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Foreshocks and aftershocks of the 2014 Iquique earthquake. Foreshocks (diamonds) and aftershocks (circles) located using the NonLinLoc software (red symbols) compared with locations in the CSN catalogue (blue symbols). a Map view. The stars correspond to the epicenters of the main events of the Iquique sequence. b, c Vertical profiles along lines A-B and C-D corresponding to the in-depth projection of the events. The segmented black line represents the seismogenic contact proposed by Hayes et al (2012)
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We study the foreshocks and aftershocks of the 1 April 2014 Iquique earthquake of Mw 8.1. Most of these events were recorded by a large digital seismic network that included the Northern Chile permanent network and up to 26 temporary broadband digital stations. We relocated and computed moment tensors for 151 events of magnitude Mw ≥ 4.5. Most of t...
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... The last historical mega-thrust earthquake in the northern zone of Chile was in 1877 [25][26][27]. A partial list of important recent earthquakes is: Antofagasta (1991) M w 8.0 [28], Tarapaca (2005) M w 7.7 [29], Tocopilla (2007) M w 7.7 [30], and Iquique (2014) M w 6.6, M w 8.1, M w 7.6 [31,32]. Each one of the previous large seisms generated a powerful chain of aftershocks. ...
... It is also important to consider some previous discussions concerning the aftershock activity in this region [31][32][33], and a zone with a low coupling [27]. Socquet et al. in 2017 [34] showed that the major shock was led by an acceleration that started aproximately eigth months before the large earthquake. ...
Seismic data have improved in quality and quantity over the past few decades, enabling better statistical analysis. Statistical physics has proposed new ways to deal with these data to focus the attention on specific matters. The present paper combines these two progressions to find indicators that can help in the definition of areas where seismic risk is developing. Our data comes from the IPOC catalog for 2007 to 2014. It covers the intense seismic activity near Iquique in Northern Chile during March/April 2014. Centered in these hypocenters we concentrate on the rectangle Lat−22−18 and Lon−68−72 and deepness between 5 and 70 km, where the major earthquakes originate. The analysis was performed using two complementary techniques: Tsallis entropy and mutability (dynamical entropy). Two possible forecasting indicators emerge: (1) Tsallis entropy (mutability) increases (decreases) broadly about two years before the main MW8.1 earthquake. (2) Tsallis entropy (mutability) sharply decreases (increases) a few weeks before the MW8.1 earthquake. The first one is about energy accumulation, and the second one is because of energy relaxation in the parallelepiped of interest. We discuss the implications of these behaviors and project them for possible future studies.
... Foreshock (red) and aftershock (blue) events from the 2014 Iquique earthquake sequence evidence significant faulting in the upper plate of the marine forearc region (Fig. 11; León-Ríos et al., 2016;Petersen et al., 2021). The seaward dip of the seismically imaged normal faults is supported by the crustal seismicity, which show a coherent and predominant west dipping mechanism as one of the possible focal planes for some of the events (Fig. 11B). ...
... Raw seismic data that supports this work is available through the IEDA repository (Tréhu, 2018). The authors thank León-Ríos et al. (2016) for providing seismicity data for the 2014 Iquique earthquake sequence. None of the authors have a conflict of interest to disclose. ...
... During the last three decades, several events of magnitude >Mw 7.0 had occurred in this region [19,21,22]. However, various studies have highlighted the potential risk for a larger earthquake in this region, including those of Ruiz et al. [18], León-Ríos et al. [23], and Ruiz and Madariaga [20]. In 2006, in response to increased seismic activity, the Integrated Plate Boundary Observatory Chile (IPOC) network was installed in northern Chile to systematically record seismic activity in this region. ...
... The rupture of the 2014 Mw8.1 Iquique earthquake, which struck on April 1, 2014, was ~200 km in length [23] and only broke a low coupling region [37,38] in the central zone of the seismic gap ( Fig. 1). Prior to the earthquake, seismic activity in the region had been increasing since 2008, culminating in foreshocks of Mw 6.6 and 6.4 on March 16 and March 17, 2014, two weeks before the mainshock. ...
