We had a damaging and (sadly) deadly earthquake in southern Peru in the last 24 hours. This is an earthquake, with magnitude M 7.1, that is associated with the subduction zone forming the Peru-Chile trench (PCT). The Nazca plate (NP) is subducting beneath the South America plate (SAP). There are lots of geologic structures on the Nazca plate that tend to affect how the subduction zone responds during earthquakes (e.g. segmentation).
In the region of this M 7.1 earthquake, two large structures in the NP are the Nazca Ridge and the Nazca fracture zone. The Nazca fracture zone is a (probably inactive) strike-slip fault system. The Nazca Ridge is an over-thickened region of the NP, thickened as the NP moved over a hotspot located near Salas y Gomez in the Pacific Ocean east of Easter Island (Ray et al., 2012).
There are many papers that discuss how the ridge affects the shape of the megathrust fault here. The main take-away is that the NR is bull dozing into South America and the dip of the subduction zone is flat here. There is a figure below that shows the deviation of the subducting slab contours at the NR.
There was an earthquake in 2013 that is almost a carbon copy of this 2018.01.14 M 7.1 earthquake. The USGS earthquake epicenters are about 20 km from each other and the USGS hypocenters are within 5 km. They also have almost identical fault plane solutions (moment tensors). Based upon the different cross sections, I am unsure whether this earthquake is in the upper or lower plate.
Based upon Stéphane‘s comment (see social media update), I need to edit my twitter post. I posted that this earthquake happened in a region of low seismogenic coupling. This was based upon Chlieh et al. (2011) GPS inversion modeling. Stéphane pointed out that the Villegas Lanza et al. (2016) show this to be in a region of higher coupling. I consider the Villegas-Lanza paper to be more up-to-date, so will favor their interpretation of the coupling along this fault. This updated analysis includes more GPS rate sites, as well as a suite of additional types of data. They also model the crust with a better version of the Peruvian Forearc Sliver, which is the most significant change in how they treated fit their data *see their figure 7). These modifications changed significantly the spatial variation in seismogenic coupling along the plate margin where the M 7.1 was located.
- Here is IRIS’ page for this earthquake.
Below is my interpretive poster for this earthquake
I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 6.5 (and down to M ≥ 5.5 in a second poster).
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange) for the M 7.3 earthquakes, in addition to some relevant historic earthquakes.
- I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.
- 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 (faintly) the MMI contours from most of the larger magnitude earthquakes for which there are data available. As mentioned above, these are estimates based upon numerical models using empirical relations between earthquakes and their shaking intensity. These MMI estimates are controlled by a variety of things, principally magnitude and distance to the fault. Some estimates are made using rectangular shaped fault sources (e.g. 2001 M 8.4), some from point source distances (e.g. 1966 M 8.1).
- I outline the MMI VII contour because (1) this is the largest MMI contour for the M 7.1 earthquake and (2) this is the “very strong” shaking intensity that can cause moderate damage to buildings. These outlines are in dashed white and are labeled in yellow for the causative earthquake magnitude. The M 7.1 MMI VII contour is from a point source, so would probably be more rectangular in reality (though the earthquake is deeper).
I include some inset figures.
- In the upper right corner is a section of the map from Rhea et al. (2010), which is a USGS map documenting the seismicity of the earth in this region. The cross section B-B’ is shown to the left. The cross section plots the earthquake depths along the profile shown on the map. The B-B’ profile crosses the subduction zone very close to where this earthquake happened. I place a blue star in the general location of today’s M 7.1 earthquake.
- In the lower right corner is a map from Chlieh et al. (2011) that shows some historic earthquake slip patches. The colors represent the amount of slip on the earthquake fault. I place a blue star in the general location of today’s M 7.1 earthquake. Note how this M 7.1 earthquake is at the boundary of the 2001 M 8.4 and 1996 M 7.7 earthquakes.
- In the upper right corner is a figure that addresses, from left to right:
- Historic (including pre-instrumental) earthquakes, their along-strike distances
- Slip patches for instrumental earthquakes; I place a blue star in the general location of today’s M 7.1 earthquake.
- Seismic moment for instrumental earthquakes; Seismic moment is the amount of energy released during an earthquake. The 2007, 1996, and 2001 earthquakes are part of their analyses and contain more details about the heterogeneous nature of earthquake faults.
