Studies of the South Napa Earthquake Aftershocks

In this paper we present studies of the aftershock sequence of the 24 August, 2014, M = 6.0 South Napa earthquake. We give the cumulative frequency-magnitude distributions of the aftershocks for several time intervals following the main shock. We give the magnitude of the largest aftershock (Bath's law) as well as the largest aftershock obtained from a Gutenberg-Richter fit to the frequency-magnitude data (modified form of Bath's law). The latter is a measure of the aftershock productivity. We also give the rates of occurrence of aftershocks as a function of time after the main shock for several magnitude ranges. The fit of this data to Omori's law is discussed. We compare the results of our study of the South Napa earthquake with our previous study of the aftershock statistics of the 28 September, 2004, M = 6.0 Parkfield earthquake. Specifically we will discuss any difference that can be attributed to the large difference in recurrence intervals for the two earthquakes. We also present studies of the three dimensional distribution of aftershock locations as a function of time and their association with the surface rupture. Aftershocks at large distances from the rupture zone will be discussed particularly those in the Geysers geothermal area.