Etienne Bertrand

• PhD, HDR
• Directeur de Recherche at Gustave Eiffel University

As a contribution to step 3 of the ESG6 blind prediction exercise, we present an application of two different, purely empirical approaches to estimate the strong ground motion at a soft site ("KUMA") from the observed ground motion at a reference rock site ("SEVO") for the two largest shocks of the Kumamoto 2016 sequence. The two methods estimate t...

This research investigates the convenience of structural identification tools to detect the rocking motion tendency, using as input the structural response to ambient vibrations. The rocking ratio and rocking spectrum are proposed as original tools to highlight the rocking motion and its frequency content. The proposed procedure allows the detectio...

As a contribution to step 3 of the ESG6 blind prediction exercise, we present an application of two different, purely empirical approaches to estimate the strong ground motion at a soft site ("KUMA") from the observed ground motion at a reference rock site ("SEVO") for the two largest shocks of the Kumamoto 2016 sequence (a foreshock with Mj=6.5, a...

We use two different purely empirical approaches to estimate the non-linear transfer function between a reference rock and a sedimentary site from recordings of weak ground motions and site-condition proxies. The modulus of the linear transfer function is first computed from weak motions and then modulated with a correction to consider non-linear s...

The presence of topography influences the seismic ground motion and may result in strong amplifications, generally at the top of hills and reliefs. The increasing urbanization of hills requires an accurate estimation of these effects even in areas of moderate seismicity. The simplified coefficients provided by the Eurocodes8 do not depend on the fr...

The presence of topography influences the seismic ground motion and may result in strong amplifications, generally at the top of hills and reliefs. The increasing urbanization of hills requires an accurate estimation of these effects even in areas of moderate seismicity. The simplified coefficients provided by the Eurocodes8 do not depend on the fr...

In 1906, an earthquake with a magnitude estimated between Mw 8.4 and 8.8 occurred in the subduction zone along the coast of Ecuador and Colombia. This earthquake caused extensive damage on the coast but had a rather small impact on the capital city of Quito, situated 180 km away. At that time, the city of Quito extended over a small area with a few...

The Le Teil earthquake (south France, 11 November 2019, Mw 4.9, 1 km depth, about 4 km of surface rupture) was felt at a distance up to about 300 km. We estimate the EMS98 intensity in each of the affected localities by collecting macroseismic observations via both individual forms, filled in by citizens (2094 testimonies), and collective forms, fi...

We report here an interesting case study of dynamic characterization of a limestone sea cliff area, named the Sutta-Rocca overhang, located near the medieval town of Bonifacio (southern Corsica, France). The site belongs to an UNESCO protected area with an important number of visitors per year. Therefore, it is of particular interest to evaluate th...

Earthquake risk reduction approaches classically apply a top-down model where scientific information is processed to deliver risk mitigation measures and policies understandable by all, while shielding end-users from the initial, possibly complex, information. Alternative community-based models exist but are rarely applied at a large scale and rely...

On November 11, 2019, a Mw 4.9 earthquake hit the region close to Montelimar (lower Rhône Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude, and the moderate to...

On November 11, 2019, a Mw 4.9 earthquake hit the region close to Montelimar (lower Rhône Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude, and the moderate to...

In seismic hazard studies, site effects assessment is based on an accurate knowledge of mechanical properties and geometry of superficial geological formations. The Lower Var Valley (Nice, southeastern France) is a 2 km wide fluvial sedimentary basin where site effects have been observed on earthquake recordings. In addition, this area is a signifi...

Following the Teil earthquake (ML5.2, Io VII-VIII), the French Central Seismological Office and National Seismic Monitoring Network (BCSF-RéNaSS) mobilised urgently via the Macroseismic Intervention Group (GIM) to estimate the macroseismic intensities (EMS98 scale) in the epicentral zone. It is made up of personnel from various organisations: Unive...

We are testing three different approaches to assess the site effects based on 1D soil column data. The first method follows the Eurocodes 8 (EC8) approach based on the determination of Vs30 soil classes, the second one is based on an empirical relationship between Vs30 and the fundamental resonance frequency of the site (f0) with a response spectra...

