NORSAR Basic Seismological Research

Abstract

Abstract : This report contains 4 separate contributions (paragraph 2.1 through 2.4), as well as abstracts of the investigations submitted as quarterly technical reports during FY92 (paragraph 2.5). A systematic analysis of teleseismic P-wave travel time and amplitude variations across the NORSAR array described in paragraph 2.1 reveals that (1) SP time and amplitude anomalies are related, (2) SP and LP time variations are only partially related and (3) LP amplitude variations are very small. It is generally appreciated that later arrivals contain important information about the seismic source and about the earth's structure. The arrival times of later phases reported to the ISC have been used for tomographic studies of the earth's deep interior by several workers. The phases of PcP and PKKP were analyzed as the detections of these phases were sufficiently numerous product meaningful statistics. The results of the investigations are given in paragraph 2.2. Synthetic seismograms may provide a better understanding of wave propagation in complex media. A novel scheme for computing 2D synthetics based on numerical solutions of the elastic wave equation using finite-difference techniques has been presented in a previous contribution. Recently this scheme has been generalized to models with free surface tomography and, in paragraph 2.3, the usefulness of synthetic seismogram analysis to elucidate wave propagation in the crust and mantle lithosphere is demonstrated. Paragraph 2.4 summarizes the status of development of the Northern Europe Regional Array Network.