Chile Earthquake Research Articles

Nonlinear numerical assessment of the seismic response of hillside RC buildings

Major damage has been reported in hilly areas after major earthquakes, primarily because of two special conditions: the variation in the seismic ground motion due to the inclined ground surface and the irregularities caused by a stepped base level in the structure. The aim of this study is to evaluate possible differences in the responses of Chilean hillside buildings through numerical linear-elastic and nonlinear analyses. In the first step, a set of response-spectrum analyses were performed on four simplified 2D structures with mean base inclination angles of 0°, 15°, 30°, and 45°. The structures were designed to comply with Chilean seismic codes and standards, and the primary response parameters were compared. To assess the seismic performance of the buildings, nonlinear static (pushover) and dynamic (time-history) analyses were performed with SeismoStruct software. Pushover analyses were used to compare the nonlinear response at the maximum roof displacement and the damage patterns. Time-history analyses were performed to assess the nonlinear dynamic response of the structures subjected to seismic ground motions modified by topographic effects. To consider the topographic modification, acceleration records were obtained from numerical models of soil, which were calculated using the rock acceleration record of the Mw 8.0 1985 Chilean earthquake. Minor differences in the structure responses (roof displacements and maximum element forces and moments) were caused by the topographic effects in the seismic input motion, with the highly predominant ones being the differences caused by the step-back configuration at the base of the structures. High concentrations of shear forces in short walls were observed, corresponding to the walls located in the upper zone of the foundation system. The response of the structures with higher angles was observed to be more prone to fragile failures due to the accumulation of shear forces. Even though hillside buildings gain stiffness in the lower stories, resulting in lower design roof displacement, maximum roof displacements for nonlinear time-history analyses remained very close for all the models that were primarily affected by the drifts of the lower stories. Additionally, vertical parasitic accelerations were considered for half the time-history analyses performed here. The vertical component seems to considerably modify the axial load levels in the shear walls on all stories.

Seismically Derived Ground Tilts Related to the 2010 Chilean Tsunami

AbstractDeveloping new ways to observe tsunami contributes to tsunami research. Tidal and deep-ocean gauges are typically used for coastal and offshore observations. Recently, tsunami-induced ground tilts offer a new possibility. The ground tilt signal accompanied by 2010 Mw 8.8 Chilean earthquake were observed at a tiltmeter network in Japan. However, tiltmeter stations are usually not as widely installed as broadband seismometers in other countries. Here, we studied broadband seismic records from Japan’s F-net and found ground tilt signals consistent with previously published tiltmeter dataset for this particular tsunamic event. Similar waveforms can also be found in broadband seismic networks in other countries, such as Taiwan, as well as an ocean-bottom seismometer. We documented a consistent time sequence of evolving back-azimuth directions of the tsunami waves at different stages of tsunami propagation through beamforming-frequency–wavenumber analysis and particle-motion analysis; the outcomes are consistent with the tsunami propagation model provided by the Pacific Tsunami Warning Center. These results shown that dense broadband seismic networks can provide a useful complementary dataset, in addition to tiltmeter arrays and other networks, to study or even monitor tsunami propagation using arrayed methods.

Displacements Before and After Great Earthquakes: Geodetic and Seismic Viewpoints

Analysis of geodetic data obtained by the global positioning system (GPS) leads to better understanding of earthquake origins and helps to interpret their sequences. For this, we cross-compare the pre- and postseismic displacements associated with great earthquakes and derived from GPS observations and seismic catalogs. In a pilot study of the 2004 Sumatra–Andaman Mw9.2 earthquake in the Indian Ocean, the 2011 Tohoku Mw9.1 earthquake in Japan, the 2010 offshore Maule Mw8.8 and the 2015 Illapel Mw8.3 earthquakes in Chile, the 2018 Kodiak Mw7.9 earthquake in the Gulf of Alaska, and the 2016 Kaikoura Mw7.8 earthquake in New Zealand, we consider GPS data from stations of the Global Navigation Satellite System (GNSS) along with integral characteristics of the regional seismic regime, including the accumulated displacement derived from the catalogs of earthquake hypocenter parameters. We did not find any prominent transient pattern in the daily geodetic measurements registered before the six great earthquakes at the nearest GNSS stations. We found that (a) the six cases exhibit different GPS versus seismic displacement correlation patterns before and after the great earthquakes, (b) the observed high variability of the correlation between geodetic ρ(t) and seismic ∑(t) integrals appears indicative of a partial contribution of earthquakes to naturally haphazard sporadic movement of lithospheric blocks of different size, and (c) GPS data confirm the existence of intermittent long periods of regionally stable levels of seismic regime reflected in the control parameter of the Unified Scaling Law for Earthquakes that may change as a result of mid- or even short-term bursts of activity associated with catastrophic events.

