Magnitude corrections for attenuation in the upper mantle

Abstract

The m b : M, relation for explosions at the Nevada Test Site (NTS) differs from those for explosions in other parts of the world. There is considerable evidence that this results mostly from high body-wave attenuation in the upper mantle beneath the western US. The authors have developed an empirical magnitude correction for body-wave attenuation and applied it to both source and receiver ends of the teleseismic body-wave path. The results imply that mb values are lower for NTS explosions than for Soviet explosions of comparable yield and seismic coupling. The authors have also developed and applied a source-depth correction to account for pP-P interference in the P-wave arrival.The body-wave magnitude resulting from these corrections is designated WIQ to distinguish it from other definitions of mb. Values of m Q determined for a world-wide set of large explosions show that a single mQ: yield relation is a fair fit to the data for the explosions with high seismic coupling.However, grouping the explosions under two mQ : yield relations gives a better fit to the data. All the studied explosions in salt or granite or below the water table fit a common M, : yield relation. Explosions from North America, Eurasia and Africa have a common m Q : M, relation.

Calibration of the M(sub s):m(sub b) Discriminant at the International Monitoring System Array NVAR (PS-47)

“…Figure 1.7 shows the M+B R+P comparison of our M,(7) and M,(7) with ± lo plotted as the horizontal lines and the estimates. showed their measurements also correlated very well with conventional NTS M, values from Basham (1969), Marshall and Basham (1972), Basham andHomer (1973), von Seggemn (1973), Marshall et al (1979), and with considerable variance in the offsets. We also compared the performance of shown also in Figure 1.7 and indicate similar scaling relationships based on the fixed-slope M+B R+P regression analysis.…”

“…Sixty-one (61) of these events have no LNN data available, are plagued by untimely data dropouts and glitches, or are too small for measurable surface wave energy. We also analyzed 21 events prior to July 1979 that were digitized from analog records in order to compare these results with previous M, studies for NTS events completed by , Marshall et al, (1979), and Stevens and Murphy (2001). Thus, this paper presents the results of our analyses of 158 NTS explosions: including 51 events from Pahute Mesa, 13 from Rainier Mesa, and 94 explosions from the Yucca Flats.…”

“…higher than Marshall et al (1979) for the 5 events in their dataset for which we had LNN data to analyze. We note that most of our nearregional estimates have better azimuthal coverage than Marshall et al (1979) who mainly used Canadian data and thus may have strong azimuthal biases. This could be a possible source for the bias.…”

“…Marshall and Basham (1972) and Rezapour and Pearce (1998) formulas, respectively). Marshall et al (1979) used the Marshall and Basham (1972) M, formula for far-regional and teleseismic distance recordings of NTS events for Rayleigh waves with periods greater than 14 seconds. We determined that the near-…”

The Surface Wave Magnitude for the 9 October 2006 North Korean Nuclear Explosion

“…Surface wave magnitudes (M s ) have also been used to estimate the yields of underground nuclear explosions (Marshall et al, 1979;Bache, 1982;Sykes and Cifuentes, 1984;Woods and Harkrider, 1995;Stevens and Murphy, 2001). Bache (1982) reported that M s = log Y relationships should provide accurate results for large events; however, increased uncertainty in the estimated yields was possible due to Rayleigh-wave radiation patterns associated with tectonic release and secondary source effects from explosions.…”