Seismological Stress Drops for Confined Ruptures Are Invariant to Normal Stress

Seismic moment and rupture length can be combined to infer stress drop, a key parameter for assessing earthquakes. In natural earthquakes, drops are largely depth-independent, which is surprising given the expected dependence of frictional on normal stresses hence overburden. We have developed transparent experimental fault that allows direct observation thousands slip events, with ruptures fully contained within fault. Surprisingly, observed independent both magnitude its heterogeneity, capturing independence seen in nature. However, we observe larger, stress-dependent when area reduced, events frequently reach edge interface. conclude confined drops, thus depth-independent tectonic earthquakes may consequence their