The density jump across the ICB and constraints on P‐reflector in the D' layer from observation of the 1992 Chinese Nuclear Explosion

Abstract

Seismic waves observed from the Chinese nuclear explosion detonated on May 21, 1992 (mb=6.6) are analyzed to detect PKiKP and PdP, reflected waves from the inner core boundary (ICB) and the D” discontinuity, respectively. A linear stacking method is applied to a large number of digital data recorded in the Japanese Islands to identify the reflected waves. The stacked data indicate a weak signal of PKiKP. PKiKP/PcP amplitude ratio of 0.03 is obtained from the stacked waveforms of PKiKP and PcP, which suggests the density jump across the ICB to be 0.6 g/cm³. This value is in agreement with previous estimates from free oscillations data. No positive evidence for the identification of PdP is suggested from the stacking process. This implies the absence of a significant P wave reflector or, if present, the impedance contrast is less than 2% in the lowermost mantle under East China. Another interpretation in terms of gradient zone thickness or reflector topography is also possible.