Some Observations Based on the Strong-Motion Accelerograms from the Thomas Creek, Nevada, Earthquake of 23 December 2015

TheThomas Creek earthquake (Mw 4.43) of 23 December 2015 was well recorded by a relatively dense network of strong-motion stations in the urban Reno area and a sparse network of calibrated seismic stations throughout Nevada. In terms of nearby station coverage, this is the best-recorded normal-faulting earthquake to have occurred in Nevada. The strong ground motions appear to be consistent with the ground-motion models used in the hazard estimates in the U.S. Geological Survey National Seismic Hazard Map at short hypocentral distances, but accelerations, velocities, and response spectral amplitudes at sampled periods may decrease slightly faster with distance than these models predict. A foreshock with M-w 3.55 preceded the mainshock by 18 s. Deconvolving the mainshock records using the foreshock recovers a source time function that is broadly similar to a Brune pulse with a rapid rise and roughly exponential decay. The source duration is about 0.5 s with three brief pulses modulating the overall shape. A notable feature of the ground motions is that the displacement at some stations in the Reno basin shows durations of 30-40 s. Given this basin response from a small earthquake, it appears that very long durations of strong motion could be expected in the event of a large earthquake on the range-front fault system.