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Great earthquakes and new insights into subduction seismogenesis Heather R. DeShon Southern Methodist University GeoPRISMS DLP Georgia Southwestern State University Feb. 27th, 2013 The earth, the very emblem of solidity, has moved beneath our feet like a thick crust over a fluid. - Charles Darwin reflecting on experiencing the Feb. 1835 great Concepción, Chile earthquake The Voyage of the Beagle, 1845 Outline •! Subduction megathrust faults and the seismogenic zone •! Subduction cycles and deformation –! Outstanding questions •! Great earthquakes –! Recent insights –! Future concerns –! New models Zandt, 2002 The Active Earth Plates - rigid lithosphere riding on a convecting mantle 3 Types of Plate Boundaries Transform Divergent Convergent Global distribution of convergent boundaries Convergent boundaries End Member Models of Subduction Zones megathrust Subduction is part of the mantle convection system Subduction and arc volcanism are great water recyclers Subduction and arc processes help build continental crust Stern, 2002 Subduction megathrust faults generate great earthquakes & tsunami 2011 Japan tsunami 1960 Chile tsunami Hilo, Hawaii damage 2004 M 9.2 Sumatra 1960 Chile earthquake 1964 Alaska tsunami 2010 Maule, Chile earthquake The megathrust and tsunamis Rupture dimensions and displacement During an earthquake, slip spreads out from the initiation point (hypocenter) over a finite distance. Seismologists calculate seismic moment (a measure of energy) by MO = A * D * µ Moment = fault area * average displacement * rigidity s ng s. ly Earthquakes are always happening somewhere. Subduction zones generate the largest earthquakes Magnitude 2 and smaller earthquakes occur several hundred times a day world wide. because megathrusts are7,long, dipping structures Major earthquakes, greater than magnitude happen more than once per month. “Great earthquakes”, magnitude higher, occurareas about once a year. with8 and big fault Energy Release Magnitude Effects 10 9 8 7 Earthquakes Energy Equivalents Chile (1960) Alaska (1964) Sumatra (2004) largest recorded eathquakes Japan (2011) destruction over vast area massive loss of life Chile (2010) San Francisco, CA (1906) great earthquake severe economic impact New Madrid, MO (1812) large loss of life Charleston, SC (1886) major earthquake Haiti (2010) damage ($ billions) Northridge (1994) loss of life (equivalent kilograms of TNT) 15,000,000,000,000 <1 476,000,000,000 Krakatoa Eruption 1 Worldʼs Largest Nuclear Test (USSR) Mount St. Helens Eruption 18 6 strong earthquake property damage 5 moderate earthquake some property damage 4 light earthquake noticeable shaking 10,000 3 minor earthquake often felt 100,000 2 generally not felt 1,000,000 120 15,000,000,000 476,000,000 Hiroshima Atomic Bomb 15,000,000 Long Island, NY (1884) 1,500 Average Tornado 476,000 15,000 Large Lightning Bolt Oklahoma City Bombing Moderate Lightning Bolt 476 15 Number of Earthquakes per year (worldwide) The left side of the figure above describes the effects of an earthquake by magnitude. The larger the number, the bigger the earthquake. Significant earthquakes are noted on the left side of the Great earthquakes – MW!8 Source: USGS Magnitude does NOT scale with fatalities Source: USGS NSF GeoPRISMS Program GeoPRISMS investigates the coupled geodynamics, earth surface processes, and climate interactions that build and modify continental margins over a wide range of timescales (from s to My), and cross the shoreline, with applications to margin evolution & dynamics, construction of stratigraphic architecture, accumulation of economic resources, and associated geologic hazards and