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

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

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

Telemetered Signals are Processed Immediately by USGS,NOAA

Event location, depth,faulting geometry,size, all automaticallydetermined by USGS,NOAA, Harvard, others byanalysis of GSN signals.Results Broadcast on WebWithin 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

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.

What we would really like to know:

Slip vectorsFor 2004Sumatra fromInversion of Regional LongPeriod Signals

Next Generation Information

• Patterns of ground motion (e.g., Shakemap)• Stress transfer calculations• Finite Faulting Characteristics:

Rupture lengthAzimuthal rupture duration variationsAzimuthal shaking variations (directivity)Fault slip distribution

Why do we care?

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

Rupture Finiteness Results in Predictable Variation of Waveforms

Azimuthal Variation of Short-Period Signals Indicates Rupture Finiteness

Ni et al., 2005Ammon et al.,2005

Array processingAs well:Ishii et al., 2005

Japanese Hi-Net array

• World’s best seismic network

• ~700 stations• Borehole sites• Short-period• Three-component• 43° - 60° from Sumatra

quake

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Method forces coherent stack at hypocenter

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Cross-correlation times correct for perturbations along each hypocenter-station ray path

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.

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Early Inversions of P waves for Slip Heterogeneity for 2004 Sumatra

Chen Ji

Y. Yagi

Y. Yamanaka

Complete Inversions of Body and Surface Waves

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

Stations perpendicularto the rupture suffer from minimal directivitydistortion.

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2D rupture imagingSingle Station! KIP

1D rupture imaging

26 December, 2004 Moment-Rate Functions

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AndamanIslands

2D Imaging (12 STFs)

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