Weak upper-mantle base revealed by postseismic deformation of a deep earthquake.

Mantle viscosity plays a key role in the Earth's internal dynamics and thermal history. Geophysical inferences of the viscosity structure, however, have shown large variability depending on the types of observables used or the assumptions imposed. Here, we study the mantle viscosity structure by using the postseismic deformation following a deep (approximately 560 km) earthquake located near the bottom of the upper mantle.

Similar scaling laws for earthquakes and Cascadia slow-slip events.

Faults can slip not only episodically during earthquakes but also during transient aseismic slip events, often called slow-slip events. Previous studies based on observations compiled from various tectonic settings have suggested that the moment of slow-slip events is proportional to their duration, instead of following the duration-cubed scaling found for earthquakes. This finding has spurred efforts to unravel the cause of the difference in scaling.