Abstract

Yield estimation of small explosions at local distances represents a challenge for the nuclear explosion monitoring community. We have examined the feasibility of using short‐period surface‐wave magnitudes, called forumla, to estimate explosion yields at local distances (<100  km). We have modified the Russell (2006)Ms formula, which was derived for periods of 8–25 s for distances beyond 50 km, for application at local distances and 1 s period. We have studied short‐period surface‐wave attenuation in diverse lithologies in order to incorporate an attenuation term in the magnitude scale, which is suitable for forumla. We have also incorporated multiple excitation corrections for forumla based on the near‐source seismic velocities, which greatly affect the source‐region amplitudes for forumla. It is important to note that in the formula the excitation is estimated from the measured forumla group velocity. We have also derived a new Butterworth filter cutout definition for filtering forumla near 1 s period at distances between 2 and 100 km. We used the new formula to estimate forumla for 39 small (37≤Y≤12,270  kg TNT equivalent) and shallow (<120  m) explosions detonated in North America in lithologies ranging from alluvium to granite. Regressions of the magnitudes with yield result in the equation forumla for chemical explosions with Y<12,270  kg. An F factor with 95% confidence was determined to be 2.25, giving lower and upper bounds on the yield estimates of Y/2.25 and Y×2.25, respectively. We applied the relationship forumla (assuming factor of 2 equivalence between chemical and nuclear) to nuclear explosions detonated at the Degelen and Shagan, Kazakhstan, test sites. The estimated yields based on forumla magnitudes were often within 20% of the true yield and had smaller F factor than the estimated yields for United States chemical explosions.

Online Material: Tables of event information and forumla estimates.

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