Persistent termini of 2004‐ and 2005‐like ruptures of the Sunda megathrust

Abstract

To gain insight into the longevity of subduction zone segmentation, we use coral microatolls to examine an 1100‐year record of large earthquakes across the boundary of the great 2004 and 2005 Sunda megathrust ruptures. Simeulue, a 100‐km‐long island off the west coast of northern Sumatra, Indonesia, straddles this boundary: northern Simeulue was uplifted in the 2004 earthquake, whereas southern Simeulue rose in 2005. Northern Simeulue corals reveal that predecessors of the 2004 earthquake occurred in the 10th century AD, in AD 1394 ± 2, and in AD 1450 ± 3. Corals from southern Simeulue indicate that none of the major uplifts inferred on northern Simeulue in the past 1100 years extended to southern Simeulue. The two largest uplifts recognized at a south‐central Simeulue site—around AD 1422 and in 2005—involved little or no uplift of northern Simeulue. The distribution of uplift and strong shaking during a historical earthquake in 1861 suggests the 1861 rupture area was also restricted to south of central Simeulue, as in 2005. The strikingly different histories of the two adjacent patches demonstrate that this boundary has persisted as an impediment to rupture through at least seven earthquakes in the past 1100 years. This implies that the rupture lengths, and hence sizes, of at least some future great earthquakes and tsunamis can be forecast. These microatolls also provide insight into megathrust behavior between earthquakes, revealing sudden and substantial changes in interseismic strain accumulation rates.

The surge of great earthquakes from 2004 to 2014

“…Back-projection of teleseismic short-period P waves from great earthquakes to image space-time locations of coherent bursts of short-period energy was introduced for the 2004 Sumatra event by . Numerous applications have been made to recent great earthquakes and a variety of methodologies have been introduced for such imaging (e.g., Walker et al, 2005;Krüger and Ohrnberger, 2005;Ishii et al, 2007;Xu et al, 2009;Ishii, 2011;Koper et al, 2011aKoper et al, , 2011bKoper et al, , 2012Meng et al, 2011;Yao et al, 2011;Mori, 2011a, 2011b;Zhang et al, 2011). Short-period seismic radiation is sensitive to slip accelerations and small-scale rupture variations, and the degree to which it can be deterministically imaged for large ruptures that have diffuse energy release from the slip zone is limited.…”

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

“…In the Sumatran subduction zone, temporal changes in long-term deformation rates have been reported to occur before or after major megathrust earthquakes [e.g., Prawirodirdjo et al, 2010;Philibosian et al, 2014;Meltzner et al, 2010Meltzner et al, , 2012. Most of these rate changes maintained a sense of displacement consistent with locking on the underlying megathrust and have been modeled as spatiotemporal variations in interseismic coupling and/or downdip limits of locking.…”

“…The coral microatolls were slabbed, X-rayed, and analyzed following the methods described by Meltzner et al, [2010Meltzner et al, [ , 2012 and Meltzner and Woodroffe [2015]. The interpreted coral cross sections and corresponding time series for the relevant corals are presented in Figures S1-S6 and Table S1 in the supporting information.…”

“…We therefore sought to quantify the magnitudes of spatial variations of sea level in this region and treated them as an independent error for the coral rate uncertainties. We added this error in quadrature to the 2 coral rate uncertainties determined by the method of Meltzner et al [2012] and then calculated the overall uncertainty associated with the displacement rate change at each site (details in Text S1). Our hypothesis is that if the summed uncertainties in the displacement rate changes at each site do not overlap at the 1 confidence level, then the spatiotemporal changes in the coral displacement rates are unlikely due to oceanographic sea level changes and more likely consistent with tectonic changes on the underlying megathrust.…”

Slip deficit in central Nepal: omen for a repeat of the 1344 AD earthquake?

“…Eastwards, it likely stopped at the Thakkola graben and near Koilabas where the Faizabad basement ridge deflects the MFT and further exhumes the Lesser Himalayas (Figs. 1 and 3), forcing rupture termination over many cycles, as do persistent barriers at subduction zones (Meltzner et al, 2012). Westwards, it extended at least to the Mahakali-Manasarovar/Burang graben limit but may have reached farther, which, allowing for a multi-decadal inbuilt age and/or reworking, could account for the 1209-1430 AD charcoal ages in a unit overlying the MFT near Ramnagar (Kumar et al, 2006;Rajendran et al, 2015).…”