The 2014 Mw 6.1 South Napa Earthquake: A Unilateral Rupture with Shallow Asperity and Rapid Afterslip

The Mw 6.1 South Napa earthquake occurred near Napa, California, on 24 August 2014 at 10:20:44.03 (UTC) and was the largest inland earthquake in northern California since the 1989 Mw 6.9 Loma Prieta earthquake. The first report of the earthquake from the Northern California Earthquake Data Center (NCEDC) indicates a hypocentral depth of 11.0 km with longitude and latitude of (122.3105° W, 38.217° N). Surface rupture was documented by field observations and Light Detection and Ranging (LiDAR) imaging (Brooks et al., 2014; Hudnut et al., 2014; Brocher et al., 2015), with about 12 km of continuous rupture starting near the epicenter and extending to the northwest. The southern part of the rupture is relatively straight, but the strike changes by about 15° at the northern end over a 6 km segment. The peak dextral offset was observed near the Buhman residence with right‐lateral motion of 46 cm, near the location where the strike of fault begins to rotate clockwise (Hudnut et al., 2014). The earthquake was well recorded by the strong‐motion network operated by the NCEDC, the California Geological Survey and the U.S. Geological Survey (USGS). There are about 12 sites within an epicentral distance of 15 km that had relatively good azimuthal coverage (Fig. 1). The largest peak ground velocity (PGV) of nearly 100  cm/s was observed on station 1765, which is the closest station to the rupture and lies about 3 km east of the northern segment (Fig. 1). The ground deformation associated with the earthquake was also well recorded by the high resolution COSMO–SkyMed (CSK) satellite and Sentinel-1A satellite, providing independent static observations.

[1]  A Pitarka,et al.  Refinements to the Graves and Pitarka (2010) Broadband GroundMotion Simulation Method , 2017 .

[2]  M. Nakatani,et al.  Earthquake cycle simulation with a revised rate- and state-dependent friction law , 2013 .

[3]  Nadia Lapusta,et al.  Towards inferring earthquake patterns from geodetic observations of interseismic coupling , 2010 .

[4]  S. DeLong,et al.  Surface slip associated with the 2014 South Napa, California earthquake measured on alinement arrays , 2014 .

[5]  A. Pitarka,et al.  Broadband Ground-Motion Simulation Using a Hybrid Approach , 2010 .

[6]  N. Anders Petersson,et al.  Ground-motion modeling of Hayward fault scenario earthquakes, part II: Simulation of long-period and broadband ground motions , 2009 .

[7]  Yehuda Bock,et al.  Parkfield earthquake: Stress-driven creep on a fault with spatially variable rate-and-state friction parameters , 2009 .

[8]  J. Avouac,et al.  Under the Hood of the Earthquake Machine: Toward Predictive Modeling of the Seismic Cycle , 2012, Science.

[9]  A. Freed,et al.  Afterslip (and only afterslip) following the 2004 Parkfield, California, earthquake , 2007 .

[10]  S. Owen,et al.  Complementary slip distributions of the largest earthquakes in the 2012 Brawley swarm, Imperial Valley, California , 2013 .

[11]  Luis Rivera,et al.  A note on the dynamic and static displacements from a point source in multilayered media , 2002 .

[12]  Timothy E. Dawson,et al.  The Mw 6.0 24 August 2014 South Napa Earthquake , 2015 .

[13]  D. L. Anderson,et al.  Theoretical Basis of Some Empirical Relations in Seismology by Hiroo Kanamori And , 1975 .

[14]  Hugo Perfettini,et al.  Postseismic relaxation driven by brittle creep: A possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks, application to the Chi-Chi earthquake, Taiwan , 2004 .

[15]  Walter H. F. Smith,et al.  Free software helps map and display data , 1991 .

[16]  Kristine M. Larson,et al.  Frictional Properties on the San Andreas Fault near Parkfield, California, Inferred from Models of Afterslip following the 2004 Earthquake , 2006 .

[17]  Felix Waldhauser,et al.  Fault structure and mechanics of the Hayward Fault, California, from double-difference earthquake locations , 2002 .

[18]  Kojiro Irikura,et al.  Surface Rupturing and Buried Dynamic-Rupture Models Calibrated with Statistical Observations of Past Earthquakes , 2008 .

[19]  D. Sandwell,et al.  Three-dimensional deformation caused by the Bam, Iran, earthquake and the origin of shallow slip deficit , 2005, Nature.

[20]  M. Simons,et al.  Post-seismic and interseismic fault creep; II, Transient creep and interseismic stress shadows on megathrusts , 2010 .

[21]  Paul Segall,et al.  Rapid afterslip following the 1999 Chi‐Chi, Taiwan Earthquake , 2002 .

[22]  Takao Kagawa,et al.  Differences in ground motion and fault rupture process between the surface and buried rupture earthquakes , 2004 .

[23]  Luis A. Dalguer,et al.  Numerical Study of Ground-Motion Differences between Buried-Rupturing and Surface-Rupturing Earthquakes , 2009 .

[24]  A. Rubin,et al.  Streaks of microearthquakes along creeping faults , 1999, Nature.

[25]  Gregory C. Beroza,et al.  High‐resolution image of Calaveras Fault seismicity , 2002 .

[26]  Chris Marone,et al.  The depth of seismic faulting and the upper transition from stable to unstable slip regimes , 1988 .

[27]  H. Zebker,et al.  Fault Slip Distribution of the 1999 Mw 7.1 Hector Mine, California, Earthquake, Estimated from Satellite Radar and GPS Measurements , 2002 .

[28]  Yehuda Bock,et al.  Frictional Afterslip Following the 2005 Nias-Simeulue Earthquake, Sumatra , 2006, Science.

[29]  Chen Ji,et al.  Source Description of the 1999 Hector Mine, California, Earthquake, Part I: Wavelet Domain Inversion Theory and Resolution Analysis , 2002 .