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Anatomy of a Megathrust Earthquake Rupture - The 2010 M8.8 Chile Quake

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Presented for an IRIS (Incorporated Research Institutions for Seismology) webinar on 9 April 2014.
Webinar can be viewed here: https://www.youtube.com/watch?v=MNcl5AZlX3k

Abstract: In February 2010, a magnitude 8.8 megathrust earthquake struck the Maule region of Central Chile - the sixth largest earthquake ever recorded. It is fast becoming one of the best-studied megathrust ruptures, allowing us a unique insight into the inner workings of subduction zone earthquakes. In the earthquake’s immediate aftermath, an international group of research institutions deployed geophysical instruments in the rupture area. A network of ~160 seismic stations on the forearc recorded over 50,000 aftershocks in the first 10 months following the earthquake.

I have used observations of P- and S-waves from aftershocks to derive a high-resolution seismic travel-time tomography of the rupture zone. Observations from ocean-bottom seismometers further improve image sharpness in the offshore portion of the seismogenic zone, where most slip occurred during the earthquake. The tomographic images reveal the distribution of P-wave velocity and Poisson’s Ratio within the earthquake rupture zone. Based on accurate aftershock locations and moment tensors, I have defined a new 3-D plate interface geometry to infer the physical structure and composition along the plate interface. I compare these velocities with the mainly geodetically observed behaviour of the fault throughout a cycle of seismic behaviour (preseismic locking, coseismic slip, postseismic deformation). This comparison allows us to understand some of the physical properties that may govern seismogenesis along the megathrust. I will reveal how both the long-lived geological structure of the forearc and the composition of the subducting oceanic plate may influence the rupture behaviour of large megathrust earthquakes. An understanding of seismic velocities along the megathrust may therefore be used to constrain the seismogenic potential of subduction zones worldwide.

Published in: Science
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Anatomy of a Megathrust Earthquake Rupture - The 2010 M8.8 Chile Quake

