Thomas Lecocq

Royal Observatory of Belgium

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Corentin Caudron

Université Grenoble Alpes

Thierry Camelbeeck

Royal Observatory of Belgium

Aurélien Mordret

Centre National de la Recherche Scientifique

Koen Van Noten

Royal Observatory of Belgium

Florent Brenguier

Université Grenoble Alpes

Raphaël De Plaen

Royal Observatory of Belgium

Kristín Jónsdóttir

Icelandic Meteorological Office

Flavio Cannavò

Istituto Nazionale di Geofisica e Vulcanologia

Andrea Cannata

University of Catania

YÇ

Yeşim Çubuk Sabuncu

Icelandic Meteorological Office

Cooperative Institutions

Centre National de la Recherche Scientifique

100

Institut des Sciences de la Terre

Institut de Recherche pour le Développement

Université Grenoble Alpes

Istituto Nazionale di Geofisica e Vulcanologia

Université Gustave Eiffel

Institut de physique du globe de Paris

Université Savoie Mont Blanc

Royal Observatory of Belgium

Université Paris Cité

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Seismic evidences of the COVID-19 lockdown measures: Eastern Sicily case of study

Andrea Cannata Flavio Cannavò Giuseppe Di Grazia Marco Aliotta Carmelo Cassisi

Abstract. During the COVID-19 pandemic, most countries worldwide put in place social interventions, consisting of restricting the mobility of citizens, aimed at slowing and mitigating the spread of the epidemic. In particular, Italy, as the first European country violently struck by the COVID-19 outbreak, applied a sequence of progressive restrictions to reduce both human mobility and human-to-human contacts from the end of February to mid-March 2020. Here, we analysed the seismic signatures of these lockdown measures in the densely populated Eastern Sicily, characterised by the presence of a permanent seismic network used for both seismic and volcanic monitoring. We specifically emphasize how the amount of the amplitude reduction of anthropogenic seismic noise (reaching ~50–60%), its temporal pattern and spectral content are strongly station-dependent. As for the latter, we exhibited that on average the frequencies above 10 Hz are the most influenced by the anthropogenic seismic noise. Finally, we found an impressive similarity between the temporal patterns of anthropogenic seismic noise and human mobility, as quantified by the mobile phone-derived data shared by Google, Facebook and Apple. These results further confirm how seismic data, routinely acquired worldwide for seismic and volcanic surveillance, can be used to monitor human mobility too.

Seismic Noise

10.5194/se-2020-136

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Citations (4)

Ambient noise multimode Rayleigh and Love wave tomography to determine the shear velocity structure above the Groningen gas field

Geophysical Journal International (2019)

Małgorzata Chmiel Aurélien Mordret Pierre Boué Florent Brenguier Thomas Lecocq

SUMMARY The Groningen gas field is one of the largest gas fields in Europe. The continuous gas extraction led to an induced seismic activity in the area. In order to monitor the seismic activity and study the gas field many permanent and temporary seismic arrays were deployed. In particular, the extraction of the shear wave velocity model is crucial in seismic hazard assessment. Local S-wave velocity-depth profiles allow us the estimation of a potential amplification due to soft sediments. Ambient seismic noise tomography is an interesting alternative to traditional methods that were used in modelling the S-wave velocity. The ambient noise field consists mostly of surface waves, which are sensitive to the Swave and if inverted, they reveal the corresponding S-wave structures. In this study, we present results of a depth inversion of surface waves obtained from the cross-correlation of 1 month of ambient noise data from four flexible networks located in the Groningen area. Each block consisted of about 400 3-C stations. We compute group velocity maps of Rayleigh and Love waves using a straight-ray surface wave tomography. We also extract clear higher modes of Love and Rayleigh waves. The S-wave velocity model is obtained with a joint inversion of Love and Rayleigh waves using the Neighbourhood Algorithm. In order to improve the depth inversion, we use the mean phase velocity curves and the higher modes of Rayleigh and Love waves. Moreover, we use the depth of the base of the North Sea formation as a hard constraint. This information provides an additional constraint for depth inversion, which reduces the S-wave velocity uncertainties. The final S-wave velocity models reflect the geological structures up to 1 km depth and in perspective can be used in seismic risk modelling.

