The static coefficient of friction describes the strength of faults and is considered to vary in nature between typical laboratory values measured on a large variety of rocks ($0.6-0.85$) and very low values for fault rocks containing talc, chlorite and kaolinite ($<0.3$). The effective frictional strength of a seismically active fault is the result of a combination of frictional properties of the fault rocks and the prevailing pore fluid pressures, which can reach supra-hydrostatic values permitting unfavourably oriented faults to slip. Here, we present an iterative inversion procedure to obtain the average static friction coefficient of a population of seismic faults, provided that stress tensor, geometry of faults and fluid pressures are adequately constrained. The application to a dataset of 48 seismically activated faults (earthquake moment magnitude, M_W $\le 3.0$) by fluid injection in crystalline basement in the Basel Enhanced Geothermal System (Switzerland) yields an average coefficient of friction of $0.66\pm 0.11$. The inversion results, which are well constrained by high-quality focal mechanisms and robust above-hydrostatic fluid pressure estimations, have uncertainty primarily dependent on the principal stress and fault plane orientations. Values of the friction coefficient in crystalline rocks in the continental basement are compatible with experimentally determined values but require supra-hydrostatic fluid pressures. A comprehensive characterization of all the frictional parameters should be required to better assess rheological and stability fault models, both for natural and human induced earthquakes.

静态摩擦系数描述了断层的强度，并被认为在各种岩石上测量的典型实验室值之间本质上是不同的（$0.6--0.85$），而含有滑石，绿泥石和高岭石（$<0.3$）。地震活动断层的有效摩擦强度是断层岩石的摩擦特性和主要的孔隙流体压力相结合的结果，孔隙流体压力可以达到超静水压力值，从而使不利的定向断层滑动。在这里，我们提出了一个迭代反演程序，以获取一系列地震断层的平均静摩擦系数，条件是应力张量，断层的几何形状和流体压力受到适当的约束。在48个地震激活断层的数据集中的应用（地震矩震级M _W $\le 3.0$）通过在巴塞尔增强型地热系统（瑞士）中的结晶地下室中注入流体产生的平均摩擦系数为 $0.66\pm 0.11$。反演结果受高质量震源机制和稳健的高于静水力的流体压力估计的制约，其不确定性主要取决于主应力和断层平面方向。大陆基底结晶岩中的摩擦系数值与实验确定的值兼容，但需要超静液压。为了更好地评估自然地震和人为地震的流变学和稳定性断层模型，需要对所有摩擦参数进行全面表征。