A Unified Model of Crustal Stress Heterogeneity From Borehole Breakouts and Earthquake Focal Mechanisms

Observations of crustal stress orientation from the regional inversion earthquake focal mechanisms often conflict with those borehole breakouts, possibly indicating local heterogeneity, either laterally or depth. To investigate this we compiled SHmax estimates previous studies for 57 near-vertical boreholes measured breakout azimuths across Los Angeles region. We identified subsets established catalogs centered around each various criteria maximum depth and lateral distance borehole. Each subset was independently inverted 3-D corresponding probability distributions, then compared breakout-derived estimate. find good agreement when both methods sample basement (breakouts are close to sediment-basement interface), mid-basin (sufficient earthquakes present within a sedimentary basin). Along basin margins, in contrast, acceptable only limited shallow earthquakes, implying short-length-scale heterogeneity <20 km. While region as whole shows evidence vertical more homogeneous state rock, over length scales 1–35 These results reconcile apparently conflicting observations observed boreholes, which primarily basins, relative homogeneity inferred mechanisms, basement, imply distinct regimes appropriate use type indicator.