Physical basis of m/sub b/:M/sub s/ and variable magnitude methods for earthquake/explosion discrimination

Journal Article · Sun Mar 10 04:00:00 EST 1985 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB090iB04p03009· OSTI ID:5984672

Stevens, J L; Day, S M

We use recent results from deterministic numerical modeling of earthquakes and explosions to develop an improved physical basis for earthquake/explosion discrimination. We use six three-dimensional finite difference simulations of earthquakes for the earthquake source models and four empirical and four numerical models for explosions in different materials. Four factors contribute to the success of the m/sub p/:M/sub s/ discriminant: source spectra, focal mechanism, near-source elastic properties, and interference of pP. Spectral differences contribute about 0.5 magnitude unit to the separation between earthquake and explosion populations for large events, but this difference vanishes for events with m/sub p/<4.5. The difference in focal mechanism (quadrupole versus monopole) contributes about 0.35 magnitude unit on the average but also introduces a scatter of +- 0.5 magnitude unit into the earthquake population. Differences in near-source elastic properties tend to increase the separation, contributing a factor of approximately (rho..cap alpha../sup 3/)/sup 1/2/ (rho is density and ..cap alpha.. is P wave speed) to the ratio of surface wave amplitude to body wave amplitude. Interference of pP improves discrimination for large, deeply buried explosions but may degrade or prevent m/sub b/:M/sub s/ discrimination of small, shallow explosions. If biases due to regional variations in propagation path are absent, or corrected for, we predict that the m/sub b/:M/sub s/ method will successfully discriminate most earthquakes from explosions, but there will be some overlap between populations at small magnitudes.

• Research Organization: S-Cubed, La Jolla, California
• OSTI ID: 5984672
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 90:B4; ISSN JGREA
• Country of Publication: United States
• Language: English

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