COULOMB STRESS EVOLUTION IN EASTERN CALIFORNIA AND WESTERN NEVADA IN THE LAST 1000 YEARS

Diffuse plate boundary regions are characterized by high deformation rates distributed over a wide zone. The correlation of seismic activity between faults in these regions is not yet well understood. The region between eastern California and western Nevada is part of such a diffuse plate boundary. The purpose of our work is to determine how faults in this region interact in terms of static stress transfer at different spatial and temporal scales. We calculated the evolution of Coulomb stress in space and time due to coseismic and postseismic static stress changes induced by large earthquakes during the last 1000 years. Our results show a pattern of coseismic static stress triggering among earthquakes in the study area, greatly amplified by posteseismic processes. Only two of the modeled events, the 1872 M_w = 7.8 Owens Valley and the 1915 M_w = 7.3 Pleasant Valley earthquakes, do not show any correlation with previous events within the region of study, but are likely connected instead to activity on the San Andreas fault and on other Basin and Range faults respectively. Most of the postseismic stress is relaxed during the first 250 years after the earthquake for most of the viscoelastic models we evaluated. Finally, two large faults that do not have any historical ruptures, the White Mountains fault and the northern Death Valley fault, have accumulated a static stress load of 30 and 80 bars respectively, comparable to the expected stress drop in an average earthquake. These values have however been calculated assuming absence of earthquakes on these two faults for the last 1000 years. Further paleoseismological investigations are therefore required for these faults to constrain the age of the last event, as any events younger than 1000 years would significantly change the calculated stresses and therefore the expected time of occurrence of the next earthquake.