摘要(英) |
The Ilan Plain, abutting the Hsueshan range to the northwest and the Central range to the south, is a triangular alluvial delta in northeast Taiwan most likely representing the southwest end of the Okinawa Trough, a back-arc basin due to the subduction of the Philippine Sea Plate underneath the Eurasia Plate. In this study, we deployed an array of ten broadband stations since Nov. 2013. The array is roughly distributed evenly on the Ilan Plain near mountain hills, which is designed to investigate the spatial variations of Moho depths.
We conduct receiver function analysis on data of teleseismic events, mostly from the southeast quadrant. The P converted to S phase (Ps) and PpPms, PsPms+PpSms multiple reflection phases at the Moho are examined. The analysis is done by time-domain iterative deconvolution, which progressively subtracted from the radial-component seismogram with the convolution of vertical-component seismogram and updated receiver function.
Results show that stations with or without starkly contrasts of H-κ stacking can roughly be divided into those in the south and those in the north Ilan Plain. For the five stations in the south Ilan Plain (SSE, DJE, LLK, SAJ, MSE), teleseismic events from the northwest, northeast and southwest quadrants are mostly unable to resolve receiver functions with clear Ps and/or multiple reflection later phases (PpPms, PsPms+PpSms). Having examined the convergent points of those events, we conclude that Moho discontinuities beneath the Hsueshan range, the Central range inland side, and the Ilan Plain are not sharp enough to generate all phases necessary for the H-κ analysis. For the five stations in the north Ilan Plain (SJY, DTE, NCH, NCE, DHE), the convergent points of events from the four quadrants are all fallen among the aforementioned regions and, for similar reasons, unresolvable of H-κ stacking.
The only scenario with starkly contrasts of H-κ stacking to be determined is those teleseismic events to the southeast quadrant of the five stations in the south Ilan Plain. They contribute the most abundant observations with derived receiver functions consistently exhibiting arrivals of Ps and PpPms, PsPms+PpSms phases. As a result, H-κ results are able to individually determine the Moho depths convergent beneath southeast of the Ilan Plain with depths ranging from 24 to 31km and the deepest one occurred near Suao. We conclude that the Moho discontinuities to the southeast of the Ilan Plain (the Central Range shore side, offshore Suao) are sharp enough to generate all phases necessary for the H-κ analysis.
Using the average κ as determined from the five stations in south Ilan Plain, we manage to estimate the Moho depths for the five stations in the north Ilan Plain and the results range from 27 to 29 km. Although the results are subject to certain level of uncertainty, it is the optimal approach under conditions of limited data.
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