Discriminating Underground Explosions from Earthquakes Using Seismic Coda Waves.
Abstract
We successfully discriminated quarry blasts and earthquakes at local distance from the observed source power spectra by using the coda Q method. To extend this discrimination method to events at regional distances, we developed the energy transfer theory for a mixture of Rayleigh and S wave propagation in a random scattering and attenuation medium. Applying this theory to the quarry blast earthquake problem at local distance, we can explain the observations satisfactorily. Our study indicates that Rayleigh wave scattering become important for events with shallow focal depth, such as quarry blasts and nuclear explosions. By fitting our,theoretical attenuation curves to observed ones at local distances, we have obtained the S and Rayleigh wave S intrinsic and scattering coefficients, and the coupled scattering coefficient of Rayleigh with S waves. Assuming that these coefficients are valid for events at regional distances, we have compared the predicted and observed coda envelope at regional distances for the purpose of discrimination between earthquakes and explosions. Our prediction shows that the Rayleigh wave S contributions become more significant for shallower events (explosions), while for deeper events (earthquakes), the Rayleigh wave's contributions are still negligible. Comparison between predicted and the data of CDSN suggests that the discrimination of earthquakes and explosions at regional distance may be possible by using the coda method for the high frequency case. For the low frequency case, we must consider the crustal effects. (MM)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 15, 1995
- Accession Number
- ADA291246
Entities
People
- Keiiti Aki
Organizations
- University of Southern California