- In the lower left corner is another figure from Chlieh et a. (2011) that provides lots of details from their analyses.
- On the left is the a plot of the Seismic Moment as before, with the addition of Moment Deficit. Moment deficit is an estimate of the amount of energy stored in the subduction zone as imparted by plate convergence. Assumptions include (at least) plate motion rates and spatial variation in the amount the fault is seismogenically locked/coupled, etc. Today’s earthquake happened nearby a 1913 M 7.8 earthquake in a region of low moment deficit.
- On the right is a plot showing the historic earthquakes again, but with the addition of the coupling ratio. The coupling ratio is the proportion of 100% of the plate motion that is contributing to the strain on the fault. A coupling ratio of 1 (100%) means that 100% of the plate motion is being accumulated as stress on the fault. A ratio of 0 (0%) means that the fault is aseismic (it is slipping all the time). I place a blue star in the general location of today’s M 7.1 earthquake. The 1942, 1996, and today’s M 7.1 earthquakes are along the southern boundary of the NR and in a region of low coupling.
USGS Earthquake Pages
- M 7.1 – 40km SSW of Acari, Peru
2018-01-14 09:18:45 UTC 15.776°S 74.744°W 36.3 km depth
- M 8.2 – near the coast of central Peru
1940-05-24 16:33:59 UTC 11.094°S 77.487°W 45.0 km depth
- M 8.1 – near the coast of central Peru
1966-10-17 21:42:00 UTC 10.665°S 78.228°W 40.0 km depth
- M 7.6 – near the coast of central Peru
1974-10-03 14:21:29 UTC 12.265°S 77.795°W 13.0 km depth
- M 7.2 – near the coast of central Peru
1974-11-09 12:59:49 UTC 12.500°S 77.786°W 6.0 km depth
- M 7.7 – near the coast of central Peru
1996-11-12 16:59:44 UTC 14.993°S 75.675°W 33.0 km depth
- M 8.4 – near the coast of southern Peru
2001-06-23 20:33:14 UTC 16.265°S 73.641°W 33.0 km depth
- M 7.6 – near the coast of southern Peru
2001-07-07 09:38:43 UTC 17.543°S 72.077°W 33.0 km depth
- M 8.0 – near the coast of central Peru
2007-08-15 23:40:57 UTC 13.386°S 76.603°W 39.0 km depth
- M 7.1 – 46km SSE of Acari, Peru
2013-09-25 16:42:43 UTC 15.839°S 74.511°W 40.0 km depth
- M 8.2 – 94km NW of Iquique, Chile
2014-04-01 23:46:47 UTC 19.610°S 70.769°W 25.0 km depth
- Here is an animation from IRIS that reviews the tectonics of the Peru-Chile subduction zone. For the animation, first is a screen shot and below that is the embedded video. This animation is from IRIS. Written and directed by Robert F. Butler, University of Portland. Animation and Graphics: Jenda Johnson, geologist. Consultant: Susan Beck, University or Arizona. Narration: Elayne Shapiro, University of Portland.
- Here is a download link for the embedded video below (34 MB mp4)
- The Rhea et al. (2016) document is excellent and can be downloaded here. The USGS prepared another cool poster that shows the seismicity for this region (though there does not seem to be a reference for this).
- Here is a great view of the Nazca Ridge as it extends to the East Pacific Rise (Ray et al., 2012).
- This shows the age progression along the NR.
- These next 3 figures are from Kumar et al. (2016) and reveal the shape of the plate boundary based upon seismicity.
- This map shows the earthquakes used in their study (color = depth, use this legend for the other map). The thin black lines show their estimate of where the slab is (the megathrust, where the Nazca plate meets the South America plate), depth in km. The NR is the grayed out polygon in the lower left part of the figure (see next map).
- This map shows where the cross section profiles are located (Kumar et al., 2016). Today’s M 7.1 earthquake plots almost exactly at the southwestern tip of the P3 profile line.
- Here are the earthquake hypocenters plotted for the 4 cross sections plotted in the map above (Kumar et al., 2016). Today’s M 7.1 earthquake plots near the westernmost limit of profile P3. Given a hypocentral depth of ~40 km, this plots in the upper plate. So, perhaps this earthquake is not on the megathrust, but along the decollement. While plotted at a different scale, the same is true when looking at the seismicity cross section from Rhea et al. (2010). Of course, these are just models and could be wrong.
