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Regional Wavefield Analysis Using Three-Component Seismic Array Data,

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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 scatteredmultipathed energy. It is only with the arrival of surface waves apparent velocity approximately 3 kms 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 SHLove 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.

Subject Categories:

  • Government and Political Science
  • Seismology
  • Seismic Detection and Detectors
  • Nuclear Weapons

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