Sergio Ruiz

University of Chile · Departamento de Geofísica

The subduction zone in northern Chile is a well-identified seismic gap that last ruptured in 1877. The moment magnitude (Mw) 8.1 Iquique earthquake of 1 April 2014 broke a highly coupled portion of this gap. To understand the seismicity preceding this event, we studied the location and mechanisms of the foreshocks and computed Global Positioning Sy...

We perform kinematic and dynamic inversion of the 24 July 2008 (M-w 6.8) Northern Iwate intermediate depth earthquake in Japan using strong-motion records from the K-NET and KiK-net networks. The rupture of this moderate magnitude earthquake is modeled as a simple elliptical patch. The optimal solutions are found comparing observed and synthetic re...

The 2010 Maule earthquake is one of the largest events ever recorded with modern instruments. We used the continuous GPS (cGPS) records to invert for the kinematic rupture process using an elliptical sub-patch approximation. In agreement with previous inversions, the largest slip is found in the northern part of the rupture zone. By cross-correlati...

1] We perform a full dynamic inversion at low frequencies of the 16 December 2007 (Mw = 6.7) northern Chile earth-quake that we model as a simple elliptical patch. We use two different stress‐friction end‐member models: asperities and barriers, finding similar results. The inversions are per-formed for strong motion data filtered between 0.02 and 0...

No large tsunamigenic earthquake has occurred in north Chile since 1877 and the region has been largely recognized as a mature seismic gap. At the southern end of the seismic gap, the 2007 Mw7.7 Tocopilla earthquake ruptured the deeper seismogenic interface, whereas the coupled upper interface remained unbroken. Seismological studies onshore show a...

This study reveals the seismic signature of the 1973 Chilean coup d’état by analyzing historical paper seismograms from September 1973. The continuous traces of the seismic activity preceding, during, and after the military coup were recorded by a Teledyne Geotech seismometer installed near (∼2 km) the presidential palace La Moneda. Our analysis re...

This study reveals the seismic signature of the 1973 Chilean coup d'état by analyzing historical paper seismograms from September 1973. The continuous traces of the seismic activity preceding, during, and after the military coup were recorded by a Teledyne Geotech seismometer installed near (∼2 km) the presidential palace La Moneda. Our analysis re...

For more than two decades, Chile’s National Seismological Center has produced a seismic catalog built by manual reading of first-arrival P and S waves recorded by local and regional stations. This catalog helped improve the knowledge regarding the Chilean subduction zone and contains several important earthquake sequences. The density of stations,...

Multiple automated tools for picking and locating seismic events have been developed in recent years to process large volumes of data and rapidly obtain extensive seismic catalogs. Here we present a Deep Learning-based seismic phase picker with a high detection rate that can correctly pick and identify phase arrivals, especially at a low signal-to-...

Large earthquakes can cause significant seismic demands, which may result in extensive damage, but also can cause non-linear soil behavior that limits the site response. We analyzed time windows of strong ground motion records of the 2011 Mw 9.1 Tohoku Earthquake and found a clear relationship between decreases in the site's predominant frequency,...

Understanding the lithological control of crustal faults near cities is important for assessing the seismic hazard and characterising complex fault systems. We studied the Mejillones Fault (MF), located near one of the strategic ports in northern Chile. The MF is an active geological fault that extends 40 km in the N-S direction and is part of an e...

Anticipating volcanic eruptions remains a challenge despite significant scientific advancements, leading to substantial human and economic losses. Traditional approaches, like Volcano Alert Levels (VAL), provide current volcanic states but do not always include eruption forecasts. Machine learning (ML) emerges as a promising tool for eruption forec...

Three-dimensional physics-based numerical simulations (3D-PBS) of the seismic response of the Santiago Basin, Chile, were performed considering a large-scale velocity model and shallow crustal earthquake scenarios, associated with the west-verging thrust San Ramón Fault. Numerical results show that competent gravelly soils in the center of the basi...

