Evaluation of Short-Period, Near-Regional Ms Scales for the Nevada Test Site

Abstract

Surface wave magnitude (M s ) estimation for small events recorded at near-regional distances will often require a magnitude scale designed for Rayleigh waves with periods less than 10 sec. We have examined the performance of applying two previously published M s scales on 7-sec Rayleigh waves recorded at distances less than 500 km. First, we modified the Marshall and Basham (1972) M s scale, originally defined for periods greater than 10 sec, to estimate surface wave magnitudes for short-period Rayleigh waves from earthquakes and explosions on or near the Nevada Test Site. We refer to this modification as , and we have useds short-period, high-quality dispersion curves to determine empirical path corrections for the 7-sec Rayleigh waves. We have also examined the performance of the Rezapour and Pearce (1998) formula, developed using theoretical distance corrections and surface wave observations with periods greater than 10 sec, for 7-sec Rayleigh s is possible to employ a near-regional single-station or sparse network to estimate surface wave magnitudes, thus allowing quantification of the size of both small earthquakes and explosions. Finally, we used a jackknife technique to determine the falsealarm rates for the -m b discriminant for this region and found that the prob-s ability of misclassifying an earthquake as an explosion is 10%, while the probability of classifying an explosion as an earthquake was determined to be 1.2%. The misclassification probabilities are slightly higher for the estimates. Our future R‫ם‬P M (7) s research will be aimed at examining the transportability of these methods.

Development of a Time-Domain, Variable-Period Surface-Wave Magnitude Measurement Procedure for Application at Regional and Teleseismic Distances, Part II: Application and Ms-mb Performance

“…Figure 9 shows that the M s (VMAX) explosion magnitudes are approximately 0.23 m.u. larger than the regionally calibrated Marshall and Basham M s (7) estimates from Bonner et al (2003). The slope of the best-fit line between the two datasets is approximately equal to 1.…”

“…We misclassified two earthquakes in the explosion population. In our previous studies based on 7-sec data (Bonner et al, 2003), we misclassified four earthquakes as explosions.…”

“…In our past research projects (Bonner et al, 2003), we tried to extend the magnitude estimation to shorter periods (e.g., 7 sec). We determined that shorter-period surface waves could be used for magnitude estimation for events with smaller m b values.…”

“…(5) The Rezapour and Pearce (1998) equation was developed by using theoretical aspects of dispersion, including Airy phase propagation, as evidenced by the 1/3 coefficient on the dispersion term, and geometrical spreading. However, because they did not consider frequency-dependent aspects of dispersion, the coefficient is not sufficient to account for dispersion effects at shorter periods (Bonner et al, 2003). The formula was adopted by the prototype International Data Center in 1998 for calculating surface-wave magnitudes at distances between 20 and 100 degrees; however, it is now used by the International Data Center to determine an M s for all surface waves recorded at distances less than 100 degrees (Stevens and McLaughlin, 2001).…”

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

“…However, because they did not consider frequency-dependent aspects of dispersion, the coefficient is not sufficient to account for dispersion effects at shorter periods (Bonner et al, 2003). The formula was adopted by the prototype International Data Center in 1998 for calculating surface-wave magnitudes at distances between 20 and 100 degrees; however, it is now used by the International Data Centre to determine an M, for all surface waves recorded at distances less than 100 degrees (Stevens and McLaughlin, 2001).…”