Intense foreshocks and a slow slip event preceded the 2014 Iquique M _w 8.1 earthquake

Abstract

The subduction zone in northern Chile is a well-identified seismic gap that last ruptured in 1877. The moment magnitude (Mw) 8.1 Iquique earthquake of 1 April 2014 broke a highly coupled portion of this gap. To understand the seismicity preceding this event, we studied the location and mechanisms of the foreshocks and computed Global Positioning System (GPS) time series at stations located on shore. Seismicity off the coast of Iquique started to increase in January 2014. After 16 March, several Mw > 6 events occurred near the low-coupled zone. These events migrated northward for ~50 kilometers until the 1 April earthquake occurred. On 16 March, on-shore continuous GPS stations detected a westward motion that we model as a slow slip event situated in the same area where the mainshock occurred.

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

“…Previous studies focused mostly on the 20 days immediately preceding the earthquake when a strong transient signal occurred [Schurr et al, 2014;Ruiz et al, 2014;Lay et al, 2014;Bedford et al, 2015;Cesca et al, 2016]. Nevertheless, a debate remains on the mechanisms leading to this foreshock activity, notably on the existence or not of aseismic slip preceding the earthquake.…”

“…The earthquake ruptured añ 150 km long portion of the subduction zone [Schurr et al, 2014;Ruiz et al, 2014], in an area that was partially locked before the earthquake [Bejar Pizarro et al, 2013;Metois et al, 2016]. The earthquake was preceded by a series of earthquake swarms beginning in July 2013 [Schurr et al, 2014;Ruiz et al, 2014].…”

“…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].…”

“…Two concurrent models have been proposed to explain the initiation of seismic rupture [Dodge et al, 1996]. A first model assumes that the accelerated moment release observed before large earthquakes [Bowman and King, 2001] is triggered by a slow slip event on the fault interface [Bouchon et al, 2013;Ruiz et al, 2014;Dodge et al, 1996]. Alternatively a slow cascade of failures eventually may trigger the main shock [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.…”