Chile Earthquake Research Articles

Seismic source analysis of two anomalous earthquakes in Northern Chile

Northern Chile is a seismically very active region driven by subduction of the Nazca plate beneath the South American plate. Anomalous focal mechanisms were reported by international agencies for two recent earthquakes with magnitudes larger than Mw 6. The September 11, 2020, Mw 6.2 Loa River earthquake occurred in the forearc under the Coastal Cordillera and had a strike-slip mechanism, while most common regional seismicity is characterised by NS-oriented, trench-parallel, thrust mechanisms, consistent with the subduction geometry. The June 3, 2020, Mw 6.8 San Pedro de Atacama earthquake occurred at intermediate depth with a normal faulting mechanism. In this case, the anomalous behavior involves the NW-SE striking of the focal mechanism, which deviate from the typical NS orientation in the region. In this study we reconstruct the rupture geometry for these two earthquakes by means of moment tensor inversion, rupture directivity analysis and aftershock distribution. Seismological results are discussed in the frame of the spatial and temporal distribution of local seismicity, which are analyzed using clustering techniques. Our results show that both earthquakes reveal the activation of seismogenic structures in the continental crust or within the subducting oceanic crust close to the subduction interface. The Loa River earthquake occurred at the base of the continental crust, at the contact with the slab. This finding highlights the role of seismicity associated with crustal faults in the South American plate, which poses a secondary seismic hazard for the region, alongside the seismicity directly associated with the subduction zone. The San Pedro de Atacama earthquake, in turn, occurred within the subducting slab. Its anomalous mechanism may indicate a local anomaly in the geometry of the subducting slab.

Incremental Pathways of Post-Disaster Housing Self-Recovery in Villa Verde, Chile

Housing reconstruction is considered the backbone of disaster recovery. The increasing losses in housing due to disasters challenge conventional top-down schemes and call for people-centred approaches to acknowledge their agency and self-recovery resources. This paper examines the pathways for housing self-recovery through resident-controlled incremental housing development. This paper focuses on the Villa Verde settlement built in the Chilean city of Constitución, which was severely impacted by the 2010 Chile Earthquake. Villa Verde, designed by the Chilean architecture studio Elemental, is one of the most notable incremental housing projects worldwide that encourage residents to extend their houses within a provided structural framework. This research aims to provide clarity in the much-needed understanding of disaster-affected people’s agency to self-recover, noted by researchers as one of the crucial elements for improving the humanitarian response in the aftermath of disasters. Through capturing the evolution of incremental housing construction, this paper presents multiple complexities resulting from the variety of households’ characteristics and needs in their process of post-disaster housing self-recovery. The resident-controlled process studied evidence that the people’s capacities and dedication to self-recover challenged the established housing framework with extensions beyond the designers’ parameters requiring further evaluation of the long-term implications of self-help constructions.

Seismic Vulnerability Assessment of the Yungay’s Historic Urban Center in Santiago, Chile

ABSTRACT In this paper, a modified empirical large-territorial-scale procedure to assess the seismic vulnerability of aggregate buildings in urban areas located within a highly seismic context is proposed. The methodology is applied to a group of unreinforced masonry (URM) aggregates located in the Yungay’s historic center in downtown Santiago, Chile. This assessment was carried out by modifying and integrating a vulnerability-index-based procedure, a specific existing approach called first level macro-seismic method used to predict seismic damage and loss scenarios through fragility curves of structural components. The procedure was calibrated using the observed damage after the 2010 Chile earthquake in 292 URM structural units. The results of this new damage index for URM aggregate buildings are used to derive Probability Mass Functions (PMFs) of the different damage states and preliminary Empirical Fragility Functions (EFFs). To the best of the authors’ knowledge, these EFFs are the first publicly available for aggregate Chilean URM buildings. This research and its results are the starting point for a more comprehensive study for assessing damage scenarios and vulnerabilities of aggregate URM buildings in historic centers of older Chilean cities. These functions may be used in risk assessment, and are useful to prioritize possible future damage mitigation strategies and other processes involving this historical heritage. We foresee that these results could be at least partially applied to other historical urban areas in Chile, and perhaps other old Latin American cities located along the subduction convergence region between the Pacific and Continental plates, which were founded similarly.

