INVESTIGATION OF THE INNER-OUTER CORE BOUNDARY STRUCTURE FROM THE SEISMOGRAMS OF A DEEP EARTHQUAKE RECORDED BY A REGIONAL SEISMIC ARRAY

摘要

PKP(Cdiff), the PKP diffraction waves after PKP-C cut-off. was identified in the PKIKP (or PKP(DF)) wave code of teleseismic seismograms from a deep earthquake in western Brazil. An an ay stacking technique was applied to the short-period waveforms from a regional seismic network in Taiwan to retrieve the wreak PKP(Cdift) waves between 159 degrees and 162 degrees. The differential travel times and slowness of PKP(Cdiff) and PKP(DF) were used to constrain the P-velocity), structure near the inner-outer core boundary (ICE). The results of this study demonstrate that in some cases the ICB structure call be constrained by data from a single event using presently available short-period regional seismic data and applying suitable array techniques. With a correction for axi-symmetric anisotropy applied to tile inner core. the results of this study agree with the PKP properties of model VMOI, a regional ICB model revised from PREM covering the ICE sampled area of this study, and model AK135, a new proposed earth model. The C-cusp position was reported at 151.4 degrees from this event. Theoretical predictions for another new proposed earth model SP6 is in significant disagreement with tile observed differential travel times between PKP(Cdiff) and PKP(DF). At a distance of 159 degrees) the residuals (observation - prediction) included the observation errors (+/-0.2 sec) are approximately +0.17 sec, -0.31 sec and +0.69 sec for VMOI, AK135 and SP6, respectively. Neither model predicts a significant differential slowness residual. This misfit along this path may be the result of the lateral heterogeneity of the sampled region near: the ICD relative to both spherically symmetric models or the complications imposed by the non-axi-symmetric anisotropy of the inner core. [References: 17]