Fault geometry and earthquakes in continental interiors

Although large earthquakes in continental interiors are much less frequent than those along plate boundaries, they have been responsible for a disproportionate amount of destruction. I present a testable model for strain accumulation and seismicity in the upper crust of continental interiors. Intersecting faults provide a focus for strain build-up, resulting in local pockets of high strain accumulation. Rigid plates typically deform at strain rates 10 10 to 10 9 strain yr , but at intersecting fault zones, strain accumulates at anomalously high rates of 10 8 to 10 7 strain yr , i.e., the strain rates are comparable with those at plate boundaries. The resulting large earthquakes are associated with relatively short return times (hundreds of years). Typically one of the intersecting faults appears to split and to offset the other ‘main’ fault (defined as a fault on which the larger offset occurs), forming two parallel strands separated by a jog. I also observe a rotation of one leg of the ‘main’ fault with respect to the other. The region of intersection is usually associated with intense fracturing, increased microseismicity and uplift.  1999 Elsevier Science B.V. All rights reserved.