (Beauval et al., 2013). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

References

Earthquake Report: El Salvador

There were a couple interesting earthquakes offshore of El Salvador “today.” These earthquakes occurred along the Middle America Trench, a low spot in the ocean formed by the subduction of the Cocos plate beneath the Caribbean plate (a convergent plate boundary). The subduction zone here typically generates earthquakes that are the result of horizontal compression (e.g. thrust or reverse earthquakes). Due to the slightly oblique plate convergence, along with preexisting structures (?), there is a large strike-slip fault system in the upper plate (the Caribbean plate) here. These are called forearc sliver faults. As these faults step left and right, they create basins. The forearc sliver faults are also co-located with the magmatic arc (the volcanoes formed because of the subducting oceanic lithosphere).
The earthquakes today are interesting because they have extensional moment tensors (a.k.a. “dilatational”). As oceanic crust subducts, it can deform (bend) and experience extension in parts of the crust when it deforms. Also, the slab (another word for the lithosphere or crust) can also experience extension from the crust being pulled down due to gravity (probably one of the major causes of plate motions), called “slab pull.”
These earthquakes may be experiencing extension for the above two reason. Alternatively, these earthquakes could be in the upper plate where the plate is experiencing along-strike (in the direction parallel to the subduction zone fault trench) extension as a result of the forearc sliver faults stretching parts of the upper plate. The orientation of these earthquakes does not preclude either of these interpretations. These earthquakes have default depths, so it is difficult to know if these are in the downgoing slab or if they are in the upper plate (Caribbean plate).
Based on the seismicity from the past century (mostly M ~6 earthquakes in this region), these earthquakes are probably not foreshocks for a larger earthquake. But, a hundred years is far from enough data to really understand ANY fault system. Seismology (and plate tectonics for that matter) is just too young a science to understand these things. Maybe after a couple thousand years we will have enough data to be able to make meaningful forecasts.
There was an earthquake on 2016.11.24 to the southeast of today’s sequence. Here is my report for that earthquake.

Here are the USGS web pages for the earthquakes.

  • 2017-05-09 14:15 M 5.2 This earthquake may be related, but probably not.
  • 2017-05-12 10:41 M 6.2 the mainshock
  • 2017-05-12 10:51 M 5.4 aftershock
  • 2017-05-12 15:22 M 4.7 aftershock

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 MMI contours for the M 6.2. I also include USGS seismicity for the past century. Here is the kml for these USGS earthquakes for magnitudes M ≥ 7.0 from 1917-2017 that I used to make this map.

  • 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 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 lower left corner, I include a subset of figures from Benz et al. (2011). There is a map that shows USGS epicenters with dots colored by depth and magnitude represented by circle diameter. There is also a cross section for this region, just to the northwest of El Salvador. Cross section B-B’ shows the earthquake hypocenters along a profile displayed on the map. Note how the subduction zone dip steepens to the northeast. I place a green star in the general location of today’s M 6.2 earthquake.
  • In the upper right corner is a tectonic summary figure from Funk et al. (2009). The authors suggest that there is a forearc sliver in this region. A forearc sliver is a large plate boundary scale strike-slip fault bounded block that is formed due to strain partitioning. When the relative plate motion at a subduction zone are not perpendicular to the megathrust fault, the motion that is perpendicular is accommodated by the megathrust fault. The plate motion that is not perpendicular to the subduction zone fault is accommodated by strike-slip faults parallel to the strike of the subduction zone fault. The authors place red arrows showing the relative motion along the plate bounding fault along the eastern boundary of this forearc sliver (these are called forearc sliver faults for obvious reasons). A classic example of a forearc sliver fault is the Sumatra fault along the Sunda subduction zone. Forearc sliver faults do not always bound a block like this and are not always parallel to the plate boundary. The Cascadia subduction zone has a series of forearc sliver faults offshore, but these are formed oblique to the plate boundary. For the case in cascadia, the plate margin parallel strain is accommodated by rotating blocks, not rigid blocks. As these blocks rotate in response to this shear couple, they rotate and form strike-slip faults between the blocks (forming “bookshelf” faults). Another plate where relative oblique motion creates rotating blocks is along the Aleutian subduction zone.
  • In the upper left corner, I include a map from CSEM EMSC. This map was prepared for the 2016.11.24 El Salvador earthquake. They plot focal mechanisms for historic earthquakes in this region. One may observe that there are compression mechanisms associated with the megathrust and that there are strike-slip (shear) mechanisms associated with the strike-slip faults on land.


  • Here is the “seismicity of the Earth” USGS series poster for this region. Click on the thumbnail below for the pdf version (13 MB pdf).

  • Here is the focal mechanism from Anthony Lomax. This orientation and sense (compression) more aligns with what we might expect for earthquakes in this region, however, note that this is still a dilatational (extentional) mechanism.

  • Here is the seismicity map and cross sections for the region to the southeast of El Salvador. The subduction zone in the El Salvador region is depicted by cross section B. Note that the subduction zone has a low angle dip in the shallow region of the fault, then steepens to 55 degrees to the east.



  • (A) Earthquake locations are from the National Earthquake Information Center (NEIC) and, in Nicaragua, were recorded by the local Nicaragua network from 1995 to 2003 operated by the Instituto Nicaraguense de Estudios Territoriales (INETER ). (B–E) Earthquake profiles are perpendicular to the Middle America Trench (MAT) and extend to the interior volcanic highlands of Central America. These profiles merge all earthquakes within a 50-km-wide swath along each transect. Seismic activity beneath the volcanic front in Nicaragua is more evident because of more data from local stations of the Nicaraguan seismic network. These shallow crustal earthquakes commonly occur within the upper 30 km of the crust and are concentrated within ~25 km of the active Central America volcanic front (CAVF).

  • Here is the summary figure from Funk et al. (2009). This map shows the detailed fault mapping the authors prepared for their manuscript. Their observations include field mapping and seismic profiles. There are several parts of this forearc sliver fault system that show how the strike-slip system bends and steps. There are restraining bends (where the s-s fault generates compression) and releasing bends (where the s-s fault generates extension). These regions are colored red and green, respectively. In the Marabios En Exchelon segment of this map there are some plate margin obvlique extensional fault bounded basins. These appear to be formed by bookshelf style faulting.