Who Has Benefited? A Socio-Ecological Chronology of Urban Resilience in the Early Reconstruction of Talca after the 27-F Earthquake, Chile 2010–2012

This article engages in the understanding of resilience from the perspective of socio-ecological systems (SES) and the reconstitution of events of recovery and reconstruction in the city of Talca after the 27-F earthquake in Chile, between 2010 and 2012. For such purposes, we have developed a chronological or timeline-analysis model. This methodology, which uses mostly ethnographic and participant-observation techniques to recapitulate these events, observes the interaction of social agents, elements of the built environment, government institutions, and other institutional functions of the urban domain within the socio-ecological panarchy. The results suggest that key events, such as local government institutional actions, the observation of probable property speculation events, and community agency efforts dismissal, among other factors, could alter both human and natural resilience processes. In turn, this could affect the capacity of this city, its inhabitants, and its social institutions to endure future crises, as a product of deteriorated and maladaptive resilience mechanisms, aside from the natural and geographical conditions of Chile, exposed to future earthquake events. Likewise, the partial loss of the civic environment in this historic city and weakened neighborhood networks, contrasting with the redevelopment of real estate in central areas, altogether portray considerable risks with regard to the (un)generated social mechanisms of resilience, affecting future developments. The final section focuses on discussing these findings and their relevance in integrating a coherent understanding of SES resilience in urban planning and governance practice, especially in cities or urban areas that are prone to natural risks or catastrophes.

Lateral Stability Limits for RC Wall Boundary Zones Based on Axial Response of Idealized Prisms

ABSTRACT Seismic performance of flexurally-dominated reinforced concrete (RC) walls largely depends on the ability of its confined end regions to withstand axial stress reversals. Observed compression failure modes in these end boundary regions during the Chile (2010) and New Zealand (2010–11) earthquakes led to extensive experimental research that involved testing isolated rectangular columns (or prisms) representative of wall boundary zones under axial cyclic loading. This study scrutinizes the effect of slenderness (height-to-thickness) ratio on the compression failure modes of such wall boundary zones. For this purpose, uniaxial cyclic tests were conducted on four doubly RC prisms representative of rectangular wall boundary zones designed in accordance with ductile detailing requirements of New Zealand Concrete Standard. The test results are presented in detail and the effect of slenderness on progression of two different types of instability, namely local and global, is elaborated. The experimental measurements are compared with the analytical predictions of three phenomenological models proposed in the literature to prevent development of out-of-plane instability in structural walls. Relationships between the effective boundary element slenderness and different compression failure modes are established using the results of this study as well as previous experimental investigations conducted by other researchers. Finally, this paper attempts to provide limitations on the ratio between unsupported wall height to wall thickness deduced from the effective boundary element slenderness limits so that protection against lateral instability in ductile structural walls could be ensured.

