Project Abstract
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We continue our 3D dynamic rupture modeling of earthquakes along the San Gorgonio Pass (SGP) section of San Andrea fault (SAF) to investigate the likelihood of through-going events in this region. Here we focus on the roles of fault geometry and loading stress around the fault by adopting in model simulations the SCEC Community Fault Model (CFM-v4) and the SCEC Community Stress Model (CSM). The Banning Fault in the SGP region is assumed to be the active strand that connects the San Bernadino (SB) segment of the SAF (north of SGP) and the Coachella Valley (CV) segment of the SAF (south of SGP). Our previous simulations using different approaches of assigning initial fault tractions have shown that the stress loading around the fault poses as a key factor in understanding the likelihood of through-going ruptures in the presence of such complex fault geometry. On the one hand, with homogeneous volume stress input, ruptures fail to break through the SGP section regardless of propagation direction or rupture mode; on the other hand, with arbitrary heterogeneous fault traction input that implies heterogeneous volume stress, ruptures do not seems to be affected much by the relatively long-wavelength features of the non-planar fault geometry. To explore the physical plausibility of through-going ruptures along SGP in more realistic situations, we adopted in our 3D dynamic rupture simulations three regional stress models for southern California that are being developed by different SCEC CSM user groups: Hardebeck_FM, SHELLS and YHSM-2013. Among these three models, only SHELLS gives absolute stresses that are constrained to satisfy equilibrium. The other two stress models, however, only provide deviatoric stresses without meaningful isotropic components. The fault tractions obtained by resolving volumetric stress fields onto the irregular fault plane revealed apparent discrepancies among the different stress models regarding their respective implications for the likelihood of through-going rupture along SGP. The SHELLS stress model yields high ratios of |Ts|/|Tn| along the fault segment in the SGP region, which implies high likelihood of such events. The Hardebeck_FM and YHSM-2013 stress models, on the contrary, results in low ratios of |Ts|/|Tn| along the fault segment in the SGP region, which implies low likelihood of such events. Due to the vital importance of stress loading in answering the likelihood question as revealed by our previous simulations, more observational studies are greatly needed to reconcile the different candidate stress models in the SCEC CSM and establish reliable and self- consistent stress input useful for physics-based studies of rupture dynamics in the region. |
