Effect of positive and negative (A-B) values assigned in the region other than asperities on the earthquake cycles

We consider the earthquake cycles in the Tohoku region, northeast Japan, especially in the Miyagi-Oki region. In that region, two or three asperities exist next to each other. Based on a rate/state friction law, we examine the effect of two friction properties of stable sliding "hpositive (A-B)"h and conditionally stable sliding "gnegative (A-B)"h assigned in the region other than the asperities at seismogenic zones. In the Miyagi-Oki region, the Pacific plate is subducting. We use a 2-D flat fault in an infinite uniform elastic medium to model asperities with stick-slip property of negative A-B values on the plate interface, following Kato (2004). He assigned stable sliding property of positive (A-B) values in the background region other than asperities. Here, we call this as "gpositive (A-B) model"h. On the other hand, according to friction experiments of granite, (A-B) value is negative from 100"E"°C to 350""°C and positive at higher temperatures (Blanpied et al,1991). A thermal model of northeast Japan (Wang and Suyehiro,1999) indicates that the depth on the subduction interface at 350"°C is 60-70km. Deduced from these two studies, the seismogenic zone in the Miyagi-Oki region should have negative (A-B) values also in the region other than asperities. We call this "gnegative (A-B) model"h. We compare these two models. First, we produce the same earthquake cycle in each one-asperity model. We define the same cycle as the one with the same recurrence time and the same distribution of afterslip and stress change. Then, we set two asperities in each model. Simulations show that afterslip propagation of first earthquake causes second earthquake and that time lag in "gnegative (A-B) model"h is shorter than one in "gpositive (A-B) model. This result suggests that "negative (A-B) model", as well as "gpositive (A-B) model"h, has potential to duplicate the complex asperity interactions observed in the Miyagi-Oki region.