Feasibility Analysis of GNSS-Reflectometry for Monitoring Coastal Hazards

Coastal hazards, such as a tsunamis and storm surges, are a critical threat to coastal communities that lead to significant loss of lives and properties. To mitigate their impact, event-driven water level changes should be properly monitored. A tide gauge is one of the conventional water level measurement sensors. Still, alternative measurement systems can be needed to compensate for the role of tide gauge for contingency (e.g., broken and absence, etc.). Global Navigation Satellite System (GNSS) is an emerging water level measurement sensor that processes multipath signals reflected by the water surface that is referred to as GNSS-Reflectometry (GNSS-R). In this study, we adopted the GNSS-R technique to monitor tsunamis and storm surges by analyzing event-driven water level changes. To detect the extreme change of water level, enhanced GNSS-R data processing methods were applied which included the utilization of multi-band GNSS signals, determination of optimal processing window, and Kalman filtering for height rate determination. The impact of coastal hazards on water level retrievals was assessed by computing the confidence level of retrieval (CLR) that was computed based on probability of dominant peak representing the roughness of the water surface. The proposed approach was validated by two tsunami events, induced by 2012 Haida Gwaii earthquake and 2015 Chile earthquake, and two storm surge events, induced by 2017 Hurricane Harvey and occurred in Alaska in 2019. The proposed method successfully retrieved the water levels during the storm surge in both cases with the high correlation coefficients with the nearby tide gauge, 0.944, 0.933, 0.987, and 0.957, respectively. In addition, CLRs of four events are distinctive to the type of coastal events. It is confirmed that the tsunami causes the CLR deduction, while for the storm surges, GNSS-R keep high CLR during the event. These results are possibly used as an indicator of each event in terms of storm surge level and tsunami arrival time. This study shows that the proposed approach of GNSS-R based water level retrieval is feasible to monitor coastal hazards that are tsunamis and storm surges, and it can be a promising tool for investigating the coastal hazards to mitigate their impact and for a better decision making.

Conditioning Factors for Re-election and Incumbency Advantage after a Natural Disaster: Evidence from a Large-scale Earthquake

Since the public assessment of political leadership is more evident during crisis events, natural disasters have become a plausible explanation for electoral outcomes and public support. This imposes a prominent challenge for developing countries, which are less prepared to deal with catastrophes. This paper proposes a theoretical and an empirical approach to evaluate the unrestricted and conditional impact of natural disasters on the continuity of local authorities. Our theoretical framework treats natural disasters as an exogenous shock that is beyond the incumbent’s influence but provides valuable information to rational voters about high-quality candidates. The empirical approach uses county-level data to test this model by estimating the impact of the Chile earthquake occurred in 2010 on re-election probability and incumbent mayor’s vote share. Aggregate- and individual-level evidence shows that incumbents’ continuity is not unconditionally threatened due to the earthquake, but contingent on conditioning factors that exacerbate or mitigate its negative effect on incumbency advantage. That is, local governments with higher human capital endowments and a better post-disaster assessment are more likely to be re-elected in Chile.

Methods for interpreting grace system data for solving geodynamic monitoring problems

The study is devoted to a detailed analysis of observational data from the GRACE space system to clarify the parameters of a catastrophic earthquake with a magnitude of MW = 8.8, which occurred in the subduction zone near the coast of Chile. Digital maps of changes in the EWH parameter over the geoid contour in the investigated seismically active region of the Chilean earthquakes of 2014 and 2015 were constructed. It is shown that there is a negative correlation between the value of the geodynamic parameter H for a strong earthquake with M W = 8.8 (distance from the hypocenter to the position of the Earth-Moon barycenter) and the equivalent water height above the geoid EWH. The highest correlation coefficient between the parameters H and EWH equal to R = -0.61 was noted during the period of registration of the number of postseismic events in the region of Central Chile. In the course of further research study the representative class of earthquakes for a detailed analysis of the variability of the EWH parameter and its relationship with geodynamic processes.

Evolution of seismic design codes of highway bridges in Chile

Chile, as a country with a long history of strong seismicity, has a record of both a constant upgrading of its seismic design codes and structural systems, particularly for bridges, as a result of major earthquakes. Recent earthquakes in Chile have produced extensive damage to highway bridges, such as deck collapses, large transverse residual displacements, yielding and failure of shear keys, and unseating of the main girders, demonstrating that bridges are highly vulnerable structures. Much of this damage can be attributed to construction problems and poor detailing guidelines in design codes. After the 2010 Maule earthquake, new structural design criteria were incorporated for the seismic design of bridges in Chile. The most significant change was that a site coefficient was included for the estimation of the seismic design forces in the shear keys, seismic bars, and diaphragms. This article first traces the historical development of earthquakes and construction systems in Chile to provide a context for the evolution of Chilean seismic codes. It then describes the seismic performance of highway bridges during the 2010 Maule earthquake, including the description of the main failure modes observed in bridges. Finally, this article provides a comparison of the Chilean bridge seismic code against the Japanese and United States codes, considering that these codes have a great influence on the seismic codes for Chilean bridges. The article demonstrates that bridge design and construction practices in Chile have evolved substantially in their requirements for the analysis and design of structural elements, such as in the definition of the seismic hazard to be considered, tending toward more conservative approaches in an effort to improve structural performance and reliability for Chilean bridges.