  • Regional tectonic map of Central America emphasizing key structures described in this paper. The El Salvador fault zone (ESFZ) is characterized by a broad right-lateral shear zone accommodating transtensional motion that results in multiple pull-apart basins . A major transition zone occurs in the Gulf of Fonseca, where strike-slip fault zones along the Central American forearc sliver change strike from dominantly east-west strikes in El Salvador to northwesterly strikes in Nicaragua. A proposed restraining bend connects faults mapped in the Gulf of Fonseca with fault scarps deforming Cosiguina volcano and faults of the Central America volcanic front north of Lake Managua . Diffuse and poorly exposed faults parallel to the Central America volcanic front in northern Nicaraguan segment are inferred to represent a young fault boundary in which right-lateral shear is accommodated over a broad zone. This model proposes a young en echelon pattern of strike-slip and secondary faults based on secondary extensional features and fi ssure eruptions along the Marabios segment of the Central America volcanic front. Lake Managua and the Managua graben are interpreted to occur at a major releasing bend in the trend of the Nicaraguan depression and are marked by the curving surface trace of the Mateare fault interpreted from aeromagnetic data. Subsequent right-lateral strike-slip motion related to translation of the Central America forearc sliver may occur along these reactivated normal faults. The Lake Nicaragua segment of the Central America volcanic front is bounded by a normal fault (LNFZ—Lake Nicaragua fault zone) offsetting the Rivas anticline, the southeastward continuation of this normal fault into Costa Rica (CNFZ—Costa Rica fault zone), and a synthetic normal fault (SRFZ—San Ramon fault zone) that we discovered in our survey of Lake Nicaragua. Transverse faults (MFZ—Morrito fault zone, JMFZ—Jesus Maria fault zone) strike approximately east-west across the Central America volcanic front. North-south–trending rift zones are abundant in El Salvador but less common in Nicaragua and may also be controlled by regional east-west extension affecting the northwestern corner of the Caribbean plate.

  • Here is a figure from a recently published summary of subduction zones from Goes et al. (2017). Note the various factors and forces to which a subducting slab is exposed.

  • Schematic diagram showing the main forces that affect how slabs interact with the transition zone. The slab sinks driven by its negative thermal buoyancy (white filled arrows). Sinking is resisted by viscous drag in the mantle (black arrows) and the frictional/viscous coupling between the subducting and upper plate (pink arrows). To be able to sink, the slab must bend at the trench. This bending is resisted by slab strength (curved green arrow). The amount the slab needs to bend depends on whether the trench is able to retreat, a process driven by the downward force of the slab and resisted (double green arrow) by upper-plate strength and mantle drag (black arrows) below the upper plate. At the transition from ringwoodite to the postspinel phases of bridgmanite and magnesiowüstite (rg – bm + mw), which marks the interface between the upper and lower mantle, the slab’s further sinking is hampered by increased viscous resistance (thick black arrows) as well as the deepening of the endothermic phase transition in the cold slab, which adds positive buoyancy (open white arrow) to the slab. By contrast, the shallowing of exothermic phase transition from olivine to wadsleyite (ol-wd) adds an additional driving force (downward open white arrow), unless it is kinetically delayed in the cold core of the slab (dashed green line), in which case it diminishes the driving force. Phase transitions in the crustal part of the slab (not shown) will additionally affect slab buoyancy. Buckling of the slab in response to the increased sinking resistance at the upper-lower mantle boundary is again resisted by slab strength.

  • This is a summary figure showing subducting slabs and where they experience downdip extension vs downdip compression (Goes et al., 2017). Their cross section for the Cocos plate does not show any region of downdip extension. This slightly favors the upper plate forearc along-strike extensional interpretation for today’s earthquakes.

  • Summary of morphologies of transition-zone slabs as imaged by tomographic studies and their Benioff stress state. Arrows on the map indicate the approximate locations of the cross sections shown around the map, with their points in downdip direction. Blue shapes are schematic representations of slab morphologies (based on the extent of fast seismic anomalies that were tomographically resolvable from the references listed). Horizontal black lines indicate the base of the transition zone (~660 km depth). For flattened slabs, the approximate length of the flat section is given in white text inside the shapes. For penetrating slabs, the approximate depth to which the slabs are continuous is given in black text next to the slabs. Circles inside the slabs indicate whether the mechanisms of earthquakes at intermediate (100–350 km) and deep (350–700 km) are predominantly downdip extensional (black) or compressional (white). Stress states are from the compilations of Isacks and Molnar (1971), Alpert et al. (2010), Bailey et al. (2012), complemented by Gorbatov et al. (1997) for Kamchatka, Stein et al. (1982) for the Antilles, McCrory et al. (2012) for Cascadia, Papazachos et al. (2000) for the Hellenic zone, and Forsyth (1975) for Scotia. The subduction zones considered are (from left to right and top to bottom): RYU—Ryukyu, IZU—Izu, HON—Honshu, KUR—Kuriles, KAM—Kamchatka, ALE—Aleutians, ALA—Alaska, CAL—Calabria, HEL—Hellenic, IND—India, MAR—Marianas, CAS—Cascadia, FAR—Farallon, SUM—Sumatra, JAV—Java, COC—Cocos, ANT—Antilles, TON—Tonga, KER—Kermadec, CHI—Chile, PER—Peru, SCO—Scotia. Numbers next to the red subduction zone codes refer to the tomographic studies used to define the slab shapes: 1—Van der Hilst et al., 1991; Fukao et al., 1992; 2—Bijwaard et al., 1998; Hafkenscheid et al., 2001; Hafkenscheid et al., 2006; 3—Fukao et al., 2001; Fukao et al., 2009; Fukao and Obayashi, 2013; 4—Bunge and Grand, 2000; Grand, 2002; 5—Karason and Van der Hilst, 2000; Replumaz et al., 2004; Li et al., 2008; 6—Miller et al., 2005; Miller et al., 2006; 7—Gorbatov et al., 2000; 8—Hall and Spakman, 2015; 9—Van der Hilst, 1989; Grand et al., 1997; Ren et al., 2007; 10—Van der Lee and Nolet, 1997; Schmid et al., 2002; 11—Sigloch et al., 2008; Sigloch, 2011; 12—Simmons et al., 2012; 13—Gorbatov and Fukao, 2005; 14—Van der Hilst, 1995; Schellart and Spakman, 2012; 15—Spakman et al., 1993; Wortel and Spakman, 2000; Piromallo and Morelli, 2003.