Mutability is an information theory tool intended to characterize sequences of non-linear phenomena (e.g., earthquakes). In this study, we used mutability to identify and analyze the depth propagation of seismicity in northern Chile. During March/April 2014, several important earthquakes struck northern Chile, including one of magnitude 8.1, producing intense but short-lived aftershock regimes. To better understand this behavior, we used data from the Integrated Plate Boundary Observatory Chile (IPOC) catalog. In a first approach, we considered 101,601 earthquakes registered from January 1, 2007 to December 31, 2014 within a rectangle defined by the coordinates 68 W–72 W and 18S22S. Based on Gutenberg–Richter analysis, earthquakes with magnitudes of >2.3 (a subset of 79,321 seisms) were selected for further analysis and were grouped by depth into overlapping bins in order to identify the depth propagation of the aftershock regimes. The largest two March 2014 earthquakes produced responses from near the surface to ~18 km depth. The largest two early April earthquakes had deeper aftershock regimes. In addition, using static information theory, we performed a detailed layer-by-layer analysis that shows that the March 2014 activity had larger response towards the surface, while the April 2014 activity showed larger activity towards the inner layers. To reach more recent years data from Centro Sismológico Nacional (CSN) covering from 2012 to the end of 2021 as used. The results show a similarity between the mutability and dynamic average depths of seismicity from 2012 to 2021. The mutability of recent years is slightly less than the historic average, which can be interpreted to reflect relaxing mechanisms that are postponing the expected megathrust event in this zone.
... The dataset contains 8362 seismic events between January 2005 and March 2017. The rupture zone was approximately 100 km by 50 km in a seismic gap zone in northern Chile [26]. The rectangle used for this zone is between 19.0°and 21.0°S ...
Studies from complex networks have increased in recent years, and different applications have been utilized in geophysics. Seismicity represents a complex and dynamic system that has open questions related to earthquake occurrence. In this work, we carry out an analysis to understand the physical interpretation of two metrics of complex systems: the slope of the probability distribution of connectivity (γ) and the betweenness centrality (BC). To conduct this study, we use seismic datasets recorded from three large earthquakes that occurred in Chile: the Mw8.2 Iquique earthquake (2014), the Mw8.4 Illapel earthquake (2015) and the Mw8.8 Cauquenes earthquake (2010). We find a linear relationship between the b−value and the γ value, with an interesting finding about the ratio between the b−value and γ that gives a value of ∼0.4. We also explore a possible physical meaning of the BC. As a first result, we find that the behaviour of this metric is not the same for the three large earthquakes, and it seems that this metric is not related to the b−value and coupling of the zone. We present the first results about the physical meaning of metrics from complex networks in seismicity. These first results are promising, and we hope to be able to carry out further analyses to understand the physics that these complex network parameters represent in a seismic system.
... Within 18° and 20°S, the northern extent of where the ridge enters the subduction zone, the trench is ∼1 km shallower than to the north and south (Geersen et al., 2018). This has been attributed either to the buoyancy of the Iquique Ridge beginning to subduct or the geometric effect of the Arica Bend on the shallow slab (Contreras-Reyes & Osses, 2010;Geersen et al., 2018;León-Ríos et al., 2016;Shrivastava et al., 2019). Using the estimate from Rosenbaum et al. (2005) that Iquique Ridge subduction started around 2 Myr ago, assuming the local convergence rate stated above and the Slab2.0 ...
The Peru‐Chile subduction zone hosts M > 8 earthquakes as well as multiple ridges on the downgoing Nazca plate, making this region well suited for investigating the formation, evolution, and potential impacts of subducting features on seismogenesis. To evaluate the physical properties and structural variability of the Iquique Ridge offshore northern Chile, we present a P wave velocity model of the Nazca plate and Iquique Ridge outboard of the 2014 M 8.1 Iquique earthquake sequence. 2D tomographic inversions of P wave traveltime data from the 2016 PICTURES (Pisagua/Iquique Crustal Tomography to Understand the Region of the Earthquake Source) controlled‐source experiment indicate that the Iquique Ridge is characterized by significant crustal thickening relative to typical Nazca plate oceanic crust, with a maximum thickness of ∼13 km beneath the most prominent portion of the Iquique Ridge and outer rise. Reduced upper crustal seismic velocities extend from the ridge eastward to the trench, which may indicate increased fracturing and/or hydration during plate bending. Corresponding multi‐channel seismic reflection data show along‐profile structural variation as well, including an intermittent Moho reflector near the onset of crustal thickening and faulting along the landward slope. The structural heterogeneity entering the Peru‐Chile Trench has potential implications for slip behavior at depth assuming that the anomalous crustal structure continues beneath the forearc. We suggest that the increased buoyant normal force associated with discrete subducted Iquique Ridge seamounts similar to the zone of thick crust imaged here could lead to localized increased interplate coupling, while entrained sediment and fractured/altered crust could facilitate aseismic slip.