Rayleigh Wave

Ambient noise level

Love wave

Seismic Noise

Seismic Tomography

Shear velocity

Phase velocity

Group velocity

10.1093/gji/ggz237

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Citations (53)

The 23 February 1828 Belgian earthquake: a destructive moderate event typical of the seismic activity in Western Europe

Journal of Seismology (2021)

Thierry Camelbeeck Elisabeth Knuts Pierre Alexandre Thomas Lecocq Koen Van Noten

Massif

Seismotectonics

Focal mechanism

10.1007/s10950-020-09977-6

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Citations (14)

Stratification at the Earth's largest hyperacidic lake and its consequences

Earth and Planetary Science Letters (2016)

Corentin Caudron Robin Campion Dmitri Rouwet Thomas Lecocq Bruno Capaccioni

Stratification (seeds)

Volcanic Gases

Seiche

Wet season

10.1016/j.epsl.2016.11.002

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Citations (13)

Characterizing Stalagmites’ Eigenfrequencies by Combining In Situ Vibration Measurements and Finite Element Modeling Based on 3D Scans

Geosciences (2020)

Aurélie Martin Thomas Lecocq Klaus‐G. Hinzen Thierry Camelbeeck Yves Quinif

Broken or deformed speleothems have been used as indicators of paleo-earthquakes since the 1990s; however, a causal link is difficult to prove except for some thin speleothems. In contrast, the presence of intact speleothems permits estimating an upper limit of the level of horizontal ground motions of past seismicity in the area. The natural frequencies of speleothems are fundamental parameters for their response to earthquakes. This study proposes a new method of in situ characterization of these natural frequencies. Tested in the Han-sur-Lesse cave (Belgian Ardennes), the method is based on recording the ambient seismic noise using three-component sensors on a stalagmite and a 3D laser scan of its shape. The ambient seismic noise records allow a precise determination of the eigenfrequencies of the stalagmite. In addition, numerical models based on the 3D scan show good consistency between measured and modeled data. The joint analysis of these two techniques concludes that the shape of the stalagmite (elliptical cross-section and shape irregularities) influence the eigenfrequencies and polarization of the modes while also causing a near-orthogonal split of natural frequencies. The motions recorded on the stalagmite show significant amplification compared to those recorded at the free surface outside the cave, which has a strong impact on seismic hazard assessment based on speleothems.

Stalagmite

10.3390/geosciences10100418

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Citations (8)

Noise-based ballistic wave passive seismic monitoring. Part 1: body waves

Geophysical Journal International (2019)

Florent Brenguier Roméo Courbis Aurélien Mordret Xander Campman Pierre Boué

SUMMARY Unveiling the mechanisms of earthquake and volcanic eruption preparation requires improving our ability to monitor the rock mass response to transient stress perturbations at depth. The standard passive monitoring seismic interferometry technique based on coda waves is robust but recovering accurate and properly localized P- and S-wave velocity temporal anomalies at depth is intrinsically limited by the complexity of scattered, diffracted waves. In order to mitigate this limitation, we propose a complementary, novel, passive seismic monitoring approach based on detecting weak temporal changes of velocities of ballistic waves recovered from seismic noise correlations. This new technique requires dense arrays of seismic sensors in order to circumvent the bias linked to the intrinsic high sensitivity of ballistic waves recovered from noise correlations to changes in the noise source properties. In this work we use a dense network of 417 seismometers in the Groningen area of the Netherlands, one of Europe's largest gas fields. Over the course of 1 month our results show a 1.5 per cent apparent velocity increase of the P wave refracted at the basement of the 700-m-thick sedimentary cover. We interpret this unexpected high value of velocity increase for the refracted wave as being induced by a loading effect associated with rainfall activity and possibly canal drainage at surface. We also observe a 0.25 per cent velocity decrease for the direct P-wave travelling in the near-surface sediments and conclude that it might be partially biased by changes in time in the noise source properties even though it appears to be consistent with complementary results based on ballistic surface waves presented in a companion paper and interpreted as a pore pressure diffusion effect following a strong rainfall episode. The perspective of applying this new technique to detect continuous localized variations of seismic velocity perturbations at a few kilometres depth paves the way for improved in situ earthquake, volcano and producing reservoir monitoring.