- Here are the figures from Chlieh et al. (2011).
- This is the map showing slip patches (1 meter contours) for earthquakes as derived by inverting GPS geodetic data. Other historic slip patches that are less well constrained are shown in gray dashed polygons. Note the NR and Nazca fracture zone. The 2001 Arequipa M 8.4 (and M 7.6) earthquakes spanned this fracture zone (so did not serve as a segment boundary for that earthquake).
- This shows the GPS derived rates of motion relative to South America. The South America and Nazca plates are shown with a Sliver between them (“accretionary prism”). This shows (1) the dominant tectonic signal is from east-west convergence due to the subduction zone and (2) that there is deformation within the Sliver (the GPS velocities rates lower from west to east). The red bars show the slip direction to earthquakes with magnitudes M > 6.0 (they are generally parallel to the GPS rates, but not everywhere).
- Here is the space-time figure on its side (making it a time-space diagram) showing earthquake rupture latitudinal limits with time, instrumental-historic slip patches, and seismic moment estimates for these earthquakes.
- This is the figure that adds moment deficit to the seismic moment plot and the coupling ratio to the slip patch map.
- This figure shows their results used to show how different parts of the subduction zone have higher or lower moment deficits. The Central Peru section shows that there is an unmet interseismic deficit, while the southern Peru profile shows that earthquakes have been keeping up with plate convergence here. The central Peru region is the region of the subduction zone shown in the 2 figures above this one (Arica, Peru is the southern boundary between the central and southern Peru regions of this subduction zone).
- Below are some figures that use seismic tomography to estimate where the slab is (Scire et al., 2017).
- This is a map showing all their profiles. The profile closest to today’s M 7.1 earthquake is profile B-B’.
- Here are profiles AA’, BB’, and CC’. I edited their figure to pull apart these three profiles (so there are some blurred areas in profiles AA and BB. I placed a blue star in the general location of the earthquake.
- Finally, here are two figures that present some observations about the geometry of the slab as it perturbates due to the NR.
- Here are some seismic velocity profiles showing how the seismic velocity changes with depth. Warm color represents a lower Vs/Vp ratio (warmer, younger slab) and cooler colors represent higher ratio (colder, older slab). These profiles show how the dip of the subducting slab changes from north to south.
- This shows their model of how the NR has been subducted in the past 11 Ma (million years).
- This is a great visualization from Dr. Laura Wagner. This shows how the downgoing Nazca plate is shaped, based upon their modeling. Today’s M 7.1 earthquake is almost due south of Nazca, Peru labeled on the map.
- Based upon Stéphane‘s comment (see social media update), I need to edit my twitter post. I posted that this earthquake happened in a region of low seismogenic coupling. This was based upon Chlieh et al. (2011) GPS inversion modeling. Stéphane pointed out that the Villegas Lanza et al. (2016) show this to be in a region of higher coupling.
- 2010.02.27 M 8.8 Earthquake Review
- 2018.01.14 M 7.1 Peru
- 2018.01.15 M 7.1 Peru Update #1
- 2017.06.30 M 6.0 Ecuador
- 2017.04.24 M 6.9 Chile
- 2017.04.23 M 5.9 Chile
- 2016.12.25 M 7.6 Chile
- 2016.11.24 M 7.0 El Salvador
- 2016.11.04 M 6.4 Maule, Chile
- 2016.04.16 M 7.8 Ecuador
- 2016.04.16 M 7.8 Ecuador Update #1
- 2015.11.29 M 5.9 Argentina
- 2015.11.11 M 6.9 Chile
- 2015.11.24 M 7.6 Peru
- 2015.11.26 M 7.6 Peru Update
- 2015.09.16 M 8.3 Chile
- 2014.04.01 M 8.2 Chile
- 2010.02.27 M 8.8 Chile
- Antonijevic, S.K., et a;l., 2015. The role of ridges in the formation and longevity of flat slabs in Nature, v. 524, p. 212-215, doi:10.1038/nature14648
- Bishop, B.T., Beck, S.L., Zandt, G., Wagner, L., Long, M., Knezevic Antonijevic, S., Kumar, A., and Tavera, H., 2017, Causes and consequences of flat-slab subduction in southern Peru: Geosphere, v. 13, no. 5, p. 1392–1407, doi:10.1130/GES01440.1.
