Early Afterslip of the 2015 Mw8.2 Illapel, Chile Megathrust Earthquake: Overlapping Slip Regions Challenge the Fixed Asperity Model
Abstract
Great subduction earthquakes are thought to rupture portions of the megathrust where interseismic coupling is high and velocity-weakening frictional behavior is dominant, releasing elastic deformation accrued over a seismic cycle. Conversely, post-seismic afterslip is often assumed to occur primarily in regions of velocity-strengthening frictional characteristics that may correlate with lower interseismic coupling. However, it remains unclear if fixed frictional properties of the subduction interface, co-seismic or aftershock-induced stress redistribution, or other factors control the spatial distribution of afterslip. We use InSAR and GPS observations to map the distribution of co-seismic slip of the 2015 Mw 8.3 Illapel, Chile earthquake and afterslip within the first 38 days following the earthquake. We find that afterslip overlaps the co-seismic slip area and propagates along-strike into regions inferred by other studies to be of high or moderate interseismic coupling. A simple partitioning of the subduction interface into regions of fixed frictional properties, or asperities, cannot reconcile our geodetic observations. Instead, stress heterogeneities, either pre-existing or induced by the earthquake, likely provide the primary control on the afterslip distribution for this subduction zone earthquake. These results contribute to a growing body of evidence that some megathrust faults are not characterized by spatially or temporally fixed asperities; rather, velocity weakening zones conducive to seismogenic rupture may migrate and change characteristics within the time spans of a single co-seismic/post-seismic earthquake sequence.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.T54C..02B
- Keywords:
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- 8104 Continental margins: convergent;
- TECTONOPHYSICSDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICSDE: 8123 Dynamics: seismotectonics;
- TECTONOPHYSICSDE: 8170 Subduction zone processes;
- TECTONOPHYSICS