Natural Disasters and Birth Rate: Evidence from the 2010 Chilean Earthquake

A major natural disaster can generate changes in the affected population’s behavior. As Chile is considered one of the countries with the highest seismic activity and has experienced several of the most intense earthquakes on record in the world, this work seeks to identify behavioral changes in the birth rate within an affected population related to a natural disaster in Chile. Based on evidence from the 2010 Chilean earthquake, an empirical study was carried out drawing on birth rate data and social data associated with earthquakes in Chile between 2004 and 2015. Two models were estimated. The first model is a difference-in-differences model for determining the effect of the disaster on the birth rate in the affected area in the post-disaster period. The second model is a triple-difference model that includes the trend of the data over time. The results indicate a positive relationship between the variation in the birth rate and the occurrence of the natural disaster. Studying the relationship between disaster events and fertility contributes to understanding the phenomena of social dynamics. This knowledge could improve public policy decision making for better planning in the face of a natural disaster.

Locking-derived tsunami scenarios for the most recent megathrust earthquakes in Chile: implications for tsunami hazard assessment

The ever-increasing data from continues geodetic networks has allowed to reveal first-order spatial relations between pre-seismic highly locked zones on the interface and regions of large coseismic slip. Here we use a distribution of locking degree and recurrence of historical earthquakes along the Chilean subduction zone to estimate the slip deficit accumulated since previous tsunamigenic earthquakes and use these constrains to simulate tsumani signals. We generate tsunami models for the recent five major tsunamigenic earthquakes in Chile during the last decade: Maule (2010), Pisagua (2014), Illapel (2015), Melinka (2016) and Valparaiso (2017). Results were compared with tsunami records to evaluate the use of locking degree as an estimate of displacement of future earthquakes and as a tool for tsunami hazard assessment. Our tsunami simulations for the Maule (2010) and Illapel (2015), earthquakes that filled a seismic gap, reproduce well the tsunami observations, for the case of Pisagua (2014), Valparaiso (2016) and Melinka (2017) although it exists a correspondence in the areas of greater degree of locking with the coseismic slip, there is also an imbalance between the energy accumulated and released in the interseismic period considered according to the historical seismicity. This indicate that the rupture of small asperities (areas that release high slip during earthquakes) may have a complex pattern of recurrence and do not fully affect a locked patch. Locking-derived tsunami scenarios represent well tsunami observations of earthquakes that ruptured a locked seismic gap, and they can be used in addition to the actual methodologies to improve the estimation of tsunami hazard.

Postseismic geodetic signature of cold forearc mantle in subduction zones

A sharp thermal contrast between the cold forearc and the hot arc and backarc is considered fundamental to various subduction-zone processes. However, direct observational evidence for this contrast is rather limited. If this contrast is present, it must cause a rheological contrast in the mantle wedge: elastic in the forearc and viscoelastic in the arc and backarc for the timescale of earthquake cycles. Here we demonstrate that postseismic deformation following large subduction earthquakes provides independent evidence for the thermally controlled rheological contrast. Specifically, we show that seaward postseismic motion is deflected upward at the edge of the cold forearc mantle wedge, causing diagnostic uplift just seaward of the volcanic arc. From numerical simulations of postseismic deformation following the 2011 moment magnitude (Mw) 9 Tohoku-oki, 2010 Mw 8.8 Maule, 2007 Mw 8.4 Bengkulu and 1960 Mw 9.5 Chile earthquakes, together with a global synthesis of postseismic uplift measurements, we find that cold forearc mantle is present irrespective of the diversity in tectonic settings. Our findings also indicate that field surveys eight years after the 1960 Chile earthquake provided some of the earliest evidence for viscoelastic postseismic deformation. We suggest that the established link between long-term thermal processes and short-term earthquake cycle deformation is important to understanding subduction-zone dynamics. Deformation after large subduction earthquakes reflects the thermal contrast between the mantle wedge and its nose, according to numerical simulations and a synthesis of postseismic uplift data from subduction zones.

