[S-SS08] 地震発生の物理・断層のレオロジー

[SSS08-07] New Split-Hopkinson pressure bar installed at Tohoku University to investigate pulverization during fault rupture.

*Eranga Gayanath Jayawickrama¹、Takuma Sekiguchi¹、Jun Muto¹、Hiroyuki Nagahama¹、Hyung-Seop Shin² (1.Tohoku University Department of Earth Science、2.Andong National University Department of Mechanical Design Engineering)

To investigate the effect of very large strain rates on rock deformation in analogs to the deformation very close to the rupture surface of large-scale faults, a new Split-Hopkinson pressure bar is installed at the Department of Earth Science, Tohoku University, Japan. The apparatus consists of a gas gun, four 20 mm diameter steel bars in a sequence of an impact bar, an incident bar, a transmitted bar, and a moment trap stationed at the end. The cylindrical core sample, placed between the two 1.5 m long incident and the transmitted bars, is compressed with a stress wave generated by the gas gun. The maximum launch velocity of the impact bar that has been tested so far in the apparatus is 23.36 m/s under a 1 MPa pressure, whereas the maximum pressure is 4 MPa. The strain, measured by the strain gauges attached at the center of each long bar, is acquired at a 1 MHz sampling rate recorded by a LabView program. The strain rate of the sample is calculated utilizing the reflected and transmitted stress waves recorded at the incident and transmitted bars, respectively. Preliminary tests conducted by granite cores with two diameters of 10 and 16 mm with the same lengths (i.e., length to diameter ratio is 1:1) are presented along with two standard metal samples (oxygen-free copper, and S45C) with the ratio of 1:2. The two metal samples generated strain rates of 2300 /s and 1480 /s at impact velocities of 23.36 and 19.06 m/s, respectively. The three granite cores with a diameter of 16 mm compressed with stress waves at impact velocities of 6.95, 10.2, and 16.12 m/s, showed several degrees of pulverization from broken yet bound by the jacket to complete powder with increasing strain rates from 370, 520, and 675 /s, respectively. The three cores with 10 mm diameter compressed under impact velocities of 6.9, 12.2 and, 15 m/s resulted in complete powder with generated strain rates of 700, 1350, and 1500 /s. This variation in the degree of pulverization has opened new insights to evaluate the energy consumed during pulverization of the rock specimens either via synchrotron facilities or by postmortem investigations. Hence, the utilization of the introduced apparatus has provided the opportunity to acquire detailed information of the energy consumed in a fault during earthquake rupture.