40 years of seismic swarms in the the BR-CP transition zone in Central Utah

Abstract

Seismicity in Central Utah, USA, exhibits a remarkable diversity in swarm activity. Swarms in the study area may alter between high and low activity phases, show a comparably continuous moment release, or a rise and fall of magnitudes over time. While some swarms repeatedly occur in the same source area for several years, other large swarms occur in areas without any significant seismic activity. The diversity is attributed to the complex geo-tectonic transition zone between the Basin and Range province (BR) and the Colorado Plateau (CP) in Central Utah, which is manifested in tectonic forcing related to E-W extension, high heat flow, and hydrothermal processes. Based on the University of Utah Seismograph Stations' catalog, we analyzed forty years of seismic swarm activity within Central Utah, USA, regarding characteristic statistical features (e.g., duration, moment release over time, spatial variations). In-depth analyses of three seismic sequences, including event detections, relocations, MT inversions, waveform-based clustering, and repeater analysis, provide unique insights into the study area's complex and diverse faulting processes. This includes (1) swarm activity at a regional Basin and Range normal fault, (2) activation of a local fault deviating from the recent regional tectonic regime, and (3) the complex triggering of swarm activity by a mainshock. In a joint discussion of the single exemplary sequences and the characteristics of swarm activity, we aim to expand the discussion on swarm activity beyond the study area and shed light on its relation to geothermal and tectonic processes.