  • Here is a figure from Dewey et al. (2004) that shows a cross section of earthquake hypocenters with symbols representing their mechanism type. There was an earthquake sequence in 2001 that had an extensional mechanism. This supports the interpretation that today’s M 6.2 sequence is in the downgoing slab.

  • Cross section of earthquake hypocenters, 1978–April 2001, classified by focal mechanism as determined by the Harvard CMT methodology (Dziewonski et al., 1981). Events are those that lie within the box labeled “Fig. 5” on Figure 4. Hypocenters of the most destructive El Salvadoran earthquakes since 1978 are labeled by their dates. Shallow-focus earthquakes for which the hypocentroid cannot be accurately determined by Harvard CMT methodology are assigned default depths of 15 km.

References

Earthquake Report: Vanuatu!

There was an earthquake along the New Hebrides Trench this morning (my time in northern California). This earthquake is located deep, possibly below the subduction zone megathrust (but probably is a subduction zone earthquake). The hypocentral depth is 169 km, while the subducting slab is mapped at between 100-120 km in this location. While the slab location has some inherent uncertainty, today’s earthquake is within the range. We probably will never really know, until there is a movie made about this earthquake (surely Hollywood will know).

There was an earthquake on 2015.10.20 that has a similar moment tensor with a slightly larger magnitude (M 7.1). There was also a sequence of earthquakes in this region in April 2016 (here is my report from 2016.04.28).

  • Here are the USGS websites for these two earthquakes.
  • 2015.10.20 M 7.1
  • 2017.05.09 M 6.8

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). In the second poster, I include seismicity from the past century.

  • 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.

    I include some inset figures in the poster.

  • In the upper right corner I include an illustration showing how Oceanic-Oceanic Subduction Zones are configured. One oceanic plate subducts beneath another oceanic plate. At some depth, the water dehydrated from the downgoing plate provides the flux for the mantle to melt. This molten mantle rises due to its decreased density, forming volcanoes. These volcanoes form a line subparallel to the subduction zone trench and we call this a magmatic arc, or an oceanic volcanic arc (or simply, the arc).
  • To the left of this schematic illustration is a plot from Benz et al. (2011). This plot shows a cross section of earthquake hypocenters. Hypocenters are the 3-D locations of earthquakes as calculated from seismologic records. This profile F-F’ is shown on the map as a yellow line with dots at the end of the line.
  • In the lower left corner I include two figures from Cleveland et al. (2014). The upper panel show USGS NEIC earthquake epicenters from 1973-2013 and GCMT moment tensors for earthquakes since 1976. There are some regions of this subduction zone that appear to have repeating earthquakes every decade or two (while other parts of the subduction zone do not). The lower panel shows these earthquakes plotted on a space-time diagram (on the right). This plot shows earthquakes with magnitudes represented by the circle diameter, plotted vs. latitude on the vertical axis and time on the horizontal axis. I place a red star in the approximate location of today’s M 6.8 earthquake.


  • Here is a version showing USGS seismicity from 1917-2017 for earthquakes with magnitudes M ≥ 7.0


  • Here is an animation that shows the seismicity for this region from 1960 – 2016 for earthquakes with magnitudes greater than or equal to 7.0.
  • I include some figures mentioned in my report from 2016.04.28 for a sequence of earthquakes in the same region as today’s earthquake (albeit shallower hypocentral depths), in addition to a plot from Cleveland et al. (2014). In the upper right corner, Cleveland et al. (2014) on the left plot a map showing earthquake epicenters for the time period listed below the plot on the right. On the right is a plot of earthquakes (diameter = magnitude) of earthquakes with latitude on the vertical axis and time on the horizontal axis. Cleveland et al (2014) discuss these short periods of seismicity that span a certain range of fault length along the New Hebrides Trench in this area. Above is a screen shot image and below is the video.

  • Here is a link to the embedded video below (6 MB mp4)
  • Here are the two figures from Cleveland et al. (2014).
  • Figure 1. I include the figure caption below as a blockquote.

  • (left) Seismicity of the northern Vanuatu subduction zone, displaying all USGS-NEIC earthquake hypocenters since 1973. The Australian plate subducts beneath the Pacific in nearly trench-orthogonal convergence along the Vanuatu subduction zone. The largest events are displayed with dotted outlines of the magnitude-scaled circle. Convergence rates are calculated using the MORVEL model for Australia Plate relative to Pacific Plate [DeMets et al., 2010]. (right) All GCMT moment tensor solutions and centroids for Mw ≥ 5 since 1976, scaled with moment. This region experiences abundant moderate and large earthquakes but lacks any events with Mw >8 since at least 1900.

  • Figure 17. I include the figure caption below as a blockquote.

  • One hundred day aftershock distributions of all earthquakes listed in the ISC catalog for the 1966 sequence and in the USGS-NEIC catalog for the 1980, 1997, 2009, and 2013 sequences in northern Vanuatu. The 1966 main shocks are plotted at locations listed by Tajima et al. [1990]. Events of the 1997 and 2009 sequences were relocated using the double difference method [Waldhauser and Ellsworth, 2000] for P wave first arrivals based on EDR picks. The event symbol areas are scaled relative to the earthquake magnitudes based on a method developed by Utsu and Seki [1954]. Hypocenters of most aftershock events occurred at <50 km depth.

  • Figure 17. I include the figure caption below as a blockquote.

  • (right) Space-time plot of shallow (≤ 70 km) seismicity M ≥ 5.0 in northern Vanuatu recorded in the NEIC catalog as a function of distance south of ~10°N, 165.25°E. (left) The location of the seismicity on a map rotated to orient the trench vertically.

  • Here is the USGS poster showing the seismicity for this region from 1900-2010 (Benz et al., 2011). Below I include the legend (not the correct scale; click on this link for the entire poster (65 MB pdf)). Note the cross section F-F’ which I plot on the poster above.


  • Here is the cross section F-F’ again, with the legend below.


