Estimation of friction parameters on plate boundaries

(1)抗震滑移与地震相互作用的数值模拟。我们使用实验室导出的速率和状态相关的摩擦定律对板块界面上的滑动行为进行了数值模拟，以了解抗震滑动对地震发生的影响。在假定速度衰减摩擦的情况下，考虑大型凹凸体的反复破裂，模拟了地震后滑动在凹凸体周围的速度增强区缓慢向外传播。通过模拟发现，震后滑动的传播特性，如传播速度，与摩擦参数有关，而传播的震后滑动可能会在小的凹凸处触发破裂，导致余震区的时间相关扩展。结果表明，利用大地测量资料和随时间变化的余震区观测到的震后滑动时空演化信息，可用于摩擦参数的估计。更进一步的…模拟结果还表明，由于摩擦特性的时间和速率依赖性，大粗糙度对滑动速度的扰动对小粗糙度的破裂特性有显著影响。在根据小重复小地震的复发模式估计滑动速度时，必须考虑这一影响。(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想震源区下方板块界面上无震滑移的时空演化。得到了切应力与滑移率、切应力与滑移率的关系式，并由此估算了减速摩擦特性。这与基于与速率和状态有关的摩擦的慢地震模型是一致的。通过对小规模重复地震的分析，估计了日本东北部海沟板块界面上的无震滑动的时空演化。为了从小重复地震数据中估计滑动速度，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采用的应力降不变的地震的经验关系有很大不同。基于微凸体的断裂力学，从理论上解释了小重复地震的经验标度关系。较少

(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