HR: 1340h
AN: S33B-1307    [Abstracts]
TI: Possible Mechanism of Earthquake Triggering due to Magnetostriction of Rocks in the Crust
AU: * Yamazaki, K
EM: kenichi@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1, Yayoi 1, Bunkyo-ku, Tokyo, 113-0032, Japan
AB: In this study, stress changes due to magnetostriction of rocks in the crust are estimated. Many studies on electromagnetic phenomena caused by earthquakes have been carried out. However, we focused on the inverse effect, that is to say possibilities of earthquakes triggered by magnetic changes. Magnetostrictions are mechanical deformations of magnetic minerals accompanied by remanent or induced magnetization changes of them. They are characterized by magnetostriction constants, which are proportional coefficients between magnetization changes and mechanical deformations. In the calculation, only the magnetostriction for induced magnetization changes is considered. The magnetostriction constant of the crust is assumed to be 1×10^{- 5} ppm/nT, which is nearly the same as that for iron. Geomagnetic secular changes derived from the IGRF model for each 5 years are used as the surrounding field, and Coulomb Failure Function changes on a horizontal plain at the depth of 5 km are estimated. The result of the calculation shows that nearly 100 Pa/year forces can be caused by the magnetostriction in some area. Recent seismological studies suggest that small stress changes such as tidal forces can trigger earthquakes. Stress changes estimated from our calculations are about one order smaller than those caused by tidal forces. However, the geomagnetic field varies far more rapidly in times of magnetic storms. In such cases, stress accumulation rates due to the magnetostriction can be larger than those due to tidal forces. Therefore, the magnetostriction can be one of the mechanisms to trigger earthquakes, and this effect is worthy to be investigated in detail. We are now planning to investigate the relationship between the magnetostriction and the seismicity statistically with the mechanisms of earthquakes taking into account. Results of them will also be discussed at the meeting.
DE: 1540 Rock and mineral magnetism
DE: 1555 Time variations: diurnal to decadal
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Seismology [S]
MN: 2007 Fall Meeting