Dual megathrust slip behaviors of the 2014 Iquique earthquake sequence

An 8 month slow slip event triggers progressive nucleation of the 2014 Chile megathrust

“…South of the main shock this precursory creep occurs in an area characterized by little interseismic coupling, while downdip and north of the main shock, the slow slip affects more coupled areas (Figure 2) [Metois et al .,2016] and may be seen as the slow rupture of locked patches surrounding the main shock. Small seismic asperities scattered in this area ruptured repeatedly [Meng et al, 2015;Lay et al, 2012]. The change in the earthquake frequency content during the foreshock sequence (a reduction of the stress drop) suggests that seismic failures widen progressively, decelerate, and start to extend into the slowly sliding, conditionally stable areas surrounding frictional asperities.…”

“…Seismic radiation spectra of interface events have been proposed, on average, to be representative of the different frictional regimes of a subduction interface [Scholz, 1998;Lay et al, 2012]; regions of unstable sliding can have large slip but generate modest amounts of short-period radiation upon failure, while smaller patchy regions of unstable sliding produce coherent short-period radiation when loaded to failure by creep of conditionally stable surrounding regions [Lay et al, 2012;Meng et al, 2015].…”

“…The maximum slip (Figure 2, black contours) occurs close to the area that started to slip before the main shock (pink), slightly downdip associated foreshock activity (pink dots), including repeating earthquakes [Meng et al, 2015]. However, the rupture extends deeper to areas that were fully locked during the interseismic period [Metois et al, 2016].…”

“…Some earthquakes have been preceded by an intense foreshock activity [Bouchon et al, 2013;Schurr et al, 2014;Ruiz et al, 2014;Lay et al, 2014;Bedford et al, 2015;Cesca et al, 2016;Kato et al, 2016;Meng et al, 2015;Hasegawa and Yoshida, 2015;Kato et al, 2012;Ozawa et al, 2012, Sato et al, 2013Bouchon et al, 2011] raising the possibility that earthquake forecasting may be achieved through a better understanding of precursory mechanisms. Two concurrent models have been proposed to explain the initiation of seismic rupture [Dodge et al, 1996].…”

“…Nevertheless, a debate remains on the mechanisms leading to this foreshock activity, notably on the existence or not of aseismic slip preceding the earthquake. Apart from the study of the foreshock sequence [Schurr et al, 2014;Ruiz et al, 2014;Lay et al, 2014;Bedford et al, 2015;Cesca et al, 2016;Kato et al, 2016;Meng et al, 2015], very little is known about any potential long-term precursors, in particular in terms of deformation.…”