A Consistently Processed Strong-Motion Database for Chilean Earthquakes

Abstract Since the 1985 M 8.0 central Chile earthquake, national strong-motion seismic networks have recorded ten megathrust earthquakes with magnitudes greater than M 7.5 at the convergent margin, defined by the contact between the Nazca and South American plates. The analysis of these earthquake records have led to improved hazard analyses and design codes for conventional and seismically protected structures. Although strong-motion baseline correction is required for a meaningful interpretation of these records, correction methods have not been applied consistently in time. The inconsistencies between correction methods have been neglected in the practical use of these records in practice. Consequently, this work aims to provide a new strong-motion database for researchers and engineers, which has been processed by traceable and consistent data processing techniques. The record database comes from three uncorrected strong motion Chilean databases. All the records are corrected using a four-step novel methodology, which detects the P-wave arrival and introduces a baseline correction based on the reversible-jump Markov chain Monte Carlo method. The resulting strong motion database has more than 2000 events from 1985 to the date, and it is available to download at the Simulation Based Earthquake Risk and Resilience of Interdependent Systems and Networks (SIBER-RISK) project website.

Strong Motion Models for Duration and Arias Intensity for Strong Motion Records in Chile

Chile presents a high seismicity and very particular characteristics due to its subductive environment and high convergence rate of the interacting plates. In this paper, ground motion models (GMM) for Arias Intensity and strong ground motion duration are developed based on recently compiled Chilean earthquakes records. The Chilean derived GMM are later compared with global and subduction models. For the duration case, two definitions are considered: significant duration and bracketed duration. Care is taken to consider newly define rupture areas for the major earthquake in the catalog, which allows to redefine the distances to be used in the analysis. The strong motion records are processed using robust techniques and standardized procedures. The model parameters are selected using a Bayesian updating method. This allows to estimate the parameters as well as their corresponding uncertainties recognizing the variability of the coefficients and of the selected model. The derived ground motion predictive model associated is validated through a residual analysis and probability distributions, obtained from the adjustment method. Additionally, for the bracketed duration analysis, a classification method based on Support Vector Machine (SVM) is used, with the aim to incorporate the records with duration of zero seconds. The comparison of the resultant model with the existing ones allows to confirm the differences that the tectonic Chilean environment produces, characterized mainly by a high relative convergence rate between plates and interplate thrust earthquakes with high magnitudes.

Some Issues in the Seismic Assessment of Shear-Wall Buildings through Code-Compliant Dynamic Analyses

Due to their excellent seismic behavior, shear wall-type concrete buildings are very popular in earthquake-prone countries like Chile. According to current seismic regulations, the performance of such structures can be indifferently assessed through linear or non-linear methods of analysis. Although all the code-compliant approaches supposedly lead to a safe design, linear approaches may be in fact less precise for catching the actual seismic performance of ductile and dissipative structures, which can even result in unconservative design where comparatively stiff buildings like reinforced-concrete shear-wall (RC-SW) buildings are concerned. By referring to a mid-rise multistory RC-SW building built in Chile and designed according to the current seismic Chilean code, the paper investigates the effectiveness of the linear dynamic analyses to predict the seismic performance of such kind of structures. The findings show that the code-compliant linear approaches (Modal Response Spectrum Analysis and Linear Time-History Analysis) may significantly underestimate the displacement demand in RC-SW buildings. This is highlighted by the comparison with the results obtained from the Non-Linear Time-History Analysis, which is expected to give more realistic results. A set of ten spectrum-consistent Chilean earthquakes was considered to carry out the time-history analyses while a distributed-plasticity fiber-based approach was adopted to model the non-linear behavior of the considered building. The paper highlights how the risk of an unsafe design may become higher when reference is made to the Chilean code, the latter considering only the Modal Response Spectrum Analysis (MRSA) without even providing corrective factors to estimate the inelastic displacement demand. The paper checks the effectiveness of some amplifying factors taken from the literature with reference to the case-study shear-wall building, concluding that they are not effective enough. The paper also warns against the danger of local soft-story collapse mechanisms, which are typical of reinforced concrete frames but may also affect RC-SW buildings when weaker structural parts made by column-like walls are present at the ground floor.

Medium-run local economic effects of a major earthquake

AbstractExisting research is inconclusive regarding the longer-term economic effects of earthquakes. We examine the medium-run impacts of the 2010 earthquake in Chile, the sixth-largest ever recorded, using value-added tax collection as a proxy for economic activity at the municipal level and a measure of local ground-shaking intensity. We find that the affected municipalities suffered a relevant and persistent drop in their economic activity of about 10%, 8–9 years after the event. We discuss the plausibility of the assumption of conditional parallel trends and show that the overall results are robust to using alternative estimation methods.

