Probing the Northern Chile Megathrust With Seismicity: The 2014 M8.1 Iquique Earthquake Sequence. Issue 12 (5th December 2019)

• Record Type: Journal Article
• Authors: Soto, H.; Sippl, C.; Schurr, B.; Kummerow, J.; Asch, G.; Tilmann, F.; Comte, D.; Ruiz, S.; Oncken, O.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 12(2019)
• Page Start: 12935
• Page End: 12954
• Publication Date: 2019-12-05
• Subjects: seismic catalog -- northern Chile -- Iquique earthquake -- aftershocks -- seismicity streak -- repeating earthquakes; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2019JB017794
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: We used data from >100 permanent and temporary seismic stations to investigate seismicity patterns related to the 1 April 2014 M8.1 Iquique earthquake in northern Chile. Applying a multistage automatic event location procedure to the seismic data, we detected and located ~19, 000 foreshocks, aftershocks, and background seismicity for 1 month preceding and 9 months following the mainshock. Foreshocks skirt around the updip limit of the mainshock asperity; aftershocks occur mainly in two belts updip and downdip of it. The updip seismicity primarily locates in a zone of transitional friction on the megathrust and can be explained by preseismic stress loading due to slow‐slip processes and afterslip driven by increased Coulomb failure stress due to the mainshock and its largest aftershock. Afterslip further south also triggered aftershocks and repeating earthquakes in several EW striking streaks. We interpret the streaks as markers of surrounding creep that could indicate a change in fault mechanics and may have structural origin, caused by fluid‐induced failure along presumed megathrust corrugations. Megathrust aftershocks terminate updip below the seaward frontal prism in the outer continental wedge that probably behaves aseismically under velocity‐strengthening conditions. The inner wedge locates further landward overlying the megathrust's seismogenic zone. Further downdip, aftershocks anticorrelate with the two major afterslip patches resolved geodetically and partially correlate with increased Coulomb failure stress, overall indicating heterogeneous frictional behavior. A region of sparse seismicity at ~40‐ to 50‐km depth is followed by the deepest plate interface aftershocks at ~55‐ to 65‐km depth, which occur in two clusters of significantly different dip. Key Points: New seismic catalog for northern Chile (18.5–22°S) contains ~19, 000 events from 1 month before to 9 months after the Iquique mainshock EW striking seismicity streaks are observed in shallower portions of the megathrust Anticorrelation between aftershocks and afterslip is observed in the deeper regions of the megathrust