Earth Planets Space, Vol. 56 (No. 8), pp. 795-801, 2004
Shingo Yoshida1, Aitaro Kato1,2, Naoyuki Kato1, and Masao Nakatani1
1Earthquake Research Institute, University of Tokyo, Tokyo 113-0032, Japan
2Institute for Frontier Research on Earth Evolution, Japan Marine Science and Technology Center, Yokohama 236-0001, Japan
(Received December 16, 2003; Revised July 9, 2004; Accepted July 12, 2004)
This paper discusses various slip modes on a plate boundary on the basis of a two-degree-of-freedom block-spring model and large-scale biaxial experiments, including a new experimental result on afterslip. We conducted slip experiments using large granite blocks with a pre-existing fault surface of 100 cm in length. Velocity-strengthening friction was given over a half of the fault length by inserting a thin Teflon sheet, while the other half retained velocity-weakening friction of the bare rock surface. Under a loading at a constant velocity, dynamic stick-slip repeated on the velocity-weakening region, causing afterslip on the velocity-strengthening region. The velocitystrengthening region experienced small coseismic slip as well, with the magnitude decreasing with the distance from the velocity-weakening region. The behaviors observed in the laboratory experiments were quantitatively simulated by a two-degree-of-freedom block-spring model, in which two blocks (Block 1 and Block 2) are connected by a liner spring and driven by a slowly moving driver. The friction on each block was assumed to obey rate and state dependent friction law. When a - b was assumed to be negative for Block 1, and positive for Block 2, afterslip occurred at Block 2. This model can also reproduce wide spectrum of slip modes by adjusting frictional parameters.
Key words: Rate- and state-dependent friction law, afterslip, asperity.