Interseismic Coupling, Megathrust Earthquakes and Seismic Swarms Along the Chilean Subduction Zone (38°–18°S)

Abstract

The recent expansion of dense GPS networks over plate boundaries allows for remarkably precise mapping of interseismic coupling along active faults. The interseismic coupling coefficient is related to the ratio between slipping velocity on the fault during the interseismic period and the long-term plates velocity, but the interpretation of coupling in terms of mechanical behaviour of the fault is still unclear. Here, we investigate the link between coupling and seismicity over the Chilean subduction zone that ruptured three times in the last 5 years with major earthquakes (

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

“…The raw acceleration records were demeaned and tapered, and a zero pad has been applied at the beginning and the end before being Figure 2. (left) Long-and short-term slip events (in blue and purple, respectively), preceding the M w 8.1 main shock, superimposed on the interseismic coupling distribution [Metois et al, 2016] in gray, and the coseismic slip 1 m contours in black. Foreshock seismic activity for the same periods is also shown (in blue, purple, and green, M w > 4).…”

“…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]. To the south, the rupture stops abruptly when it reaches the metastable areas affected by the long-term aseismic precursor (blue).…”

“…Inversion of these 8 month preseismic displacements (from July 2013 to mid-March 2014) suggests that a slow slip event occurred on the subduction interface (Figure 2, blue contours), surrounding the main shock slip patch. South of the main shock, the slow slip occurs in a zone of low coupling during the interseismic period [Metois et al, 2016], while it rather affects areas characterized by intermediate locking downdip and north of the main shock. The geodetic precursor is collocated with long-term foreshock activity (Figure 2, blue dots).…”

“…The M w 8.1 2014 Iquique earthquake occurred within the North Chile seismic gap, which had not experienced a megathrust rupture since 1877 [Bejar Pizarro et al, 2013;Metois et al, 2016]. 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 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].…”