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Teleseismic waveform modeling including geometrical effects of superficial geological structures near to seismic sources

Institute de Géodynamique, 250, rue Albert Einstein, Sophia-Antipolis I, 06560 Valbonne, France

Abstract

We analyze observed seismograms of 21 events recorded at teleseismic distances in France from nuclear explosions detonated at Nevada Test Site (NTS). Variations of the displacement waveform, duration, and amplitude are studied in terms of influence of the explosion's source medium and location in the laterally heterogeneous Yucca Flat basin. The analysis is made using numerical modeling of data that simulate the modifications of the original source signal by the geometry of the surrounding geological structure. Spalling and nonlinear effects are not included in computations. The numerical simulations of the variations are processed using a mixed symbolic and numerical algorithm developed to simulate the ground motions that may be recorded in any kind of two-dimensional heterogeneous nonvertical structures. This algorithm is linked (1) to the discrete wavenumber-boundary integral equation method and to the reciprocity theorem to simulate the displacement field radiated to far-field distances by the source site geological structure, and (2) to ray propagation to propagate the displacement field across the mantle from the source region to the receiver. Variations of the computed displacement amplitudes are as large as a factor of 2 from one detonation point to another. The shapes of the observed seismograms are modeled with good reliability for most of the 21 events in the frequency band studied, i.e., 0.2 to 2.5 Hz. A set of 21 relative yield estimates are derived, which include the source site response and thus the amplitude variations induced by the heterogeneous structure of the source region.

This article has been cited by other articles:

				I. N. Gupta, T. R. Zhang, and R. A. Wagner Low-frequency Lg from NTS and Kazakh nuclear explosions--observations and interpretation Bulletin of the Seismological Society of America, October 1, 1997; 87(5): 1115 - 1125. [Abstract] [PDF]