The Southern Patagonian Icefield (SPI) lies above an area of slow convergence between Antarctic and South-America plates, where limited seismicity is recorded by global or regional seismic networks. To understand the seismic behavior of this zone, we analyze two years of continuous broad-band data recorded by 27-seismometers, deployed around the SP...

In subduction zones, the forearc crust transitions from a highly fractured wedge near the trench to a less fractured basement near the volcanic arc. Here we study the role of wedge integrity on the frequency content of strong ground motion produced by subduction earthquakes in Northern Chile. Our data includes aftershocks from the 2014 Mw 8.1 Iquiq...

This paper reports the results of 1D and 2D dynamic numerical simulations of a cross section on fine-grained soils in the north of the Santiago Basin, Chile. The seismic response of the cross section was evaluated in scenarios with the materials modeled with both a linear elastic model and the non-linear Hardening Soil Small (HSS) model. The seismi...

Seismic data collected before volcanic eruptions holds important clues for forecasting future eruptions. However, many volcanoes have short monitoring histories or have infrequent eruptions. Here, we aim to enhance volcanic eruption forecasting through machine learning, tackling challenges in generalizing eruption precursors across diverse volcanoe...

Large intraplate intermediate-depth (IID) events are the most destructive to Chilean structures and they occurred throughout the country. Cities located above the hypocenters of these large earthquakes have been completely destroyed. In recent years, only small- and moderate-magnitude IID events have been reported below Santiago, the most populated...

We use continuous and survey GNSS data to image the spatial and temporal evolution of afterslip during the 2 months following the Mw 8.3 2015 Illapel earthquake. Our approach solves for the incremental daily slip at the subduction interface using nonnegative least squares with spatial and temporal Laplacian regularization constraints. We find that...

Earthquake swarms commonly occur along the Chilean subduction zone, witnessing fast seismic and slow aseismic slip behavior at the plate interface. However, the largest seismic swarms observed in Chile, particularly in the Copiapó-Atacama region, remain poorly documented, and the underlying processes have yet to be understood. Here, we perform seis...

Four years ago, using survey GPS measurements, the first deep slow slip event (SSE) was detected in Chile (near Copiapó, Atacama region), unrelated to any major earthquake. It was located between 40 and 60 km depth on the subduction interface, lasted approximately 18 months (2014-2016.5) and reached an equivalent magnitude of Mw~6.9. The single per...

El volcán Láscar (23°22'S-67°44'O) es el volcán más activo del norte de Chile, ubicado en la Región de Antofagasta. En este trabajo, utilizando la sismicidad volcano-tectónica ocurrida entre marzo y julio del 2018 registrada por una red temporal conformada por 10 estaciones sismológicas, se construyó un modelo tomográfico 2D de Vp y razón Vp/Vs con...

Four years ago, using survey GPS measurements, the first deep slow slip event (SSE) was detected in Chile (near Copiapó, Atacama region), unrelated to any major earthquake. It was located between 40 and 60 km depth on the subduction interface, lasted approximately 18 months (2014–2016.5) and reached an equivalent magnitude of Mw 6.9. The single per...

Los estudios relacionados a la sismicidad en la placa superior en la región de Coquimbo son escasos, considerando importantes fallas geológicas en el sector. Una de estas fallas es la denominada Puerto Aldea al suroeste de la ciudad de Tongoy. Esta estructura de orientación norte-sur tiene una extensión en planta aproximada de 60 km, y de acuerdo a...

We study the 2020 Mw 6.8 Calama earthquake sequence that occurred within the subducting oceanic Nazca plate. The mainshock is modeled via waveform inversion using a dynamic rupture model, while detection and location techniques are used to better characterize its aftershock sequence. We analyze the local seismotectonic and thermal context of the su...

Results from an ambient noise tomography, gravimetric studies, and local geophysical surveys are combined to develop three representative cross-sections of the Santiago Basin, Chile, that include the main geological features and the wave velocities of the materials. One-dimensional (1D) and two-dimensional (2D) seismic responses were simulated for...

