Estimation of friction parameters on plate boundaries

(1)地震滑动与地震相互作用的数值模拟。我们使用实验室推导的速率和状态相关的摩擦定律对板界面的滑动行为进行了数值模拟，以了解地震滑动对地震发生的影响。考虑到一个大粗糙体的重复破裂，其中假设速度减弱摩擦，我们模拟震后滑动在粗糙体周围的速度增强区域缓慢向外传播。模拟结果表明，地震后滑动的传播速度等特性与摩擦参数有关，并且地震后滑动的传播可能在小的凹凸处引发破裂，从而导致余震区域的随时间扩展。结果表明，从大地测量资料中观测到的震后滑动的时空演变和随时间变化的余震区域可能有助于估计摩擦参数。此外，模拟结果表明，由于摩擦特性的时间和速率依赖性，大粗糙体破裂引起的滑动速度扰动显著影响小粗糙体的破裂特性。在利用小重复地震的重现模式估计滑动速度时，必须考虑到这种效应。(2)大地测量和地震资料分析。利用GPS资料估算了东海地震假定震源下方板块界面地震滑动的时空演化。得到了剪切应力与滑移、剪切应力与滑移率之间的关系，并据此估计了缓速摩擦性能。这与基于速率和状态相关摩擦的慢震模型是一致的。利用小重复地震分析，估算了日本东北部日本海沟板块界面地震滑动的时空演化规律。为了从小重复地震资料中估计滑动速度，需要同震滑动与震级之间的关系。小重复地震的经验关系与通常地震的经验关系有显著不同，通常地震的应力降是恒定的。基于粗糙体断裂力学，对小重复地震的经验标度关系进行了理论解释。少

(1) Numerical simulation about interaction between aseismic sliding and earthquakes. We performed numerical simulations of sliding behavior on plate interfaces using laboratory-derived rate- and state-dependent friction laws to understand the effects of aseismic sliding on earthquake occurrence. Considering recurrence rupture of a large asperity, where velocity-weakening friction was assumed, we modeled postseismic sliding propagating slowly outward in velocity-strengthening region around the asperity. From the simulations, we found the property of propagating postseismic sliding, such as the propagation speed, depends on friction parameters, and the propagating postseismic sliding may trigger rupture at small asperities, causing time dependent expansion of aftershock areas. The results indicate that the observations about space-time evolution of postseismic sliding from geodetic data and about time dependent aftershock areas may be useful for estimating friction parameters. Furthermor … More e, the simulations indicate that perturbation in sliding velocity due to rupture of a large asperity significantly affects the characteristics of rupture of small asperities because of time and rate dependence of frictional characteristics. This effect must be taken into consideration in estimating sliding velocity from recurrence pattern of small repeating earthquakes. (2) Analysis of geodetic and seismic data. The spatio-temporal evolution of aseismic sliding on the plate interface below the hypothetical source area of the Tokai earthquake was estimated from GPS data. We obtained the relations between shear stress and slip and between shear stress and slip rate, and velocity-weakening frictional property was estimated from the relations. This is consistent with a model for slow earthquakes on the basis of the rate- and state-dependent friction. The spatio-temporal evolution of aseismic sliding on the plate interface along the Japan trench, northeastern Japan, was estimated from the analysis of small repeating earthquakes. In order to estimate sliding velocities from the data of small repeating earthquakes, the relation between coseismic slip and magnitude is required. The empirical relation for small repeating earthquake is significantly different from that has been used for usual earthquakes, in which stress drop is constant. On the basis of fracture mechanics of an asperity, a theoretical explanation for the empirical scaling relation for the small repeating earthquakes was obtained. Less