Rupture characterization of the 2014 Napa Valley earthquake from 3 different perspectives

The extensive strong-ground motion data of the August 24 Mw 6.1 Napa Valley earthquake exhibits an interesting pattern of the strong ground motion. Although the slip models based on seismic and geodetic data revealed mainly north-north-west rupture propagation, the largest ground acceleration of 0.94g was observed at a station south of the hypocenter, presumably associated with the initiation stage of this earthquake. Here, the kinematic and dynamic rupture process of this earthquake is studied using the strong-ground motion data in the vicinity (< 40 km) of the epicentre of the Napa Valley earthquake. Three inversion algorithms are applied. First, a conventional non-linear finite fault inversion is conducted to constrain the overall slip history using relatively long period (> 1 s) seismic data. Second, a dynamic finite fault inversion, which approximates the rupture as multiple elliptical cracks, is carried out to understand what are the stress and strength conditions on the fault that produces a rupture history that is compatible with the observed data. Finally, an iterative Landweber back-projection algorithm is used to constrain the finer spatio-temporal rupture history associating with the high frequency radiation. The efforts particularly focus on the initiation stage of the fault rupture.