A 15 year slow‐slip event on the Sunda megathrust offshore Sumatra

Abstract

In the Banyak Islands of Sumatra, coral microatoll records reveal a 15 year‐long reversal of interseismic vertical displacement from subsidence to uplift between 1966 and 1981. To explain these coral observations, we test four hypotheses, including regional sea level changes and various tectonic mechanisms. Our results show that the coral observations likely reflect a 15 year‐long slow‐slip event (SSE) on the Sunda megathrust. This long‐duration SSE exceeds the duration of previously reported SSEs and demonstrates the importance of multidecade geodetic records in illuminating the full spectrum of megathrust slip behavior at subduction zones.

A paleogeodetic record of variable interseismic rates and megathrust coupling at Simeulue Island, Sumatra

“…This advocacy is well justified in light of what we now understand about the host of tectonic processes that occur on megathrusts during the interseismic period of the seismic cycle. Transient processes such as slow slip events, afterslip, and viscoelastic relaxation of the mantle (that can potentially extend over time periods beyond a seismic cycle) can alter deformation patterns and stress states on megathrusts over long time periods [e.g., Suito and Freymueller , ; Paul et al , ; Meade and Loveless , ; Fu and Freymueller , ; Tsang et al , ] and thus complicate the interpretation of interseismic deformation.…”

Isolated regions of remote triggering in South/Southeast Asia following the 2012 Mw 8.6 Indian Ocean earthquake

“…It is worth noting that a systematic search for slow‐slip events with GPS resulted in null results along the Sumatra subduction zones [ Feng et al ., ]. However, a possible 15 year slow‐slip event between 1966 and 1981 was inferred from coral microatoll records in the same region [ Tsang et al ., ]. These studies highlight the importance of additional seismological search for possible ambient tremors in these regions to better understand the relationships among slow‐slip events, tremor, and megathrust earthquakes.…”

Hunt for slow slip events along the Sumatran subduction zone in a decade of continuous GPS data

“…We would normally interpret such large events simply as a change in coupling on that area of the megathrust, although it is unclear whether the change of coupling is just a manifestation of very long SSEs. To detect these events, much longer, multidecadal GPS records and/or paleogeodetic data [ Tsang et al , ] would be required.…”

“…The Sumatran subduction zone used to be an example of having had no SSEs identified, until recently, a postulated very long SSE was discovered in coral microatoll records [ Tsang et al , ]. Based on a long‐term vertical reversal from subsidence to uplift in coral records, this SSE is inferred to have occurred on the Sunda megathrust in the Banyak Islands between 1966 and 1981.…”