Papers by Gonzalo Montalva
Bulletin of Earthquake Engineering
IEEE Access
This paper proposes crowd estimation technology to help authorities make the right decisions in t... more This paper proposes crowd estimation technology to help authorities make the right decisions in times of crisis. Specifically, deep learning models have faced these challenges, achieving excellent results. In particular, the trend of using single-column Fully Convolutional Networks (FCNs) has increased in recent years. A typical architecture that meets these characteristics is the autoencoder. However, this model presents an intrinsic difficulty: the search for the optimal dimensionality of the latent space. In order to alleviate such difficulty, we propose a dual architecture consisting of two cascaded autoencoders. The first autoencoder is responsible for carrying out the masked reconstruction of the original images, whereas the second obtains crowd maps from the outputs of the first one. In this way, our architecture improves the location of people and crowds in Focal Inverse Distance Transform (FIDT) maps, resulting in more reliable count estimates concerning a single autoencoder architecture.
Seismological Research Letters
One way to study the physical process that occurs behind earthquakes and how they affect differen... more One way to study the physical process that occurs behind earthquakes and how they affect different sites depending on the source type and the geological structure of the site is the shape of the Fourier spectrum. A parameter related to the shape of the spectrum is the spectral decay factor—kappa (κ), which characterizes how the amplitude of the Fourier acceleration spectrum decays at high frequencies. The parameter κ can be important in the characterization and estimation of the surface seismic demand, being useful in, for example, the adjustment of ground-motion prediction equations. We calculate the values of κ and its site component κ0 from 36 seismic stations of the National Seismological Network of Chile to determine the dependence that this parameter has to the site conditions as well as to the properties of the path in which greater values of κ are observed for subduction earthquakes that occur in the interface between the Nazca and the South American plates, compared with t...
Geotechnical, geological and earthquake engineering, 2022
Remote Sensing
Coastal areas concentrate a large portion of the country’s population around urban areas, which i... more Coastal areas concentrate a large portion of the country’s population around urban areas, which in subduction zones commonly are affected by drastic tectonic processes, such as the damage earthquakes have registered in recent decades. The seismic cycle of large earthquakes primarily controls changes in the coastal surface level in these zones. Therefore, quantifying temporal and spatial variations in land level after recent earthquakes is essential to understand shoreline variations better, and to assess their impacts on coastal urban areas. Here, we measure the coastal subsidence in central Chile using a multi-temporal differential interferometric synthetic aperture radar (MT-InSAR). This geographic zone corresponds to the northern limit of the 2010 Maule earthquake (Mw 8.8) rupture, an area affected by an aftershock of magnitude Mw 6.8 in 2019. The study is based on the exploitation of big data from SAR images of Sentinel-1 for comparison with data from continuous GNSS stations. W...
Pattern Recognition and Tracking XXXIII
Earthquake Spectra, 2022
This article describes a liquefaction database that contains a summary of 209 liquefaction, non-l... more This article describes a liquefaction database that contains a summary of 209 liquefaction, non-liquefaction, and marginal case histories compiled from the 2010 Mw 8.8 Maule, 2014 Mw 8.2 Iquique, 2015 Mw 8.3 Illapel, and 2016 Mw 7.6 Melinka earthquakes, where the liquefaction phenomenon caused damage to buildings, bridges, roads, and drainage systems, generating millions in losses at the infrastructure level. The database structure is organized into nine main tables that contain site information, geotechnical tests, and seismic parameters. The main tables include the locations of the sites, surface evidence of liquefaction or absence of them, geotechnical parameters from boreholes, and geophysical and laboratory tests. The database contains 7977 m of standard penetration test logs and 390 m of cone penetration test soundings from 209 sites explored. In addition, the seismic parameters of these earthquakes include ground-motion intensity measures estimated for each site. The informat...
Soil Dynamics and Earthquake Engineering, 2019
Due to the unique subsoil conditions prevailing in the Mexico City basin, seismic risk has been s... more Due to the unique subsoil conditions prevailing in the Mexico City basin, seismic risk has been strongly correlated to site effects. Thus, during the Mw 8.1 09/19/1985 subduction fault earthquake, and its strong aftershock Mw 7.5 09/21/1985, extensive damage was observed in the area, along with the loss of thousands of lives, despite these events had an epicentral distance of around 430 km from Mexico City. The observed damage was mostly due to site affects originated by the high plastiCity clay deposits found in the basin, which lead to large amplifications, and duration elongation of the ground motions coming from the epicenter. In addition, a frequency content modification occurs, which in turn, leads to a double resonance effect between the incoming ground motions, soil deposits, and the damaged buildings. Exactly 32 years after this devastating event, the Mw 7.1 09/19/2017 normal fault earthquake, reminded us of the importance of accounting for site effects, and most importantly the need to carry out a proper characterization of basin geometry, soil profile configuration, hydraulic conditions, and maintenance-structure periodic assessments of the building stock in Mexico City. This is required to reduce uncertainties of seismic vulnerability studies for extreme-event seismic hazard scenarios. In this paper, the role of site response and seismic soil-structure interaction as key factors responsible of the observed damage in the City is revisited, through series of 3D finite difference models of typical structure-foundation-soil typologies found at the areas where most of the damage was observed, highlighting its clear impact in the final damage distribution observed around the City.
