COULOMB STRESS AND EARTHQUAKE PATTERNS IN DIFFUSE PLATE BOUNDARY REGIONS: AN EXAMPLE FROM WESTERN NEVADA AND EASTERN CALIFORNIA, USA

The region east of the Sierra Nevada that encompasses the northern Eastern California Shear Zone (ECSZ), Walker Lane (WL), and the westernmost part of the Basin and Range province (B&R) is part of a diffuse plate boundary. In this region earthquakes occur in spatially and temporally complex patterns.

In order to better understand the spatio-temporal relationship among significant earthquakes in this area, we modeled the evolution of coseismic, postseismic and interseismic Coulomb stress changes (ΔCFS) in this region at two different spatio-temporal scales. In the first example we examined seven historical and instrumental M_w ≥ 6 earthquakes that struck the region around Owens Valley (northern ECSZ) in the last 150 years. In the second example we expanded our study area to all of the northern ECSZ, WL and western B&R, examining seventeen paleoseismological and historical major surface-rupturing earthquakes (M_w ≥ 6.5) that occurred in the last 1400 years.

Our results show that in both cases the majority of the studied events (100% in the first case, and 80% in the second) are located in areas of combined coseismic and postseismic positive ΔCFS. This relationship is robust, as shown by control tests with random earthquake sequences. We also show that the White Mountain fault has accumulated up to 30 bars of total ΔCFS (coseismic + postseismic + interseismic) in the last 150 years, and the Hunter Mountain, Fish Lake Valley, Black Mountain, and Pyramid Lake faults have accumulated 40, 45, 54 and 37 bars respectively in the last 1400 years. Such values are comparable to the average stress drop in a major earthquake, and all these faults may be therefore close to failure.