We evaluate the non-linear site response at the stations of the Japanese Kik-Net network by computing the ratio between the Fourier spectra of the recordings at the surface and at the downhole station. When the amplitude of the input signal increases, we observe a shift of the resonance peaks towards lower frequencies, characteristic of non-linear...

A network of “personal seismometers” is intended to complement Haiti’s national seismic network to engage and inform residents about earthquake hazards and preparation.

Complex networks of high-tech sensors are tough to operate and maintain in developing countries – but new low-costs, low-maintenance instruments may help. Because they are “connected objects” they also provide new opportunities to engage the civil society in citizen-science. Here we describe a seismological instrumentation experiment in Haiti with...

Complex networks of high-tech sensors are tough to operate and maintain in developing countries – but new low-costs, low-maintenance instruments may help. Because they are “connected objects” they also provide new opportunities to engage the civil society in citizen-science. Here we describe a seismological instrumentation experiment in Haiti with...

Lebanon is situated on the 1000 km long Levant transform fault that separates the Arabic from the African tectonic plates. In Lebanon, the Levant fault splits up into a set of ramifications that had, in the past, generated major destructive earthquakes causing a lot of destruction and thousands of casualties. The most devastating one was the 551 A....

Seismic ground motion is strongly dependent on the site geotechnical characteristics. This phenomenon must be considering in risk mitigation through the evaluation of soil response. The soil response to a cyclic solicitation is not only depending on the soil parameters but also on the level of the shaking. This non-linear behavior is especially imp...

Because of its geodynamic context, its extreme geography (transition from a deep basin to high mountains in less than 80 km), its concentration of stakes (human, urban centers, economic), combining to the increase of the coastal population density, the french Riviera forms an ideal laboratory to study natural hazards and risks. This is particularly...

This article presents the main results of the validation phase of the PRENOLIN project. PRENOLIN is an international benchmark on 1D nonlinear (NL) site‐response analysis. This project involved 19 teams with 23 different codes tested. It was divided into two phases; with the first phase verifying the numerical solution of these codes on idealized s...

A two-year seismological experiment in Rognes (South Eastern France) confirms the site effects responsible for the severe damage experienced during the 1909 Provence earthquake. Many experimental and numerical studies have been dedicated to quantify and understand the effect of topography on seismic ground motion. However, these local amplification...

Quito, the capital city of Ecuador, with a population close to three million inhabitants, is located in an earthquake-prone region that has been struck by important events in the past. The city is built on the hanging wall of an active reverse fault, constituting a piggy-back basin filled with volcanic and fluvial origin deposits. To date, the Quit...

The structural motion of a tall reinforced concrete (RC) building on alluvial soil in Nice (France) is continuously recorded using accelerometers. The structural behavior of the building is studied using operational modal analysis (OMA) to identify its dynamic properties, a finite element (FE) model to reproduce the building response, and empirical...

Seismic ground motion is strongly dependent on the site geotechnical characteristics. This phenomenon must be taking into account in risk mitigation through the evaluation of soil response. The soil response to a cyclic solicitation is not only depending on the soil parameters but also on the level of the shaking. This non-linear behavior is especi...

Amplification of the seismic ground motion is often observed in presence of strong topography or in sedimentary basins in which the seismic waves are trapped. The study of site effects can be achieved by the analysis of seismological recordings. Measurement campaigns at specific sites allowed highlighting high amplification for some frequencies but...

The city of Quito has been damaged several times in the past by important earthquakes. The seismic hazard assessment is thus an important issue and especially, the site effect question. The Quito basin deep structure remains unknown and the potential impact of seismic waves has yet to be evaluated. The National Accelerometric Network (RENAC) that b...

PREdiction of NOn-LINear soil behavior (PRENOLIN) is an international benchmark aiming to test multiple numerical simulation codes that are capable of predicting nonlinear seismic site response with various constitutive models. One of the objectives of this project is the assessment of the uncertainties associated with nonlinear simulation of 1D si...