- Chlieh, M., et al., 2011. Interseismic coupling and seismic potential along the Central Andes subduction zone in JGR, v. 116, B12405, doi:10.1029/2010JB008166
- Espurt, N., Baby, P., Brusset, S., Roddaz, M., Hermoza, W., Regard, V., Antoine, P.-O., Salas-Gismodi, R., and Bolaños, R., 2007. How does the Nazca Ridge subduction influence the modern Amazonian foreland basin? in Geology, v. 35, no. 6, p. 515-518.
- Hayes, G. P., D. J. Wald, and R. L. Johnson, 2012. Slab1.0: A three-dimensional model of global subduction zone geometries, J. Geophys. Res., 117, B01302, doi:10.1029/2011JB008524.
- Kumar, A., et al., 2016. Seismicity and state of stress in the central and southern Peruvian flat slab in EPSL, v. 441, p. 71-80. http://dx.doi.org/10.1016/j.epsl.2016.02.023
- Ray., J.S., et al., 2012. Chronology and Geochemistry of Lavas from the Nazca Ridge and Easter Seamount Chain: an ~30 Myr Hotspot Record in Journal of Petrology, v. 53., no. 7, p. 1417-1448.
- Rhea, S., Tarr, A.C., Hayes, G., Villaseñor, A., Furlong, K.P., and Benz, H.M., 2010. Seismicity of the Earth 1900-2007, Nazca plate and South America: U.S. Geological Survey Open-File Report 2010-1083-E, 1 map sheet, scale 1:12,000,000.
- Scire, A., Zandt, G., Beck, S., Long, M., and Wagner, L., 2017, The deforming Nazca slab in the mantle transition zone and lower mantle: Constraints from teleseismic tomography on the deeply subducted slab between 6°S and 32°S: Geosphere, v. 13, no. 3, p. 665–680, doi:10.1130/GES01436.1.
- Villegas-Lanza, J.C., et al., 2016. Active tectonics of Peru: Heterogeneous interseismic coupling along the Nazca Megathrust, rigid motion of the Peruvian Sliver and Subandean shortening accommodation in JGR, doi: 10.1002/2016JB013080
These are from this current sequence
Some Relevant Discussion and Figures
Satellite-derived bathymetry (Smith & Sandwell, 1997) of the SE Pacific Basin, showing the Nazca Ridge, Easter Seamount Chain and other features of the Nazca plate. Locations of dredge stations from which samples of this study were obtained are marked. All samples except those labeled with DM (for R.V. Dmitry Mendeleev cruise 14), and GS (for GS7202)
were collected during the Drift expedition. The dashed line near seamount 115 roughly marks the boundary between the NR and ESC, and the inset shows an enlarged view of the elbow region connecting the two.
Distribution of 40Ar39Ar ages of NR, ESC and Easter Island (EI) volcanic rocks vs along-chain distance from Salas y Gomez (SyG). Also shown are the data for lava fields and small seamounts west of EI. Lavas of the East Rift of the Easter Microplate (ER-EMP) are assigned an age of 0 Ma. Our data (plateau ages for all samples fromTable 2 except the total fusion age for DRFT 100-2 and isochron ages for DRFT 115-2 and 126-1) are indicated by filled circles and, for two anomalously young NR samples (DRFT 84-1 and 85-1), by hexagons. Open circles and other symbols are data from O’Connor et al. (1995). Error bars indicate 2s uncertainties on age, if larger than the size of the symbol. The inclined continuous and dashed lines represent linear regressions performed using the algorithm of York et al. (2004) on data for the ESC and NR, respectively, considering the 2s errors on age (years) only (i.e. assuming no significant error resides in the dredge-site locations). Data for the anomalously young DRFT 84 and 85 samples, EI, and seamounts and lava fields west of it are not included in the regressions. These regressions equate to plate motion speeds of 181 and 10·70·1cma1 during the formation of the NR and ESC, respectively. The dashed vertical line roughly marks the boundary between the NR and ESC.
Map of first motion focal mechanisms plotted in lower hemisphere projec-tion. Mechanisms are color coded by earthquake depth and mainly show normal faulting across the study area. Solid lines are slab contours from Antonijevic et al.(2015). See Figs. S4 and S5 of the supplementary material for zoom-in map of focal mechanism for events inside the red and blue box respectively.