... There is a high research interest to better understand the complex rupture processes of that earthquake. Several papers were published that, among others, analyse the fore-and aftershock series, rupture extent, locking degree, slow-slip events, kinematic rupture processes and reverse fault reactivation BINDI et al. 2014;CESCA et al. 2016;CILIA et al. 2017;DUPUTEL et al. 2015;GONZÁLEZ et al. 2015;GUSMAN et al. 2015;HAYES et al. 2014;HERMAN et al. 2016;JARA et al. 2018;KATO et al. 2014;KATO et al. 2016; LEÓN-RÌOS et al. 2016;LIU et al. 2015;MENG et al. 2015;PIÑA-VALDÉS et al. 2018;RUIZ et al. 2014;SOCQUET et al. 2017). SCHURR et al. 2020 identified a seismic asperity that broke with the mainshock which happened north-east of this asperity. ...
... The electromagnetic transient TEM geophysical study carried out in the northern part of the Pampa The red beach balls represent the focal mechanisms of the foreshock, main shock and the main aftershock events, as obtained from the Global CMT catalogue (Dziewonski et al. 1981 ). The red dots are the relocated seismicity from March to July 2014 as obtained from León-Ríos et al. (2016). The black rectangle shows the study area. ...
... These results validate the accuracy of the meshes and justifying the use of the coarser mesh, which leads to computationally cheaper simulations by about a factor of six. We use a 1-D earth model of P-and S-wave speed that was used by León-Ríos et al. (2016) to determine the hypocentral locations of the Iquique earthquake sequence. It is a modification of a model built by Husen et al. (1999) for the Antofagasta region (300 km south of Iquique), as presented in Fig. 4. We set the shear attenuation coefficient to 600 for all depths and use Stacey absorbing conditions for the four vertical faces and for the bottom face of the grid in order to simulate a semi-infinite regional medium of elastic elements and a free-surface condition at the top. ...
... The 1-D model of V p , V s and density(Husen et al. 1999;León- Ríos et al. 2016) used in this study. ...
During earthquakes, structural damage is often related to soil conditions. Following the 01 April 2014 Mw 8.1 Iquique earthquake in Northern Chile, damage to infrastructure was reported in the cities of Iquique and Alto Hospicio. In this study, we investigate the causes of site amplification in the region by numerically analyzing the effects of topography and basins on observed waveforms in the frequency range 0.1–3.5 Hz using the spectral element method. We show that topography produces changes in the amplitude of the seismic waves (amplification factors up to 2.2 in the frequency range 0.1–3.5 Hz) recorded by stations located in steep areas such as the ca. 1 km-high coastal scarp, a remarkable geomorphological feature that runs north–south, that is, parallel to the coast and the trench. The modeling also shows that secondary waves—probably related to reflections from the coastal scarp—propagate inland and offshore, augmenting the duration of the ground motion and the energy of the waveforms by up to a factor of three. Additionally, we find that, as expected, basins have a considerable effect on ground motion amplification at stations located within basins and in the surrounding areas. This can be attributed to the generation of multiple reflected waves in the basins, which increase both the amplitude and the duration of the ground motion, with an amplification factor of up to 3.9 for frequencies between 1.0 and 2.0 Hz. Comparisons between real and synthetic seismic waveforms accounting for the effects of topography and of basins show a good agreement in the frequency range between 0.1 and 0.5 Hz. However, for higher frequencies, the fit progressively deteriorates, especially for stations located in or near to areas of steep topography, basin areas, or sites with superficial soft sediments. The poor data misfit at high frequencies is most likely due to the effects of shallow, small-scale 3D velocity heterogeneity, which is not yet resolved in seismic images of our study region.
... The 2014 Iquique earthquake on 1st April broke a central segment between 19°S and 21°S of the north Chilean seismic gap, which previously ruptured in 1877 during a M∼9 earthquake (Figure 1; Comte & Pardo, 1991). A long precursory phase preceded the 2014 mainshock (e.g., Bedford et al., 2015) and devolved into an intense foreshock series before the 2014 Iquique mainshock Cesca et al., 2016;Herman et al., 2016;León-Ríos et al., 2016;Schurr et al., 2014;Yagi et al., 2014). The 2014 Iquique earthquake did not result in enough shallow rupture to trigger a significant tsunami in the Pacific Ocean Lay et al., 2014). ...
... Similar elevated aftershock seismicity updip of the mainshock area has been reported for other subduction zones (e.g., Tilmann et al., 2010) and has elsewhere been correlated to changes in the slope or subducting plate topography interacting with the upper plate (Wang & Bilek, 2014). The elevated Iquique aftershock activity in the shallow marine forearc was previously described in studies using land stations only (León-Ríos et al., 2016;Schurr et al., 2020;Sippl et al., 2018;Soto et al., 2019). However, the seismicity of the marine forearc occurs far outside the land network, resulting in increased uncertainties and a systematic bias in hypocenters for offshore earthquakes. ...
