Abstract

We investigate the relations between properties of seismicity patterns in southern California and the surface heat flow using a relocated earthquake catalog. We first search for earthquake sequences that are well separated in time and space from other seismicity and then determine the epidemic type aftershock sequence (ETAS) model parameters for the sequences with a sufficient number of events. We focus on the productivity parameter α of the ETAS model that quantifies the relative efficiency of an earthquake with magnitude M to produce aftershocks. By stacking sequences with relatively small and relatively large α values separately, we observed clear differences between the two groups. Sequences with a smaller α have a relatively large number of foreshocks and relatively small number of aftershocks. In contrast, more typical sequences with larger α have relatively few foreshocks and larger number of aftershocks. The stacked premainshock activity for the more typical latter sequences has a clear increase in the day before the occurrence of the main event. The spatial distribution of the α values correlates well with the surface heat flow: areas of high heat flow are characterized by relatively small α, indicating that in such regions the swarm-type earthquake activity is more common. Our results are compatible with a damage rheology model that predicts swarm-type seismic activity in areas with relatively high heat flow and more typical foreshock–mainshock–aftershock sequences in regions with normal or low surface heat flow. The high variability of α in regions with either high or low heat flow values indicates that at local scales additional factors (e.g., fluid content and rock type) may influence the seismicity generation process.

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