Modeling short-period crustal phases (anti P, Lg) for long-range refraction profiles

Conference · Thu Jan 01 04:00:00 EST 1981

OSTI ID:5626817

Olsen, K H; Braile, L W; Stewart, J N

The short-period seismic phases known as anti P and Lg are often recorded at distances of 200 to 1000 km on long-range refraction profiles and are usually the largest amplitude features on record sections in this distance range. Anti P and Lg propagate as multiple reflected compressional and shear waves in a crustal waveguide whose principal boundaries are the Moho and the free surface. Equivalently, they can be interpreted as the interference pattern produced by a superposition of higher mode P and SV waves propagating in a leaky waveguide. For the compressional waves the waveguide efficiency is a strong function of frequency and depends on the presence or absence of low-velocity layers within a few km of the surface, such as the deep sedimentary section commonly found in active tectonic areas. The low-velocity surface layers create constructive interference effects for upcoming P-waves incident at near grazing angles at the free surface and lead to efficient anti P propagation. The 550-km-long profile eastward from SHOAL to Delta, Utah is analyzed here. We have used a modified reflectivity method computer program to model crustal phases for the SHOAL-Delta profile. We find that the synthetics realistically model the observed anti P characteristics. The decay of anti P amplitudes with distance is dominated by surface reflection leakage from the waveguide rather than by anelastic attenuation due to Q of crustal rocks.

• Research Organization: Los Alamos National Lab., NM (USA)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 5626817
• Report Number(s): LA-UR-81-3297; CONF-810773-1; ON: DE82004340
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580201* -- Geophysics-- Seismology & Tectonics-- (1980-1989)
COMPUTER CODES
EARTH CRUST
GEOPHYSICAL SURVEYS
MATHEMATICAL MODELS
NEVADA
NORTH AMERICA
ROCKY MOUNTAIN REGION
SEISMIC P WAVES
SEISMIC SURFACE WAVES
SEISMIC SURVEYS
SEISMIC WAVES
SHOAL EVENT
SURVEYS
USA
UTAH
VELA PROJECT
WAVEGUIDES
WESTERN REGION