On 10 September, 2008, an Mw 5.7 earthquake occurred under the Central Valley of northern Chile near the town of Pica at a depth of ∼33 km within the continental crust of the South America plate. We find this earthquake to be a high stress‐drop, reverse‐oblique event that generated unusually high ground accelerations of up to 0.67g. Overall, its ob...

We study the 2020 MW 6.8 Calama earthquake sequence that occurred within the subducting oceanic Nazca plate. The mainshock is modeled via waveform inversion using a dynamic rupture model, while detection and location techniques are used to better characterize its aftershock sequence. We analyze the local seismotectonic and thermal context of the su...

We study the 2020 MW 6.8 Calama earthquake sequence that occurred within the subducting oceanic Nazca plate. The mainshock is modelled via waveform inversion using a dynamic rupture model, while detection and location techniques are used to better characterize its aftershock sequence. We analyze the local seismotectonic and thermal context of the s...

In the South‐Central Andes, the crustal structures driving the tectonic evolution of the Andean Cordillera remain unresolved. So far, most seismological studies focused on the subduction interface, leaving crustal seismicity and its relationship with crustal deformation and Andean volcanism mostly unconstrained. However, because of their large numb...

On 16 September 2015, the Mw 8.3 Illapel megathrust earthquake broke the subduction contact of the Nazca plate beneath the South American plate, causing unexpectedly high tsunami waves that strongly impacted the coast along the Coquimbo region in central–northern Chile. Here, we report results from a postearthquake and tsunami survey, evidencing a...

We studied the along-dip influence of the Copiapó ridge subduction in the Atacama region, North-Central Chile by building a new seismicity catalog, including similar events and non-volcanic tremors (NVTs). We also obtained a 3-D tomographic model for P- and S-waves velocity (and the implied Vp/Vs ratio). We identify down-dip segmentation involving...

We studied the along-dip influence of the Copiapó ridge subduction in the Atacama region, North-Central Chile by building a new seismicity catalog, including similar events and non-volcanic tremors (NVTs). We also obtained a 3-D tomographic model for P- and S-waves velocity (and the implied Vp/Vs ratio). We identify down-dip segmentation involving...

Understanding the extensional processes in tectonic context at the transition from continental to oceanic spreading is fundamental to obtain new insights about formations of new oceans. To that scope, we study a large and long‐lived earthquake swarm occurring in 2020–2021 in a back‐arc rift (the Bransfield Basin) south of the South Shetland Islands...

Dehydration of the oceanic subducting slab promotes the formation of magmatic arcs, intra-slab intermediate-depth seismicity, and hydration of the overlying mantle wedge. However, the complex permeability structure of the overriding plate controls the magma and fluid migration and their accumulation at shallower depths. In this regard, mapping the...

The 22 May 1960 Mw 9.5 Valdivia megathrust earthquake, with a rupture length close to 1000 km in the central–south Chile, is the largest recorded earthquake in the modern times. The city of Valdivia is located about 300 km south of the northern boundary of the rupture in front of one of the largest asperities of the earthquake. In this article, we...

An earthquake sequence occurred in the Atacama region of Chile throughout September 2020. The sequence initiated by a mainshock of magnitude Mw6.9, followed 17 hours later by a Mw6.4 aftershock. The sequence lasted several weeks, during which more than a thousand events larger than Ml 1 occurred, including several larger earthquakes of magnitudes b...

An earthquake sequence occurred in the Atacama region of Chile throughout September 2020. The sequence initiated by a mainshock of magnitude Mw6.9, followed 17 hours later by aMw6.4 aftershock. The sequence lasted several weeks, during which more than a thousand events larger than Ml 1 occurred, including several larger earthquakes of magnitudes be...

During the 2016–2017 Central Italy earthquake sequence, a series of moderate to large earthquakes M > 5 occurred near the Amatrice and Norcia towns. These events are recorded on a dense seismic network, providing relevant observational evidence of complex earthquakes in time and space. In this work, we used this substantial data set to study the gr...

