CRUSTAL STRUCTURE ALONG THE COAST OF CALIFORNIA FROM SEISMIC-REFRACTION MEASUREMENTS

Journal Article · Tue Oct 15 04:00:00 EDT 1963 · Journal of Geophysical Research (U.S.)

DOI:https://doi.org/10.1029/JZ068i020p05777· OSTI ID:4701076

Healy, J H

Two reversed seismic-refraction profiles were recorded between Los Angeles and San Francisco in 1961. The three shot points were located in Santa Monica Bay near Los Angeles, offshore near San Francisco, and at Camp Roberts, about halfway between Los Angeles and San Francisco. The velocity of P along these profiles is 6.1 plus or minus 0.1 km/sec with possible exceptions near San Francisco and near Los Angeles, where the scatter in the arrival times indicates complex near-surface velocity variations. The velocity of P, between Los Angeles and Camp Roberts is 8.2 plus or minus 0.1 km/sec, and between Camp Roberts and San Francisco it is 8.0 plus or minus 0.2 km/sec. There is no indication of an intermediate crustal layer in the travel times of first arrivals. Computed depths to the M discontinuity, if the crust consists of a single layer, are 35 km at Jos Angeles, 23 km at Camp Roberts, and 23 km at San Francisco. Refractions from crustal layers of intermediate velocity need not appear as first arrivals, and, in the extreme, the depth to the M discontinuity may be one-third greater than the thickness of a one-layer crust. Amplitude measurements on seismograms from the drilled-hole shot point at Camp Roberts give the attenuation with distance for P/sub g/as r/sup -2.13/. The combined data for P from the two shot points in the ocean give the attenuation with distance as r/sup -1.74/. The scatter in the measured amplitudes of P/sub n/ is too large to determine a rate of attenuation with distance, but the data indicate that attenuation in the 150 to 300-km range is less than r/sup -3/. (auth)

• Research Organization: Geological Survey, Denver
• Sponsoring Organization: USDOE
• NSA Number: NSA-17-041003
• OSTI ID: 4701076
• Journal Information: Journal of Geophysical Research (U.S.), Journal Name: Journal of Geophysical Research (U.S.) Vol. Vol: 68; ISSN JGREA
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ABSORPTION
CALIFORNIA
DISTRIBUTION
EARTH
EARTH CRUST
GEOLOGY, MINERALOGY, AND METEOROLOGY
LAYERS
MEASURED VALUES
QUANTITATIVE ANALYSIS
REFRACTION
ROCKS
SEISMOLOGY
SHOCK WAVES
THICKNESS
UNDERGROUND EXPLOSIONS
USA
VARIATIONS
VELOCITY