资源环境科技发展态势分析平台

Fault slip is predominantly localized onto narrow slip zones embedded within broader zones of fault rock and subsidiary damage. As earthquakes re-rupture the same slip zone multiple times, the composition and geometry of the slip zone significantly affect dynamic processes. Here we use three large cross-sectional exposures of an exhumed fault to show that the thickness of a slip zone that accommodated seismic slip varies by an order of magnitude over tens of meters along strike. Geostatistical analyses show that the thickness variations are characterized by a correlation length scale of similar to 1 m and a characteristic spacing of 2-4 m. We suggest that the spacing between regions of correlated thickness represents the dimension of contact asperities on the fault. Similar magnitude variations in slip zone thickness should be generic to faults in the brittle crust, implying that slip-weakening mechanisms such as thermal pressurization are spatially variable during seismic slip.

Plain Language Summary During an earthquake, rocks on either side of a fault slip past one another. At the interface between the moving rocks, the fault contains a layer of broken and ground up rock pieces. This layer is heated during the earthquake slip due to the friction between the rocks. If heated sufficiently, the layer can undergo physical or chemical changes that cause it to lubricate the fault, allowing the earthquake rupture to grow large. The rate of heating of the layer depends on properties such as heat capacity, and on the thickness of the layer-thinner layers heat faster than thicker layers. If the layer has variable thickness, then the heating and consequently lubrication effect will also be variable. In this study, we measured the layer thickness in an ancient fault now exposed at the Earth's surface, which experienced earthquakes in the past. Our high-resolution data show that the layer thickness is highly variable, but that the spatial pattern of the variability can be predicted statistically. These results allow us to predict how effectively faults are lubricated faults in regions experiencing earthquakes today, and improve our understanding of the physical processes that cause earthquakes deep in the Earth's crust.