Government performance, geophysical-related disasters, and institutional trust: A comparison of Chilean and Haitian responses after an earthquake

This article investigates the effect of government performance assessment after the 2010 earthquakes in Chile and Haiti on institutional trust. Available data from the 2010/2012 AmericasBarometer survey are used to estimate the immediate effects and those linked to the rebuilding process. Results show that performance assessment of Chilean institutions’ ability to manage the earthquake positively affected institutional trust, whereas the above relationship only holds for Haitian municipalities and the National Police. The evidence reveals the relevance of strengthening the crisis-handling skills displayed by local and national governments to avoid erosion in institutional social capital, a key aspect for development.

The giant 1960 tsunami in the context of a 6000‐year record of paleotsunamis and coastal evolution in south‐central Chile

AbstractThe tsunami associated with the giant 9.5 Mw 1960 Chile earthquake deposited an extensive sand layer above organic‐rich soils near Queule (39.3°S, 73.2°W), south‐central Chile. Using the 1960 tsunami deposits, together with eye‐witness observations and numerical simulations of tsunami inundation, we tested the tsunami inundation sensitivity of the site to different earthquake slip distributions. Stratigraphically below the 1960 deposit are two additional widespread sand layers interpreted as tsunami deposits with maximum ages of 4960–4520 and 5930–5740 cal BP. This >4500‐year gap of tsunami deposits preserved in the stratigraphic record is inconsistent with written and geological records of large tsunamis in south‐central Chile in 1575, 1837, and possibly 1737. We explain this discrepancy by: (1) poor preservation of tsunami deposits due to reduced accommodation space from relative sea‐level fall during the late Holocene; (2) recently evolved coastal geomorphology that increased sediment availability for tsunami deposit formation in 1960; and/or (3) the possibility that the 1960 tsunami was significantly larger at this particular location than other tsunamis in the past >4500 years. Our research illustrates the complexities of reconstructing a complete stratigraphic record of past tsunamis from a single site for tsunami hazard assessment.

Comparative Qualitative and Quantitative Analyses of the Seismic Performance of Water Networks during the Maule 2010, Christchurch 2010–2011, and Tohoku 2011 Earthquakes

Recovery of damaged water supply systems after severe earthquakes is one of the priorities to return to normal conditions. Water supply systems are intrinsically interdependent with other important lifelines such as transportation, energy, health care, and industrial sectors. These interdependencies need to be better understood by means of empirical data and analytical models. This paper is primarily of archival nature and describes empirical impact data of large earthquakes in Chile (Maule 2010), New Zealand (Christchurch 2010–2011), and Japan (Tohoku 2011) on their respective drinking water systems, and summarizes damage observations, emergency actions, and restoration processes within a resilience framework focused on metrics of robustness and rapidity. The archival nature of this article is justified by the paramount importance of systematic data collection to improve network resilience for future analytical models that aim to predict the response and recovery of water networks. Moreover, based on the collected data, the effectiveness of response actions and implemented countermeasures are evaluated relative to the observed earthquake performance of the system components. Important observations are derived to understand the main factors causing water supply system outages, the effectiveness of strategies used, and their capacity to restore the service.

Social work, neoliberalism, and post-disaster intervention: The 1985, 2010, and 2015 Chilean earthquakes

The article analyzes the contexts and specificities of post-disaster social work intervention based on the testimonies of social workers who participated in the recovery and normalization processes after the earthquakes of 1985, 2010, and 2015 in Chile. The neoliberal context has influence in the social intervention. As neoliberalism deepens, there is more technology and better access to material resources, but at the same time, professional autonomy and community knowledge decrease. Research suggests there is a need for further critical discussion about how social work has been colonized by neoliberalism, even in seemingly neutral issues such as post-disaster intervention.

Earthquake exposure, adverse childhood experiences, and psychosocial functioning in Chilean children: A longitudinal study.

The impact of an 8.8 magnitude Chilean earthquake on elementary school students' psychosocial functioning was assessed along with exposure to adverse childhood experiences (ACEs). Skills for Life,a national school-based mental health program in Chile, routinely assesses first- and third-grade students' psychosocial functioning and classroom adaptation. Students (N = 19,627) were screened before (2009) and after (2011) the 2010 earthquake with parent- and teacher-report measures and with a parent-report of four ACEs (family psychopathology, child chronic illness, family social isolation, father absence). Earthquake exposure was categorized as mild, moderate, or severe for Chile's 15 regions. Multilevel models analyzed the unadjusted and adjusted impacts of earthquake exposure and ACEs on functioning while clustering for school- and district-level effects. In covariate-adjusted models, earthquake exposure and three ACEs were significantly associated with worsened psychosocial functioning; earthquake exposure and all four ACEs were significantly associated with worsened classroom adaptation. New family psychopathology, B = 1.90, p < .001; chronic illness, B = 2.25, p < .001; and severe earthquake impact, B = 1.29, p < .001, held the strongest negative effects on psychosocial well-being. Moderate, B = 3.04, p = .011, and severe earthquake exposure, B = 2.53, p = .047, and new family psychopathology, B = 1.99, p < .001, were associated with the worst classroom functioning 1-year postdisaster. Findings suggest that both exogenous and home-based stressors can have significant consequences for children's psychosocial functioning and classroom adaptation, and routine screening helps quantify how individual students are affected by chronic versus acute stressors.

