Silent triggering: Aseismic crustal faulting induced by a subduction slow slip event

- InSAR successfully used to invert for deformation due to a slow slip event.
- InSAR reveals interaction between subduction SSE and crustal faults.
- Analysis shows that SSEs can trigger deformation events on upper plate faults.

Slow Slip Events (SSEs) are a form of fault slip behaviour whose importance has only been recognised in the last decade at subduction zone plate boundaries worldwide. Here, we show one of the first examples of the use of Interferometric Synthetic Aperture Radar (InSAR) data to document deformation during an SSE on the Hikurangi subduction interface in New Zealand. Although much of the deformation that we observe is attributable to slow slip on the subduction interface, the InSAR data also reveals surface offsets of up to 1-2 cm across a major crustal fault during the period of the slow slip event. In order to fit the observations, we find that reverse aseismic slip is required along a portion of the Wellington fault where the Coulomb Failure Stress changes (ΔCFS), due to the SSE, are in excess of 0.01 MPa. This is the first-ever documented example of a subduction interface SSE triggering a transient slip event on a major upper plate fault, and it has wide-ranging implications for the role that SSEs can play in time-dependent seismic hazard.