On 3 March 2020, the first case of COVID-19 was confirmed in Chile. Since then, the Ministry of Health has imposed mobility restrictions, a global policy implemented to mitigate the propagation of the virus. The national seismic network operating throughout Chile provides an opportunity to monitor the ambient seismic noise (ASN) and determine the e...

We apply kinematic and dynamic modeling to the 2015 Mw8.3 Illapel, Chile, earthquake constrained by continuous high‐rate GPS and strong motion data. Kinematic inversion by elliptical patches allows us to rapidly outline the ruptured area with different time windows and frequency ranges. The preferred solution indicates that the main large patch in...

We studied the broad-band spectra of the 8 largest earthquakes that have occurred in Chile in the last 25 years using strong-motion records and 1-Hz high-rate GNSS (cGNSS) data. To avoid the numerical instability problem with the double integration of the accelerograms, we computed velocity spectra integrating the acceleration time series in the sp...

We perform kinematic and dynamic source inversions of four interplate thrust earthquakes that occurred near the trench at the base of the continental wedge in Northern Chile and we compare them to deeper intraplate events. The magnitudes of these interplate events were between Mw 6.3 and Mw 6.5, with hypocentral depths varying between 17.8 km and 2...

The region around the Mejillones Peninsula is characterized by major onshore and offshore fault systems. The existence of major splay faults in these fault systems has been debated. To improve our undestanding of seismotectonic processes affecting the MP, we built a new catalog of aftershocks of the 1995 Antofagasta earthquake (Mw 8.1) recorded by...

On 3 March 2020, the first case of COVID-19 was confirmed in Chile. Since then, the Ministry of Health has imposed mobility restrictions, a global policy implemented to mitigate the propagation of the virus. The national seismic network operating throughout Chile provides an opportunity to monitor the ambient seismic noise (ASN) and determine the e...

The seismic response of the Santiago City, the capital of Chile with more than 5.5 million inhabitants, is controlled by the properties of the shallower quaternary deposits and the impedance contrast with the underlying Abanico formation, among other factors. In this study, we process continuous records of ambient seismic noise to perform an ambien...

We investigate the variations of the seismic source properties and aftershock activity using kinematic inversions and template-matching, for six large magnitude intermediate-depth earthquakes occurred in northern Chile. Results show similar rupture geometry and stress drop values between 7–30 MPa. Conversely, aftershocks productivity systematically...

Seismicity along subduction interfaces is usually dominated by large mainshock-aftershocks sequences indicative of a continuum distribution of highly coupled large asperities. In the past decades, however, the increased resolution of seismic catalogues at some subduction zone seems to indicate instead a more complex rheological segmentation of the...

The Magallanes-Fagnano fault (at ~52-55ºS) is a continental NW-SE transform fault zone that marks the boundary between the South American Plate (north) and the Scotia Plate (South). In 1949, two crustal seismic events of estimated magnitude M>7 were located in this area using teleseismic records. Although, this region is scarcely populated, such sh...

The Santiago City is located in Central Chile on a sedimentary basin, whose seismic response is controlled by the properties and geomorphology of the shallower quaternary deposits, as well as the impedance contrast with the underlying geological formations, among other factors. In this study, we built three representative two-dimensional (2D) cross...

The intra‐arc Liquiñe‐Ofqui Fault System (LOFS) is an active transpressive fault zone located in the Patagonian Andes of Chile. In 2007, a seismic sequence occurred in the Aysén Fjord region of Chilean Patagonia along the LOFS, with a Mw 6.2 main earthquake that triggered dozens of landslides, some of which induced tsunami waves that caused severe...

The third sentence in the Acknowledgments section, “Support for J. Mieres Madrid to visit OSU and SIO was provided by CONICYT/FONDECYT grant 11170047(Un. Chile; J. Ruiz and E. Contreras-Reyes),” should be replaced by the three sentences below. Support for JMM to visit OSU and SIO was provided by grant CHILE-USA2002 (CONICYT), to E. Contreras-Reyes...

