Statistical evidence of a seismic quiescence before the Mw8.1 Iquique
earthquake, Chile
Abstract
The 2014 Iquique seismic crisis (Chile), culminating with a Mw 8.1
earthquake, April 1st, highlights a complex unlocking of the North Chile
subduction interface which has been considered as a seismic gap since
1877. During the year preceding this event, at least three seismic
clusters were observed: in July 2013 and January and March 2014. These
clusters possibly indicate aseismic slip transients accompanying the
progressive destabilization of the plate contact. Recent studies have
proposed large-scale slab deformation as a potential trigger for the
megathrust earthquake; However, no evidence of gradual unlocking of the
interface or transient deformation has yet been found in the seismic
rate. To address this question, we develop a dense earthquake catalog
during the fifteen months preceding the mainshock from the continuous
waveform dataset recorded by the Integrated Plate Boundary Observatory
Chile (IPOC) and Iquique Local Network (ILN) networks. After
declustering the seismicity, a space-time analysis highlights a
large-scale acceleration of the seismicity along the interface while it
decelerates at intermediate-depths. We then demonstrate the existence of
a seismic quiescence down-dip of the mainshock rupture before the July
2013 cluster. We propose that this seismic quiescence is related to
fluid circulation and/or aseismic motion along upper-plate crustal
fault(s).