Microseismicity Appears to Outline Highly Coupled Regions on the Central Chile Megathrust. Issue 11 (10th November 2021)

• Record Type: Journal Article
• Authors: Sippl, C.; Moreno, M.; Benavente, R.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 11(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-11-10
• Subjects: Central Chile -- interplate coupling -- megathrust -- Mogi doughnut -- seismicity; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2021JB022252
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: We compiled a novel microseismicity catalog for the Central Chile megathrust (29°–35°S), comprising 8, 750 earthquakes between April 2014 and December 2018. These events describe a pattern of three trenchward open half‐ellipses, consisting of a continuous, coast‐parallel seismicity band at 30–45 km depth, and narrow elongated seismicity clusters that protrude to the shallow megathrust and separate largely aseismic regions along strike. To test whether these shapes could outline highly coupled regions ("asperities") on the megathrust, we invert GPS displacement data for interplate locking. The best‐fit locking model does not show good correspondence to seismicity, possibly due to lacking resolution. When we prescribe high locking inside the half‐ellipses, however, we obtain models with similar data fits that are preferred according to the Bayesian Information Criterion (BIC). We thus propose that seismicity on the Central Chile megathrust may outline three adjacent highly coupled regions, two of them located between the rupture areas of the 2010 Maule and the 2015 Illapel earthquakes, a segment of the Chilean margin that may be in a late interseismic stage of the seismic cycle. Plain Language Summary: The largest earthquakes commonly occur along plate boundary faults, where one tectonic plate slides under another. How big such earthquakes can get depends on the properties of the fault, which often vary along its length. By identifying and locating thousands of small earthquakes on the plate boundary fault in Central Chile, we have found a curious pattern: these earthquakes describe three half‐ellipses, inside which only few earthquakes occur. We believe that this pattern can show us regions of the plate boundary fault where stress is accumulated to be one day released in a large earthquake. Aseismic patches are the ones that accumulate stress and are thus being "loaded" for a larger earthquake, whereas those that constantly produce small earthquakes are only storing part of the energy that is provided by the convergence of plates. We think that our results provide additional information on the state of the plate boundary fault in Central Chile. Key Points: Plate interface seismicity in Central Chile outlines three half‐ellipses These seismicity patterns may define the outline of highly coupled regions GPS data is shown to be compatible with the existence of such features