References

Earthquake Report: Denali fault, British Columbia

This is an interesting earthquake for a number of reasons. The epicenters of the largest earthquakes in this series (M 6.2 and M 6.3) align just off-strike from the Dalton section of the Denali fault (DF) which was mapped as having offset Holocene features by Plafker et al (1977), though there were no numerical ages to support their interpretation. This is just north of the Chilkat River section of the DF and just north of the Chatham Strait section of the DF. These sections of the Denali fault have not been found to be active (though they may be and today’s earthquake sequence suggests that they are!). There are many faults mapped in this region based upon the British Columbia data catalogue.
The moment tensor for the M 6.3 is also slightly misaligned to the orientation (strike) of the Denali fault here. Also interesting because the USGS has been putting forth significant effort on an investigation of the Quuen Charlotte (QCF)/Fairweather fault to the south of these earthquakes. The Chatham Strait fault splinters eastwards from the QCF and connects to the Denali fault just south of this sequence. The Chatham Strait fault was recognized to have dextral slip (right-lateral strike-slip) by Hudson et al. (1982; and references therein) using offsets of geologic units. These and earlier authors found up to 150 km of separation (offset) of these post-middle Cretaceous rocks.
UPDATE: Dr. Rick Koehler (UNR) informs me that the Chilkat section is now included in the Dalton section of the Denali fault.

  • Here are the USGS websites for the two largest earthquakes.
  • 2017.05.01 12:31 M 6.2
  • 2017.05.01 14:18 M 6.3

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 plot USGS epicenters from 1917-2017 for magnitudes M ≥ 3.5. For some of the larger magnitude earthquakes, I include moment tensors (blue) and a focal mechanism (orange) that shows the sense of motion on the faults. I outline the aftershock region of this current sequence in dashed white lines. Here is the USGS kml query file that I used to create this map. Here is a USGS kml file that only includes the earthquakes M ≥ 5.5.

  • 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. Based upon the alignment of the two mainshocks and the regionally mapped faults, I interpret these to be right-lateral strike-slip faults.
  • 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.

  • In the lower left 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. I place a blue star in the general location of today’s earthquake sequence.
  • In the upper left corner is a map from the USGS that shows the regional tectonic boundary fault system. The USGS has been working on the onshore and offshore segments of the Queen Charlotte fault for the past few years. For the region of the QCF that is in Canada waters, the Canada Geological Survey has been studying there.
  • In the upper right corner are the MMI intensity maps for the two earthquakes listed above: 2017 M 6.3 & 6.2. 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). The data seem to fit slightly better to the California empirical relations, which makes sense because this region of Canada/USA is a series of accreted terranes (sequences of subduction zone and oceanic crust material that has been accreted to the North America plate during subduction zone convergence).
  • To the left of these DYFI maps is a map from Walton et al. (2015) that shows extents of some of the large earthquakes along the QCF. They also plot the seismicity and focal mechanism from the 2012 Haida Gwaii earthquake and 2013 QCF sequences.
  • In the lower right corner is a map showing these accreted terranes (British Columbia Geological Survey, 2011).


  • Here is the map from Hauessler et al., 2014.

  • Here is the USGS fault map. I include their figure text below as blockquote.

  • Study region along the Queen Charlotte-Fairweather fault offshore southeastern Alaska. Rectangles show locations of the two USGS-led marine geophysical surveys in May and August 2015. The third cruise was offshore Haida Gwaii, British Columbia, and southern Alaska in September 2015 (see inset map). CSF, Chatham Strait fault; CSZ, Coastal shear zone; LIPSF, Lisianski Inlet-Peril Strait fault; QCFF, Queen Charlotte-Fairweather fault.

  • This is the figure from Walton et al. (2015) showing the extent of some historical ruptures along the QCF.

  • Regional tectonic setting of the Queen Charlotte fault (QCF), including major fault traces. The inset shows regional location. Because of the angle of the Pacific plate vector and the geometry of the QCF, convergence along the fault increases to the south. The bold X on the QCF marks a 10° change in strike of the QCF at 53.2° N, south of which is an obliquely convergent segment of the QCF undergoing convergence rates up to ∼20 mm=yr. The QCF is bounded to the north by the Yakutat block and to the south by the Explorer triple junction. Rupture zones defined by aftershocks for major historic earthquakes along the margin are indicated by dashed black outlines (Plafker et al., 1994). Aftershocks
    circles) and focal mechanisms for the 2013 Mw 7.5 Craig earthquake and the 2012 Mw 7.8 Haida Gwaii earthquake are also included, along with a magnitude scale for aftershocks (derived from the Global Centroid Moment Tensor catalog; Ekström et al., 2012; see Data and Resources). DE, Dixon Entrance; TWS, Tuzo Wilson seamounts; DK, Dellwood Knolls; TF, Transition fault; FF, Fairweather fault; PSF, Peril Strait fault; CSF, Chatham Strait fault.

  • Here is a figure from some of the early work on the Chatham Strait fault (Lathram, 1964).

  • Map showing geologic features displaced by the Chatham Strait fault.

  • Here is a great map showing the Denali fault system and some of the paleoseismologic sites on the eastern sections of this fault system (Redfield and Fitzgerald, 1993).

  • Simplified schematic terrane map of Alaska after Coe et. al. [1985] and Howell et al. [1985], showing the locations of major tectonostratigraphic terranes, structures, relative motion vector(RMV) analysis sites, and other localities mentioned in the text. Note that the Yakutat terrane extends offshore. RMV sites on the DFS are marked with a solid dot. Site 1 of the DFS is on the Togiak/Tikchik fault. Sites 2 and 3 of the DFS are on the Holitna fault. Sites 4-7 of the DFS are on the Farewell fault. Sites 8-10 of the DFS are on the McKinley strand of the Denali fault. Sites 11 and 12 of the DFS is on the Shakwak fault. Site 13 of the DFS is on the faiton Fault. Site 14 of the DFS is on the Chatham Strait fault.

  • Here is the map showing the Terranes in British Columbia. This map shows a more regional view than the one on the interpretive poster above.

  • The framework of the Cordilleran orogen of northwestern North America is commonly depicted as a ‘collage’ of terranes – crustal blocks containing records of a variety of geodynamic environments including continental fragments, pieces of island arc crust and oceanic crust. The series of maps available here are derived from a GIS compilation of terranes based on the map published by Colpron et al. (2007) and Nelson and Colpron (2007), and include modifications from recent regional mapping. These maps are presented in a variety of digital formats including ArcGIS file geodatabase (.gdb), shapefiles (.shp and related files) and Map Packages (.mpk), as well as in a number of graphic formats (Adobe Illustrator CS3, CorelDraw X3, PDF and JPEG). The GIS data include individual terrane layers for British Columbia, Yukon and Alaska, as well as a layer showing selected major Late Cretaceous and Tertiary strike-slip faults. Graphic files derived from the GIS compilation were prepared for the Northern Cordillera (Alaska, Yukon and BC), the Canadian Cordillera (BC and Yukon), Yukon, and British Columbia. These maps are intended for page-size display (~1:5,000,000 and smaller). Polygons are accurate to ~1 km for Yukon and BC, and ~5 km for Alaska. More detailed geological data are available from both BC Geological Survey and Yukon Geological Survey websites. Descriptions of the terranes, their tectonic evolution and metallogeny can be found in Colpron et al. (2007), Nelson and Colpron (2007), Colpron and Nelson (2009).

