Frictional Strength, Stability, and Potential Shear Heating on Icy Satellite Faults

We determined the frictional strength and stability of polycrystalline ice and ice‐ammonia to constrain fault behavior on icy satellites such as Enceladus and Europa. Friction experiments including velocity steps and slide‐hold‐slide tests were conducted to measure the steady‐state coefficient of friction, velocity dependence and healing between temperatures of 98 and 248 K at a normal stress of 100 kPa. Rate‐state friction parameters determined from velocity steps provide stability values. The friction results are used to infer fault strength and frictional heating of an icy crust with depth for both a pure ice crust and one containing ammonia. We find a reduced coefficient of friction for an ammonia‐bearing crust and stronger velocity dependence in the presence of partial melt. The temperature dependence of fault stability maps a seismogenic zone with depth analogous to the synoptic model for terrestrial fault stability, where we find instability between 0.7 and 3.9 km with a return to stability from 4.6 km if we assume a 6 km ice shell. We consider the role of sliding velocity and fault thickness on localized frictional heating in both systems and estimate the depth of melt generation in an ammonia‐bearing crust. Our results imply that faults at conditions similar to icy satellites can be seismogenic.

我们测定了多晶冰和冰 - 氨的摩擦强度和稳定性，以约束恩克拉多斯和欧罗巴等冰卫星上的断层行为。进行了包括速度阶跃和滑动 - 保持 - 滑动试验在内的摩擦实验，以便在100千帕的法向应力下，在98至248开尔文的温度范围内测量稳态摩擦系数、速度依赖性以及愈合情况。由速度阶跃确定的速率 - 状态摩擦参数提供了稳定性数值。摩擦结果被用于推断纯冰地壳以及含氨地壳的断层强度和冰质地壳随深度的摩擦生热情况。我们发现含氨地壳的摩擦系数降低，并且在存在部分熔体的情况下速度依赖性更强。断层稳定性的温度依赖性绘制出了一个随深度变化的地震活动带，这类似于陆地断层稳定性的天气学模型，在该模型中，如果我们假设冰壳厚度为6千米，我们发现在0.7至3.9千米之间存在不稳定性，而从4.6千米开始恢复稳定。我们考虑了滑动速度和断层厚度在这两个系统中对局部摩擦生热的作用，并估算了含氨地壳中熔体产生的深度。我们的结果表明，在类似于冰卫星的条件下，断层可能会引发地震。