Investigating relationships between surface rupture and multiple source parameters of earthquakes

Surface rupture produced by earthquakes can pose great threat on near-surface infrastructures and elevate damages. Accessing the potential of surface rupture along faults is critical to mitigating such hazards. It is commonly suggested that earthquakes with Mw>6.5 will break the surface. However, there are events with much smaller magnitudes rupturing the ground. To understand the potential controlling mechanisms, we first collect source parameters for earthquakes with  and  surface-breaching events in seismically active regions including west China, North America, Europe, Taiwan, Japan, and Iran. For strike-slip and normal events, almost all earthquakes with magnitudes over 6.7 broke the surface. In contrast, buried and surface-breaching events co-exist with moderate magnitude (6.0-6.7). For reverse events, there is no clear magnitude boundary, as thrust buried events can be quite large due to the downdip size of the seismogenic zone. The relocated hypocenter depths for moderate-to-large events are concentrated at depth of 5 -20 km with no systematic difference between buried and surface-breaching ruptures. Differently, all  surface-breaching events occurred at very shallow depths (<5 km). We also conduct dynamic rupture simulations and propose two conceptual models to explain whether or not ruptures may break the surface. The first model represents a fault with a continuous but heterogeneous seismogenic zone (velocity-weakening) that can hold moderate-to-large earthquakes. In this case, ruptures need to overcome the shallow velocity-strengthening zone (VS) with certain energy sink to reach the surface. Therefore, a thinner shallow RS zone and a higher stress drop of the earthquake can promote surface rupture, consistent with our observations. However, ruptures nucleating from different locations on heterogeneous faults may lead to different surface rupture patterns and final magnitudes, shedding lights on the diverse behaviors among moderate earthquakes. The second model is for small surface-breaching earthquakes. Those events are supposed to occur on shallow isolated velocity-weakening patches, consistent with the fact that usually no large earthquakes have been reported on the same fault zones. Such asperities may be formed on bodies with high-strength materials, leading to energetic ruptures with intense stress release. Our study contributes to the understanding of the surface rupture behaviors references for assessing near-surface damage in future earthquakes.