Paleoseismic and Geologic Data for Earthquake Simulations

Lisa B. Grant and Miryha M. Gould

Overview

• Paleoseismic data is needed to understand and simulate long time scale, multi-cycle fault behavior for predictive simulation

• Uncertainty in paleoseismic observations is a major challenge for data assimilation

• Existing paleoseismic databases for hazard calculations should be modified for predictive simulations

• Paleoseismic data can identify areas for predictive simulations of fault interactions

Primary Objective of the ACES Science Plan

“…to develop physically based numerical simulation models for the complete earthquake generation process and to assimilate observations into these models at all time and space scales relevant to the earthquake cycle” (Mora, ACES Proceedings 2000).

Significance of Geologic Data

• Fault data provides framework for simulations

• Paleoseismic data is required for modeling multi-cycle rupture behavior

San Andreas fault (courtesy of J R. Arrowsmith)

Paleoseismic DataDescribes pre-instrumental earthquakes

• Site specific geologic investigations• Data sets are small, sparse and analog• Quantification of uncertainty is a major

challenge for data assimilation• Existing paleoseismic databases for probabilistic

seismic hazard assessment include• Direct measurements

• Interpreted parameters

Direct Measurements and Interpreted Data

• Site specific (point) measurements

• Date of last rupture• Dates of multiple

ruptures• Average recurrence

interval• Surface displacement• Slip rate

• Fault segments and segment properties (spatially averaged)

• Characteristic recurrence interval

• Magnitude• Rupture extent• Slip distribution

(visualization by Peggy Li)

Example Fault Database from California (CDMG)

San Andreas Fault, California

(courtesy of J R. Arrowsmith)

Fault Segments

Slip Rates (mm/yr)By Segment

Slip Rates (mm/yr) atMeasurement Sites

Per Segment

At MeasurementSites

Average Recurrence Interval(years)

1600 year Southern San Andreas Fault Earthquake Dates and Interpreted Rupture History

New data sites

Paleoseismology of the San Andreas Fault System

Bulletin Seismological Society of AmericaEdited by Grant, Lettis and Schwartz

• Dedicated Issue• Expected late 2002• New sites• Additional data and

reduced uncertainty at existing sites

A Northward Propagating Earthquake Sequence in Coastal

Southern California?

L. B. Grant and T. K. Rockwell, in press, SRL

Example of using paleoseismic data to identify potentially hazardous areas for predictive simulation

Deformation and Fault Slip Rates in S. CaliforniaFrom Geodetic and Paleoseismic Measurements

Coulomb Stress Change Model

(Stein et al.Science, 1994)

Suggests northern Newport-Inglewood fault is close to failure

Dates of Most Recent Rupture from Paleoseismic Research

Questions for Predictive Simulation: - Is this a northward propagating rupture sequence? - When will the northern Newport-Inglewood Fault Zone rupture?

S. California Coastal Fault Zone

Conclusions

• Paleoseismic data is needed to understand and simulate long time scale, multi-cycle fault behavior for predictive simulation

• Uncertainty in paleoseismic observations is a major challenge for data assimilation

• Existing paleoseismic databases for hazard calculations should be modified for predictive simulations

• Paleoseismic data can identify areas for predictive simulations of fault interactions

The End