Three-dimensionalPandSvelocity structure in the Coalinga Region, California

摘要: The Coalinga earthquake sequence of 1983 provided a unique opportunity to perform three-dimensional velocity and hypocenter inversion in an area complex structure dominated by folding blind thrusts. Additionally, since other varied geological geophysical studies have been completed this area, the solution could be compared interpretations. Inversion 7696 P 1511 S first arrivals from earthquakes 696 refraction shots produced model with grid spacing 1–2 km hypocentral area. overall shape location features correspond well mapped surface geology. yields details folds where resolution is good general lower. amounts structural relief inferred for local are similar values geologic data. has several distinctive features. There linear high-velocity body (6.1–6.5 km/s), about 25 long, 6 8 depth, that may represent fragment Coast Range ophiolite. A shallow low-velocity zone (LVZ), which extends 20 along fold axis at depth correlates LVZs observed both reflection data, indicate high pore pressure caused lateral compressive strain. Deeper occur within Franciscan material characterized horizontal or southwest dipping zones thickness, 4–8 wide 5–10 long. These multiple thrust faults. Their locations geometry consistent faults seismic compares prior two-dimensional models gravity. sedimentary section agrees reflections Cenozoic strata. Compared model, velocities but more detailed it uses gravity computed amplitude. Both simple one-dimensional initial derived interpretation were tried. starting gave best results. different than because set stations, lower fewer arrival times. While patterns variation Vp Vs, Vs tends smearing can somewhat