  • Here is a map showing all the mapped faults in this region. I drew a dashed blue line connecting the M 6.3 and M 6.2 epicenters. Note (if one clicks on the map to see a larger version) that the orientation of this alignment is oblique to the fault orientations (which are generally aligned sub parallel to the Denali fault). This map comes from the British Columbia data catalogue.

  • UPDATE: Dr. Sean Bemis posted this model on Sketchfab. Dr. Bemis used 1948 aerial imagery, in Agisoft Photoscan software, to create this 3-D model using the method called “Structure For Motion” (SFM). He then exported the model to Sketchfab. Agisoft has academic pricing for their software. However, there is also free software available that does the stuff the Photoscan does (though one may need to use multiple apps).
  • There is a north-south lineation that aligns nicely with the strike-line formed between the M 6.3 & M 6.2 epicenters (not shown on the 3-D model).

References:

  • Benz, H.M., Tarr, A.C., Hayes, G.P., Villaseñor, Antonio, Hayes, G.P., Furlong, K.P., Dart, R.L., and Rhea, Susan, 2010. Seismicity of the Earth 1900–2010 Aleutian arc and vicinity: U.S. Geological Survey Open-File Report 2010–1083-B, scale 1:5,000,000.
  • Haeussler, P., Leith, W., Wald, D., Filson, J., Wolfe, C., and Applegate, D., 2014. Geophysical Advances Triggered by the 1964 Great Alaska Earthquake in EOS, Transactions, American Geophysical Union, v. 95, no. 17, p. 141-142.
  • Hudson, Travis, Plafker, George, and Dixon, Kirk, 1982, Horizontal offset history of the Chatham Strait fault, in Coonrad, W.L., ed., The United States Geological Survey in Alaska, Accomplishments during 1980, Geological Survey Circular 844, p. 128-131
  • Lathram, E.H., 1964. Apparent Right-Lateral Separation on Chatham Strait Fault, Southeastern Alaska in GSA Bulletin, v. 75, p. 249-252.
  • Plafker, G., 1969. Tectonics of the March 27, 1964 Alaska earthquake: U.S. Geological Survey Professional Paper 543–I, 74 p., 2 sheets, scales 1:2,000,000 and 1:500,000, http://pubs.usgs.gov/pp/0543i/.
  • Redfield, T.F. and Fitzgerald, P.G., 1993. Denali Fault System of Southern Alaska: An Interior Strike_slip Structure Responding to Dextral and Sinistral Shear Coupling in Tectonics, v. 12, no. 5, p. 1195-1208
  • West, M.E., Haeussler, P.L., Ruppert, N.A., Freymueller, J.T., and the Alaska Seismic Hazards Safety Commission, 2014. Why the 1964 Great Alaska Earthquake Matters 50 Years Later in Seismological Research Letters, v. 85, no. 2, p. 1-7.

Earthquake Report: Chile Update #1

Well, I thought more to compare this ongoing earthquake sequence with the 1985 M 8.0 earthquake. This, in context with the 2010 and 2015 earthquakes. My initial report based upon the M ~4-5.9 swarm is here and my report on the “current” M 6.9 mainshock is here.
More information about the background for the tectonics along the plate boundary, please refer to those earlier reports.
I used the USGS epicenters for earthquakes with magnitudes M ≥ 2.5. For each earthquake (1985, 2010, and 2015) I chose a month of seismicity beginning 3 days before the mainshock. Then I digitized the general outline of the earthquakes. This is a rough approximation for the slip patch for each of these earthquakes. I separated the interface earthquakes from the triggered outer rise earthquakes into separate polygons for the 2010 and 2015 earthquakes (they both appear to have triggered earthquakes in the downgoing Nazca plate to the west of the subduction zone fault, where it flexes in response to subduction here.
This current sequence is about the same magnitude and along-strike size as the 1971 earthquake (M 7.0). This sequence also lies within the 1985 earthquake aftershock region (and also within the northernmost area of the 2010 aftershock region). The M 6.9 could still be a foreshock of a larger earthquake. The 1985 earthquake was preceded by 3 earthquakes in the M 4-5.5 range. But, looking into the past, there are instances when this part of the fault only ruptures a small patch (1971, 1873, 1851). Given that this part of the fault slipped recently (2010), it seems more probable that there won’t be a larger earthquake (M > 8.0). This is difficult to know because we don’t really know the state of stress on the fault (how ready it is to rupture in an earthquake). I still cannot stop thinking about the Juan Fernandez Ridge and how this plays a part in this story.
I include the moment tensors from each of the Great Earthquakes, as well as the 2017 M 6.9 earthquake.

  • In the interpretive poster below
    • I outline the 1985 aftershock region in black dashed lines
    • I outline the 2010 aftershock region in blue dashed lines
    • I outline the 2015 aftershock region in white dashed lines
    • I outline the 2017 aftershock region in red dashed lines

Other Blogs about this earthquake sequence

Below is my interpretive poster for this earthquake. Click on the map to enlarge.

  • 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.

    I include one inset figure in the poster.

  • In the upper right corner I present Figure 2 from Beck et al. (1998 ) on the map, the space-time plot of historic and prehistoric earthquakes associated with the Chile subduction zone. I add a green line showing my interpretation for the strike length of the 2015 M 8.3 earthquake. Originally it appeared to match the 1943 and 1880 earthquakes, though it appears to extend further along strike. The 1922 and 1880 strike lengths are not well constrained, so this 2015 earthquake may indeed be slipping the same patch of this part of the subduction zone. Indeed, Juan Fernandez Ridge may be a structural boundary that may cause segmentation in this part of the subduction zone. If it does, it does not do so every time, as evidenced by the strike-length of the 1730 AD and 1647 AD earthquakes. I placed a green triangle at the approximate location of this 2017 swarm. This M 6.9 appears to be correlative in space with the 1985 earthquake (albeit a much smaller magnitude, closer to the 1971 in size).


