Along-strike distribution of seismicity and large slow slip correlated with gravity at the Nankai Trough

Various earthquakes and slow slip phenomena occur in different locations in the down-dip direction at subduction zones, for example, at the Nankai Trough, Japan. Many earthquakes, tectonic tremors, and slow slip events have occurred on the deeper side of the source areas of the past megathrust earthquakes. We show that three regions with high background seismicity correspond to the source areas of the large (> equivalent moment magnitude 6.5) slow slip events. These regions do not correspond to active areas of tectonic tremors. We note that considering broad-scale variations along the strike of the subduction zone, the three regions also correspond to areas with low free-air gravity anomalies. This fact implies that widespread stress perturbations in the along-strike direction, possibly coupled with pore fluid effects, may control the occurrence of seismic and aseismic slip on subduction faults regardless of whether at the plate interface or within the plate.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the occurrence of various earthquakes and slow slip phenomena in subduction zones. It is found that regions with high background seismicity correspond to the source areas of large slow slip events, which are not associated with tectonic tremors. Furthermore, these regions also coincide with areas of low free-air gravity anomalies. This suggests that widespread stress perturbations, possibly coupled with pore fluid effects, control seismic and aseismic slip on subduction faults.