Regional moment:magnitude relations for earthquakes and explosions

Abstract

We present Mo:mb relations using mb(Pn) and mb(Lg) for earthquakes and explosions occurring in tectonic and stable areas. The observations for mb(Pn) range from about 3 to 6 and show excellent separation between earthquakes and explosions on Mo:mb plots, independent of the magnitude. The scatter in Mo:mbobservations for NTS explosions is small compared to the earthquake data. The Mo:mb(Lg) data for Soviet explosions overlay the observations for U. S. explosions. These results, and the small scatter for NTS explosions, suggest weak dependence of Mo:mb relations on emplacement media. A simple theoretical model is developed which matches all these observations. The model uses scaling similarity and conservation of energy to provide a physical link between seismic moment and a broadband seismic magnitude. Three factors, radiation pattern, material property, and apparent stress, contribute to the separation between earthquakes and explosions. This theoretical separation is independent of broadband magnitude. For U.S. explosions in different media, the material property and apparent stress contributions are shown to compensate for one another, supporting the observations that Mo:mb is nearly independent of source geology.

Regional seismic discrimination research at LLNL

“…We are presently investigating techniques to measure moment using the very stable coda methods described in the Geophysical Characterization section. In our initial studies M,:mb(P,) appears to have the potential to correctly classify shallow earthquakes, but it appears to have trouble with mine collapses as shown in Figure Sc (Patton and Walter, 1994). Note that mine collapses are correctly classified in the 6-8 Hz P A g ratios in Figure Sa .…”

“…Another type of regional discriminant that shows promise is based on comparisons of moment to magnitude (Patton and Walter, 1993;Woods et al, 1993). This is a regional extension of the traditional long-period:short-period discriminants like M,:mb but is not limited only to those events large enough to generate surface waves.…”

“…(b) Combined 6-8 Hz Pn/Lg, PR/Lg and 1-2/64 Hz Lg coda ratio averaged for MNV-KNB (Walter et al, 1995). (c) Regional n/l, versus m/7(P,l) (Patton and Walter, 1993 (GoIdstein, 1995). Note shaIlow earthquakes (filled squares) are a problem for (a) and (b) but not (c) and (d), while collapses are a problem for (c) but not (a) and (d).…”

Status report on method and results for new discriminants and combinations of discriminants for different ranges

“…Promising model-based methods include the moment-magni tude discriminant (e.g., Patton and Walter, 1993) and waveform modeling. These discriminants are particularly important because they are based on a physical model.…”

Ground Motion Simulations To Investigate The Feasibility Of Space-Based Seismometry

“…This will likely lead to an underestimate of the magnitude and is thus somewhat more conservative than choosing the 'stable' region scaling. Patton and Walter (1994) reported a relation between seismic moment, expressed in Newton-meters (N-m) and body-wave magnitude for the Nevada Test Site, also a 'tectonic' region: log M 0 = 9.55 + 1.12 m b Moment magnitude, M W , is related to seismic moment (Kanamori, 1977) by…”