Effects of Tectonic Release on Broadband Regional Distance Bodywaves.
Abstract
Although the distortion of explosion long-period waves is documented at upper mantle distances, the signature is much more subtle at regional and near-field distances. We document the robustness of the observation of sP in underground nuclear explosions waveforms of events which have large F factors. Although 'slapdown' has not been added to the synthetic, seismograms, the strong azimuthal variation can be explained by the simple addition of a double couple (tectonic release). We also calibrate the size of tectonic release for 18 Pahute Mesa events by comparing their SH waves with those of two western United States earthquakes. In general, the signature of tectonic release appears to be strongly frequency-dependent. We performed a moment tensor inversion at three Pahute Mesa events (CHESIRE, FARM and POOL) in different frequency bands in an attempt to isolate the 'dispersion' of the deviatoric component of the moment tensor. Although the apparent size of tectonic release source decreases, the orientation appears to be constant. The moments of the tectonic release at regional distance also are inconsistent with near-field estimates. We developed a model for near-field tectonic release, which requires a distributed source (shear dislocation takes place at the elastic radius). Using BOXCAR and HALFBREAK waveforms, we performed a constrained moment tensor inversion to obtain the tectonic release orientation. This near-field orientation is in excellent agreement with the far-field results.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1987
- Accession Number
- ADA194247
Entities
People
- Kim Junkyoung
- Terry C. Wallace
- William E. Holt
Organizations
- University of Arizona