Asperity models and characteristic earthquakes

Summary. An asperity model is presented, including the effects of coupled elementary faults. This coupling is introduced by way of percolation theory. We postulate that the elementary faults have a typical size, whose dimensions are of order 0.3–0.4 km, and two kinds of characteristic earthquakes are obtained, one in the low magnitude range involving the rupture of a single elementary fault, and one in the high magnitude range involving a percolated cluster of faultlets, whose dimensions are proportional to the total fault. The magnitude–frequency relation of this model is constructed and the Gutenberg–Richter relation is obtained with a b value of 1 in the range of intermediate earthquakes. A relative enhancement in the probability of occurrence of large earthquakes is also observed. This effect is associated with 'characteristic earthquakes', whose magnitudes are related to the size of the active fault. Possible premonitors are discussed.