Tonatiuh Dominguez, Cecilio J. Rebollar, and Hubert Fabriol
Attenuation of coda waves at the Cerro Prieto geothermal field, Baja California, Mexico
Bulletin of the Seismological Society of America (October 1997), 87(5):1368-1374

Abstract:
We analyzed coda waves from 22 local events recorded by a temporary network of seismic stations deployed in the Cerro Prieto geothermal field of Baja California, Mexico, to estimate coda attenuation Q _c in the frequency range 6 to 24 Hz. We used Sato's (1977) single scattering model for a coda window of 12.5+ or -2.5 sec beginning at twice the S-wave travel time. all events analyzed were located within the exploitation area with depths up to 6 km and source-to-receiver distances less than 8 km. At frequencies of 3, 4, and 5 Hz, rms amplitudes of coda to S waves showed no clear decay or even negative Q _c values. This could be due to the inability of the theory to fit the data at low frequencies as it was suggested by Fehler et al. (1992). Within the range of variation, five of the seven stations showed similar Q _c values that ranged from about 200 at 6 Hz to about 490 at 24 Hz. Assuming a power-law dependence of the form Q _c (f) = Q ₀ f (super eta ) , we estimated a value of Q ₀ = 111.5+ or -23 and a frequency dependence eta of 0.41+ or -0.1. We found site effects at two stations that were located close to hot springs and mud pools.