  1. 1. Anatomy of a megathrust earthquake rupture: The 2010 Mw 8.8 Maule, Chile quake Stephen Hicks, Andreas Rietbrock, Isabelle Ryder Liverpool Earth Observatory, University of Liverpool, UK Chao-Shing Lee National Taiwan Ocean University, Taiwan Matt Miller Universidad de Concepción, Chile Email: s.hicks@liverpool.ac.uk @seismo_steve
  2. 2. The overriding / underlying question… scientific aims community response rupture zone imaging megathrust properties lessons learnt
  3. 3. The overriding / underlying question… scientific aims community response rupture zone imaging megathrust properties lessons learnt
  4. 4. The overriding / underlying question… Fracture zone Ridge Seamount Crustal faults Subduction channel sediments Batholiths scientific aims community response rupture zone imaging megathrust properties lessons learnt
  5. 5. The overriding / underlying question… Can we physically identify asperities and barriers along the megathrust? scientific aims community response rupture zone imaging megathrust properties lessons learnt
  6. 6. The overriding / underlying question… Can we physically identify asperities and barriers along the megathrust? Megathrust dynamics Material properties scientific aims community response rupture zone imaging megathrust properties lessons learnt
  7. 7. Earthquake segmentation Maule segment Recognised as a mature seismic gap (Ruegg et al., 2009, PEPI) Longest-standing seismic gap in Chile Historic rupture areas from Métois et al (2012), JGR Nazca plate scientific aims community response rupture zone imaging megathrust properties lessons learnt South American plate
  8. 8. Earthquake segmentation Maule segment Recognised as a mature seismic gap (Ruegg et al., 2009, PEPI) Longest-standing seismic gap in Chile Historic rupture areas from Métois et al (2012), JGR Nazca plate scientific aims community response rupture zone imaging megathrust properties lessons learnt South American plate
  9. 9. Closing the gap: 27 Feb 2010 6th largest recorded earthquake magnitude 8.8 rupture length 500 km Constitución Concepción Pichilemu SANTIAGO Arauco Peninsula Image from Google EarthTM, Landsat (2013) scientific aims community response rupture zone imaging megathrust properties lessons learnt
  10. 10. International Maule Aftershock DSeisemicp inlstorumyemnts perovnidetd by Field & logistics support from Universidad de Concepción scientific aims community response rupture zone imaging megathrust properties lessons learnt
  11. 11. International Maule Aftershock Deployment From the Pacific coast to the Andes … scientific aims community response rupture zone imaging megathrust properties lessons learnt
  12. 12. International Maule Aftershock Deployment 160 land stations Data available through IRIS repository Virtual network code _IMAD XS – French 3A – British XY - United States German data: www.webdc.eu network code - ZE scientific aims community response rupture zone imaging megathrust properties lessons learnt
  13. 13. International Maule Aftershock Deployment 160 land stations + 37 OBS stations Data available through IRIS repository Virtual network code _IMAD XS – French 3A – British XY - United States German data: www.webdc.eu network code - ZE scientific aims community response rupture zone imaging megathrust properties lessons learnt
  14. 14. The overriding / underlying question… Can we physically identify asperities and barriers along the megathrust? Megathrust dynamics Material properties scientific aims community response rupture zone imaging megathrust properties lessons learnt
  15. 15. Modelling slip on the megathrust scientific aims community response rupture zone imaging megathrust properties lessons learnt
  16. 16. Modelling slip on the megathrust scientific aims community response rupture zone imaging megathrust properties lessons learnt
  17. 17. Modelling slip on the megathrust most slip between trench and coastline max slip 16m at northern asperity Coseismic slip model from Moreno et al. (2012), EPSL scientific aims community response rupture zone imaging megathrust properties lessons learnt
  18. 18. Aftershock seismicity Locations from Rietbrock et al. (2012), GRL scientific aims community response rupture zone imaging megathrust properties lessons learnt
  19. 19. Aftershock seismicity A’ Locations from Rietbrock et al. (2012), GRL C A B B’ D C’ E D’ E’ Distance from trench (km) scientific aims community response rupture zone imaging megathrust properties lessons learnt
  20. 20. Aftershock seismicity A’ C B B’ D C’ E D’ E’ Locations from Rietbrock et al. (2012), GRL Gap in seismicit y Distance from trench (km) A scientific aims community response rupture zone imaging megathrust properties lessons learnt
  21. 21. The overriding / underlying question… Can we physically identify asperities and barriers along the megathrust? Megathrust dynamics Material properties Local earthquake tomography scientific aims community response rupture zone imaging megathrust properties lessons learnt
  22. 22. Imaging the subsurface: seismic tomography scientific aims community response rupture zone imaging megathrust properties lessons learnt
  23. 23. Tomographic inversion steps P- & S-wave arrival times Initial event locations 1-D starting model scientific aims community response rupture zone imaging megathrust properties lessons learnt
  24. 24. Tomographic inversion steps P- & S-wave arrival times Initial event locations 1-D starting model Least squares Updated event locations inversion 2-D velocity model (vp & vp/vs ratio) scientific aims community response rupture zone imaging megathrust properties lessons learnt
  25. 25. Tomographic inversion steps P- & S-wave arrival times Initial event locations 1-D starting model Least squares Updated event locations inversion Final 3-D velocity model Final event locations Least squares inversion 2-D velocity model (vp & vp/vs ratio) scientific aims community response rupture zone imaging megathrust properties lessons learnt
  26. 26. Tomographic inversion steps P- & S-wave arrival times Resolutio n? Initial event locations 1-D starting model 2-D velocity model (vp & vp/vs ratio) Least squares Updated event locations inversion Least squares inversion Final 3-D velocity model Final event locations Inversion algorithm: SIMUL2000 (Thurber & scientific aims community response rupture zone imaging megathrust properties Ebleessrohnasr tle-Parhntillips,1999)
  27. 27. Imaging the rupture zone: data 160 land + 37 OBS stations 670 aftershocks 38,000 P-wave picks14,000 S-wave picks scientific aims community response rupture zone imaging megathrust properties lessons learnt
  28. 28. 2D velocity structure Resolutio n limits Focal mechanisms from: Agurto et al. (2012), EPSL Hayes et al. (2013), GJI Coastline scientific aims community response rupture zone imaging megathrust properties lessons learnt
