Frictional Afterslip Following the 2005 Nias-Simeulue Earthquake, Sumatra

Abstract

Continuously recording Global Positioning System stations near the 28 March 2005 rupture of the Sunda megathrust [moment magnitude (Mw) 8.7] show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust, with a major fraction of this slip in the up-dip direction from the main rupture. Eleven months after the main shock, afterslip continues at rates several times the average interseismic rate, resulting in deformation equivalent to at least a M(w) 8.2 earthquake. In general, along-strike variations in frictional behavior appear to persist over multiple earthquake cycles. Aftershocks cluster along the boundary between the region of coseismic slip and the up-dip creeping zone. We observe that the cumulative number of aftershocks increases linearly with postseismic displacements; this finding suggests that the temporal evolution of aftershocks is governed by afterslip.

Stable creeping fault segments can become destructive as a result of dynamic weakening

“…Right after the event, both patches combine to form one locked region, with the surrounding areas experiencing accelerated postseismic slip, amply documented in observations (Hsu et al, 2006;Bruhat et al, 2011;Ozawa et al, 2011). The subsequent fault behavior features two smaller earthquakes, at 4432 and 4589 years, which nucleate in and rupture patch A but fail to rupture patch B.…”

“…The response of our model illustrates that. The cases of seismic events being arrested by large creeping regions are well-documented, for example, the 2004 Parkfield earthquake (e.g., Johanson et al, 2006), the 2005 Nias earthquake (Hsu et al, 2006), and the 2007 Pisco earthquake (Perfettini et al 2007). This may imply that, in those areas, the creeping regions are not susceptible to coseismic weakening.…”

Comparison of postseismic afterslip models with aftershock seismicity for three subduction-zone earthquakes: Nias 2005, Maule 2010 and Tohoku 2011

“…An agreement in the decay function would result in a linear correlation between the cumulative number of aftershocks and the cumulative displacement and such a correlation was indeed observed for continental strike-slip (e.g. Savage & Yu 2007;MurrayMoraleda & Simpson 2009;Wang et al 2009;Yang & Ben-Zion 2009) and other subduction zone events (Perfettini & Avouac 2004a;Hsu et al 2006;Ozawa et al 2012). Wennerberg & Sharp (1997) show that the cumulative moment from seismicity is proportional to the cumulative number of aftershocks multiplied by the integral of the frequency-magnitude distribution assuming that the seismicity rate is high enough that the Gutenberg-Richter distribution is 'filled in' for any time interval.…”

“…This logarithmic law is thus commonly used to fit afterslip displacements (e.g. Hsu et al 2006;Kreemer et al 2006;Freed 2007;Savage & Svarc 2009). In case long postseismic or preseismic data are available eqs (2) and (3) can be expanded with an additional linear term (at) representing the interseismic deformation.…”

“…An underlying assumption in this chain of arguments is that the nucleation time of the aftershocks governed by the time evolution of the stress is negligible (e.g. Hsu et al 2006;Helmstetter & Shaw 2009).…”