Double-Difference Location and Ground-Truth Classification of the 2008 Mogul, Nevada, Very Shallow Earthquake Sequence

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A long sequence of shallow earthquakes occurred west of Reno, Nevada during 2008 beneath a community called Mogul (Anderson et al. , 2009; Tibuleac et al. , 2011). This sequence began with a swarmlike series in early 2008 and was punctuated by an M w 5.0 earthquake on 26 April 2008. (06:40:10 UTC and 10:40:10 p.m. 25 April local time). The mainshock was followed by a fairly typical aftershock sequence through the remainder of 2008. The sequence consisted of over 2000 earthquakes with M L≥1.0, concentrated in depths between 1 and 4 km and ranging in magnitude up to M w 5.0 (mainshock). The swarmlike activity prior to the mainshock provided time to instrument the epicentral area with temporary broadband and strong‐motion stations, in advance of the occurrence of the largest events. These stations complemented the Nevada and California permanent seismic monitoring stations and the high‐quality broadband stations of the Earthscope Transportable Array network deployed in Nevada during 2008. The primary objective of this study was a detailed investigation of this sequence of earthquakes in terms of location and ground‐truth (GT) classification. Compared with earthquakes at typical depths, these shallow earthquakes have near‐field ground motions with uncharacteristically high amplitudes and rapid attenuation with distance (Anderson et al. , 2009). For our investigations, we used a unique broadband and strong‐motion recording database, obtained from stations as close as 1 km from the epicenter of the mainshock and most of the smaller events. These sensors recorded waveforms that we have organized into a database including near‐field and seismic‐network recordings of all the M L≥1.0 earthquakes of the sequence located by the Nevada Seismological Laboratory (NSL). We have relocated the Mogul earthquakes with hypoDD, incorporating P and S cross correlations. Location shifts as large as several hundred meters were observed when compared with the original catalog …