Deep mass redistribution prior to the 2010 Mw 8.8 Maule (Chile) Earthquake revealed by GRACE satellite gravity

Subduction zones megathrust faults constitute a considerable hazard as they produce most of the world's largest earthquakes. However, the role in megathrust earthquake generation exerted by deeper subduction processes remains poorly understood. Here, we analyze the 2003 – 2014 space-time variations of the Earth's gravity gradients derived from three datasets of GRACE geoid models over a large region surrounding the rupture zone of the Mw 8.8 Maule earthquake. In all these datasets, our analysis reveals a large-amplitude gravity gradient signal, progressively increasing in the three months before the earthquake, North of the epicentral area. We show that such signals are equivalent to a 60km3 water storage decrease over 2 months and cannot be explained by hydrological sources nor artefacts, but rather find origin from mass redistributions within the solid Earth on the continental side of the subduction zone. These gravity gradient variations could be explained by an extensional deformation of the slab around 150-km depth along the Nazca Plate subduction direction, associated with large-scale fluid release. Furthermore, the lateral migration of the gravity signal towards the surface from a low coupling segment around −32.5∘ North to the high coupling one in the South suggests that the Mw 8.8 earthquake may have originated from the propagation up to the trench of this deeper slab deformation. Our results highlight the importance of observations of the Earth's time-varying gravity field from satellites in order to probe slow mass redistributions in-depth major plate boundaries and provide new information on dynamic processes in the subduction system, essential to better understand the seismic cycle as a whole.

Post-disaster recovery for family firms: The role of owner motivations, firm resources, and dynamic capabilities

Natural disasters (e.g., earthquakes and pandemics) negatively affect firms and their stakeholders. These disasters disrupt the operations of firms and lives of people by generating a shock in the system. Small firms are especially vulnerable to the shocks and disturbances resulting from these disasters. Since small firms, especially family firms, are key economic contributors and agents of recovery in any community, understanding their post-disaster recovery processes is critical. Therefore, this study examines the post-disaster recovery processes of small family firms. We utilize a grounded theory approach to analyze and propose that resources and socioemotional wealth priorities influence the post-disaster recovery of small family firms. Utilizing the 8.8 Richter scale earthquake in Chile in 2010 as a natural disaster, we examine the eight-year lagged data of 20 small family firms with disrupted operations. Our findings have important implications for small firms experiencing the negative consequences of disruptions, including those experiencing the COVID-19 pandemic-induced disruption.

Geological evidence of an unreported historical Chilean tsunami reveals more frequent inundation

Assessing tsunami hazards commonly relies on historical accounts of past inundations, but such chronicles may be biased by temporal gaps due to historical circumstances. As a possible example, the lack of reports of tsunami inundation from the 1737 south-central Chile earthquake has been attributed to either civil unrest or a small tsunami due to deep fault slip below land. Here we conduct sedimentological and diatom analyses of tidal marsh sediments within the 1737 rupture area and find evidence for a locally-sourced tsunami consistent in age with this event. The evidence is a laterally-extensive sand sheet coincident with abrupt, decimetric subsidence. Coupled dislocation-tsunami models place the causative fault slip mostly offshore rather than below land. Whether associated or not with the 1737 earthquake, our findings reduce the average recurrence interval of tsunami inundation derived from historical records alone, highlighting the importance of combining geological and historical records in tsunami hazard assessment.

Evolution of Seismic Site Classification According to the Criteria in Chilean Design Codes

Design codes establish seismic site classifications to determine the seismic demand of a structure according to the response of the soil foundation under the action of earthquake ground motions; the site classification can even condition the feasibility of a project. The occurrence of great earthquakes in Chile has tested its design codes, generating much information and experience regarding the seismic design of structures that have allowed researchers to identify variations in seismic demands according to the kind of ground foundation and to propose seismic site classification methods in Chilean regulations since the 1930s; countries in the vanguard of seismic design, such as the USA, Japan, and New Zealand, proposed methods even earlier. In this document, the evolution of methodologies for seismic site classification according to the criteria in Chilean codes is analysed from their implementation in the 1930s to the most recently proposed design code NCh 433, 2018–2021. Although the distinctive features of each country shape the criteria in their design codes, clear knowledge of the evolution of established criteria from their origins is considered an important tool that contributes to the better understanding, interpretation and application of the seismic site classification methodologies contained in a design code with better criteria. Likewise, the review indicates a distinct need to conduct a continuous evaluation of the classification criteria supported by records of new earthquakes, as well as by physical and numerical models that allow incorporating variables which condition the response of the terrain such as topography, lateral heterogeneities, and basic effects.

