Investigation of an unusually shallow earthquake sequence in Mogul, NV from a discrimination perspective

Abstract:

The primary objective of this study is a detailed investigation of an unusually shallow earthquake sequence that occurred in 2008 in Mogul, west of Reno, Nevada. The main shock Mw 5.0 of this sequence occurred at 2.8 km below the surface and satisfied criteria for GT1 qualification. High amplitude near-field ground motions and rapid attenuation with distance were investigated for the Mogul main shock and principal fore- and aftershocks. Seismic moment, stress drop, and corner frequency for the ML > 3.0 Mogul earthquakes were estimated using 1) Spectral fitting and 2) Lg coda ratios. The source time function and the stress drop of the main shock were also probed using Empirical Green’s Functions. The stress drop estimates ranged from 3 to 14 MPa. Investigations of the effect of source depth on P and S spectra and spectral ratios, signal complexity, and mb-Ms discrimination are also discussed in comparison to deeper earthquake sequences and explosions within 100 km of Mogul, and in comparison to sets of earthquakes and nuclear explosions which occurred on or near the Nevada Test Site. According to preliminary results, the Mogul main shock classifies as an earthquake, however, discrimination becomes difficult for a foreshock and an aftershock with ML>3.9.