Accession Number : ADA331475

Title :   Shear Wave Generation from Contained Explosions

Descriptive Note : Scientific rept.

Corporate Author : CALIFORNIA INST OF TECH PASADENA SEISMOLOGICAL LAB

Personal Author(s) : Ahrens, Thomas J. ; Liu, Cangli

PDF Url : ADA331475

Report Date : 18 JUL 1996

Pagination or Media Count : 37

Abstract : The usefulness of the amplitude ratio of seismic phases such as Lg/P, as well as the ratio of magnitudes to discriminate explosions from earthquakes depends, in part, on the efficiency of shear wave production from seismic sources. We are studying shear wave generation at the source, initially from explosions within limestone blocks. Initially the samples are subjected to hydrostatic stress. However, we will be able to also simulate tectonic strain energy release in future experiments. Using a 1.6m long, 0.8m diameter sample subjected to an ambient pressure of up to 1 MPa, with a centrally placed explosive source, we propose to study the amplitude of shear wave generation of stress wave induced radial cracking in symmetric and asymmetric cavities. In unstressed rock, this shear wave production is expected to be controlled in part by the natural anisotropy of the rock. We expect to measure the SIP ratio from tamped explosions using (0.2 to 2 gram charges). Later tests will be conducted in partially decoupled asymmetric cavities, and the resultant shear wave radiation pattern will be compared to previous detailed finite element calculations of P and S wave radiation versus frequency and angle for elliptical cavities of aspect ratios in the range of 1:3 to 1:10. In order to measure the P and S waves generated from explosions, we developed a measurement method that is given in detail in this report. The initial test results for the tamped and decoupled explosions in cylindrical cavities in limestone show that the amplitude of SV/P for the decoupled experiment in limestone is -0.7, whereas it varies over a range of -1 to 3 for overdriven cavities, depending on angle from the cylindrical axis. Moreover, tensional cracks are generated in these cavities which resemble those inferred to have occurred in a similar geometry in the Sterling experiment.

Descriptors :   *UNDERGROUND EXPLOSIONS, *EARTHQUAKES, *SEISMOLOGY, *SECONDARY WAVES, SURFACE WAVES, FINITE ELEMENT ANALYSIS, ANISOTROPY, LIMESTONE, SEISMIC WAVES, HYDROSTATICS, ASPECT RATIO, DISCRIMINATE ANALYSIS, RADIATION PATTERNS, ELASTIC WAVES.

Subject Categories : Seismology
      Explosions

Distribution Statement : APPROVED FOR PUBLIC RELEASE