Predictive Modeling of Seismicity Sequences in

Southern California

Julia ClarkDavid D. Bowman

California State University, Fullerton

Schematic Diagram of the Seismic Cycle

from Ellsworth et al., 1981

•Many current models of Accelerating Moment Release fit seismicity data to an analytic function

Accelerating Seismicity Function

• One of the most commonly used functions is the

Power-Law time-to-failure equationBufe and Varnes (1993); Sornette and Sammis

(1995)

Where (t) is the seismic energy release at time t, tf is the time of the earthquake, and A,B and m are fitted parameters describing the shape of the function

• This function takes the form:

(t ) = A - B(tf-t)m

325 km

600 km

325 km

RMS Residuals

200 km

1952 Kern County EarthquakeSelecting a circular region

Bowman et al., 1998

All California Earthquakes M≥6.51950-1995

Bowman et al., 1998

Critical Regions

Circular RegionsA simple systematic method to calculate critical regions

using an arbitrary shape that is easy to program,but is not based on geology.

A New MethodThe idea is to model critical regions as the region of stress

accumulation before an earthquake.

Stress Accumulation Regions• The stress field from loading a locked fault patch is the same as the stress field created by slipping the fault backwards.• This permits us to calculate the Coulomb Stress Change for the future earthquake, and look for accelerating seismicity in the regions of increased stress.

What is “Coulomb Stress Change”?

From King et al., 1994

Slipping Fault Slipping FaultSeismic Slip Seismic Slip

Creep at Depth

FutureEarthquake

Calculate from motion on all adjacent faultsplus creep at depth

Stress Change From Loading a Locked Patch on a Simple Fault

Negative Slip

FutureEarthquake

Creep at Depth

=

Where are pre-earthquake stresses?

Accelerating Seismicity in Stress Accumulation Regions

Bowman and King, 2001

No?

Yes?

Future California Earthquakes?

• Fault Senerios

• Coulomb Stress Region

• Seismicity Analysis

• Southern California Faults

Summer Project