Loading mechanism and scaling relations of large interplate earthquakes

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• 作者：Matsu'ura ; Mitsuhiro ; Sato ; Toshinori
• 关键词：lithosphere-asthenosphere coupling ; base loading ; edge loading ; interplate earthquake ; moment-length relation
• 刊名：Tectonophysics
• 出版年：1997
• 出版时间：August 15, 1997
• 年：1997
• 卷：277
• 期：1-3
• 页码：189-198
• 全文大小：674 K

文摘

We have done a numerical simulation of tectonic loading at transform plate boundaries with a lithosphere-asthenosphere coupling model subject to steady relative plate motion. In this model a seismic fault is represented by a locked patch with a finite length on an infinitely long vertical dislocation surface cutting the entire lithosphere. Through the numerical simulation we have obtained the following results. Stress accumulation on the fault is partly due to viscous drag at the base of the lithosphere (base loading) and partly due to dislocation pile-ups at horizontal edges of the fault (edge loading). If the viscosity of the asthenosphere is less than 10¹⁸ Pa s, the base loading is not effective, since its rate exponentially decays very soon. If the viscosity of the asthenosphere is greater than 10²⁰ Pa s, both types of loading are effective, and then the stress accumulation rate in the early stage of loading is formally written as = V_pl(a + ), where V_pl is a rate of relative plate motion and L is a fault length. When the fault length L is small, the effect of edge loading (the second term) is dominant, and the stress accumulation rate is in proportion to the inverse of L. When the fault length L is large, the effect of base loading (the first term) becomes dominant, and the stress accumulation rate is independent of L. It is well-known that the general L-cubed dependence of seismic moment M₀ breaks for large interplate earthquakes. This break in the moment-length relation can be ascribed to difference in loading mechanism between small and large earthquakes. From the results of numerical computation, if interplate earthquakes have the same stress drop regardless of their fault lengths, we may derive a L-squared dependence of M₀ for large interplate earthquakes and a linear L-dependence of M₀ for very large interplate earthquakes.