Some background about the heterogeneous megathrust in this region

  • Here is the first of two figures from Moreno et al., 2010. Note that the M 6.9 is close in space to the 1985 earthquake. Also note the along strike heterogeneous seismogenic coupling. I include the figure caption 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.

  • Here is the second of the two figures from Moreno et al. (2010).

  • Relationship 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.

References:

Earthquake Report: Chile!

Well, we had another earthquake in the region of a recent (yesterday and the day before) swarm offshore of Valparaiso, Chile (almost due west of Santiago, one of the largest cities in Chile). My previous report on the M 4-5 earthquakes can be found here. The earlier swarm was a series of shallower earthquakes (though some were of intermediate depth and some were deeper). The M 6.9 earthquake, in contrast, is deeper and likely on the megathrust. The slab contours are at 20 km and the hypocentral depth is 25 km (pretty good match considering the uncertainty with the location of the megathrust). Another difference is that the M 6.9 has a greater potential (likelihood, or chance) to damage people or their belongings.

Here are the USGS websites for these earthquakes

  • 2017.04.22 22:46 M 4.9
  • 2017.04.23 01:49 M 4.5
  • 2017.04.23 02:36 M 5.9 (mainshock)
  • 2017.04.23 02:43 M 4.8
  • 2017.04.23 02:52 M 4.8
  • 2017.04.23 03:00 M 4.8
  • 2017.04.23 03:02 M 4.9
  • 2017.04.23 19:40 M 5.6
  • 2017.04.24 21:38 M 6.9 (triggered mainshock)

I took a look at the seismicity from the past century. Here are Google Earth kml files from the USGS website for earthquakes from 1917-2017 with magnitudes M ≥ 5.0, M ≥ 6.0, and M ≥ 7.0.

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 epicenters for earthquakes from 1917-2017 with magnitudes M ≥ 6.0. I outline the regions of the subduction zone that have participated in earthquake slip during the 21st century (in white dashed polygons). I include USGS moment tensors from the largest earthquakes. I plot the focal mechanism for the 1960 earthquake from Moreno et al. (2011). Note the gap in seismicity in the region of the 1960 M 9.5 earthquake, except for the 2016 M 7.6 earthquake. Also, note how the 1960 and 2010 earthquake slip patches overlap.
Much of the subduction zone has ruptured, except for some spots between the 2001 and 2015 earthquakes. In 2015, I speculated that the region north of the 2015 earthquakes constituted a seismic gap. This region may get filled by a Great subduction zone earthquake or may continue to slip in moderate sized earthquakes (or be aseismic). There was an earthquake in 1877 that spanned 19-23 degrees (overlapping with the 2014 earthquake). This is shown on the Schurr et al. (2014) figure below).

  • 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.

    I include some inset figures in the poster.

  • In the lower left corner, I include a map and a cross section of the subduction zone just to the south of this Sept/Nov 2015 swarm (Melnick et al., 2006). I placed a green triangle at the approximate location of this 2017 swarm.
  • In the upper right corner I present Figure 2 from Beck et al. (1998 ) on the map, the space-time plot of historic and prehistoric earthquakes associated with the Chile subduction zone. I add a green line showing my interpretation for the strike length of the 2015 M 8.3 earthquake. Originally it appeared to match the 1943 and 1880 earthquakes, though it appears to extend further along strike. The 1922 and 1880 strike lengths are not well constrained, so this 2015 earthquake may indeed be slipping the same patch of this part of the subduction zone. Indeed, Juan Fernandez Ridge may be a structural boundary that may cause segmentation in this part of the subduction zone. If it does, it does not do so every time, as evidenced by the strike-length of the 1730 AD and 1647 AD earthquakes. I placed a green triangle at the approximate location of this 2017 swarm. This M 6.9 appears to be correlative in space with the 1985 earthquake (albeit a much smaller magnitude, closer to the 1971 in size).
  • In the lower right corner I include two figures from Moreno et al. (2010). The upper one shows the spatial extent of historic subduction zone earthquakes in this region, the GPS velocities, and the fraction of plate convergence attributed to fault seismogenic coupling. The lower panel shows the amount of slip that is attributed to the 1960 and 2010 earthquakes (on the left) and various measures of seismicity and slip deficit (on the right). I place a green star in the general location of the M 6.9 and a green horizontal bar that matches the latitude of this M 6.9 earthquake.
  • In the upper left corner, I include a local map showing the MMI contours for the M 6.9 earthquake. I include the USGS moment tensors from most of the earthquakes in this swarm, including the M 6.9 earthquake.


  • As mentioned above, this earthquake has the potential to cause more harm than the earlier earthquakes due to its larger magnitude. Below is the USGS report that includes estimates of damage to people (possible fatalities) and their belongings from the Rapid Assessment of an Earthquake’s Impact (PAGER) report. More on the PAGER program can be found here. An explanation of a PAGER report can be found here. PAGER reports are modeled estimates of damage. On the top is a histogram showing estimated casualties and on the right is an estimate of possible economic losses. This PAGER report suggests that there will be quite a bit of damage from this earthquake (and casualties). This earthquake has a high probability of damage to people and their belongings.

  • UPDATE: Below are some observations of the tsunami. This comes from the Pacific Tsunami Warning Center.

  • Here is the figure from Lin et al. (2013) that shows the tectonic context of the 2010 Maule earthquake. 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].

  • Here is a cross section of the subduction zone just to the south of this 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 ).

  • Here is the first of two figures from Moreno et al., 2010. Note that the M 6.9 is close in space to the 1985 earthquake. I include the figure caption 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.

  • Here is the second of the two figures from Moreno et al. (2010).

  • Relationship 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.

  • Here is the Beck et al. (1998) space time diagram.

Here is an animation of seismicity from the 21st century

Useful Resources

References:

Earthquake Report: Chile!

There have been a number of earthquakes along the subduction zone offshore of Chile. These have happened near the boundary of two Great Earthquakes from 2010 and 2015. This region may be a segment boundary along the subduction zone, albeit possibly a non persistent one. The Juan Ferndandez ridge may control this segmentation. While this is in a region of low slip for the 2010 and 2015 earthquakes, due to the proximity of the Juan Fernandez fracture zone (which possibly promotes smaller earthquakes), there may not be a larger earthquake here. If there is, it might look something like the 1971 earthquake, with a magnitude of low 7 or so. (which could still be quite damaging).

