Oral Presentation

Several previous studies have used different stress indicators to provide constraints on crustal stress in Southern California. They noted that regional and local stress variations exist at various spatial scales and degrees of heterogeneity, and transitions from one state of stress to another occur over distances of only a few kilometers. Similar local scale stress heterogeneities have been identified in other regions and are believed to be controlled by phenomena such as active faulting, gravitational collapse, local intrusions, density and strength contrasts, basin geometry, and topography. The majority of data compiled in the SCEC CSM are derived from focal mechanism inversions and geodetic velocity‐based strain rates. However, because boreholes sample the uppermost crust, where stress is more heterogeneous than at depth, they provide a rich dataset that should be embedded in a more homogenous regional stress field to better address how the different scales of stress heterogeneity and complexity impact dynamic rupture models of high‐risk fault systems. We will summarize results on the stress regimes and SHmax orientations obtained from >100 wells at depths < 3 km located along the Newport-Inglewood fault system, the Wilmington blind-thrust fault, and fault systems in the Santa Barbara Channel. Our results highlight the possibility of stress variations near active faults at length-scales less than 1 km and provide much needed observational constraints on in-situ stress, which are useful for validating the CSM.