Using Transportable Array and CREST data to define seismicity in the Rio Grande Rift

Active low strain-rate deformation across the Rio Grande Rift within the Western U.S. presents the possibility that strain is released through widespread small magnitude earthquakes. In order to define seismicity across the rift and understand its tectonic significance, we construct a catalog of small magnitude earthquakes from 2007-2010. Colorado has never had a statewide seismic network, thus previous catalogs are limited to that from the USGS and from short-term temporary seismometer deployments. New Mexico seismicity is monitored with regional networks around Socorro and Carlsbad, though not statewide. This study is the first opportunity to locate events in a spatially and temporally comprehensive network from the USArray Transportable Array (TA) experiment supplemented by the Colorado Rockies Experiment and Seismic Transects (CREST) seismic experiment (Karlstrom et al., 2012). Our earthquake catalog will supplement the USArray Array Network Facility (ANF) catalog with smaller magnitude events and refined regional velocity models. We use earthquake detection and location programs to create a raw catalog of associated events and initial locations from 254 seismic stations surrounding the Rio Grande Rift. Detection processing and event association parameters have been chosen specifically to extend the magnitude threshold relative to the ANF catalog (from 3.0 to approximately 1.5) . Mine blasts will be removed by manual waveform identification from the final catalog. The catalog is compared with catalogs of existing small seismic networks near and in the rift, for example, the New Mexico Tech Seismic Network. Questions of interest include: 1) Can earthquakes be identified that are rift-related? 2) What do the patterns of seismicity tell us about the tectonics of the Rio Grande Rift? Preliminary results show event associations to ML 0.0, although magnitude completeness is higher, and several hundred events are identified each month in 2008. Tectonic events will be compared to possible induced seismic events in the Raton basin along the Colorado - New Mexico border and southeastern New Mexico. Magnitude-frequency relations and catalog completeness will be analyzed to further characterize seismic events.