Decoupling of Pacific subduction zone guided waves beneath central Japan: Evidence for thin slab
Decoupling of Pacific subduction zone guided waves beneath central Japan: Evidence for thin slab
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日本中部太平洋俯冲带导波的解耦：薄板片的证据
DOI：
10.1002/2014jb011562
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
and T. Maeda
中科院分区：
文献类型：
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作者：
Padhy;S.;T. Furumura;and T. Maeda
基于中等规模（M4.5-6）深源地震（h>350 km）的波形分析和高频（高达8 Hz）波传播的有限差分法（FDM）模拟，研究了日本东北俯冲带的精细地震结构。强regionalS波衰减异常的特定源-接收器的路径连接发生在日本海中部的事件发生在日本群岛（本州）的北方的弧前站记录的集群被用来模拟俯冲太平洋板块的更深层次的结构，最近的地壳断层扫描显示，在日本海下可能向西板撕裂的证据。观测到的异常S波衰减和随后的高频尾波的特征可以通过非均匀板模型中地震波的二维（2-D）FDM模拟来捕获，包括板在深度处的减薄，这也与由于板中的低Q或弱得多的非均匀性而导致的高频S波急剧衰减的其他可能原因进行了比较。模拟结果清楚地表明，由于板块几何形状的变化（即，板变薄），而不是由于物理性质的变化，如由于板中较低的-Q和较弱的不均匀性。这样一个薄区域的存在使俯冲板块中的高频板导S波能量散焦到周围的地幔中，并起到几何反波导的作用。根据模拟结果的序列，我们建议减薄的太平洋板块在深度俯冲日本东北部，本地化的中部本州，与观测结果一致。
The fine‐scale seismic structure of the northeast Japan subduction zone is studied based on waveform analyses of moderate‐sized (M4.5–6), deep‐focus earthquakes (h>350 km) and the finite difference method (FDM) simulation of high‐frequency (up to 8 Hz) wave propagation. Strong regionalSwave attenuation anomalies for specific source‐receiver paths connecting the cluster of events occurring in central part of the Sea of Japan recorded at fore arc stations in northern and central Japanese Islands (Honshu) are used to model the deeper structure of the subducting Pacific Plate, where recent teleseismic tomography has shown evidence for a possible slab tear westward beneath the Sea of Japan. The character of the observed anomalousSwave attenuation and the following high‐frequency coda can be captured with the two‐dimensional (2‐D) FDM simulation of seismic waves in heterogeneous plate model, incorporating the thinning of the plate at depth, which is also compared with other possible causes of dramatic attenuation of high‐frequencySwave due to low‐Qor much weaker heterogeneities in the slab. The results of simulation clearly demonstrate that the dramatic loss of high‐frequencySwavefield from the plate into the surrounding mantle occurred due to the variation in the plate geometry (i.e., thinning of the plate) at depth near the source rather than due to variation in physical properties, such as due to the lowered‐Qand weaker heterogeneities in the plate. The presence of such a thin zone defocuses the high‐frequency slab‐guidedSwave energy from the subducting plate into the surrounding mantle and acts as a geometric antiwaveguide. Based on the sequence of simulation results obtained, we propose thinning of Pacific Plate at depth subducting beneath northeastern Japan, localized to central part of Honshu, in agreement with the observations.