Fracture Energies at the Rupture Nucleation Points of Large Strike-slip Earthquakes

Abstract:

Some studies indicate that the fracture energy tends to increase with earthquake magnitude. In this research earthquake cycles along a pure strike slip fault are simulated with a rate- and state-dependent friction law to obtain the fracture energies at rupture nucleation points. We are trying to model a common continental strike-slip fault with the imposed slip rate at the deeper part of 0.015m per year. Velocity-weakening friction (a-b<0) region is set to 10-30km, which is the typical locked zone of continental earthquakes. Different normal stress (100, 200 and 400MPa) and different characteristic slip distance of friction L (0.01-0.2) are used in the simulation. The fracture energy at the rupture nucleation point for every case is calculated from the relation between shear stress and slip.

The simulation results show the fracture energy at the nucleation point is consistent with the theoretical expectation. The theoretical relationship between fracture energy and the amount of slip in the deep aseismic zone can be derived with fracture mechanics. In this theory, when the energy release rate at the tip of the aseismic slip zone exceeds fracture energy, an earthquake occurs. The energy release rate is proportional to the square of the amount of the deep aseismic slip during an interseismic period, which can be estimated from the recurrence interval Tr of earthquakes and the deep imposed slip rate Vpl.

The estimated equation will be used to calculate fracture energies in some actual faults and then examine its dependence on the magnitude of earthquakes.