Effects of changes in temperature and fluid pressure on dynamic earthquake rupture in a thermo-poroelastic medium

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15540401
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Solid earth and planetary physics
• Research Institution: The University of Tokyo
• Principal Investigator: YAMASHITA Teruo The University of Tokyo, Earthquake Research Institute, Professor, 地震研究所, 教授 (10114696)
• Project Period (FY): 2003 – 2004
• Keywords: pooelastic nedia / earthquake / fault / slip weakening

Research Abstract

We theoretically study thermo-hydraulic effects on dynamic earthquake rupture. First, the system of governing equations is derived assuming a thereto-poroelastic medium, and then numerical calculations are carried out based on these equations. Non-linear feedbacks among changes in temperature, fluid pressure and fault slip are shown to play important roles in the rupture dynamics. For example, the duration of fault slip is found to be longer than expected from the classical Griffith crack model located in an elastic medium because of these feedbacks ; the deviation from the solution for the Griffith crack model is larger when the thickness of heated fault zone is larger. The feedbacks also produce slip-weakening behavior and gradual slip onset. Slip-weakening distance is shown to be larger when the rate of fluid outflow from the heated fault zone is larger. A tendency is also found in our simulations that smaller-size events have smaller stress drops, which is consistent with some seismological observations ; the difference in the stress drop between small-and large-size events is larger when the permeability of the medium is smaller. This occurs because ongoing fault slip tends to raise fluid pressure. Our simulations in this paper suggest that scaling relation between small-and large-size earthquakes are rather complicated because of thermo-hydraulic effects.