One of the most notable seismic sequences in modern times was recorded in May 1960 along the southern Chilean subduction zone. The sequence started on 21 May with the Mw 8.1 Concepción earthquake; 33 hr later the Mw 9.5 Valdivia megathrust earthquake occurred, the largest ever recorded in the instrumental period. These events changed the geomorphol...

To investigate the dynamic response of the outer accretionary prism updip from the patch of greatest slip during the 2010 Mw 8.8 Maule earthquake (Chile), 10 ocean-bottom seismometers (OBSs) were deployed from May 2012 to March 2013 in a small network with an inter-instrument spacing of 7–10 km. Nine were recovered, with four recording data from in...

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 precedi...

The Juan Fernandez Islands (JFI) are located in the Pacific Ocean 675 km west of the Chilean coast. This archipelago has historically been affected by large tsunamis. Robinson Crusoe Island (RCI), the main island of the JFI, was first inhabited in 1749. Since then, several tsunamis have destroyed RCI port structures and sometimes caused deaths. Gro...

Most of the recorded seismicity in central Chile can be linked to the subduction of the Nazca Plate. To the east, a much smaller fraction is observed at 0-30 km depths beneath the western Andean thrust. Paleoseismic studies evidenced the occurrence of at least two major earthquakes (M ≥ 7) over the past 17 kyr, associated with the San Ramón fault:...

On 20 January 2019, Coquimbo and La Serena cities (central Chile) were shaken by an intraplate earthquake of Mw 6.7 located at 70 km depth. High PGA values and macro-seismic intensities were reported. The mainshock was followed by more than 150 aftershocks higher than M L 2.5, a seismic sequence completely recorded by local stations. Using a 3D vel...

In southern Chile, at ˜46:2°S and ˜75:2°W, the active spreading center between the Nazca and Antarctic plates is colliding with the South American plate, forming the Chile triple junction (CTJ). For 1 yr, from March 2009 to February 2010, five ocean-bottom seismometers (OBSs) were deployed over the CTJ. We used a portion of the OBS data to study th...

La cuenca de Santiago presenta una geometría compleja sobre la que habitan más de 6 millones de personas, presentando sectores con altos contrastes de impedancia entre el suelo y la roca basal que pueden evidenciar el fenómeno de efecto de sitio. En particular, en la zona noroeste de la cuenca se han observado daños severos para los terremotos de V...

We have studied the spectra of large subduction earthquakes in Chile at short epicentral distances. In this work we concentrate on the Mw 8.2, Iquique earthquake of 1 April 2014. For such a large event, in most stations we cannot separate P and S waves; which arrive very close together and interfere to produce the static displacement field. We find...

Destructive megathrust earthquakes, such as the 2015 Mw 8.3 Illapel event, frequently affect Chile. In this study, we assess the damage of the 2015 Illapel Earthquake in the Coquimbo Region (North-Central Chile) using the MSK-64 macroseismic intensity scale, adapted to Chilean civil structures. We complement these observations with the analysis of...

The Mw 8.8 Maule earthquake occurred in Central Chile is the largest event recorded instrumentally since Mw 9.5 Valdivia 1960 mega-thrust earthquake. Many authors obtained rupture models for this earthquake using low-frequency data providing a general image of its kinematic rupture. The high-frequency domain is poorly constrained. The seismic ruptu...

Recent studies have proposed that nucleation zones, seismic barriers and high-slip patches of megathrust earthquakes correlate with physical heterogeneities, both in the oceanic/subducting plate and in the continental wedge. We present a density-depth model along the Nazca-South America subduction margin, from 18°S to 23°30'S, where a partial segme...

Forecasting surface seismic intensities is the main objective of much of the research in seismic engineering. The seismic demand for tall buildings, bridges, and wind farms, and other existing ‘slender’ structures is predominantly at low frequencies, and are usually outside the range of the design spectra prescribed by codes. This article presents...