The Pedernales Mw7.8 earthquake that occurred on the subduction interface between the Nazca plate and the Southamerican plate on April 16th 2016 caused extensive damages to several coastal cities of Ecuador. The event was well recorded by a large number of accelerometric stations both in the near field and all over the country. A total of 62 record...

To provide better insight into seismic ground motion in the Port-au- Prince metropolitan area, we investigate site effects at 12 seismological stations by analyzing 78 earthquakes with magnitude smaller than 5 that occurred between 2010 and 2013. Horizontal-to-vertical spectral ratio on earthquake recordings and a standard spectral ratio were appli...

The Nice prefecture is equipped by 24 accelerometric sensors, located at different levels, which continuously record the building response. A finite element model of the building is created based in design plans and information about materials provided during the conception project. Such model is used to obtain the natural frequencies of the struct...

Analysis of ambient vibration records enables the dynamic structural behaviour identification trough Operational Modal Analysis (OMA) techniques. This study uses a set of recordings of a 22-storey Reinforced Concrete (RC) building in Nice (France), where no remarkable damages are detected since it is instrumented. Signals acquired using acceleromet...

Le projet a pour objectif l'identification des propriétés dynamiques du bâti existant à partir des enregistrements sismologiques. Une connaissance précise de ces paramètres (fréquences modales et vitesse de propagation des ondes) permet de définir empiriquement la réponse dynamique de la structure. Ces paramètres varient dans différents contextes m...

Site effects may be assessed using a standard soil classification parameter, V-S30 (the harmonic average shear-wave velocity in the first 30 m); however, this index does not account for the complexity of the velocity profile, especially its variability at depth. In the present study, in addition to V-S30, we propose consideration of the gradient of...

On April 7 th 2014, an earthquake of magnitude Mw 4.9 stroke the Ubaye valley in the French Alps. It was one of the largest events well recorded in the Alps since the damaging earthquake that occurred close to Annecy in 1996 [Courboulex et al., 1999; Thouvenot et al., 1998]. We computed its moment magnitude (Mw 4.9) and its focal mechanism that dep...

During one month, in October and November 2010, the region of Sampeyre (Western Alps, Italy) was struck by a seismic activity of several hundred events. The location of 287 events recorded at least by three stations showed a diffuse swarm ranging between 8 and 13 km depth. The number of earthquakes in the database was increased thanks to a detailed...

Following the Mw 7.3 Martinique earthquake, November 29th, 2007, a post-seismic survey was conducted by the Bureau Central Sismologique Français (BCSF) for macroseismic intensities assessment. In addition to the inventories, ambient vibration recordings were performed close to the particularly damaged zones in the free-field and the buildings. The...

This article investigates the effects of the nonlinear behavior of soils on site response, through various earthquake recordings from the KiK-net database in Japan. This network is composed of more than 688 surface-borehole instruments, from which a characterization of the shear-and compressive-wave velocity profiles down to the borehole depth is a...

We present the preliminary results of a study with the aim of understanding how some combinations of source and site effects can generate extreme ground motions in the city of Port au Prince. For this study, we have used the recordings of several tens of earthquakes with magnitude larger than 3.0 at 3 to 14 stations from three networks: 3 stations...

Les effets de site représentent un enjeu important pour la prévention parasismique, puisqu’ils peuvent aggraver considérablement les dommages lors d’un séisme. La connaissance de la réponse des sols aux séismes permet d’adapter la réglementation parasismique à ces contraintes lors de l’élaboration de microzonages et de Plan de Prévention des risque...

Site effects represent a critical challenge in the field of earthquake prevention since these effects are capable of seriously exacerbating damage whenever an earthquake strikes. Knowledge of the soil response to seismic activity allows adapting earthquake protection regulations to better incorporate these constraints during the process of defining...

Here we present first results of a joint effort undertaken in ongoing European project NERA -JRA1, which aims at establishing scientifically solid and practically acceptable propositions to incorporate surface topography effects in seismic hazard estimates. We assembled a dataset of both ambient vibration and earthquake recordings acquired at 40 Eu...