environmental management. •! Two broadly integrated initiatives Subduction Cycles & Deformation Rift Initiation & Evolution •! Research at Primary Sites & through Thematic Studies A Relevant SCD Key Question B. 1 2 3 4 Mw 5 6 7 9 8 Silent EQ 1 year e 7 ETS 1 month 6 SSE 1 day 5 d 4 ak es c Gap ea rth qu 1 hour ow 3 a 2 Sl log[Characteristic duration (s)] What governs the size, location and frequency of great subduction zone earthquakes and how is this related to the spatial and temporal variation of slip behaviors observed along subduction faults? VLF 1 b ular Reg es uak hq eart 0 LFE −1 −2 10 11 12 13 14 15 16 17 18 log[Seismic moment (N m)] 19 20 21 Ide et al. 2007 Unzipping the Sunda subduction zone 2004-2013 Focal Mechanisms Seismologists represent motion along a fault using lower hemisphere projections – beachballs Reverse faults, like subduction megathrust faults, have the colored quadrant centered in the circle Unzipping the Sunda subduction zone 2004-2013 Backprojection Models: Watching slip happen Moment rate function seconds Ishii et al., 2005 Alex Hutco The 2004 tsunami SUMATRA-ANDAMAN EARTHQUAK 1994 deep Bolivia earthquake (Mw 0 8.3) and about 40 times that of the 2001 Peru earthquake (Mw 0 8.4) (Fig. 3). Slip process of the 2004 event. The 2004 Sumatra-Andaman earthquake had the longest known earthquake rupture. Short-period seismic body waves (0.5 to 0.25 s) show azimuthally varying durations that indicate that the seismic rupture front propagated to about 1200 km north of the epicenter with a rupture velocity of about 2.0 to 3.0 km/s and that short-period radiation was generated for at least 500 s (38). Array analysis of 1- to 2-s period seismic waves from Hi-net stations in Japan yields compatible results (39). Analysis of longer period body waves and surface waves demonstrates that most of the slip that generated seismic waves was concentrated in the southern half of the rupture zone, with diminishing, increasingly oblique slip toward the north on the fault (9). The seismic moment of models that successfully match the long-period body- and surface-wave data is about 1.5 times as large as the CMT moment, consistent with free oscillation observations (10). The seismic model does not, however, account for all observations. Geodetic constraints require two to three times more slip in the north (40). This suggests rupture of the •! >250,000 fatalities •! Run-up heights >4 m Banda Aceh •! Tsunami last longer than earthquake shaking Fig. 7. (Left) Tsunami model at a time of 1 hour 55 min after earthquake initiation, computed f composite slip model with fast slip (50-s rise time) in the southern portion of the rupture and s slip (3500-s rise time) in the north. The northward propagating rupture velocity is about 2 k 2004 MW 9.2 megathrust earthquake, 2007 MW 8.4 megathrust earthquake & 2010 MW 7.8 tsunami earthquake 2005 MW 8.7 Nias earthquake & Afterslip Hsu et al., 2006 Largest intraplate earthquakes ever recorded Gut reaction: These intraplate earthquakes were caused by strike-slip faulting within Indian Plate oceanic lithosphere. N – S oriented fracture zones project into the area of the earthquakes and are the likely faults offset during these events. M 8.6 M 8.2 Investigator Ridge 2012-Magnitude 8.6 and 8.2 OFF W COAST NORTHERN SUMATRA Ninetyeast Ridge ! Aftershocks and backprojection results soon tell a different story 2010 MW 8.8 Maule, Chile earthquake ab 1943 M = 7. 7.9 9 32° S 32° SS 32° án Nazca plate –1 1.00 1985 M = 7. 7.8 8 0.75 1928 M ≈ 8 0.75 0.50 0.50 0.25 0.25 0.00 Santiago Santiago 32° S Fig. 2 0.00 Santiago 34° SS 34° Aftershock location er Ju a n F d n án 32° S ez r i dge ≥ 85% ≥ 75% 33° S Nazca Fig. 2 plate –1 34° S m yr 66 m 34° S m yr Volcano 38° SS 38° 42° S South America plate 1960 Sliver M = 9. 