Peter M. Shearer

We compute and analyze stress drops for 4175 earthquakes (ML 0–5) in the 2008 Mogul, Nevada, swarm–mainshock sequence using a spectral decomposition approach that uses depth-dependent path corrections. We find that the highest stress-drop foreshocks occur within the fault zone of the Mw 4.9 mainshock, nucleating at the edges of seismicity voids and concentrating near complexities in the fault geometry, confirming and extending inferences from prior work based on empirical Green’s functions for ∼150 of the larger Mogul earthquakes. The region of the highest stress-drop foreshocks is not reruptured by aftershocks, whereas low-stress-drop areas are consistently low during both the foreshock and aftershock periods, implying that stress drop depends on inherent individual fault properties rather than timing within the sequence. These results have implications for swarm evolution and fault activation within complex 3D structures.