2021 IEEE 4th 5G World Forum (5GWF), 2021
Seismological Research Letters, 2021
Time-dependent earthquake forecast depends on the frequency and number of past events and time si... more 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 r...
GeoFlorida 2010, 2010
In this work a random field model for shear‐wave velocity profiles is presented. This model is co... more In this work a random field model for shear‐wave velocity profiles is presented. This model is compared with an existing model. Their relative merits in terms of their validity for use in site response analyzes are evaluated. A large database of site profiles from sites in Japan is used to calibrate the parameters of the random field models. Randomly generated profiles using both random field models are generated and compared with measured profiles. The uncertainties associated with the shear wave velocity measurements (ie epistemic ...
Earthquake Spectra, 2012
Soil liquefaction occurred at many sites during the 2010 Maule, Chile, earthquake, often leading ... more Soil liquefaction occurred at many sites during the 2010 Maule, Chile, earthquake, often leading to ground failure and lateral spreading. Of particular interest are the effects of liquefaction on built infrastructure. Several buildings were damaged significantly due to foundation movements resulting from liquefaction. Liquefaction-induced ground failure also displaced and distorted waterfront structures, which adversely impacted the operation of some of Chile's key port facilities. Important case histories that document the effects of ground failure on buildings, ports, and industrial facilities are presented in this paper.
Earthquake Spectra, 2010
The Mw 8.4 23 June 2001 Southern Peru earthquake generated intense ground motions in a large regi... more The Mw 8.4 23 June 2001 Southern Peru earthquake generated intense ground motions in a large region encompassing southern Peru and northern Chile. The earthquake was recorded by seven strong motion stations with peak ground accelerations ranging from 0.04 g to 0.34 g for site-to-fault distances ranging from about 70 km to 220 km. At this time, there are no other strong motion records for an earthquake of this magnitude. Hence, the strong motion data set from this earthquake is unique and of particular interest to engineers dealing with seismic design in subduction regions. This paper presents an engineering analysis of the strong motion records. Shear-wave velocity profiles were measured using Spectral Analysis of Surface Waves methods at four stations. Measured shear-wave velocities are high, indicating that all sites classify as stiff soil sites (Site C) according to the International Building Code classification scheme. The strong motion set is characterized by strong high freque...
Bulletin of the Seismological Society of America, 2011
Abstract Estimates of single-station standard deviation can be used as a lower bound to probabili... more Abstract Estimates of single-station standard deviation can be used as a lower bound to probabilistic seismic hazard analyses that remove the ergodic assumption on site response. This paper presents estimates of single-station standard deviation using data from the KiK-net network. The KiK-net network has a dense array of stations that recorded a large number of earthquakes over the period of study, both at the surface and at colocated borehole instruments. The large number of records implies that there are a large number of stations ...
Earthquake Spectra, 2012
A set of observations on site effects and damage patterns from the Mw8.8 Maule, Chile, earthquake... more A set of observations on site effects and damage patterns from the Mw8.8 Maule, Chile, earthquake is presented, focusing on identification of structural damage variability associated with nonuniform soil conditions and subsurface geology. Observations are reported from: (1) the City of Santiago de Chile (Américo Vespucio Norte Ring Highway, Ciudad Empresarial business park), (2) the Municipality of Viña del Mar, and (3) the City of Concepción, extending over 600 km along the Chilean coast. Reconnaissance information and ground motion recordings from the megathrust event are combined with site investigation data in the regions of interest. Comparisons against macroseismic observations related to uneven damage distribution from the Mw8.0 1985 Valparaíso earthquake are discussed. Complexities associated with identifying the mechanics and underlying physical processes responsible for the manifestation of these effects are elucidated.
DESCRIPTION GEER recconnaissance report for the 2014 Iquique Earthquake, Chile
Resumen Este artículo presenta un resumen de las observaciones realizadas durante un reconocimien... more Resumen Este artículo presenta un resumen de las observaciones realizadas durante un reconocimiento de los efectos geotécnicos del sismo de Pisco ocurrido el 15 de agosto del 2007 en la zona central de la costa del Perú. Este sismo de magnitud (Mw) 8.0 causó daños importantes a obras de ingeniería civil en una amplia zona que incluye las ciudades de Ica, Pisco, Cañete y Chincha. Desde una perspectiva geotécnica, los aspectos más relevantes de este sismo son la gran extensión de licuación de suelo observada en la zona ...
Single station sigma allows for a more realistic estimation of expected seismic demand. The use o... more Single station sigma allows for a more realistic estimation of expected seismic demand. The use of single-station sigma in a non-ergodic Probabilistic Seismic Hazard Analsyis framework avoids the double counting of uncertainties and allows for the more rigorous incorporation of site and path effects into hazard estimations. We present a ground motion prediction model (GMPE) developed from a catalogue that includes Chilean interplate and inslab events. The model is used to evaluate the quantity of uncertainty that can be attributed to source, path, site effects, and what can be treated as pure aleatory uncertainty. Our results show remarkable agreement with other studies in some components of the overall uncertainty, but differences in other components, which shed light into the areas that could be advanced in the future. Site characterization and prediction of Vs30 through proxies represent a key challenge and where leap improvement can be achieved.
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Papers by Gonzalo Montalva