Tectonic Setting of the Offshore and Onshore Santa Maria Basin and Surrounding Regions
Published:January 01, 1994
1994. "Tectonic Setting of the Offshore and Onshore Santa Maria Basin and Surrounding Regions", Seismotectonics of the Central California Coast Ranges, Ina B. Alterman, Richard B. McMullen, Lloyd S. Cluff, D. Burton Slemmons
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Transpressive plate motion in the coastal region between Monterey Bay and Los Angeles is distributed over a complex system of active strike-slip faults, subparallel reverse and reverse-oblique faults, and related folds. Seismotectonic responses to interplate stresses vary markedly along this portion of the plate margin. Coastal central California is divided into structurally and physiographically distinct seismotectonic domains separated by major, predominantly Quaternary, boundary faults. Internally, seismotectonic domains are marked by distinctive styles and orientations of Quaternary faulting and folding, historical seismicity patterns, geomorphic expression, and basement rock characteristics. Five principal seismotectonic domains are recognized in this study: Transverse Ranges domain, Santa Maria Basin-San Luis Range domain, coastal Franciscan domain, Salinian domain, and western San Joaquin Valley domain. Major domain boundaries include the San Andreas, Nacimiento-Rinconada, San Gregorio-Hosgri, Big Pine, and Santa Monica-Raymond-Sierra Madre-Cucamonga faults.
The Transverse Ranges domain is characterized by pronounced north-northeast-oriented maximum horizontal compressive stress and associated Quaternary crustal shortening, west-trending reverse and left-lateral reverse-oblique faults and earthquake focal mechanisms, and a frequent occurrence of damaging earthquakes. The Santa Maria Basin-San Luis Range domain has low to moderate rates of Quaternary tectonism, active west- to northwest-striking reverse faults, and low to moderate seismicity with mainly reverse and left-lateral reverse-oblique focal mechanisms. The coastal Franciscan domain includes numerous northwest-striking, mainly northeast-dipping, faults with uncertain earthquake potentials. Moderate seismicity and reverse and right-lateral reverse-oblique earthquake focal mechanisms indicate significant northeast-directed convergence and broad internal deformation of weak Franciscan Complex basement. The Salinian domain includes a moderate- to high-relief western region marked by abundant northwest-striking faults with uncertain Quaternary histories, and an eastern region with generally low relief and few recognized surface faults. Seismicity within the domain is sparse, typically with right-lateral strike-slip focal mechanisms. The western San Joaquin Valley domain is marked by young folds associated with active thrust and reverse faults in its central and southern portions and both shear and contractional deformation in the north. Seismicity occurs at a low to moderate rate, with mainly reverse and thrust fault focal mechanisms.