Variations in Apparent Stress and b Value Preceding the 2010 Mw8.8 Bio-B\xedo, Chile Earthquake

We calculated apparent stresses for 70 earthquakes (MW ≥ 5.0) occurring in the aftershock region of the 2010 MW8.8 Bio-Bío earthquake from January 1990 to September 2019. We identified that the average apparent stress was approximately 0.487 MPa between January 1990 and December 2005 and approximately 1.063 MPa within the period from January 2006 to January 2010. The latter one is 2.2-fold greater than the former, representing a significant difference as determined by a z test, with a 99% confidence level. Moreover, we analyzed the temporal evolution of the apparent stress and found that apparent stress rapidly increased from 0.43 to 1.2 MPa during the pre-event period from March 2006 to the occurrence of the Bio-Bío MW8.8 mainshock, and this increased apparent stress was found to be significant at the 98% confidence level. Furthermore, we calculated the spatial distribution of the apparent stress in the study region and observed two higher-apparent-stress regions, within one of which the epicenter of the MW8.8 event was located. On the basis of the inverse correlation between b value and stress, the temporal evolution and spatial distribution of b values were calculated and compared with those of the apparent stress. The comparison showed that the b values decreased approximately 4 years before the occurrence of the mainshock, while the apparent stress increased substantially; for the region of lower b, the apparent stress is higher, and vice versa. Therefore, the inverse correlation between b value and stress is supported by the results obtained in the present study and can be probably considered as one of the precursors to great earthquakes.

Viscoelastic relaxation of the upper mantle and afterslip following the 2014 MW8.1 Iquique earthquake

An improved understanding of postseismic crustal deformation following large subduction earthquakes may help to better understand the rheological properties of upper mantle and the slip behavior of subduction interface. Here we construct a three-dimensional viscoelastic finite element model to study the postseismic deformation of the 2014 MW8.1 Iquique, Chile earthquake. Elastic units in the model include the subducting slab, continental and oceanic lithospheres. Rheological units include the mantle wedge, the oceanic asthenosphere and upper mantle. We use a 2 ​km thick weak shear zone attached to the subduction fault to simulate the time-dependent stress-driven afterslip. The viscoelastic relaxation in the rheological units is represented by the Burgers rheology. We carry out grid-searches on the shear zone viscosity, thickness and viscosity of the asthenosphere, and they are determined to be 1017 ​Pa ​s, 110 ​km and 2 ​× ​1018 ​Pa ​s, respectively. The stress-driven afterlsip within the first two years is up to ~47 ​cm and becomes negligible after two years (no more than 5 ​cm/yr). Our results suggest that a thin, low-viscosity oceanic asthenosphere together with a weak shear zone attached to the fault are required to better reproduce the observed postseismic deformation.

Variations of the total electronic concentration in the ionosphere in seismically active region

In this work we studied the variations in the total electron concentration (TEC) obtained from measurements of the global navigation system GPS in the preparation zone for the 2010 catastrophic Chilean earthquake (Mw = 8.8) under calm background conditions at a minimum of 24 solar activity (SA) cycles. The analysis of the geodynamic activity and ionospheric TEC disturbances in the seismically active region of this catastrophic earthquake is carried out. A computational technique has been developed that can be used to study TEC variations over seismically active regions.

Riddles of the Assamese Earthquake of 1897. The Greatest Earthquake of All Greats

The Assamese earthquake occurred at the dawn of seismology and left us a few mysteries. The main mystery is the energy of the event because the nature and extent of the destruction do not correspond to modern estimates. Opinions of scientists on this issue differ significantly. From the European seismograms, Mr. Richter calculated the magnitude of the earthquake equal to MS = 8.7. Subsequently, his associates corrected the magnitude to the value MS = 8.0 [1]. Other estimates of the energy release of the earthquake are known to be 8.4 × 1018 J, 4.8 x 1019 J, and some scholars generally ascribe to Assamese, and not the Great Chilean earthquake, 1960 (1.33 × 1020 J) the laurels of the strongest earthquake in the entire history of the world. Our calculation shows figure 1.57 × 1021J. The difference in the above estimates is not just big, it is huge! What is the reason for this scatter? And was the Assamese earthquake the Greatest of all Greats?