  29. 29. 2D velocity structure Resolutio n limits Focal mechanisms from: Agurto et al. (2012), EPSL Hayes et al. (2013), GJI Coastline scientific aims community response rupture zone imaging megathrust properties lessons learnt
  30. 30. 2-D velocity structure Coastline scientific aims community response rupture zone imaging megathrust properties lessons learnt Resolutio n limits
  31. 31. 2-D velocity structure Coastline scientific aims community response rupture zone imaging megathrust properties lessons learnt Resolutio n limits
  32. 32. 3-D velocity structure A B C D E A’ B’ C’ D’ E’ Event catalogue and cross-section locations scientific aims community response rupture zone imaging megathrust properties lessons learnt
  33. 33. 3-D velocity structure Resolutio n limits Coastline Arauco Concepción Cobquecura Constitución Pichilemu A B C D E A’ B’ C’ D’ E’ Event catalogue and cross-section locations Distance from trench (km) scientific aims community response rupture zone imaging megathrust properties lessons learnt
  34. 34. 3-D velocity structure Arauco Concepción Cobquecura Constitución Pichilemu A B C D E A’ B’ C’ D’ E’ Resolutio n limits Coastline Event catalogue and cross-section locations Distance from trench (km) scientific aims community response rupture zone imaging megathrust properties lessons learnt
  35. 35. Forearc anomalies: imaging capability Input model scientific aims community response rupture zone imaging megathrust properties lessons learnt
  36. 36. Forearc anomalies: imaging capability Input model Recovered model scientific aims community response rupture zone imaging megathrust properties lessons learnt
  37. 37. Forearc body: composition & origin Observations vp ~ 7.8 km/s; vp/vs ratio ~ 1.8 scientific aims community response rupture zone imaging megathrust properties lessons learnt
  38. 38. Forearc body: composition & origin Observations vp ~ 7.8 km/s; vp/vs ratio ~ 1.8 Positive gravity anomaly Composition Ultramafic (weakly serpentinised?) Christensen (2010), Int. Geol. Rev. vp at 25 km depth Origin Subducted topographic anomaly? Hicks et al. (2012), GRL Gravity anomaly from EGM2008 (Pavlis et al., 2012, JGR) Forearc gravity model from Hicks et al. (2012), GRL. scientific aims community response rupture zone imaging megathrust properties lessons learnt
  39. 39. Forearc body: composition & origin Observations Composition Origin Subducted topographic anomaly? Hicks et al. (2012), GRL Root of Paleozoic granite batholith? Triassic extensional phase? Vásquez et al. (2011), J. Geol. vp at 25 km depth vp ~ 7.8 km/s; vp/vs ratio ~ 1.8 Positive gravity anomaly Ultramafic (weakly serpentinised?) Christensen (2010), Int. Geol. Rev. scientific aims community response rupture zone imaging megathrust properties lessons learnt
  40. 40. The overriding / underlying question… Can we physically identify asperities and barriers along the megathrust? Megathrust dynamics Material properties of the megathrust scientific aims community response rupture zone imaging megathrust properties lessons learnt
  41. 41. Megathrust geometry Good agreement with global / regional plate interface models Uniform megathrust geometry throughout Maule segment Moment tensors from: Agurto et al. (2012), EPSL Hayes et al. (2013), GJI scientific aims community response rupture zone imaging megathrust properties lessons learnt
  42. 42. Shedding light on megathrust properties scientific aims community response rupture zone imaging megathrust properties lessons learnt
  43. 43. Shedding light on megathrust properties scientific aims community response rupture zone imaging megathrust properties lessons learnt
  44. 44. Correlating with seismic cycle behaviour Preseismic locking • >70% contours: Moreno et al., 2010 scientific aims community response rupture zone imaging megathrust properties lessons learnt
  45. 45. Correlating with seismic cycle behaviour Preseismic locking • >70% contours: Moreno et al., 2010 Coseismic rupture • Slip: Moreno et al., 2012 • High freq: Kiser & Ishii (2011) scientific aims community response rupture zone imaging megathrust properties lessons learnt
  46. 46. Correlating with seismic cycle behaviour Preseismic locking • >70% contours: Moreno et al., 2010 Postseismic • Afterslip >1m: Lin et al.,2013 • Relocated interface aftershocks Coseismic rupture • Slip: Moreno et al., 2012 • High freq: Kiser & Ishii (2011) scientific aims community response rupture zone imaging megathrust properties lessons learnt
  47. 47. Aftershock distribution Arauco Concepción Cobquecura Constitución Pichilemu Distance from trench (km) scientific aims community response rupture zone imaging megathrust properties lessons learnt
  48. 48. Correlating with seismic cycle behaviour Coseismic rupture • Slip: Moreno et al., 2012 • High freq: Kiser & Ishii (2011) Preseismic locking • >70% contours: Moreno et al., 2010 Postseismic • Afterslip >1m: Lin et al.,2013 • Relocated interface aftershocks scientific aims community response rupture zone imaging megathrust properties lessons learnt
  49. 49. Down-dip segmentation of the megathrust scientific aims community response rupture zone imaging megathrust properties lessons learnt
  50. 50. Implications for the Maule megathrust 1 2 3 Ultramafic bodies in forearc may inhibit rupture propagation Minimal slip (seismic or aseismic) where vp > 7.5 km/s High vp/vs correlates with up-dip limit of seismogenesis 4 Afterslip may be compositionally-driven scientific aims community response rupture zone imaging megathrust properties lessons learnt
  51. 51. Can we physically identify asperities and barriers along the megathrust? Up-dip barrier: Fluid-saturated sediments Down-dip barrier: Long-lived ultramafic bodies in crust
  52. 52. Lessons learnt scientific aims community response rupture zone imaging megathrust properties lessons learnt
  53. 53. Lessons learnt from deployment 1 2 3 4 Ocean-bottom measurements can fully explore seismogenic zone – further investment and planning needed Involve OBS communities into future rapid deployments Active-source experiments may reveal megathrust structure in seismic gaps Instrument pools needed for rapid responses scientific aims community response rupture zone imaging megathrust properties lessons learnt
  54. 54. From Maule to Iquique Earthquake locations (Mw > 5.5) and preliminary finite fault model from NEIC (USGS) Image from Google EarthTM, Landsat (2013)
  55. 55. Shifting focus northward Earthquake catalogue from Servicio Centro Sismológico Nacional, Chile www.sismologia.cl
  56. 56. Shifting focus northward M8.4 Southern Peru earthquake, 2001
  57. 57. Future progress… Use of slip models and high-res seismic images gives unique view of subduction faults Seismic velocities could help estimate rupture size potential of future earthquakes Dense ocean-bottom observations of foreshock and aftershock sequences in remaining seismic gaps Email: s.hicks@liverpool.ac.uk Web: http://pcwww.liv.ac.uk/~es0u719b

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