Rupture Directivity of the 25 October 2022 Mw 5.1 Alum Rock Earthquake

Abstract The 25 October 2022 Mw 5.1 Alum Rock earthquake shows strong evidence for southeast rupture directivity along the central Calaveras fault (CCF), as indicated by observed ground motions and simulated kinematic ruptures. Peak accelerations (PGAs) peak velocities (PGVs) are notably higher to southeast, with an order of magnitude difference stations at same distance but different azimuths. In addition, PGAs lower than that predicted ground-motion models a factor 3 on average in all directions, indicating low stress drop (∼1.57 MPa). Directivity function modeling simulations both indicate propagation velocity between 2.3 2.5 km/s. We suggest southward relatively may be typical M ∼5 earthquakes this portion CCF.