... The combined analysis of the 2014 Iquique aftershocks and the seismic reflection image of the marine forearc within the rupture area offers the possibility to link short term deformation associated with a single seismic cycle to the permanent deformation history of an erosive convergent margin. Previous studies of the marine forearc structure of the 2014 Iquique earthquake related the updip aftershock seismicity to postseismic processes, including postseismic relaxation or afterslip (Cesca et al., 2016;León-Ríos et al., 2016;Soto et al., 2019). In contrast to Soto et al. (2019), our aftershock catalog, which is based on 23 months of amphibious and deep crustal MCS data, does not resolve any E-W elongated streaks of seismicity. ...
The aftershock distribution of the 2014 Mw 8.1 Iquique earthquake offshore northern Chile, identified from a long-term deployment of ocean bottom seismometers installed eight months after the mainshock, in conjunction with seismic reflection imaging, provides insights into the processes regulating the up-dip limit of coseismic rupture propagation. Aftershocks up-dip of the mainshock hypocenter frequently occur in the upper plate and are associated with normal faults identified from seismic reflection data. We propose that aftershock seismicity near the plate boundary documents subduction erosion that removes mass from the base of the wedge and results in normal faulting in the upper plate. The combination of very little or no sediment accretion and subduction erosion over millions of years has resulted in a very weak and aseismic frontal wedge. Our observations thus link the shallow subduction zone seismicity to subduction erosion processes that control the evolution of the overriding plate.
... The continental crust is also characterized by the presence of a low density and low velocity zone in its trenchward part, which is interpreted as a consequence of high fracturing associated with subduction erosion (e.g., Maksymowicz et al., 2018). Relocation of aftershocks of the Iquique earthquake (León-Ríos et al., 2016) show that the aftershocks do not occur near the trench (Fig. 2. This low velocity zone is expected to be associated with stable slip and aseismic deformation. ...
On April 1, 2014, a large earthquake (Mw = 8.1) ruptured the central part of a historic seismic gap in northern Chile. In order to study the relationship between the co-seismic rupture characteristics and the crustal structure of the subduction zone, we processed a trench-perpendicular seismic reflection profile acquired across the zone of maximum slip and generated a P-wave velocity model. The results show a frontal prism in the continental wedge characterized by low velocities that increase rapidly towards the shore and acted as a barrier for trench-ward propagation of aftershocks. Landward, a transition zone with increasing upper crust velocity (4–5 km/s) concentrates most of the aftershocks. In addition, a trench-ward dipping set of fault zones is observed along the continental wedge associated to the Iquique forearc basin formation (1.5 km thick at the depocenter on this profile). We identify three stratigraphic units within the basin. A landward tilt and thickness increase is detected in each stratigraphic unit, along with growth strata and domino structures, suggesting landward migration of syn-extensional deformation in response to basal subduction erosion. By extrapolating our results to the plate boundary and based on published focal mechanisms of intra-crustal seismicity, we find a strong spatial correlation between the Iquique basin and the highest slip area for the 2014 earthquake, suggesting long-term extensional deformation due to coseismic tensional stresses.
... Focal mechanisms (beachballs) related to the Iquique earthquake sequence, compiled from global catalogs (GEOFON Data Centre and Global CMT project) as well as fromHayes et al. (2014),Cesca et al. (2016), andLeón-Ríos et al. (2016) ...
... We finally associated several sets of published focal mechanisms (Cesca et al., 2016;Hayes et al., 2014;León-Ríos et al., 2016; GEOFON Data Centre (geofon.gfz-potsdam.de) and Global CMT project (www.globalcmt.org) with our relocated events in order to better constrain hypocentral depths of earthquakes with unfavorable event-station geometry and to inform our interpretations of fault kinematics. ...
... Additional waveform data were used from the MEJIPE temporary network deployed by FU Berlin (Salazar et al., 2013) accessed via EIDA web services as well as from a temporary network deployed by the Chilean ONEMI, DGF, and CSN institutions accessed from CSN upon request. Earthquake focal mechanisms were obtained from GEOFON Data Centre (see above), globalCMT (https:// www.globalcmt.org/), and from published compilations by Cesca et al. (2016), Hayes et al. (2014), and León-Ríos et al. (2016). We thank the authors of these studies for supplying their focal mechanism solutions. ...
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.
