HR: 0800h
AN: S31A-0278    [Abstracts]
TI: Determining Subsurface Structure From Microtremors Using a Passive Circular Array
AU: * Folger, D S
EM: folger@geo.utep.edu
AF: University of Texas at El Paso, 500 W University Ave, El Paso, TX 79968 United States
AU: Doser, D I
EM: doser@geo.utep.edu
AF: University of Texas at El Paso, 500 W University Ave, El Paso, TX 79968 United States
AU: Velasco, A A
EM: velasco@geo.utep.edu
AF: University of Texas at El Paso, 500 W University Ave, El Paso, TX 79968 United States
AB: The amount of damage to a structure during an earthquake is related to the ground motion at that site. Therefore, it is important to study seismic waves that propagate through specific soil types to understand site response. However, active seismic surveys are susceptible to noise interference and are limited due to spatial need while boreholes are costly. We develop a method using a passive array to study Rayleigh waves from microtremors, waves originating from building appliances, cars, pedestrians walking, etc. By using everyday noises as the source, site-specific analysis can be done in urban areas without worrying about noise interference or disturbing the public with explosions or other loud active sources. The array is comprised of short period Texans, self contained geophones, which record continuously for 24 hours. Our technique differs slightly from traditional SPAC (SPatial Auto-Correlation) methods used in passive arrays. We first cross correlate time windows between two receivers then stack the correlations to determine a phase delay. Performing the correlation at different frequencies will create a dispersion curve that can be inverted for shear velocity. This approach is similar to the two-station phase delay method used in regional tomography studies at much longer periods. Stacking removes off-azimuth energy, so we do not need to assume a source direction. Preliminary results from a previous passive array survey conducted near El Paso, Texas show 1-D velocity models can be created by cross-correlating noise at various frequencies. We will conduct another survey in alluvium sands at Rio Bosque Park east of El Paso. We will validate the results with active seismic refraction and surface wave survey results as well as other geophysical techniques to determine if a passive array using microtremors is an accurate method of determining subsurface structure.
DE: 0900 EXPLORATION GEOPHYSICS
DE: 0935 Seismic methods (3025, 7294)
DE: 7200 SEISMOLOGY
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7255 Surface waves and free oscillations
SC: Seismology [S]
MN: Fall Meeting 2005