Earthquake segmentation in northern Chile correlates with curved plate geometry (original) (raw)
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Geophysical Research Letters, 2016
We analyzed the coseismic and early postseismic deformation of the 2015, M w 8.3 Illapel earthquake by inverting 13 continuous GPS time series. The seismic rupture concentrated in a shallow (<20 km depth) and 100 km long asperity, which slipped up to 8 m, releasing a seismic moment of 3.6 × 10 21 Nm (M w = 8.3). After 43 days, postseismic afterslip encompassed the coseismic rupture. Afterslip concentrated in two main patches of 0.50 m between 20 and 40 km depth along the northern and southern ends of the rupture, partially overlapping the coseismic slip. Afterslip and aftershocks confined to region of positive Coulomb stress change, promoted by the coseismic slip. The early postseismic afterslip was accommodated~53% aseismically and~47% seismically by aftershocks. The Illapel earthquake rupture is confined by two low interseismic coupling zones, which coincide with two major features of the subducting Nazca Plate, the Challenger Fault Zone and Juan Fernandez Ridge.
The 2010 Mw 8.8 Maule Megathrust Earthquake of Central Chile, Monitored by GPS
Science, 2011
Large earthquakes produce crustal deformation that can be quantified by geodetic measurements, allowing for the determination of the slip distribution on the fault. We used data from Global Positioning System (GPS) networks in Central Chile to infer the static deformation and the kinematics of the 2010 moment magnitude (Mw) 8.8 Maule megathrust earthquake. From elastic modeling, we found a total rupture length of ~500 kilometers where slip (up to 15 meters) concentrated on two main asperities situated on both sides of the epicenter. We found that rupture reached shallow depths, probably extending up to the trench. Resolvable afterslip occurred in regions of low coseismic slip. The low-frequency hypocenter is relocated 40 kilometers southwest of initial estimates. Rupture propagated bilaterally at about 3.1 kilometers per second, with possible but not fully resolved velocity variations.
The Seismic Sequence of the 16 September 2015Mw 8.3 Illapel, Chile, Earthquake
Seismological Research Letters, 2016
On 16 September 2015, the M w 8.3 Illapel, Chile, earthquake broke a large area of the Coquimbo region of north-central Chile. This area was well surveyed by more than 15 high-rate Global Positioning System (GPS) instruments, installed starting in 2004, and by the new national seismological network deployed in Chile. Previous studies had shown that the Coquimbo region near Illapel was coupled to about 60%. After the M w 8.8 Maule megathrust earthquake of 27 February 2010, we observed a large-scale postseismic deformation, which resulted in a strain rate increase of about 15% in the region of Illapel. This observation agrees with our modeling of viscous relaxation after the Maule earthquake. The area where upper-plate GPS velocity increased coincides very well with the slip distribution of the Illapel earthquake inverted from GPS measurements of coseismic displacement. The mainshock started with a small-amplitude nucleation phase that lasted 20 s. Backprojection of seismograms recorded in North America confirms the extent of the rupture, determined from local observations, and indicates a strong directivity from deeper to shallower rupture areas. The coseismic displacement shows an elliptical slip distribution of about 200 km × 100 km with a localized zone where the rupture is deeper near 31.3°S. This distribution is consistent with the uplift observed in some GPS sites and inferred from field observations of bleached coralline algae in the Illapel coastal area. Most of aftershocks relocated in this study were interplate events, although some of the events deeper than 50 km occurred inside the Nazca plate and had tension (slab-pull) mechanisms. The majority of the aftershocks were located outside the 5 m contour line of the inferred slip distribution of the mainshock.
Geophysical Journal International, 2015
, a magnitude M w 8.1 interplate thrust earthquake ruptured a densely instrumented region of Iquique seismic gap in northern Chile. The abundant data sets near and around the rupture zone provide a unique opportunity to study the detailed source process of this megathrust earthquake. We retrieved the spatial and temporal distributions of slip during the main shock and one strong aftershock through a joint inversion of teleseismic records, GPS offsets and strong motion data. The main shock rupture initiated at a focal depth of about 25 km and propagated around the hypocentre. The peak slip amplitude in the model is ∼6.5 m, located in the southeast of the hypocentre. The major slip patch is located around the hypocentre, spanning ∼150 km along dip and ∼160 km along strike. The associated static stress drop is ∼3 MPa. Most of the seismic moment was released within 150 s. The total seismic moment of our preferred model is 1.72 × 10 21 N m, equivalent to M w 8.1. For the strong aftershock on 2014 April 3, the slip mainly occurred in a relatively compact area, and the major slip area surrounded the hypocentre with the peak amplitude of ∼2.5 m. There is a secondary slip patch located downdip from the hypocentre with the peak slip of ∼2.1 m. The total seismic moment is about 3.9 × 10 20 N m, equivalent to M w 7.7. Between the rupture areas of the main shock and the 2007 November 14 M w 7.7 Antofagasta, Chile earthquake, there is an earthquake vacant zone with a total length of about 150 km. Historically, if there is no big earthquake or obvious aseismic creep occurring in this area, it has a great potential of generating strong earthquakes with magnitude larger than M w 7.0 in the future.
Journal of Geophysical Research: Solid Earth, 2018
The 2014 Iquique-Pisagua M w 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.