Seismic Noise

Seismometer

Passive seismic

Microseism

Rayleigh Wave

Ambient noise level

Dispersive body waves

Coda

10.1093/gji/ggz440

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Citations (31)

MSNoise: Not Only dv/v! A Framework for Continuous Seismic Data Analysis

2015 AGU Fall Meeting (2015)

Aurélien Mordret Thomas Lecocq Raphaël De Plaen Corentin Caudron Florent Brenguier

Source

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Citations (0)

Bedrock morphology modelling using geologically-dependant empirical equations between resonance frequency and bedrock depth

Koen Van Noten Xavier Devleeschouwer Céline Goffin Bruno Meyvis Thomas Lecocq

Bedrock

Source

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Citations (1)

Path and site effects deduced from merged transfrontier internet macroseismic data of two recent <i>M</i>4 earthquakes in northwest Europe using a grid cell approach

Solid Earth (2017)

Koen Van Noten Thomas Lecocq Christophe Sira Klaus‐G. Hinzen Thierry Camelbeeck

Abstract. The online collection of earthquake reports in Europe is strongly fragmented across numerous seismological agencies. This paper demonstrates how collecting and merging online institutional macroseismic data strongly improves the density of observations and the quality of intensity shaking maps. Instead of using ZIP code Community Internet Intensity Maps, we geocode individual response addresses for location improvement, assign intensities to grouped answers within 100 km2 grid cells, and generate intensity attenuation relations from the grid cell intensities. Grid cell intensity maps are less subjective and illustrate a more homogeneous intensity distribution than communal ZIP code intensity maps. Using grid cells for ground motion analysis offers an advanced method for exchanging transfrontier equal-area intensity data without sharing any personal information. The applicability of the method is demonstrated on the felt responses of two clearly felt earthquakes: the 8 September 2011 ML 4.3 (Mw 3.7) Goch (Germany) and the 22 May 2015 ML 4.2 (Mw 3.7) Ramsgate (UK) earthquakes. Both events resulted in a non-circular distribution of intensities which is not explained by geometrical amplitude attenuation alone but illustrates an important low-pass filtering due to the sedimentary cover above the Anglo-Brabant Massif and in the Lower Rhine Graben. Our study illustrates the effect of increasing bedrock depth on intensity attenuation and the importance of the WNW–ESE Caledonian structural axis of the Anglo-Brabant Massif for seismic wave propagation. Seismic waves are less attenuated – high Q – along the strike of a tectonic structure but are more strongly attenuated – low Q – perpendicular to this structure, particularly when they cross rheologically different seismotectonic units separated by crustal-rooted faults.

Intensity

Grid cell

Massif

10.5194/se-8-453-2017

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Citations (32)

Seasonal Snow Cycles and Their Possible Influence on Seismic Velocity Changes and Eruptive Activity at Ruapehu Volcano, New Zealand

Journal of Geophysical Research Solid Earth (2024)

Alexander Yates Corentin Caudron Aurélien Mordret Philippe Lesage Virginie Pinel

Abstract Understanding volcanic eruption triggers is critical toward anticipating future activity. While internal magma dynamics typically receive more attention, the influence of external processes remains less understood. In this context, we explore the relationship between seasonal snow cycles and eruptive activity at Ruapehu, New Zealand. This is motivated by apparent seasonality in the eruptive record, where a higher than expected proportion of eruptions (post‐1960) occur in spring (including the two previous eruptions of 2006 and 2007). Employing recent advancements in passive seismic interferometry, we compute sub‐surface seismic velocity changes between 2005 and 2009 using the cross‐wavelet transform approach. Stations on the volcano record a higher velocity in winter, closely correlated with the presence of snow. Inverting for depth suggests these changes occur within the upper 300 m. Notably, we observe that the timing of the previous two eruptions coincides with a period associated with an earlier velocity decrease at approximately 200–300 m depth relative to the surface. Reduced water infiltration (as precipitation falls as snow) is considered a likely control of seasonal velocities, while modeling also points to a contribution from snow‐loading. We hypothesize that this latter process may play a role toward explaining seasonality in the eruptive record. Our findings shed light on the complex interactions between volcanoes and external environmental processes, highlighting the need for more focused research in this area. Pursuing this line of inquiry has significant implications toward improved risk and hazard assessments at not just Ruapehu, but also other volcanoes globally that experience seasonal snow cover.

10.1029/2024jb029568

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Citations (0)