Characterization of Earthquake Clustering and Swarms in Central New Mexico from 2002–2009 Associated with the Socorro Magma Body

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ABSTRACT Increased seismicity in central New Mexico is associated with a midcrustal magma body underlying an extensional rift zone, with earthquakes typically occurring in spatially compact clusters with occasional swarms occurring within limited time periods. Seismic swarms are observed in a range of environments and can be indicative of a variety of geophysical processes. To identify the primary geophysical processes governing central New Mexico earthquake clustering and swarming, we first relocated seven years (2002–2009) of earthquakes for the area above the Socorro magma body (SMB). The resulting catalog was used to define spatial–temporal and temporal–magnitude patterns, significant b-values, cluster and swarm variance and planarity, correlation coefficient variations for event pair P waves, and focal mechanisms. Spatial–temporal migration of swarms, typically indicative of aseismic or fluid-driven earthquake sequences, is not observed for the majority of SMB swarms. Other observed seismic characteristics of SMB clusters and swarms suggest complex rupture, as planarity, focal mechanisms, and available b-values are similar to those typically observed in mainshock–aftershock sequences. However, temporal–magnitude patterns, diffusivity rates of 1–10 m2/s, highly correlated waveforms, and swarm durations are indicative of fluid pressure-driven earthquake triggering. Based on these documented cluster and swarm patterns, we suggest complex rupture related to fluid-pressure triggering along pre-existing Rio Grande rift faults.