9.5 5 motion 75° 75°WW 38° S Crustal faulting Crustal faulting 40° S Arauco peninsula LiquiñeOfqui fault zone 40° S 71° 71°WW Longitude 69° 69°WW 75° W 42° S 75° 75°WW 73° 73°WW 71° 71°WW 38° S 39° S GPS station 200 200km km 42° SS 42° 37° S South America plate GPS station Sliver motion 200 200km km 73° 73°WW 2010 1960 40° SS 40° 36° S 10 m 5m 1m 36° S 1m e –Peru t re nch 38° S Postseismic relaxation Concepción 10 m 5m Concepción Arauco peninsula 36° SS 36° 20 m 15 m Postseismic relaxation Concepción nc 36° S tre 1835 M ≈ 8.5 and 2010 M = 8.8 8. 8 h 35° S Ch ile –Per u Latitude 66 m bEarly Latitude ern Ju a n F r i dge NATURE | Vol 467 | 9 September 2010 Fraction of plate convergence a 1.00 1906 M = 8. 8.4 4 z de 30° S 30 mm yr –1 Fraction of plate convergence 30 mm yr –1 34° S c bc 30° SS 30° 30° S Chil o Interseismic plate coupling – predictive value? LETTERS LETTERS NATURE | Vol 467 | 9 September 2010 69° 69°WW Longitude the 2010Methods). Maule earthquake 1 | Tectonic the2010 study area,earthquake data, observations and see online-only Maule (for references ata,Figure observations and setting ofthe 74° W 73° W 72° W Longitude 40° S 71° W 0 200 km 5 N p Figure 3 | Relationship between pre, co- and postseismic 75° W 73° W 71° W 69° slip distribution during theW2010 ( patterns. a, Coseismic USGS slip model26) and 1960 (green contours; from ref. 3 overlain onto pre-seismic locking pattern (red shading $0 early (during the first 48 h post-shock) M $ 5 aftershock lo (for references see online-only Methods). circle sizes scale with magnitude; GEOFON data29). b, His Moreno et al., 2010 2011 MW 9.0 Tohoku-oki, Japan, earthquake Slip in the 2010 Chile and 2011 Japan events B04311 LAY ET AL.: MEGATHRUST RUPTURE DOMAINS Maximum slip is ~50 m in the Japan earthquake! via backprojection Figure 1. Maps summarizing rupture characteristics for (a) the 11 March 2011 Tohoku, Japan (Mw 9.0) and (b) the 27 February 2010 Maule, Chile (Mw 8.8) earthquakes. The white stars indicate the epicentral locations used for each rupture model. The coseismic slip distributions are those determined from highrate GPS recordings for the Tohoku event by Yue and Lay [2011] and for the Chile event by Koper Lay et al., 2012 Part of houses swallowed by tsunami burn in Sendai, Miyagi Prefecture (state) after Japan was struck by a strong earthquake off its northeastern coast Friday, March 11, 2011. New York Times The tsunami waves traveled far inland, the wave of debris racing across the farmland, carrying boats and houses with it. The Future: Cascadia History of earthquakes: the turbidite record A. Full or nearly full rupture, 19 events B. Mid-Southern rupture, 3-4 events. C. Rupture from central Oregon southward, 10-12 events. D. S Oregon/N California events, minimum of 7-8 events. Chris Goldfinger, OR State Tremor recurrence varies along Cascadia ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! "#$%&'()*'!+(%!,--.(/!0112!! Tremor lies downdip of the seismogenic zone Hyndman et al., 1995; Wech and Creager, 2011 Summary • Each new earthquake brings further insight into the seismogenic zone • Fault complexity may be related to variable frictional stability conditions along the fault • Fault behavior may vary from seismic cycle to seismic cycle Lay et al., 2012 Acknowledgements •! NSF GeoPRISMS and Margins program •! Collaborators: Susan Bilek, Susan Schwartz, Cliff Thurber, Bob Engdahl, Jeremy Pesicek, Haijiang Zhang, Sri Widiyantaro, Wolfgang Rabbel, Melissa Driskell, Shishay Bisrat 6 subduction megathrust earthquakes over the last 106 years account for over half of the energy released during that time.