Possible Seismo Ionospheric Anomalies before the 2016 Mw 7.6 Chile Earthquake from GPS TEC, GIM TEC and Swarm Satellites

The recent advances in space based ionospheric measurements can help to investigate seismic precursors before earthquake with multi-parameter observations and more dedicated instrumentations. In this paper, seismo ionospheric anomalies before the December 25, 2016, Mw 7.6, Chile earthquake are investigated in Total Electron Content (TEC) and Global Ionosphere Map (GIM). The temporal TEC from GPS stations and GIM show enhancement during 5- 10 days (local daytime) before main shock. Similarly, spatial TEC confirms abnormal dense cloud at LT=12h-14h on December 21, 2016, that lingers over the epicenter of Chile earthquake. On the other hand, the geomagnetic indices show Dst < -50nT of low intensity variation. Similarly, Kp > 3 on December 21, 2016 within 5-10 days before the Mw 7.6. This study emphasizes that the ionosphere anomalies may not be the possible association of earthquakes induced variation but it is due to the active storm conditions (Kp>3).

Bienestar Subjetivo ante la ocurrencia de desastres naturales. El caso del terremoto del 2010 en Chile

Bienestar Subjetivo ante la ocurrencia de desastres naturales. El caso del terremoto del 2010 en Chile

Benchmarking the Optimal Time Alignment of Tsunami Waveforms in Nonlinear Joint Inversions for the Mw 8.8 2010 Maule (Chile) Earthquake

Finite-fault models for the 2010Mw8.8 Maule, Chile earthquake indicate bilateral rupture with large-slip patches located north and south of the epicenter. Previous studies also show that this event features significant slip in the shallow part of the megathrust, which is revealed through correction of the forward tsunami modeling scheme used in tsunami inversions. The presence of shallow slip is consistent with the coseismic seafloor deformation measured off the Maule region adjacent to the trench and confirms that tsunami observations are particularly important for constraining far-offshore slip. Here, we benchmark the method of Optimal Time Alignment (OTA) of the tsunami waveforms in the joint inversion of tsunami (DART and tide-gauges) and geodetic (GPS, InSAR, land-leveling) observations for this event. We test the application of OTA to the tsunami Green’s functions used in a previous inversion. Through a suite of synthetic tests we show that if the bias in the forward model is comprised only of delays in the tsunami signals, the OTA can correct them precisely, independently of the sensors (DART or coastal tide-gauges) and, to the first-order, of the bathymetric model used. The same suite of experiments is repeated for the real case of the 2010 Maule earthquake where, despite the results of the synthetic tests, DARTs are shown to outperform tide-gauges. This gives an indication of the relative weights to be assigned when jointly inverting the two types of data. Moreover, we show that using OTA is preferable to subjectively correcting possible time mismatch of the tsunami waveforms. The results for the source model of the Maule earthquake show that using just the first-order modeling correction introduced by OTA confirms the bilateral rupture pattern around the epicenter, and, most importantly, shifts the inferred northern patch of slip to a shallower position consistent with the slip models obtained by applying more complex physics-based corrections to the tsunami waveforms. This is confirmed by a slip model refined by inverting geodetic and tsunami data complemented with a denser distribution of GPS data nearby the source area. The models obtained with the OTA method are finally benchmarked against the observed seafloor deformation off the Maule region. We find that all of the models using the OTA well predict this offshore coseismic deformation, thus overall, this benchmarking of the OTA method can be considered successful.

Maria Graham and the Chilean earthquake of 1822: contextualizing the first female-authored article in Transactions of the Geological Society

Abstract This chapter explores the background to the first female-authored article in the Transactions of the Geological Society (published in 1824) and outlines the controversy later caused by the article. The author, Maria Graham (1785–1842), has generally been assumed not to have been a geologist herself, and is therefore often excluded from discussions of women's early contributions to geology. This chapter demonstrates that this was not the case, and that Graham had a strong interest in geology and some competence in the discipline. It further situates Graham in a flourishing culture of early nineteenth-century ‘polite science’, and argues that the episode, when parsed correctly, demonstrates the perhaps surprising extent to which women were able to participate in contemporary geological enquiry and debate, even as they undoubtedly laboured under considerable disadvantages compared with their male counterparts.