Energy balance of fault motions, and radiated seismic energy and seismic efficiency of shallow earthquakes.

Abstract

The energy balance of earthquake fault motions is analysed, and expressions for seismic energy and seismic efficiency are derived in terms of physical quantities at the seismic source, such as initial stress, sliding frictional stress, rupture velocity and so on. In this paper an antiplane strain crack model is employed.It is shown that shallow strike-slip earthquakes will have very low seismic efficiency. Seismic wave energy, calculated on the basis of the crack model proposed in this paper, is generally smaller than that expected from the Gutenberg-Richter relation by about an order of magnitude. If the rupture velocity is approximately equal to shear wave velocity, we get the expression for seismic wave energy Es, Es≅0.23Δσ2LW2/μ, where L, W, μ, and Δσ are fault length, width, rigidity and stress drop on the fault surface respectively. The above expression can be employed as a rough estimate of the seismic wave energy.