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Two Moho-Depth Earthquake Swarms along the Sierra Microplate Basin and Range Boundary Region

Emily L. Maher, Ken D. Smith, Rachel L. Hatch, Kent M. Graham, Neal W. Driscoll, & Noah Conway

Published August 15, 2018, SCEC Contribution #8692, 2018 SCEC Annual Meeting Poster #068

Two unprecedented near Moho-depth earthquake sequences, 2003-04 and 2011-12, occurred along the eastern Sierra Microplate northern Walker Lane boundary at ~30 km depth separated by ~50 km. Whereas typical seismogenic depths in this tectonic setting between 15-18 km, depths for the two sequence are well constrained and range between ~25-35 km. The N. Tahoe, California, sequence occurred over a 6 month time period in 2003-2004 and consisted of over 1600 located events with a largest ML 2.2. The second swarm occurred in 2011 over a 9 month period below Sierraville, California. For this sequence, 2235 deep events were located beneath Sierra Valley with the largest at magnitude ML 1.9. Initial relocations for both swarms (Smith et al, 2004; Smith et al., 2006) indicate that they occur along structures with a nearly identical strike (~N45°W) and dip (~50°NE). In addition each sequence defines a planar structure, 7x7 in extent. On 29 September 2011, a single deep earthquake occurred at the midpoint of the two sequences further implying that the swarms occurred along the same deep geologic structure. Potential causes for the two deep swarms relate to deep basaltic injection or fluid injection at near Moho depths. However there is currently no evidence for volcanic type earthquake sources. We review phase picks for the sequences to improve available first motions for focal mechanisms, stress inversions and ‘GrowClust’ (Trugman and Shearer, 2017) relocations. Here we present results of a continuing analysis of these unique earthquakes for a better understanding the interaction between the Sierra Microplate and the Basin and Range boundary region at these latitudes.

Maher, E. L., Smith, K. D., Hatch, R. L., Graham, K. M., Driscoll, N. W., & Conway, N. (2018, 08). Two Moho-Depth Earthquake Swarms along the Sierra Microplate Basin and Range Boundary Region. Poster Presentation at 2018 SCEC Annual Meeting.

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