Characterizing the spectrum of slip behavior at the Sumatran subduction zone with long-term geodetic records
Tsang, Louisa Lok Hang
Date of Issue2016-03-23
Asian School of the Environment
I present three studies that depict the spatio-temporal spectrum of slip behavior on the Sunda megathrust. These studies illuminate new characteristics of slip behavior on the Sunda megathrust, which are important for gaining a comprehensive understanding of the earthquake cycle at the Sumatran subduction zone. First, from an ~1100-year-long paleogeodetic record at Simeulue Island, I discover that time-variable vertical deformation rates can be explained by changes in interseismic fault coupling over time. Also, the pattern of fault coupling preceding earthquakes between two seismic cycles may not necessarily be the same, even though the earthquakes themselves have a similar rupture pattern. Our results highlight the need for researchers to treat interseismic fault coupling maps as a snapshot of conditions on the fault that can change with time. Second, I present paleogeodetic time series that reveal a 15-year reversal in vertical displacements from 1966 to 1981. I examine a range of oceanographic and tectonic processes that can potentially explain these observations, and find that the most likely explanation is a 15-year-long slow slip event on the Banyak Islands section of the Sunda megathrust. This event is the longest lasting slow slip event reported at any subduction zone around the world, and is the first to be discovered in Sumatra. Third, I examine long GPS postseismic time series to unravel the spatio-temporal distribution of afterslip following the 2007 Mw 8.4 Bengkulu earthquake, and investigate its spatial relationship with the 2010 Mw 7.8 “tsunami earthquake” that occurred updip of the 2007 event. A key finding is that afterslip borders and overlaps the 2010 rupture area, and that localized increases in strain rates caused by afterslip may have advanced rupture of this patch in 2010.
DRNTU::Science::Geology::Volcanoes and earthquakes