Map showing locations of (a) trench-parallel (BB) and trench-perpendicular (P1, P2, P3, and P7) transects used to plot seismicity cross-sections. Red tick marks on BBrepresents distance interval of 100 km.
Seismicity cross-sections (P1, P2, P3, and P7) perpendicular to the trench. Earthquakes within ±35 km are projected onto each cross-section. The solid line in each cross section is the slab contour from Antonijevic et al.(2015). Red star in each trench-perpendicular cross section marks the intersection with BBcross section. See Figs. S2 and S3 of the supplementary material for the remaining set of trench-parallel and trench-perpendicular seismicity cross-sections.
Seismotectonic setting of the Central Andes subduction zone with rupture of large (Mw > 7.5) subduction earthquakes on the Peru-Chile megathrust since 1746. The Central Andes sliver is squeezed between the Nazca plate and the South America Craton. Convergence rate of the Nazca plate relative to the South America Craton (black arrow) is computed from Kendrick et al. . Shortening across the Subandean foothills is represented with the red arrows (assumed parallel to the Nazca/South America plate convergence). Red contours are the 1000 m of the Andes topography and the 5000 m to 3000 m bathymetric contour lines. Historical ruptures are compiled from Beck and Ruff  and Dorbath et al.
. Slip distributions of the 2007 Mw = 8.0 Pisco, 1996 Mw = 7.7 Nazca, 2001 Mw = 8.4 Arequipa and 2007 Mw = 7.7 Tocopilla earthquakes were determined from joint inversions of the InSAR and GPS data (this study). These source models include coseismic and afterslip over a few weeks to a few months depending on case. Slip contours are reported each 1-m. The color scale indicates slip amplitude.
Interseismic geodetic measurements in the Central Andes subduction zone. Horizontal velocities determined from campaign GPS measurements are shown relative to South America Craton. Inset shows unwrapped interseismic interferogram in mm/a projected in the line of sight (LOS) direction of the ERS-1/2 satellites [Chlieh et al., 2004]. The convergence of the Nazca plate relative to South America (black arrows) is mainly accommodated along the Peru-Chile megathrust (green arrows) with a fraction taken up along the subandean fold and thrust belt (red arrows). Red bars represent the slip direction of Mw > 6 Harvard CMT (http://www.seismology.harvard.edu/CMTsearch.html).
Historical and recent large megathrust earthquakes in central and southern Peru. (left) Dates, extents and magnitudes of historical megathrust earthquakes. (middle) We used these parameters and the ruptures areas to estimate the distribution of moment released by historical events of 1746 (Mw8.6– 8.8), 1868 (Mw8.8), 1940 (Mw8.0), 1942 (Mw8.2), 1966 (Mw8.0), 1974 (Mw8.0) and 1913 (Mw7.8). To improve consistency the rupture areas of the Mw8.0 1940/1996/1974 earthquakes (shown in Figure 1), were rescaled using the rupture area of the 2007 Mw8.0 Pisco earthquake as a reference. (right) The along-trench variations of the seismic moment associated to each earthquake.
Comparison of interseismic coupling along the megathrust with ruptures of large megathrust earthquakes in central and southern Peru. (left) Interseismic coupling map for 3-plate model Short4; it indicates that where the Nazca ridge and the Nazca fracture zone subduct, the interseismic coupling is low. The largest earthquake there is the Mw8.1–8.2 earthquake of 1942. It is not clear whether the 1942 rupture propagated through the Nazca ridge or stopped south of it. High interseismic coupling patches correlate well with regions that experienced great megathrust earthquake Mw8.8 in 1868 and Mw8.6–8.8 in 1746. In the south, the presence of two wide asperities separated by a wide aseismic patch may
explain partially the seismic behavior of this segment in the last centuries. Individual ruptures of these asperities would produce Mw8 events, as in 2001, but their simultaneous rupture could generate great Mw > 8.5 earthquakes as in 1604 or 1868. The along-strike coincidence of the high coupling areas (orange-red) with the region of high coseismic slip during the 2001 Arequipa and 2007 Pisco earthquakes suggests that strongly coupled patches during the interseismic period may indicate the location of future seismic asperities. (right) Moment deficit (dashed lines) since the last great earthquake of 1868, 1942 and 1746 compared with the seismic moment released during recent and historical
earthquakes of Figure 8. The moment deficit is computed from the rate of moment deficit predicted by model Short4 considering a steady state interseismic process (Max) or 50% of it (Min) to account for time-variable interseismic process and transient events.