The earthquakes from today and yesterday form a range of about 1 1/2 magnitudes (M 4.2- M 5.9). This may be considered a swarm (when there are a series of earthquakes along a fault with similar magnitudes), though there is an M 5.9 that could be considered the mainshock. But, I would not get hung up on terminology as that is not very important. However, there is a great page with a discussion about swarms, including some good examples.

Here are the USGS websites for these earthquakes

I took a look at the seismicity from the past century. Here are Google Earth kml files from the USGS website for earthquakes from 1917-2017 with magnitudes M ≥ 5.0, M ≥ 6.0, and M ≥ 7.0.

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 epicenters for earthquakes from 1917-2017 with magnitudes M ≥ 5.0. I outline the regions of the subduction zone that have participated in earthquake slip during the 21st century (in white dashed polygons). I include USGS moment tensors from the largest earthquakes. I plot the focal mechanism for the 1960 earthquake from Moreno et al. (2011). Note the gap in seismicity in the region of the 1960 M 9.5 earthquake, except for the 2016 M 7.6 earthquake. Also, note how the 1960 and 2010 earthquake slip patches overlap.
Much of the subduction zone has ruptured, except for some spots between the 2001 and 2015 earthquakes. In 2015, I speculated that the region north of the 2015 earthquakes constituted a seismic gap. This region may get filled by a Great subduction zone earthquake or may continue to slip in moderate sized earthquakes (or be aseismic). There was an earthquake in 1877 that spanned 19-23 degrees (overlapping with the 2014 earthquake). This is shown on the Schurr et al. (2014) figure below).

  • 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.

    I include some inset figures in the poster.

  • In the lower left corner, I include a 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 as part of the 2010 earthquake sequence. I placed a green triangle at the approximate location of this 2017 swarm.
  • In the lower right corner, I include a time-space diagram from Moernaut et al. (2010). There is also a map showing the fracture zones. I placed a green triangle at the approximate location of this 2017 swarm.
  • Above the Moernaut et al. (2010) figure, I present Figure 2 from Beck et al. (1998 ) on the map, the space-time plot of historic and prehistoric earthquakes associated with the Chile subduction zone. This space-time plot overlaps slightly with the Moernaut figure. I add a green line showing my interpretation for the strike length of the 2015 M 8.3 earthquake. Originally it appeared to match the 1943 and 1880 earthquakes, though it appears to extend further along strike. The 1922 and 1880 strike lengths are not well constrained, so this 2015 earthquake may indeed be slipping the same patch of this part of the subduction zone. Indeed, Juan Fernandez Ridge may be a structural boundary that may cause segmentation in this part of the subduction zone. If it does, it does not do so every time, as evidenced by the strike-length of the 1730 AD and 1647 AD earthquakes. I placed a green triangle at the approximate location of this 2017 swarm.
  • In the upper right corner is a space-time figure showing earthquakes for the past few centuries. This diagram does not overlap with the Beck figure. This figure shows the outline of some subduction zone earthquakes and shows how the 2014 earthquake is composed of two earthquakes (an M 8.1 and an M 7.6) that ruptured different but adjacent patches of the subduction zone.
  • In the upper left corner, I include a local map showing the MMI contours for the M 5.9 earthquake. I include the USGS moment tensors from most of the earthquakes in this swarm.


  • Here is the figure from Lin et al. (2013) that shows the tectonic context of the 2010 Maule earthquake. 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].

  • Here is a cross section of the subduction zone just to the south of this 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 March 2015, there was some seismicity in this September/November 2015 earthquake slip region. I put together an earthquake report about those earthquake of magnitudes M = 5.0-5.3. I speculate that the 1922 earthquake region is a seismic gap. Note that this September/November 2015 earthquake region is along the southern portion of the seismic gap that I labeled on the map below.
  • Here is a map that shows the recent swarm of ~M = 5 earthquakes. There are moment tensors for the earthquakes listed below, some recent historic subduction zone earthquakes. I placed the general along-strike distance for older historic earthquakes in green (and labeled their years). The largest earthquake ever recorded, the Mw = 9.5 Chile earthquake, had a slip patch that extends from the south of the map to just south of the 2010 earthquake swarm. The 2010 and 2014 earthquake swarm epicenters are plotted as colored circles, while most other historic earthquake epicenters are plotted as gray circles. Note how this March 2015 swarm is at the northern end of the 1922/11/11 M 8.3 earthquake. At the bottom of this page, I put a USGS graphic about what these moment tensor plots (beach balls) tell us about the earthquakes.

  • Here is the first space-time figure from Schurr et al., 2014. I include their caption as blockquote below.

  • Map of Northern Chile and Southern Peru showing historical earthquakes and instrumentally recorded megathrust ruptures. IPOC instruments used in the present study (BB, broadband; SM, strong motion) are shown as blue symbols. Left: historical1,2 and instrumental earthquake record. Centre: rupture length was calculated using the regression suggested in ref. 28, with grey lines for earthquakes M .7 and red lines for Mw .8. The slip distribution of the 2014 Iquique event and its largest aftershock derived in this study are colour coded, with contour intervals of 0.5 m. The green and black vectors are the observed and modelled horizontal surface displacements of the mainshock. The slip areas of the most recent other large ruptures4,5,7 are also plotted. Right: moment deficit per kilometre along strike left along the plate boundary after the Iquique event for moment accumulated since 1877, assuming current locking (Fig. 3a). The total accumulated moment since 1877 from 17u S to 25u S (red solid line) is 8.97; the remaining moment after subtracting all earthquake events with Mw .7 (grey dotted line) is 8.91 for the entire northern Chile–southern Peru seismic gap

  • Here is the Beck et al. (1998) space time diagram.

  • Finally, here is the southernmost space-time diagram from Moernaut et al. (2010). These data are largely derived from Melnick et al. (2009).

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

Here is an animation of seismicity from the 21st century

Useful Resources

References:

Earthquake Report: Gulf California!

There was an earthquake yesterday in the Gulf of California nearby a series of earthquakes that happened in 2015 and earlier in 2013. The 2017 and 2013 earthquakes are happening along a fault that forms the Carmen Basin and the 2015 earthquakes are rupturing a fault that appears to be in the middle of the Farallon Basin. Here is my Earthquake Report for the 2013 earthquake (an early report, so it is rather basic). Here is my Earthquake Report for the 2015 earthquake sequence. This is an update to the initial 2015 report.

