Response of the San Jacinto fault zone to static stress changes from the 1992 Landers earthquake

M. Nic Bhloscaidh and J. McCloskey

School of Environmental Sciences, University of Ulster

C. J. Bean

School of Geological Sciences, University College Dublin

Coulomb stresses and aftershocks

Landers sequence

Southern California, 1992

CFS

San Jacinto Fault Zone

San Andreas Fault Zone M6.1 Joshua Tree23rd April 1992

M7.3 Landers28th June 1992

M7.1 Hector Mine16th October 1999

20km

M6.5 Big Bear28th June 1992

California Geological Survey

The 1992 Landers earthquake sequence

Landers pre-seismicity

R – aftershock rater – pre-seismicity rate

Mallman and Zoback (2005)

Changes in rate after Landers

The San Jacinto Fault Zone

SAN BERNARDINO

SAN JACINTO

ANZA

Sanders and Kanamori (1984)

Coulomb Stress TriggeringCFSln

r

R

0CFS

0ln r

R

0CFS

0ln r

R

0CFS

0ln r

R

Correlation between rate changes and static stress changes

San Bernardino

San Jacinto

Anza

6.578.0

The Coulomb Rate-State model

AreR /CFS)0(

A

CFS

r

R

)0(ln

attA ee

rtR

//CFS )1(1)(

]CFS)1ln([)( //CFS atTA eeAr

TN

Dieterich, 1994

Estimating the parameters of the CRS model

bars4.0A

years8at

Conclusions

We find a statistically significant positive correlation between the change in rate and the magnitude of the Coulomb stress change, with a correlation coefficient of 0.76 (5.6σ).

This result is an important step in the validation of Coulomb stress based methods for quantitative seismicity forecasting.

The correspondence between Coulomb stress changes and observed rate changes is sensitive to strong heterogeneity in aftershock locations and orientations associated with the presence of large-scale structure in aftershock study areas.

Where the regional structure is mapped, incorporating it explicitly into Coulomb stress models may improve the performance of quantitative Coulomb stress based forecasts.