: Seismological recordings allow examining local seismicity and teleseismic events in various sites. From these data, we produce site transfer functions proving that each site has its own response. Numerical simulation is an interesting tool to understand and try reproducing these phenomena. In a previous work, we have used a discontinuous Galerkin...

This paper presents empirical correlations between amplification factors and simple site parameters derived from a large subset of the KiK-net data. The amplification factor is estimated from the ratios between the surface and down-hole horizontal response spectra, corrected for the varying depths and impedance of the down-hole sites (Cadet et al....

This paper presents empirical correlations between amplification factors and simple site parameters derived from a large subset of the KiK-net data. The amplification factor is estimated from the ratios between the surface and down-hole horizontal response spectra, corrected for the varying depths and impedance of the down-hole sites (Cadet et al....

After the 2009 April 6th Mw 6.3 L’Aquila earthquake (Central Italy) the Italian Civil Defense Department promoted the microzoning study in the ten zones in the epicentral area that suffered major damage. In this paper we present the activities and the results concerning a temporary seismic network installed in the historical L’Aquila city center in...

During the microzonation studies of the April 6th, 2009 L’Aquila earthquake, we observed local seismic amplifications in the Roio area—a plane separated from L’Aquila city center by mount Luco. Six portable, digital instruments were deployed across the plain from 15 April to mid-May 2009. This array recorded 152 aftershocks. We analyzed the ground...

The southern Alps–Ligurian basin junction is one of the most seismically active zone of the western Europe. A constant microseismicity and moderate size events (3.5 < M < 5) are regularly recorded. The last reported historical event took place in February 1887 and reached an estimated magnitude between 6 and 6.5, causing human losses and extensive...

One of the strongest historical earthquakes in France metropolitan territory occurred in 1909, in Provence, south of France. In the eighties, a scenario study predicted that a similar earthquake may lead to more than the 46 deaths of 1909 and a tremendous economical cost caused by increasing urbanisation in this area. The 1909 maximal intensity was...

The 6th of April 2009, at 3:32 local time, a Mw 6.3 earthquake hit the Abruzzo region (central Italy) causing more than 300 casualties. The epicenter of the earthquake was 95km NE of Rome and 10km from the center of the city of L’Aquila, the administrative capital of the Abruzzo region. This city has a population of about 70,000 and was severely da...

This article proposes a new framework for the inclusion of site effects in empirical ground-motion prediction equations (GMPEs) by characterizing stations through their one-quarter wavelength velocities and assessed confidence limits. The approach is demonstrated for 14 stations of the French accelerometric network (Réseau Accélérométrique Permanen...

In the months following the April 6th, 2009, L’Aquila earthquake, several Italian and foreign research institutions installed dozens of seismic stations to monitor more than 100 localities with the aim of studying the local site effects in the epicentral area (upper and middle Aterno valley). The stations (accelerometers and velocimeters) have been...

In this study, we compute site amplification estimates and response spectral ratios for different acceleration time histories scaled to different PGA's by propagating them through 1D soil models with stochastic variation of their mechanical properties. We use three models of wave propagation: the widely known equivalent linear model (EQL) (Schnabel...

For earthquake resistance assessment of existing structures as well as for new constructions design, observed strong motion records are commonly used as input either for laboratories shacking table experiment or for computer modelling. Until the early 1990s, strong-motion data was relatively difficult to obtain and process and, in addition, the amo...

Quantitative assessment of site effects, is a major issue in seismic hazard and engineering seismology studies. The frequency dependent site amplifications, observed since decades during the past earthquakes over the world, are known to be mainly caused by reverberations and resonance effects of S-waves within unconsolidated sediments overlaying st...

Site effects associated with local geological conditions constitute an important part of any seismic hazard assessment. Many examples of catastrophic consequences of earthquakes have demonstrated the importance of reliable analyses procedures and techniques in earthquake hazard assessment and in earthquake risk mitigation strategies. Ambient vibrat...

