Seismological investigations in the Livermore Valley Region, California. Part 1: geologic setting and p-velocity models
P-wave travel times from 223 well-recorded earthquakes and five times explosions recorded by the USGS-LLNL seismic network are inverted simultaneously for one- and three-dimensional velocity structure and hypocenter locations. Initial one-dimensional velocity inversions indicate a fairly strong positive velocity gradient in the upper crust to depths of about 6 km. Calculated station delays show a good correlation with geologic structure. Arrivals at stations within the Livermore Valley are delayed by about 0.4 sec relative to those located to the south in the Diablo Range where relatively high velocity rocks of the Franciscan Formation are exposed. The Franciscan basement appears to occur at a depth of about 5 to 8 km beneath the valley. Three-dimensional models show that the strongest velocity contrasts occur along the eastern and southern edges of the valley where lower velocity down-dropped Tertiary sediments and basin-fill alluvium are found in structural contact with higher velocity Late Mesozoic and Tertiary sediments of the Altamont anticline and the Diablo Range. The low velocity basin structure is truncated along the western margin of the Livermore Valley by the Calaveras fault across which higher velocity Cretaceous and Tertiary formations are exposed. Relocated aftershocks from the Livermore earthquake sequence show a good correlation with the surface trace of the northwest-trending Greenville fault. In the southeast corner of the Livermore Valley, a number of short (5 km or less), linear, and discontinuous epicentral zones are observed. These seismic lineations appear to define a conjugate set of right-stepping faults in a right lateral shear zone.
- Research Organization:
- Lawrence Livermore National Lab., CA (USA)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 5610035
- Report Number(s):
- UCRL-53169-Pt.1; ON: DE82005847
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580201* -- Geophysics-- Seismology & Tectonics-- (1980-1989)
CALIFORNIA
DATA
EARTH CRUST
EARTHQUAKES
EXPERIMENTAL DATA
GEOLOGIC STRUCTURES
INFORMATION
LAWRENCE LIVERMORE LABORATORY
MATHEMATICAL MODELS
NATIONAL ORGANIZATIONS
NORTH AMERICA
NUMERICAL DATA
SEISMIC EVENTS
SEISMIC P WAVES
SEISMIC WAVES
SEISMICITY
SEISMOLOGY
US AEC
US DOE
US ERDA
US ORGANIZATIONS
USA
WESTERN REGION