Large Earthquake Rapid Finite Rupture Model Products

1. Large Earthquake Rapid Finite Rupture Model Products Thorne Lay (UCSC) USGS/IRIS/NSF International Workshop on the Utilization of Seismographic Networks Within the Global Earth Observation System of Systems Washington, DC Aug. 23-24, 2005

2. Standard Seismic Operations • Continously record ground motion, transmit to analysis center • Detect P wave arrivals (automatic/analyst) • Associate arrival times • Locate events (hypocenter and origin time) • Measure amplitudes of P, Surface waves • Compute magnitudes (mb, Ms, Mm) • Bulletin: Location/Origin time/Magnitude

3. Further Point-Source Seismic Analyses • First-motion focal mechanism (e.g., USGS/NEIC) • Energy from integrated ground velocity (e.g., USGS/NEIC) • Body waveform focal mechanism, seismic moment (e.g., USGS moment tensor, Mw) • Source time function (time history of faulting process) (e.g., U. Michigan) • Moment tensor inversion from body and/or surface waves (e.g., Harvard CMT, Mw) • Refined catalog parameters

4. Telemetered Signals are Processed Immediately by USGS,NOAA Event location, depth, faulting geometry, size, all automatically determined by USGS, NOAA, Harvard, others by analysis of GSN signals. Results Broadcast on Web Within 15 minutes to 6 hours Within 9 minutes of the event, the U.S. Pacific Tsunami Warning System Characterized this as a Great 8+ Event

5. A point-source representation of the 2004 Sumatra-Andaman event is an inadequate characterization of a 1300-km long rupture. Even the CMT solution underestimated the seismic moment by a factor of 2-3. For LARGE events we should routinely seek finite-source parameters.

6. What we would really like to know: Slip vectors For 2004 Sumatra from Inversion of Regional Long Period Signals

7. Next Generation Information • Patterns of ground motion (e.g., Shakemap) • Stress transfer calculations • Finite Faulting Characteristics: Rupture length Azimuthal rupture duration variations Azimuthal shaking variations (directivity) Fault slip distribution Why do we care?

8. Value of Finite Source Models • Identify actual fault plane • Assess tsunami excitation more confidently • Predict damage patterns • Evaluate aftershock/triggering potential • Quantify tectonic process involved • Advance understanding of earthquake processes

9. Rupture Finiteness Results in Predictable Variation of Waveforms

10. Azimuthal Variation of Short-Period Signals Indicates Rupture Finiteness Ni et al., 2005 Ammon et al., 2005 Array processing As well: Ishii et al., 2005

11. Japanese Hi-Net array • World’s best seismic network • ~700 stations • Borehole sites • Short-period • Three-component • 43° - 60° from Sumatra quake

12. Method forces coherent stack at hypocenter Cross-correlation times correct for perturbations along each hypocenter-station ray path

13. Rupture Image from Hi-Net • Ishii et al. (2005) use Japanese Hi-Net short-period data to back-project along the rupture zone. See a clear northward migration of the rupture front.

14. Early Inversions of P waves for Slip Heterogeneity for 2004 Sumatra Chen Ji Y. Yagi Y. Yamanaka

15. Complete Inversions of Body and Surface Waves

16. Doing it QUICKLY: Isolation of Source Time Functions by Deconvolution of Surface Wave Impulse Response

17. Stations perpendicular to the rupture suffer from minimal directivity distortion.

18. 2D rupture imaging Single Station! KIP

19. 1D rupture imaging

20. 26 December, 2004 Moment-Rate Functions

21. 2D Imaging (12 STFs) Andaman Islands Nicobar Islands

22. Conclusions • Robust seismological techniques exist to rapidly and routinely determine finite faulting parameters for large events (>7.0) • Full waveform deconvolution can recover source time history readily, and give 1D and 2D fault slip models quickly • Complete body wave and surface wave inversion can be done routinely • Finite fault parameters can aid in tsunami and shaking hazard assessment