Active tectonic deformation at the eastern margin of the California Coast Ranges; results of the BASIX and CALCRUST programs
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Open-File Report↗
Geology topics
T.V. McEvilly
Publications and source records attributed to T.V. McEvilly.
Seismic evidence for a lower-crustal detachment beneath San Francisco Bay, California
Results from the San Francisco Bay area seismic imaging experiment (BASIX) reveal the presence of a prominent lower crustal reflector at a depth of ∼15 kilometers beneath San Francisco and San Pablo bays. Velocity analyses indicate that this reflector marks the base of Franciscan assemblage rocks and the top of a mafic lower crust. Because this compositional contrast would imply a strong rheological contrast, this interface may correspond to a lower crustal detachment surface. If so, it may represent a subhorizontal segment of the North America and Pacific plate boundary proposed by earlier thermo-mechanical and geological models.
California↗
Crustal structure of Yunnan province, People's Republic of China, from seismic refraction profiles
Seismic refraction, profiles in Yunnan Province, southwestern China, define the crustal structure in an area of active tectonics on the southern end of the Himalaya-Burma arc. The crustal thickness ranges from 38 to 46 kilometers, and the relatively low mean crustal velocity indicates a crustal composition compatible with normal continental crust and consisting mainly of meta-sedimentary and silicic intrusive rocks, with little mafic or ultramafic component. This composition suggests a crustal evolution involving sedimentary processes on the flank of the Yangtze platform rather than the accretion of oceanic island arcs, as has been proposed. An anomalously low upper-mantle velocity observed on one profile but not on another at right-angles to it may indicate active tectonic processes in the mantle or seismic anisotropy.
Yunnan Province↗
In-situ seismic wave velocity monitoring
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Open-File Report↗
Extended reflection survey of the San Andreas fault zone
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Open-File Report↗
Earthquakes near Parkfield, California: Comparing the 1934 and 1966 sequences
Moderate-sized earthquakes (Richter magnitude ML 5 1/2) have occurred four times this century (1901, 1922, 1934, and 1966) on the San Andreas fault near Parkfield in central California. In many respects the June 1966 sequence was a remarkably detailed repetition of the June 1934 sequence, suggesting a recurring recognizable pattern of stress and fault zone behavior.
California↗