Deep crustal fluids and their relation to cutoff depths of crustal earthquakes in the North Ibaraki area of northeastern Japan inferred from reflected S-waves

IF 2.7 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Tectonophysics Pub Date : 2024-07-06 DOI:10.1016/j.tecto.2024.230415
Takahiro Shiina , Yuta Amezawa , Haruo Horikawa , Kazutoshi Imanishi , Takahiko Uchide
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Abstract

Crustal fluids play an essential role in the activity of crustal earthquakes. The north Ibaraki area in northeastern Japan has shown intense crustal seismicity after the 2011 Tohoku-oki earthquake. In this area, it is discussed that crustal fluids are supplied from the deep part of the Earth's crust and contribute to the genesis of these crustal earthquakes. To investigate the distribution of crustal fluids in this area, we focused on reflected S-waves, which are highly sensitive to the presence of crustal fluids. We developed an approach based on the Markov chain Monte Carlo method to precisely and quantitatively estimate the location of the crustal reflector and its geometry. The obtained results showed that the crustal reflector was located at depths of 15–25 km and dipped shallowly to the northwest. The crustal reflector was positioned above the region characterized by low seismic wave velocity and electrical resistivity anomalies in the lower crust, suggesting that the crustal reflector is the uppermost boundary of a fluid-rich zone. The distribution of the fluid-rich zone closely corresponded to the cutoff depths of crustal earthquakes. This fluid-rich zone was likely the source of the fluid that enhanced seismicity in the shallow part of the crust in the target area. In contrast, the fluid-rich zone itself may have suppressed the genesis of crustal earthquakes. We hypothesized that hydrothermal fluids might affect the shallowing of these cutoff depths. If the hydrothermal fluid was contained in the fluid-rich zone, it could induce a shallow brittle-ductile transition by increasing the temperature of the surrounding rocks.

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根据反射 S 波推断的日本东北部北茨城地区深层地壳流体及其与地壳地震截止深度的关系
地壳流体在地壳地震活动中起着至关重要的作用。日本东北部的茨城北部地区在 2011 年东北大地震后出现了强烈的地壳地震。该地区的地壳流体来自地壳深部,对地壳地震的发生起着重要作用。为了研究该地区地壳流体的分布情况,我们重点研究了对地壳流体的存在高度敏感的反射 S 波。我们开发了一种基于马尔科夫链蒙特卡洛法的方法,以精确定量地估计地壳反射体的位置及其几何形状。结果表明,地壳反射体位于 15-25 千米深处,向西北方向浅倾。地壳反射体位于下地壳低地震波速度和电阻率异常区域的上方,表明地壳反射体是富流体区的最上边界。富流体区的分布与地壳地震的截止深度密切相关。该富流体带很可能是增强目标区域地壳浅部地震活动的流体来源。相反,富流体区本身可能抑制了地壳地震的发生。我们假设热液可能会影响这些分界线深度的变浅。如果热液包含在富液区内,它可能会通过提高周围岩石的温度来诱发浅层脆性-韧性转变。
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来源期刊
Tectonophysics
Tectonophysics 地学-地球化学与地球物理
CiteScore
4.90
自引率
6.90%
发文量
300
审稿时长
6 months
期刊介绍: The prime focus of Tectonophysics will be high-impact original research and reviews in the fields of kinematics, structure, composition, and dynamics of the solid arth at all scales. Tectonophysics particularly encourages submission of papers based on the integration of a multitude of geophysical, geological, geochemical, geodynamic, and geotectonic methods
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