In seismic risk studies, the assessment of lithologic site effect is based on an accurate knowledge of mechanical properties and geometry of superficial geological formations. Therefore, we built a 3D subsurface model in the city of Nice, southeastern France, using not only geological and geotechnical data but also geophysical inputs. We used espec...

Lors d'une étude de risque sismique, évaluer ces effets de site est une des étapes essentielles car les conditions géologiques amplifient les mouvements et aggravent les dommages. La caractérisation de sites pouvant intéresser une large région il est nécessaire de mettre au point des stratégies d'étude rapides et peu coûteuses. Les méthodes d'inves...

Seismic risk scenario has already been established for major urban centre by the past, but it is of importance to assess also the seismic risk in wide areas with sparse dwelling centres and few connecting roads. The concept developed ion this paper consists in linking, for each element at risk, vulnerability values together with hazard values, in o...

Seismic risk scenario has already been established for major urban centre by the past, but it is of importance to assess also the seismic risk in wide areas with sparse dwelling centres and few connecting roads. The concept developed consists in linking, for each element at risk, vulnerability values together with hazard values, in order to produce...

Numéro spécial du BLPC sur les risques sismiques, 2007

Lors d’études récentes de microzonage sismique, le BRGM a utilisé deux méthodes géophysiques dans l’objectif de mieux contraindre les données géologiques et de suppléer au manque de sondages géotechniques. La technique H/V bruit de fond et la méthode SASW sont théoriquement complémentaires : La méthode H/V doit donner la fréquence de résonance du s...

Since 1996 a 20-m depth borehole is instrumented by two accelerometers close to the airport of Pointe-à-Pitre (French West Indies). We use recordings at both stations in order to estimate the soil response of the site. The noise due to the airport activity and the station characteristics explain the few usable records at the station. Only 6 earthqu...

Assessment of lithologic site effects is based on an accurate knowledge of properties and geometry of superficial geological formations, i.e. ideally a 3D-4G subsurface model (Geology, Geomorphology, Geophysics, Geotechnics). Such a model has been achieved using a 3D geomodeler ("Geological Editor" developed at BRGM) that allows building 3D volumes...

For the realisation of a seismic microzonation study, the geotechnical model is mainly based on geotechnical and geological data and much less commonly on seismological data. The geophysical methods as H over V spectral ratios using a single station and noise signal (H/V method) or the spectral analyses of surface wave (SASW) are poorly used at pre...

An investigation of the teleseismic P-wave coda is performed using the single-scattering approximation. The method allows one to image short-wavelength scale (<=2 km) velocity and density heterogeneities and structures that are barely detected by traveltime tomography. Source effects are removed by using receiver functions for data interpretation,...

Broadband receiver functions analysis is commonly used to evaluate the fine-scale S-velocity structure of the lithosphere. We analyse teleseismic P-waves and their coda from 30 selected teleseismic events recorded at three seismological stations of to the French TGRS network in the Alpes Maritimes. Receiver functions are computed in the time domain...

En étudiant la propagation des ondes de volume, nous pouvons d'une part oaractériser les variations brutales des propriétés physiques des matériaux et d'autre part évaluer l'anisotropie du manteau. Le calcul des fonctions de transfert apporte une normalisation des signaux sismologiques en supprimant les effets de la source et de la propagation des...

To investigate the influence of inherited inhomogeneity in a lithosphere under extension, we studied the deep structure of Corsica, an island in the Mediterranean sea, at the boundary of the extensional Tyrrhenian basin, using a temporary array of eight broad-band seismographs. Between the stations in the western Hercynian part of the island and th...

For two months, ground motions induced by natural seismicity were recorded by 4 dense arrays, each of them including 9 seismological receivers. The target zone is a 400 km2 area and displays a characteristic topographic organization. The sites correspond to flat valleys filled with surficial soft sediments. The data recorded during this experiment...

Italy's Mt.Vesuvius has been slumbering for a long time, but its silence could preface an eruption with potentially disastrous effects for 600,000 people living on the volcano's slopes. To assess the scenario of the next eruption, the National Group of Volcanology (GNV) of the Italian National Council of Researches (CNR) has fostered research aimed...