Accession Number : ADP204466

Title :   Regional Wavefield Analysis Using Three-Component Seismic Array Data,

Corporate Author : SOUTH CAROLINA UNIV COLUMBIA

Personal Author(s) : Wagner, Gregory S. ; Owens, Thomas J.

PDF Url : ADP204466

Report Date : 14 AUG 1995

Pagination or Media Count : 9

Abstract : An example of regional wavefield analysis using three-component seismic array data is presented. We examine the high-frequency (0.5-5.0 Hz) wavefields from three events that occurred in or near the Nevada Test Site (NTS), two underground nuclear tests and one earthquake, observed at the IRIS Joint Seismic Program three-component array located approximately 400 km to the south at Pinon Flat Observatory (PFO). The three-component array data are first displayed as broadband bearing-time records (BTR) which provide a time history of the propagation direction of coherent direct and scattered signals crossing the array; these displays are used primarily as a guide for further analysis. The BTRs reveal significant differences in the three wavefields. These differences are somewhat surprising in light of the fact that these data have essentially sampled the same terrain between NTS and PFO. The BTRs show that the P and S codas, and the Lg wavetrains for these three events contain a considerable amount of forward scattered/multipathed energy. It is only with the arrival of surface waves (apparent velocity approximately 3 km/s) that the coda becomes more random in nature. The fact that much of this later coda cannot be modeled as plane waves suggests that it is not scattered from distant sources. The Lg wavetrain for one event is examined in detail. A spectogram, and P-SV; SH BTRs computed using the three component array data reveal that the early portion of this particular Lg wavetrain is comprised of two linearly polarized SH/Love waves and a Rayleigh wave. The most prominent arrival in this Lg wavetrain is examined in more detail. When plotted in three dimensions, the tangential and elliptical components of particle motion are more pronounced.

Descriptors :   *SEISMIC DETECTION, *SEISMIC WAVES, *ARMS CONTROL, *NUCLEAR EXPLOSION DETECTION, *EARTHQUAKES, SCATTERING, SYMPOSIA, SURFACE WAVES, MONITORING, UNDERGROUND EXPLOSIONS, TERRAIN, NUCLEAR EXPLOSION TESTING, SEISMIC DATA, SEISMIC DISCRIMINATION, TREATIES, SEISMIC VELOCITY, PLANE WAVES, BANDPASS FILTERS, RAYLEIGH WAVES, SEISMIC ARRAYS, NEVADA, LOVE WAVES.

Subject Categories : Government and Political Science
      Seismology
      Seismic Detection and Detectors
      Nuclear Weapons

Distribution Statement : APPROVED FOR PUBLIC RELEASE