SEISMIC-REFRACTION MEASUREMENTS OF CRUSTAL STRUCTURE BETWEEN SANTA MONICA BAY AND LAKE MEAD

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

DOI:https://doi.org/10.1029/JZ068i020p05837· OSTI ID:4692734

Roller, J C; Healy, J H

A reversed seismic-refraction profile was recorded between Santa Monica Bay, California, and Lake Mead, Nevada, during November 1961. Depth to the M discontinuity was determined to be approximately 29 km at Santa Monica Bay, 36 km under the Transverse Ranges, 26 km under the Mojave Desert, and 30 km at Lake Mead. Prominent events on the seismograms in the distance range 30 to 150 km are interpreted as reflections from the M discontinuity and from a crustal layer of intermediate velocity. These reflected events are used to make a detailed interpretation of crustal structure. The velocity of compressional waves in the mantle immediately below the M discontinuity was determined to be 7.8 km/sec. The velocity of compressional waves in the intermediate layer is near 7.0 km/sec. The apparert velocity of the direct arrival in the crustal rocks near the surface is 8.3 km/sec northeast of Santa Monica Bay and 6.1 km/sec southwest of Lake Mead. The higher apparent velocity for the direct arrival from Santa Monica Bay seems to be the result of thinning toward the east of low-velocity rocks near the surface. These low-velocity near-surface rocks are Cenozoic sedimentary rocks and fractured and weathered granitic and metamorphlc rocks. The velocity of Sa was determined to be 3.4 km/sec near Lake Mead. A prominent phase of apparent velocity 6.3 to 5.4 km/sec was recorded at distances beyond 200 km. This phase is identified as P and is interpreted as a reflection from the intermediate layer. Amplitude measurements support the conclusion that the P phase is a reflected arrival. (auth)

• Research Organization: Geological Survey, Denver
• Sponsoring Organization: USDOE
• NSA Number: NSA-17-041007
• OSTI ID: 4692734
• 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

CALIFORNIA
DISTRIBUTION
EARTH
EARTH CRUST
GEOLOGY, MINERALOGY, AND METEOROLOGY
GRANITES
MEASURED VALUES
NEVADA
REFLECTION
REFRACTION
ROCKS
SEISMOLOGY
SHOCK WAVES
THICKNESS
UNDERGROUND EXPLOSIONS
USA
VARIATIONS
VELOCITY