Accession Number : ADA332575
Title : The Effects of Anisotropy on Regional Wave Propagation.
Descriptive Note : Final rept. 15 Nov 93-30 Apr 97,
Corporate Author : YALE UNIV NEW HAVEN CT DEPT OF GEOLOGYAND GEOPHYSICS
Personal Author(s) : Park, Jeffrey J.
PDF Url : ADA332575
Report Date : OCT 1997
Pagination or Media Count : 11
Abstract : Crustal rocks can be highly anisotropic, due to (1) oriented minerals (2) oriented cracks, and/or (3) thin layers of material with different elastic stiffnesses. Crustal Love and Rayleigh surface waves couple strongly for anisotropic structures that do not possess a vertical axis of symmetry, and cause explosion to generate significant shear motion on the transverse component 0 seismograms. We developed theory and 1-D layered-media synthetic seismogram codes for anisotropy with an arbitrary axis of symmetry. One code version can synthesize surface waves with periods 100 > T > 0.4 sec. Another code version can synthesize teleseismic body wave reverberations up to 5 Hz. We determined that a tilted axis of symmetry enhances Love-Rayleigh coupling and the scattering of P-waves (compressional) to S-waves (shear). Using P-S scattering, we found evidence for strong (> 10%) anisotropy in the deepest and shallowest crustal layers beneath seismic station ARU (Arti, Russia), an 'open' seismic observatory proximal to the Novaya Zemiya nuclear test site. We also developed a wavelet-base signal processing algorithm that picks out correlated 'signals' from uncorrelated 'noise' in an optimally bandpassed manner Using the Terrascope regional array in California, we applied this algorithm to reconstruct, for a single correlated signal, anomalous amplitudes and polarizations at individual stations, allowing more 'signal' to be recovered than via standard 'stacking'
Descriptors : *RAYLEIGH SCATTERING, *ANISOTROPY, *SEISMIC ARRAYS, ANOMALIES, POLARIZATION, SURFACE WAVES, ELASTIC PROPERTIES, EXPLOSIONS, DRIFT, VERTICAL ORIENTATION, EARTH CRUST, RUSSIA, CALIFORNIA, REVERBERATION, STRATIFICATION, MINERALS, SEISMOLOGICAL STATIONS, IGNEOUS ROCK.
Subject Categories : Geology, Geochemistry and Mineralogy
Distribution Statement : APPROVED FOR PUBLIC RELEASE