Microstructure of pores in rocks under high pressure and its control on seismic velocity and electrical conductivity

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K04102
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: University of Toyama
• Principal Investigator: Watanabe Tohru 富山大学, 学術研究部都市デザイン学系, 教授 (30262497)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 地殻 / 流体 / 地震波速度 / 電気伝導度 / 亀裂

Outline of Final Research Achievements

High-pressure experiments and numerical experiments on the closure of fracture were conducted to understand the fluid geometry in the upper- and mid-crust. In the crust, there exist numerous fractures of various sizes. Asperities on fracture surfaces come into contact when fractures are closed under pressure. Fluids must exist in remaining pore spaces around asperity contacts. High pressure experiments showed that the deformation of asperity contacts is accommodated by microcracking. Acoustic emissions were clearly observed during the increase in pressure. Fine particles (< 50 micrometers), which must be the product of microcracking, were observed on the fracture surfaces after loading. Numerical experiments, which considered only elastic deformation of asperity contacts, could not reproduce the increase in electrical resistance under pressure. Remaining pore spaces around asperities should be studied further through microstructural observations of fracture surfaces after loading.

Free Research Field

固体地球物理学

Academic Significance and Societal Importance of the Research Achievements

上部・中部地殻には様々なスケールの亀裂が存在する。流体は亀裂の「閉じ残り」部分に存在するため，亀裂がどのように閉鎖し，どのような閉じ残りが存在するかは，地殻の流体量を推定する上で不可欠な情報である。２０２０年以降活発な活動を続けている能登半島北部の地震は，地殻内の流体が関係していると考えられている。「閉じ残り」についての理解は，流体量の定量的評価および，流体の地震への関与の理解につながるものである。