Developing a Predictive Capability for P-to-S Discriminants
Description:
Earthquakes sources produce greater shear wave (S) energy than explosions, which dominantly produce compressional wave (P) energy. The measured ratio of P to S energy (P-to-S phase amplitude ratios) has therefore served as discriminant between explosions and earthquakes at regional distances for decades. Recent work demonstrates that the power of this discriminant to be uncertain at local monitoring distances. Sparse station coverage and poor velocity model representation for crustal phases limits the ability to average observations over azimuths and increases travel time uncertainties. Discrimination between earthquakes and explosions at local distances therefore presents a continuing challenge for monitoring.
This work presents a probabilistic means to quantify discrimination performance at local distances. We demonstrate this method against a data set that includes thousands of picks from hundreds of analyst-reviewed waveforms that were sourced by both explosions and earthquakes in Nevada. Using this dataset, we first measure P-to-S discriminants across 10 frequency bands between 1 and 32 Hz at stations that were less than 405 km from source, and correct for path, site, and source effects. We then construct empirical density functions from these data and use probability theory to model them with validated parametric density functions. These density function models quantify our discrimination error rates. By setting an acceptable Type I error rate, we define objective thresholds for discrimination that predict our ability to discriminate between explosions and earthquakes, versus source magnitude. We lastly discuss schemes to forecast discrimination rates for new events.
Session: Exploiting Explosion Sources: Advancements in Seismic Source Physics [Poster]
Type: Poster
Date: 4/19/2023
Presentation Time: 08:00 AM (local time)
Presenting Author: Richard A. Alfaro-Diaz
Student Presenter: No
Invited Presentation:
Authors
Richard Alfaro-Diaz Presenting Author Corresponding Author rad@lanl.gov Los Alamos National Laboratory |
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Developing a Predictive Capability for P-to-S Discriminants
Category
Exploiting Explosion Sources: Advancements in Seismic Source Physics