Characterizing Afterslip and Ground Displacement Rate Increase Following the 2014 Iquique‐Pisagua M_w 8.1 Earthquake, Northern Chile

Abstract

The 2014 Iquique‐Pisagua Mw 8.1 earthquake ruptured only parts of the 1877 Northern Chile‐Southern Peru seismic gap. Here we present a comprehensive analysis of 152 continuous and campaign Global Positioning System time series that captured more than a decade of interseismic loading prior to the event and 2 years of afterslip. In high spatiotemporal resolution, our data document upper plate response not only at the coseismically affected latitudes but also at the adjacent Loa plate segment to the south. Using a combination of elastic and viscoelastic half‐space models of different stages of the seismic cycle, we found that the highly coupled, former seismic gap contains a narrow low coupling zone at 21°S latitude. Just after the 2014 earthquake, this zone acts as a barrier impeding afterslip to continue southward. Possible reasons for this impediment could involve crustal heterogeneities or coupling discontinuities at the plate interface. After 2 years, afterslip cumulates to a maximum of ~89 cm and becomes negligible. Global Positioning System observations south of the inferred seismotectonic barrier reveal a deformation rate increase in the second year after the event. Our slip models suggest that this could be caused by a downdip coupling increase, perhaps bringing the highly coupled southern Loa segment closer to failure. Taken together, our results reveal (1) the interaction between different areas undergoing stress release and stress buildup in a major seismic gap, (2) constraints for the temporal variation of coupling degree in different stages of the seismic cycle, and (3) the influence of large earthquakes at adjacent segments.

Dynamically Triggered Changes of Plate Interface Coupling in Southern Cascadia

“…Coupling changes similar to the MTJ have been observed in several subduction zones in other parts of the world. The closest analogue to the Mendocino case was observed south of the Iquique earthquake in Chile, where interface coupling appeared to increase after the earthquake on a distant enough part of the plate interface to preclude static triggering (Hoffmann et al, ). Several other changes in megathrust coupling have been observed in Chile and are potentially also associated with earthquakes (Jara et al, ; Klein et al, ; Melnick et al, ).…”

Seismicity Structure of the Northern Chile Forearc From >100,000 Double‐Difference Relocated Hypocenters

“…If an along‐strike barrier, which is also apparent in the afterslip pattern of the Iquique earthquake (Hoffmann et al, ), is indeed present at ∼21 ∘ S, an interesting question is whether this segmentation is permanent. A permanent segment boundary would imply that the area exhibits different rheological and/or frictional properties of the plate interface than elsewhere along strike, as has been proposed for the Mejillones Peninsula further south (Victor et al, ).…”

Linear Relationship Between Aftershock Productivity and Seismic Coupling in the Northern Chile Subduction Zone

“…For illustration, the Figure S3 shows the temporal and spatial distribution of the P12 mainshocks which are selected by the standard parameters. The intense aftershock sequences of the two largest events (2007 M 7.8 Tocopilla and 2014 M 8.1 Iquique) cluster in space and time around the rupture zone (Hoffmann et al, ; Schurr et al, , ), while the activity related to mainshocks in the range between 4 and 6, which is analyzed in section , is almost evenly distributed. Note that many small mainshocks have no recorded aftershocks; nonetheless, their aftershock productivity ( N a =0) is taken into account when the average aftershock numbers and rates are calculated.…”