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

Abstract

An ∼1100 year long paleogeodetic record of land‐height change along the Simeulue section of the Sumatran subduction zone reveals significant variations in vertical motion rates. From an ∼267 year long record, we develop models to explain rate variations in the decades before the 1861, 2004, and 2005 great earthquakes. The record shows that rates accelerated by a factor of 4 to 10 in the decades before the 1861 earthquake; one plausible explanation is a significant increase in the depth of interseismic coupling on the Sunda megathrust under Simeulue. Despite similarity of the 1861 and 2005 coseismic rupture patterns, the pattern of coupling during the decades before the two earthquakes may have been different. Most GPS observations of interseismic deformation at subduction zones span only a decade or two; our results highlight the need to treat GPS‐derived coupling maps as only a snapshot of fault conditions that are temporally variable.

Structural Control on Downdip Locking Extent of the Himalayan Megathrust

“…Viscoelastic models and postseismic and paleogeodetic observations show that geodetic velocities above a fault naturally vary over time throughout the earthquake cycle (e.g., Chuang & Johnson, ; Hetland & Hager, ; Meltzner et al, ; Tsang et al, ). While Nepal has generally been seismically quiescent during the period of geodetic observation modeled here (1990s–2015), large earthquakes in the past century may still be contributing a small postseismic signal that could affect the interseismic velocities.…”

Afterslip following the 2007 Mw 8.4 Bengkulu earthquake in Sumatra loaded the 2010 Mw 7.8 Mentawai tsunami earthquake rupture zone

“…The 2007 coseismic and afterslip geodetic moment amounts to ∼7.73–8.20 × 10 21 N m. The geodetic moment of the 2007 and 2010 sequences collectively represents ∼30–44% of the moment estimated to have been released during the 1833 earthquake ( M w 8.8–8.9 [ Philibosian et al , ]). We caution though, that this is only a first‐order estimate, since there are uncertainties in the amount of seismic moment released along this section of the megathrust during the 1833 earthquake, and we have evidence that elsewhere in Sumatra (and therefore perhaps here too) rates of interseismic strain accumulation may not be constant over time [ Meltzner et al , ; Tsang et al , ].…”

A Geodesy‐ and Seismicity‐Based Local Earthquake Likelihood Model for Central Los Angeles

“…Likelihoods (plotted with a (a) linear or (b) logarithmic y axis) of observing at least one mainshock of or exceeding a given magnitude in the study area over a 1-, 10-, 100-, or 1,000-year period as indicated, assuming that individual mainshocks obey a Poisson process. Second, we assume that interseismic deformation rates are time-independent, which may be untrue (e.g., Mavrommatis et al, 2014;Tsang et al, 2015). The blue lines and error bars are the same assuming a tapered G-R distribution.…”