Effects of pore fluid pressure and tectonic stress on diverse seismic activities around the Mt. Ontake volcano, central Japan
Effects of pore fluid pressure and tectonic stress on diverse seismic activities around the Mt. Ontake volcano, central Japan
复制标题
孔隙流体压力和构造应力对日本中部御岳火山周围各种地震活动的影响
DOI：
10.1016/j.tecto.2013.10.005
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发表时间：
2013
期刊：
影响因子：
2.9
通讯作者：
T. Okuda
中科院分区：
文献类型：
--
作者：
Terakawa;T.;Y. Yamanaka;H. Nakamichi;T. Watanabe;F. Yamazaki;S. Horikawa;T. Okuda
为了了解孔隙流体压力和构造应力对产生不同地震活动的影响，我们在2009-2011年夏季在日本中部的一座活火山——御武山附近部署了11个临时地震台站。我们从位于御岳山周围50 km范围内的临时站和永久站记录的地震数据中获得了约束良好的震源机制解。利用震源机制层析成像方法对数据集进行三维孔隙流体压力场估计，并考虑构造应力格局的空间变化。在御岳山东南侧和东侧5 ~ 12 km深度处发现了100 ~ 150 MPa的超压流体储层。自1976年以来，这个地区经历了地震群活动。许多地震事件集中在超压流体储层边缘，孔隙流体压力梯度较大。这说明大量的流体流动会通过孔隙流体压力升高导致断层强度降低而引发地震事件。许多小事件（M < 3）发生在相对于构造应力格局不利定向或严重错向的已有断层上，表明这些事件是由超压流体驱动的。而微震云和较大事件（M≥3）的宏观破裂面似乎释放了稳定板块俯冲产生的构造应力。地震行为变化的临界事件震级（Mc= 3）可以用孔隙流体压力非均质性的长度尺度来表征。这个数量可能是该地区最大事件震级的一个指标。
To understand the effects of pore fluid pressure and tectonic stress in generating diverse seismicity, we deployed 11 temporary seismic stations around an active volcano, Mt. Ontake, in central Japan during the summers of 2009–2011. We obtained well-constrained focal mechanism solutions from the seismic data recorded at the temporary stations and permanent stations located within 50 km around Mt. Ontake. We estimated the 3-D pore fluid pressure field, taking into consideration spatial changes in the tectonic stress pattern, by applying the method of focal mechanism tomography to the dataset. We found overpressurized fluid reservoirs with a peak of 100–150 MPa at depths between 5 and 12 km in the southeast and east flanks of Mt. Ontake. This region has experienced earthquake swarm activity since 1976. Many seismic events concentrated at the edge of the overpressurized fluid reservoirs, where pore fluid pressure gradients are steep. This indicates that a large amount of fluid flow would trigger seismic events by decreasing fault strength caused by an increase in pore fluid pressures. Many small events (M < 3) occurred on pre-existing faults that are unfavorably oriented or severely mis-oriented relative to the tectonic stress pattern, indicating that these events are driven by overpressurized fluids. However, the macroscopic rupture planes of microseismic clouds and larger events (M ≥ 3) appear to release tectonic stresses produced by steady plate subduction. The critical event magnitude (Mc= 3) at which seismic behavior changes would be characterized by a length scale of pore fluid pressure heterogeneity. This quantity might be an indicator of the maximum event magnitude in the region.