Rupture history of 2014 M_w 6.0 South Napa earthquake inferred from near‐fault strong motion data and its impact to the practice of ground strong motion prediction

Abstract

The spatiotemporal rupture history of the 2014 South Napa earthquake is constrained using near‐fault strong motion records. An aggressive source parameterization with 1372 subfaults is adopted to match the signals in the transverse components up to 4 Hz. The result reveals that the rupture of the Napa earthquake initiated at a depth of 9.84 km and propagated mainly to north‐northwest (NNW) and updip on a 13 km long fault patch. A gradual increase in average rise time when the rupture propagates to shallower depth is observed. However, it is the rupture of a small (Mw 4.9), isolated, and high stress drop fault patch that excited the largest ground acceleration at stations south of the epicenter. Such fine‐scale rupture heterogeneity shall be considered during seismic hazard analysis.

3D displacement field retrieved by integrating Sentinel-1 InSAR and GPS data: the 2014 South Napa earthquake

“…Other interpolation techniques such as the Inverse Distance Weighting (IDW) will be explored in future developments by taking into account the spatial discontinuity due to the fault system. Finally, as revealed by several studies [Barnhart et al, 2015;Brocher et al, 2015;Ji et al, 2015], the earthquake epicenter is located 1.7 Km westward of the known West Napa Fault system, and it mostly ruptured unmapped portions of this fault system. Therefore, to fully address all of the observed features, as well as to provide new insights about the slipping fault, additional investigations are required regarding, for example, the inversion of the optimized 3D co-seismic deformation field and the spatial and temporal distribution of the seismicity associated to the main shock.…”

Stability of rapid finite‐fault inversion for the 2014 Mw6.1 South Napa earthquake

“…The most significant slip patch is located to the upper left of the hypocenter, which means that the rupture mainly propagated to the north and at the shallow depth. This is consistent with other seismic and geodetic studies [ Barnhart et al ., ; Dreger et al ., ; Feng et al ., ; Ji et al ., ; Melgar et al ., ; Wei et al ., ]. Most slip distributions shown in Figures a and b seem relatively tight and smoothed, which are close to joint and geodetic GPS/interferometric synthetic aperture radar models [ Barnhart et al ., ; Dreger et al ., ; Feng et al ., ; Melgar et al ., ], but differ with results of velocity waveform inversions of strong motion data [ Ji et al ., ; Wei et al ., ].…”

“…By considering the centroid time of subfault STFs, we calculated the slip‐weighted average rupture velocities for each rupture model. They are between 2.7 and 3.1 km/s, close to 2.9–3.0 km/s obtained by other waveform inversions [ Dreger et al ., ; Ji et al ., ; Melgar et al ., ; Wei et al ., ]. In inversions of R > 10 km, subfault STFs show similar rupture times and durations but different amplitudes (moment rate).…”

Ambient noise‐based monitoring of seismic velocity changes associated with the 2014 Mw 6.0 South Napa earthquake

“…The 24 August 2014 M w 6.0 South Napa earthquake is the largest earthquake in the San Francisco Bay Area, California, since the 1989 M w 6.9 Loma Prieta earthquake. Inversions of seismic and geodetic data reveal a notable updip and northwest rupture directivity toward to the city of Napa [ Dreger et al ., ; Ji et al ., ; Melgar et al ., ; Wei et al ., ]. The 2014 South Napa earthquake rupture is characterized by a single elongated patch approximately 10 km with a maximum slip of about 1 m. Continuous geodetic observations suggest that the postseismic deformation primarily propagated to the southeast in a depth of 0–2 km and released a maximum slip of ~35 cm [e.g., Fielding et al ., ; Murray et al ., ; Brocher et al ., ; Funning et al ., ].…”