The Anisotropic Fractured Rock in Vicinity of the San Jacinto Fault Zone, Southern California From S-Coda Waves
Recently ( AGU Full Meeting 2004, 2005 ) we discussed the influence of seismic scattering in anisotropic rock on the S-coda waves attenuation, coda quality factor Qc and intensity of back scattering energy, Cc. Now we improve our method of anisotropy study based on coda waves of 102 3-components records from 11 local earthquakes, ml = 4.0 - 5.0 of 10 ANZA stations.Examining different parts of coda envelope ( 1. 16 sec - 41 sec, 2. 22 sec - 58 sec ) we found two types of crustal anisotropy.1. The S-coda waves polarized in a plane with the strike 126° and dip 72° has the smallest attenuation, or maximum value of Qc. The largest attenuation has polarization direction that is consistent with a vector normal to that plane. The coefficient of anisotropy equals 14.2 %. We suggest this type of anisotropy is controlled by the San Jacinto Fault Zone.2.A plane with the largest values of Qc has the strike ~ 26° and dip varies from 51° to 79°. Coefficient of anisotropy varies from 3.9 % to 9.3 %. On our suggestion there is a tectonic stress induced anisotropy in vicinity of the Fault Zone.The azimuthal variations of Qc and Cc are best fit with an anisotropic term A × cos ( 2 Az + φ ).
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 5144 Wave attenuation;
- 7203 Body waves;
- 7205 Continental crust (1219)