Fractal asperities, invasion of barriers, and interplate earthquakes

I present a model to explain seismicity variations along consuming and transform fault plate boundaries. The basic assumptions of the model are: (1) plate boundary fault zones consist of asperities and barriers, which are defined as having negative and positive a-b values, respectively, of rate and state dependent friction laws, (2) circular-shaped asperities are distributed in a fractal manner, such that an asperity contains smaller asperities inside, (3) pore fluid pressure can be elevated almost to the lithostatic only in barriers (called invasion of barriers), and (4) a region whose barriers are invaded can rupture as an earthquake. Based on these assumptions, I re-estimate fault areas of interplate earthquakes along the San Andreas and near Japan. The derived relation between fault area and seismic moment for these earthquakes determines the fractal dimension of asperities to be 1.4, and nine smaller asperities are contained in a larger one of which the radius is 4.8 times those of the smaller ones. Various modes of invasion of barriers with a fractal distribution of asperities can explain the seismological phenomena such as variations of seismic coupling along plate boundaries, two types of earthquake families, and co-existence of the Gutenberg-Richter’s law and characteristic repeating earthquakes.