Great earthquakes and new insights into subduction seismogenesis

Transcription

1 Great earthquakes and new insights into subduction seismogenesis Heather R. DeShon Southern Methodist University GeoPRISMS DLP Georgia Southwestern State University Feb. 27th, 2013

2 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 great Concepción, Chile earthquake The Voyage of the Beagle, 1845

3 Zandt, 2002 Outline! Subduction megathrust faults and the seismogenic zone! Subduction cycles and deformation! Outstanding questions! Great earthquakes! Recent insights! Future concerns! New models

4 The Active Earth

5 Plates - rigid lithosphere riding on a convecting mantle

6 3 Types of Plate Boundaries Divergent Transform Convergent

7 Global distribution of convergent boundaries Convergent boundaries

8 End Member Models of Subduction Zones megathrust

9 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

10 Subduction megathrust faults generate great earthquakes & tsunami 2011 Japan tsunami 1960 Chile tsunami 1964 Alaska tsunami 2010 Maule, Chile earthquake Hilo, Hawaii damage 2004 M 9.2 Sumatra 1960 Chile earthquake

11 The megathrust and tsunamis

12 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 M O = A * D *µ Moment = fault area * average displacement * rigidity

13 Subduction zones generate the largest earthquakes because megathrusts are long, dipping structures with big fault areas Magnitude Effects largest recorded eathquakes destruction over vast area massive loss of life great earthquake severe economic impact large loss of life major earthquake damage ($ billions) loss of life strong earthquake property damage moderate earthquake some property damage Earthquakes Chile (1960) Alaska (1964) Sumatra (2004) Japan (2011) Chile (2010) San Francisco, CA (1906) New Madrid, MO (1812) Charleston, SC (1886) Haiti (2010) Northridge (1994) Long Island, NY (1884) < ,500 Energy Equivalents Krakatoa Eruption Worldʼs Largest Nuclear Test (USSR) Mount St. Helens Eruption Hiroshima Atomic Bomb Average Tornado Energy Release (equivalent kilograms of TNT) 15,000,000,000, ,000,000,000 15,000,000, ,000,000 15,000, , light earthquake noticeable shaking minor earthquake often felt generally not felt 10, ,000 1,000,000 Large Lightning Bolt Oklahoma City Bombing Moderate Lightning Bolt 15, Number of Earthquakes per year (worldwide)

14 Great earthquakes M W!8 Source: USGS

15 Magnitude does NOT scale with fatalities Source: USGS

16 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.

17 ! Two broadly integrated initiatives Subduction Cycles & Deformation Rift Initiation & Evolution! Research at Primary Sites & through Thematic Studies

18 A Relevant SCD Key Question 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? log[characteristic duration (s)] B year 1 month 1 day c M w 1 hour Gap a VLF b Slow earthquakes Silent EQ ETS SSE d Regular earthquakes e 1 LFE log[seismic moment (N m)] Ide et al. 2007

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20 Unzipping the Sunda subduction zone

21 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

22 Unzipping the Sunda subduction zone

23 Backprojection Models: Watching slip happen seconds Moment rate function Ishii et al., 2005 Alex Hutco

24 The 2004 tsunami! >250,000 fatalities! Run-up heights >4 m Banda Aceh! Tsunami last longer than earthquake shaking

25 2004 M W 9.2 megathrust earthquake, 2007 M W 8.4 megathrust earthquake & 2010 M W 7.8 tsunami earthquake

26 2005 M W 8.7 Nias earthquake & Afterslip Hsu et al., 2006

27 Largest intraplate earthquakes ever recorded! 2012-Magnitude 8.6 and 8.2 OFF W COAST NORTHERN SUMATRA 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. Ninetyeast Ridge M 8.6 M 8.2 Investigator Ridge

28 Aftershocks and backprojection results soon tell a different story

29 2010 M W 8.8 Maule, Chile earthquake

30 ab 1943 M = S 32 SS 32 án Nazca plate M = M Santiago Santiago 32 S Fig 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 S South America plate 1960 Sliver M = motion WW 38 S Crustal faulting Crustal faulting 40 S Arauco peninsula LiquiñeOfqui fault zone 40 S WW Longitude WW 75 W 42 S WW WW WW 38 S 39 S GPS station km km 42 SS S South America plate GPS station Sliver motion km km WW SS 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 m 15 m Postseismic relaxation Concepción nc 36 S tre 1835 M 8.5 and 2010 M = h 35 S Ch ile Per u Latitude 66 m bearly Latitude ern Ju a n F r i dge NATURE Vol September 2010 Fraction of plate convergence a M = z de 30 S 30 mm yr 1 Fraction of plate convergence 30 mm yr 1 34 S c bc 30 SS S Chil o Interseismic plate coupling predictive value? LETTERS LETTERS NATURE Vol September 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 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

31 2011 M W 9.0 Tohoku-oki, Japan, earthquake

32 Slip in the 2010 Chile and 2011 Japan events Maximum slip is ~50 m in the Japan earthquake! via backprojection Lay et al., 2012

33 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, New York Times The tsunami waves traveled far inland, the wave of debris racing across the farmland, carrying boats and houses with it.

34 The Future: Cascadia

35 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, events. D. S Oregon/N California events, minimum of 7-8 events. Chris Goldfinger, OR State

36 Tremor recurrence varies along Cascadia!!!!!!!!!!!!!!!! "#$%&'()*'!+(%!,--.(/!0112!!

37 Tremor lies downdip of the seismogenic zone Hyndman et al., 1995; Wech and Creager, 2011

38 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

39 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.