Friction Laws Based on Monotonic and Cyclic Rotary Shear Tests

Tuesday, 16 December 2014
Chun Jung Lai1, Jia-Jyun Dong1, Tetsuhiro Togo2, Che-Ming Yang1, Chyi-Tyi Lee1 and Toshihiko Shimamoto3, (1)NCU National Central University of Taiwan, Jhongli, Taiwan, (2)Seismotectonics Research Group, Institute of Earthquake and Volcano Geology, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan, (3)Institute of Geology, China Earthquake Administration, Beijing, China
Rotary-shear friction experiments have been successfully used to study the earthquake dynamics and catastrophic landslides in the past two decades. Recent studies indicated that the friction behaviors of fault gouge materials under oscillatory shear are different from those under monotonic shear. Experimental results revealed that the accelerating and decelerating motion caused weakening and strengthening, while undergoing overall slip weakening. In this study, we try to approximate the temporal variation of friction coefficient during accelerating/decelerating slip based on a velocity-displacement dependent friction law derived from monotonic rotary shear tests. The approximated results show a full strength recovery behavior when the slip velocity equals to zero, which cannot depict the experimental results. A frequency dependent factor was introduced into the friction law to improve the approximation. The mechanisms behind the differences of friction behaviors between the oscillatory and monotonic rotary shear tests will be explored.