Who is to Blame? Analysis of Government and News Media Frames During the 2014 Earthquake in Chile

ABSTRACT This study relies on Entman’s definition of frames and framing functions to analyze how the Chilean government and news media framed a natural disaster occurring in Chile in 2014. Using structural topic modeling, 705 news stories and 174 official press releases were analyzed to identify under which conditions the media may attribute blame when natural disasters are framed beyond the realm of an accident. Findings indicate the government portrayed its own performance as a successful one where all actors did their job to minimize disaster consequences. Yet, the media narrative did not reflect the government’s efficiency frame, portraying the official response as a result of lessons learned from a previous disaster. Taken together, the results suggest that when the media align with a particular political side, disaster characteristics are not the main issue to report on. This study departs from a description of journalistic practices in time of disasters towards a more complex view of the relationship between government and the press when it comes to disaster coverage.

How Good is a Paleoseismic Record of Megathrust Earthquakes for Probabilistic Forecasting?

Abstract Time-dependent earthquake forecast depends on the frequency and number of past events and time since the last event. Unfortunately, only a few past events are historically documented along subduction zones where forecasting relies mostly on paleoseismic catalogs. We address the role of dating uncertainty and completeness of paleoseismic catalogs on probabilistic estimates of forthcoming earthquakes using a 3.6-ka-long catalog including 11 paleoseismic and 1 historic (Mw≥8.6) earthquakes that preceded the great 1960 Chile earthquake. We set the clock to 1940 and estimate the conditional probability of a future event using five different recurrence models. We find that the Weibull model predicts the highest forecasting probabilities of 44% and 72% in the next 50 and 100 yr, respectively. Uncertainties in earthquake chronologies due to missing events and dating uncertainties may produce changes in forecast probabilities of up to 50%. Our study provides a framework to use paleoseismic records in seismic hazard assessments including epistemic uncertainties.

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Comment on ‘Evidence for a large strike-slip component during the 1960 Chilean earthquake’ by H. Kanamori, L. Rivera and S. Lambotte

SUMMARY Based on numerous studies of the relevant geodetic data, a low-angle thrusting mechanism has been assigned to the 1960 Chile earthquake. Kanamori, Rivera and Lambotte recently suggested that a component of dextral slip comparable to the thrusting be included in the mechanism to satisfy long-period, teleseismic observations. The absence of geodetic evidence for that huge strike-slip component is the subject of this comment. The geodetic data are largely measurements of coseismic uplift associated with the earthquake but include eight measurements of the coseismic change in shear strain. Because strike-slip produces relatively little uplift except near the end points of the rupture, identification of that strike-slip component in the geodetic data depends upon the measured, shear-strain change. I consider elastic, half-space models of oblique slip on the plate interface possibly supplemented by simultaneous dextral slip on the nearby, intra-arc Liquiñe-Ofqui Fault Zone. Slip is assumed to be uniform along strike. The best fits to the geodetic data for these models furnish little evidence for strike-slip on those structures. To satisfy the long-period, teleseismic data, Kanamori et al. proposed six examples, each of which requires a large amount of dextral slip. Because the long-period, teleseismic data do not define the slip distributions, I have used the best fits of those examples to the geodetic data to define those distributions. The large thrusting near the deformation front required by those slip distributions implies large uplift there, contrary to the uplift inferred from the inversion of tsunami data. However, an acceptable fit to the geodetic data and the tsunami data for the six examples suggested by Kanamori et al. can be obtained if the seismic moments specified by them are reduced by a factor ∼1.8, a factor within the uncertainties in estimating seismic moments of the 1960 Chile earthquake. The presence of strike-slip in those reduced-moment examples despite the lack of geodetic evidence for strike-slip is due to a remarkable coincidence that requires careful balancing of contributions from the shallower (depths &amp;lt; 70 km) coseismic sources against those from the deeper coseismic sources to nullify the geodetic evidence for strike-slip. Such balancing is possible, but it is remarkable that the balancing is so nearly perfect that it nullifies the geodetic evidence for strike-slip and thereby confounds the interpretation of the geodetic data.