The Discrimination Potential of Crustal Resonance Phases
Abstract
It is unlikely that regional data recorded at a newly installed array of stations could be used immediately to reliably discriminate events because of uncertainties about the local characteristics of wave propagation. However, the stations would immediately begin to record P sub nl data from small local events. This raises the possibility that the earthquake data base could be used to calibrate the array for discrimination purposes. The relationships is studied between long period P sub nl data and high frequency regional phases in the western U.S. This report examines the phase P sub g. The high frequency p sub g phase for small, shallow events typically appears as a complex arrival with a duration of several tens of seconds. This is much longer than the possible duration of the effective source time function even with depth phases taken into account. This phenomenon can be explained by synthesizing P sub g using generalized rays which is a practical computational procedure for a simple layer over a half space crustal model. If model responses are computed by progressively adding in rays with one reverberation in the crust, then two and so on, it is observed that a sequence of high frequency arrivals develops spanning the typical duration of P sub g. Each successive resonance phase is associated with a higher order reverberation in the crust. If each arrival contributes a typical amount of high frequency scattered energy, the long duration of P sub g is simple to understand. Keywords: Seismic discrimination.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 15, 1987
- Accession Number
- ADA196096
Entities
People
- Donald V. Helmberger
- L. J. Burdick