2000 Western Pacific Geophysics Abstract (Chen)

Chen, P., C. R. Bina, and E. A. Okal, Intermediate-depth Seismicity, slab stress, and volcanism in subduction zones of the western Pacific plate, Eos, Transactions of the American Geophysical Union, Western Pacific Geophysics Meeting Supplement, T42B-09, 2000.


The observable spatial associations of volcanism with Wadati-Benioff zones and features (distributions and stress patterns) of intermediate-depth seismicity are strong functions of slab thermal structure. Thus, we investigate observations along the Kurile trench and the Izu-Bonin trench, where the along-strike variation of slab thermal structure is minor for the former but significant for the latter. Our primary results are three-fold. (1) Along the Kurile arc, volcanism and intermediate-depth seismicity are homogeneous and continuous, and the depths from volcanic front to slab surface are relatively constant. On the other hand, these features display heterogeneous and discontinuous patterns along the Izu-Bonin arc. This confirms the importance of slab thermal structure in understanding such observations. (2) A seismic gap between 200 and 250 km depth extends horizontally from northern Japan throughout the Kurile arc. Another gap between 150 and 200 km depth in southern Japan extends southward to the Bonin trench, with depth and width increasing to the south. (3) The principal compressional axes for intermediate-depth earthquakes north of 25 N exhibit mostly NW-SE trends, despite variations in trench azimuth. This suggests that the slab stress field in this region is more closely related to absolute plate motion direction than to trench geometry.

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