Cumulative deficit of moment and seismic moment released due to major subduction earthquakes since the 16th century (top) in central Peru and (bottom) in southern Peru. The cumulative deficit of moment is predicted from the rates of 3-plate models Short4 in central Peru and Short10 in southern Peru (Table 5 and Figure 4). The uncertainties of moment released by historical events lead to a minimum and maximum moment released (see Table S8 in the auxiliary material). The uncertainties on the cumulative deficit of moment allow that nonlinear interseismic and viscous processes could have released 50% of the accumulated moment deficit. The remaining fraction should reflect elastic strain available to drive future earthquakes unless it would have been totally released by anelastic deformation of the forearc.
Map showing seismic station locations (squares—broadband; inverted triangles—short period) for individual networks used in the study and topography of the central Andes. Slab contours (gray) are from the Slab1.0 global subduction zone model (Hayes et al., 2012). Earthquake data (circles) for deep earthquakes (depth >375 km) are from 1973 to 2012
magnitude >4.0) and were obtained from the U.S. Geological Survey National Earthquake Information Center (NEIC) catalog (https:// earthquake .usgs .gov /earthquakes/). Red triangles mark the location of Holocene volcanoes (Global Volcanism Program, 2013). Plate motion vector is from Somoza and Ghidella (2012). Cross section lines (yellow) are shown for cross sections.
Trench-perpendicular cross sections through the tomography model. Velocity anomalies are shown in blue for fast anomalies, red for slow anomalies. Cross section locations are as shown in Figure 1. Dashed lines are the same as in Figure 6. Yellow dots are earthquake locations from the EHB catalog (Engdahl et al., 1998). Solid black line marks the top of the Nazca slab from the Slab1.0 model (Hayes et al., 2012).
Three-dimensional model of the structure of shear-wave velocities between 2106 and2186. a–c, Shear-wave velocities and seismicity at depths of 75km (a), 105km (b) and 145km (c), and transects along the northern reinitiating steep slab (A–A9, B–B9), flat slab (C–C9) and southern steep slab (D–D9) segments. Colours indicate velocity deviations, dVs/Vs (%); contours show absolute velocities in kilometres per second (numbered). a–c, Black circles represent stations used in our study; red triangles are Holocene volcanoes; green stars are earthquakes within 20km of the depth shown; black lines refer to cross-sections shown in e–h. The grey dashed line in b and c shows the location of the trench 10Ma (ref. 8); the black dashed line (labelled ‘T’) indicates the location of the slab tear. ‘R’ refers to the resumption of steep subduction at the eastern edge of the flat slab. d, Inferred flat-slab geometry along the Nazca Ridge track, and slab tear north of the ridge. e–h, Cross-sections of slab segments shown in a–c. Black dots show earthquake locations from this study; black inverted triangles are stations; red triangles are Holocene volcanoes; orange triangle represents the location of a measurement of unusually high heat flow15. Dashed lines show the inferred top of the slab. The thick black line shows the crustal thickness.
Proposed evolution of the Peruvian flat slab. a–f, Proposed contours of the subducted slab, assuming that the ridge remains buoyant for 10Ma after entering the trench. The approximate location of the subducted ridge is denoted by the black rectangular outline. Brown areas show areas of the continent underlain by flat slab at each time step. Triangles indicate volcanoes active during the 2 Myr following the time of the frame shown22. The location of the South American continent relative to the Nazca Ridge follows ref. 8. In a, we show the location of the projection of the mirror image of the Nazca Ridge (in yellow) that formed synchronously with the Nazca Ridge on the Pacific Plate when these plates were first created at the spreading centre following ref. 8. In e, red triangles show volcanism from 3Ma to 2 Ma, and brown triangles show volcanism from 2 Ma to 1 Ma. In f, volcanism is shown for 1Ma to 0 Ma (not including Holocene volcanism). g, Modern seismicity fromthis study (large circles) with depths.50 km, and contours as they would be if the removal of the ridge did not affect the longevity of the flat slab. h, Modern seismicity from this study and local seismicity at depth .50 km, as reported in the ISC catalogue for years 2004–2014, shown as smaller circles17. We plot our observed slab contours on the basis of our earthquake locations and the location of high-velocity anomalies in our tomographic results. Dashed lines indicate contours that are less certain, either because of a paucity of earthquakes or because they lie outside of our region of good tomographic resolution. The pink triangular shape shows the region with very limited seismicity that may indicate a slab window caused by tearing and the reinitiation of normal
Mw7.1 #earthquake Peru: Seismogram recorded in Thailand, almost exactly (within 50km) at the opposite side of the Earth from the Peru epicenter: The PKIKP waves traveled along an almost straight line through the center of the Earth! https://t.co/Us8138HZRK https://t.co/7pusl3I6c9 pic.twitter.com/8D9Zkh4PSY
— Anthony Lomax 🌍 (@ALomaxNet) January 14, 2018
Approx. loc. #Peru Mw7.1 #earthquake on nearby recent tomographic models (Antonijevic et al 2015, Kumar et al 2016, Bishop et al 2017).
