Three-dimensional velocity structures of Mount Fuji and the South Fossa Magna, central Japan
Three-dimensional velocity structures of Mount Fuji and the South Fossa Magna, central Japan
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DOI：
10.1029/2005jb004161
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发表时间：
2007-03-30
影响因子：
3.9
通讯作者：
Ohminato, Takao
中科院分区：
文献类型：
--
作者：
Nakamichi, Haruhisa;Watanabe, Hidefumi;Ohminato, Takao
利用高密度地震台阵2002年至2005年的到时资料，给出了日本富士山和南大峡谷的P波速度(V-P)、S波速度(V-S)以及P波与S波速度比(V-P/V-S)的三维结构。高分辨率数据集和改进的方法不仅揭示了几个与以前研究一致的速度特征，而且还揭示了与富士山下火山过程有关的速度结构和南大佛萨山的碰撞构造。富士山下7-17公里处有一个低V-P、低V-P、低V-P/V-S和低V-P/V-S异常，这与深部低频地震的位置相对应。速度异常与DLF位置的吻合表明，低V-P/V-S地区可能富含H2O、CO2等超临界挥发性流体，并可能在DLF地震的孕育中发挥重要作用。该异常在15~25公里深度上覆有较深的低V-P、低V-P、低V-P/V-S异常，可能代表玄武岩部分熔融带。箱根山以下6~14公里处有低V-P、低V-S和低V-P/V-S异常。富士山以下震源分布上限对应的等速面(V-P=6.0公里/S和V-S=3.5公里/S)可能定义了菲律宾海板块的上表面，其是否存在于富士山下的地震空区一直存在争议。
We present the three-dimensional structures of the P wave velocity (V-P), S wave velocity (V-S) as well as the P wave to S wave velocity ratio (V-P/V-S) beneath Mount Fuji and the South Fossa Magna, Japan, using arrival time data collected from 2002 to 2005 by a dense seismograph array. The high-resolution data set and improved methodology reveal not only several velocity features that are consistent with previous studies but also important new details that clarify the velocity structures associated with volcanic processes beneath Mount Fuji and the collision tectonics of the South Fossa Magna. One such particular feature is a low-V-P, low-V-S and low-V-P/V-S anomaly at depths of 7-17 km beneath Mount Fuji that corresponds with the locations of deep low-frequency (DLF) earthquakes. The coincidence of the velocity anomaly and the DLF locations suggests that supercritical volatile fluid, such as H2O and CO2, may be abundant in the low-V-P/V-S region and may play an important role in generating DLF earthquakes. This anomaly overlies a deeper low-V-P, low-V-S and high-V-P/V-S anomaly at depths of 15-25 km that may represent a zone of basaltic partial melt. A low-V-P, low-V-S and low-V-P/V-S anomaly is seen at depths of 6-14 km beneath Mount Hakone. Isovelocity surfaces (V-P = 6.0 km/s and V-S = 3.5 km/s) corresponding to the upper limit of hypocenter distribution below Mount Fuji may define the upper surface of the Philippine Sea plate whose existence in a seismic gap beneath Mount Fuji has been controversial.