    Here are the USGS web pages for these earthquakes


    2013

  • 2013.10.19 M 6.4

  • 2015

  • 2015.09.13 M 6.6
  • 2015.09.13 M 5.3
  • 2015.09.13 M 4.9
  • 2015.09.13 M 5.2

  • 2017

  • 2017.03.29 M 5.7

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 epicenters for earthquakes from 1917-2017 with magnitudes M ≥ 6.5.

  • 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 suspect that the fault that ruptured is eastward vergent (dipping to the west), so the west dipping nodal plane is probably the primary fault plane. However, this region of Kamchatka has numerous upper plate thrust and reverse faults (so the primary fault plane could be the other one, dipping to the east).
  • 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.

  • In the upper left corner I include a map that shows the tectonic setting of this region, with the geological units colored relative to their age and type (marine or continental).This is from a paper that discusses the interaction between spreading ridges and subduction trenches (Fletcher et al., 2007).
  • In the upper right corner I include a larger saled version of this map with the same seismicity plotted, but without the MMI contours. One can see the shape of the seafloor and how this is formed due to plate tectonics. Note the spreading ridge in the lower right corner and the parallel ridges formed as the plates extend from the ridge. The magnitude scale is slightly different than the main map.
  • In the lower left corner I include a map from the 2015 earthquake series. I include this because I labeled the Basins formed by the enechelon steps in this plate boundary. In my 2015 report, I provide more maps that include the names of some of these fracture zones (the transform plate boundary strike-slip faults).


  • Here is a great diagram showing the major faults in the region. I include their figure caption below.

  • (A) Simplified map of the Gulf of California region and Baja California peninsula showing the present plate boundary and some major tectonic features related to the plate-tectonic history since 12 Ma. The Gulf extensional province in gray is bounded by the Main Gulf Escarpment (bold dashed lines), which runs through the Loreto area and is shown in Figure 3. The Salton trough in southern California is merely the northern part of the Gulf extensional province. (B) Map of part of the southern Gulf of California and Baja California peninsula showing bathymetry (in meters), the transform–spreading-ridge plate boundary, and the location of subsequent figures with maps. The bathymetry is after a map in Ness and Lyle (1991) and the transform–spreading-ridge plate boundary is from Lonsdale (1989). The lines with double arrows are the three proposed rift segments modified here after Axen (1995); MS—Mulege´ segment, LS—Loreto segment, TS—Timbabichi
    segment.

  • This map shows the magnetic anomalies and the geologic map for the land and the youngest oceanic crust.

  • (A) Tectonic map of the southern Baja California microplate (BCM) and Gulf of California extensional province (GEP). The Magdalena fan is deposited on oceanic crust of the Farallon-derived Magdalena microplate located west of Baja California. Deep Sea Drilling Project Site 471 is shown as black dot on the Magdalena fan. Abbreviations: BCT—Baja California trench, BM—Bahia Magdalena, LC—Los Cabos block, T—Trinidad block, LP—La Paz, PV—Puerto Vallarta, SMSLF—Santa Margarita–San Lazaro fault, TAF—Tosco-Abreojos fault, TS—Todos Santos, V—Vizcaino peninsula. Geology is simplifi ed from Muehlberger (1996). Interpretation of marine magnetic anomalies, with numbers denoting the chron of positively magnetized stripes, is from Severinghaus and Atwater (1989) and Lonsdale (1991).

  • This map shows a more broad view of the magnetic anomalies through time.

  • Map-view time slices showing the widely accepted model for the two-phase kinematic evolution of plate margin shearing around the Baja California microplate. (A) Configuration of active ridge segments (pink) west of Baja California just before they became largely abandoned ca. 12.3 Ma. (B) It is thought that plate motion from 12.3 to 6 Ma was kinematically partitioned into dextral strike slip (325 km) on faults west of Baja California and orthogonal rifting in the Gulf of California (90 km). This is known as the protogulf phase of rifting. (C) From 6 to 0 Ma faults west of Baja California are thought to have died and all plate motion was localized in the Gulf of California, which accommodated ~345 km of integrated transtensional shearing. Despite its wide acceptance, our data preclude this kinematic model. In all frames, the modern coastline is blue. Continental crust that accommodated post–12.3 Ma shearing is dark brown. Unfaulted microplates of continental crust are light tan. Farallon-derived microplates are light green. Middle Miocene trench-filling deposits like the Magdalena fan are colored dark green. Deep Sea Drilling Project Site 471 is the black dot on the southern Magdalena microplate. Yellow line (296 km) in the northern Gulf of California connects correlated terranes of Oskin and Stock (2003). Maps have Universal Transverse Mercator zone 12 projection with mainland Mexico fixed in present position.

  • Here is the Earthquake Report Poster from the 2015 sequence.

This is a nice simple figure, from the University of Sydney here, showing the terminology of strike slip faulting. It may help with the following figures.

Here is a fault block diagram showing how strike-slip step overs can create localized compression (positive flower) or extension (negative flower). More on strike-slip tectonics (and the source of this image) here.


Here is another great figure showing how sedimentary basins can be developed as a result of step overs in strike slip fault systems (source: Becky Dorsey, University of Oregon, Dept. of Geological Sciences).


I also put together an animation of seismicity from 1065 – 2015. First, here is a map that shows the spatial extent of this animation.


Here is the animation link (2 MB mp4 file) if you cannot view the embedded video below. Note how the animation begins in 1965, but has the recent seismicity plotted for reference.

    There have been two large magnitude earthquakes in this region over the past 50 years.

  • 2007.09.01 M 6.1
  • 2010.10.21 M 6.7

This is an animation from Tanya Atwater. Click on this link to take you to yt (if the embedded video below does not work).

Here is an animation from IRIS. This link takes you to yt (if you cannot view the embedded version below). Here is a link to download the 21 MB mp4 vile file.


This is a link to a tectonic summary map from the USGS. Click on the map below to download the 20 MB pdf file.

References:

  • Fletcher, J.M., Grove, M., Kimbrough, D., Lovera, O., and Gehrels, G.E., 2007. Ridge-trench interactions and the Neogene tectonic evolution of the Magdalena shelf and southern Gulf of California: Insights from detrital zircon U-Pb ages from the Magdalena fan and adjacent areas in GSA Bulletin, v. 119, no. 11/12, p. 1313-1336.
  • Umhoefer, P.J., Mayer, L., and Dorse, R.J., 2002. Evolution of the margin of the Gulf of California near Loreto, Baja California Peninsula, Mexico in GSA Bulletin, v. 114, no. 7, p. 849-868.

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/].

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