Today earthquake seems slightly deeper, and with steeper fault than subduction interface. Intraplate, slab-push (compressive) event ? pic.twitter.com/QFQN8h0HN2
— Robin Lacassin (@RLacassin) January 14, 2018
Update S #Peru M7.1 #earthquake, all estimates (USGS, Geoscope, GFZ) now converge: Mw7.1, depth 38-48km, thrust mechanism, NW-SE fault planes
Depth compatible with megathrust interface, but fault planes perhaps too steep. Likely too deep for significant #tsunami. pic.twitter.com/mkq7OwkHh1
— Robin Lacassin (@RLacassin) January 14, 2018
Watch the earthquake waves from the M7.1 #Peruearthquake cross seismometers in the US #earthquake #Peru pic.twitter.com/ISLupe4bta
— IRIS Earthquake Sci (@IRIS_EPO) January 14, 2018
Más fotografías y últimas noticias sobre el reciente #terremoto de 7.1 ML ocurrido frente a costas Arequipeñas. Se confirma segundo fallecido en distrito de #BellaUnión y más de 100 heridos hasta el momento.
Capturas: Frase Corta Arequipa – Santiago Neyra#Arequipa #Acarí #Chala pic.twitter.com/Z4Jy4OCNkN
— Julio Montenegro G. (@Juliohydraulics) January 14, 2018
Global body wave for M7.1 #Peru #earthquake https://t.co/XoWXbXWq69 pic.twitter.com/EaAHfFpE8M
— IRIS Earthquake Sci (@IRIS_EPO) January 14, 2018
BBC News – Peru: Earthquake leaves two dead and dozens injured https://t.co/rOzEpPWdYo
— Anthony Lomax 🌍 (@ALomaxNet) January 14, 2018
Destructions along coast of S #Peru after Mw7.1 #earthquake.
At least 2 fatalities, more that 100 injuried… https://t.co/5YRCFaT1Sb
— Robin Lacassin (@RLacassin) January 14, 2018
Based on seismicity map (from emsc) and focal mechanism (usgs) and depth, M7.1 Peru quake could be intra-slab? (I do not have the time or technology for a more in depth investigation, unfortunately.) pic.twitter.com/HuqtaHHCUx
— Jascha Polet (@CPPGeophysics) January 14, 2018
El #sismo de hoy en #Lomas #Acarí (7.1Mw) ocurre en una zona donde ya habíamos identificado Acoplamiento Sísmico (energía disponible). “Tengamos en cuenta el resto de áreas en el país”. En esta zona ocurrieron sismos importantes en: 1913(M7.8), 1942(M8.2), 1996(M7.6), 2013 (7.1) pic.twitter.com/VrzJzHqDpy
— Juan Carlos Villegas (@peruvill) January 14, 2018
#Breaking #Tsunami Buoy Has Detected 1 Meter High #TsunamiWaves Off The Coast Of #Chile From Shallow 7.3 #PeruEarthquake #Peru #TakeCover #SafetyBeforeStupidity #GetToHighGround pic.twitter.com/5otT85rrk4
— ImMikeRobertson 🇺🇸 (@ImMikeRobertson) January 14, 2018
This tweet suggests that the coupling is not so low in the quake area https://t.co/i6ZlSjIaxr
— Stéphane Baize (@stef92320) January 15, 2018
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