During the second period of Contract #14-08-0001-1833 (Earthquake and Seismicity Research using SCARLET and CEDAR), we continued and completed research in three main areas: 1) Multimode analysis of Rayleigh type Lg in Southern California. This research is currently being complemented by a similar study in Central California along the West side of the Sierra Nevada, using CalNet stations. 2) A theoretical study of dispersion and attenuation of elastic waves due to multiple scattering from inhomogeneities. This is essentially a first step toward an interpretative model of high frequency apparent attenuation properties in the crust in Southern California. 3) An analysis of anisotropic Pn velocities near the big bend of the San Andreas fault, which provides some constraints on the nature of the plate boundary between Pacific and North America below the crust.
Other projects are being pursued, which include: 1) the statistical analysis of S wave routine picks on CEDAR to constrain estimates of the Poisson ratio in the crust, 2) an effort to use P/SV amplitude ratio to constrain focal mechanism for local events, and 3) a study of frequency content of signals from foreshocks and aftershocks of the October 15, 1979 Imperial Valley earthquake. Preliminary findings along these lines will be reported at the Fall meeting of the American Geophysical Union. This research is continuing under Contract #14-08-0001-19270, together with continued efforts to characterize historical and recent seismicity in California. We confine the following report to projects already completed or nearing completion.
