期刊
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
卷 126, 期 6, 页码 -出版社
AMER GEOPHYSICAL UNION
DOI: 10.1029/2021JB021831
关键词
fluid pressure; slow earthquake; Nankai Trough
资金
- Japan Society for the Promotion of Science KAKENHI [JP19H02006, JP19K21907, 17H06455, JP16H06476]
- Scientific Research on Innovative Areas Science of Slow Earthquakes
- Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy [EXC-2077 - 390741603]
This study analyzes the subsurface pore pressure by studying the upwelling flow of drilling mud from a borehole in the Nankai Trough, and estimates the pressure level by examining porosities and modeling aquifer sizes. The research suggests the existence of multiple overpressured aquifers in the Nankai Trough region, which may contribute to fault stability and slow earthquakes observed in the area.
Pore pressure plays a key role in the generation of earthquakes in subduction zones. However, quantitative constraints for its determination are quite limited. Here, we estimate the subsurface pore pressure by analyzing the transient upwelling flow of drilling mud from borehole C0023A of the International Ocean Discovery Program (IODP) Expedition 370, in the Nankai Trough off Cape Muroto. This upward flow provided the first direct evidence of an overpressured aquifer in the underthrust sediments off Cape Muroto. To estimate the pre-drilling pore pressure in the overpressured aquifer around a depth of 950-1,050 m below sea floor, we examined the measured porosities of core samples retrieved from nearby IODP wells; we then proceeded to explain the observed time evolution of the flow rate of the upwelling flow by modeling various sized aquifers through solving a radial diffusion equation. It was observed that for a permeability of 10(-13) m(2), the aquifer possessed an initial excess pore pressure of similar to 5-10 MPa above the hydrostatic pressure, with a lateral dimension of several hundred meters and thickness of several tens of meters. The overpressure estimates from the porosity-depth profile at Site C0023 differ from those at other drill sites in the region, suggesting the possible existence of multiple overpressured aquifers with a patchy distribution in the underthrust sediments of the Nankai Trough. As pore pressure is relevant in maintaining fault stability, the overpressured aquifers may be the source of slow earthquakes that have been observed around the drilling site.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据