Strength of stick-slip and creeping subduction megathrusts from heat flow observations

Strong yet creeping megathrust faults Powerful faults in subduction zones, called “megathrust faults,” produce the largest earthquakes on Earth. Gao and Wang use heat flow data to show that when the faults subduct jagged sea floor, they generate tamer earthquakes than do faults that subduct smooth sea floor. The rugged sea floor brings irregularities into the fault that cause it to deform slowly over time, which results in a comparatively higher fault strength and lower seismicity. The finding has a direct impact on assessing regional earthquake and tsunami hazards. Science, this issue p. 1038 Megathrusts subducting rugged sea floor have high fault strength but do not unleash great earthquakes. Subduction faults, called megathrusts, can generate large and hazardous earthquakes. The mode of slip and seismicity of a megathrust is controlled by the structural complexity of the fault zone. However, the relative strength of a megathrust based on the mode of slip is far from clear. The fault strength affects surface heat flow by frictional heating during slip. We model heat-flow data for a number of subduction zones to determine the fault strength. We find that smooth megathrusts that produce great earthquakes tend to be weaker and therefore dissipate less heat than geometrically rough megathrusts that slip mainly by creeping.

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