Direct Estimation of Explosion Pn Green’s Functions Applied to Teleseismic P-wave Intercorrelations for North Korean Nuclear Tests

Abstract

Seismic yields and explosion source time functions for the six declared underground nuclear tests at the North Korean test site are estimated using teleseismic waveform equalization (intercorrelation) incorporating improved source structure inferred from regional distance Pn phases. Explosion source time functions estimated by previous modeling efforts are deconvolved from the broadband Pn observations to extract direct estimates of the Pn Green’s functions. Very consistent signals are found for station MDJ (to the north) for all but the 2006 event, and a 1D layered elastic model is determined that matches the corresponding pPn signals for the larger events. The much simpler Pn Green’s functions found for INCN (to the south) are well modeled using a half-space structure. The 1D structures are incorporated into intercorrelations for teleseismic P observations. Very similar results are found using the layered MDJ model for all azimuths, or when azimuthally varying the source velocity model to have a half-space structure for stations to the south, and/or using a half-space structure for the 2006 event at all azimuths. The relative yield estimates from intercorrelation are thus stable with respect to specific 1D source structures; the full effects of 3D elastic and nonelastic structures are yet to be considered.