Articles | Volume 4, issue 2
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
the Creative Commons Attribution 3.0 License.
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
the Creative Commons Attribution 3.0 License.
Study on the limitations of travel-time inversion applied to sub-basalt imaging
Departament de Estructura i Dinàmica de la Terra, Institut de Ciències de la Terra Jaume Almera-ICTJA-CSIC, C/ Lluís Solé i Sabarís s/n, 08028, Barcelona, Spain
Departament de Estructura i Dinàmica de la Terra, Institut de Ciències de la Terra Jaume Almera-ICTJA-CSIC, C/ Lluís Solé i Sabarís s/n, 08028, Barcelona, Spain
R. W. Hobbs
Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK
Related subject area
SeismologyOcean bottom seismometer (OBS) noise reduction from horizontal and vertical components using harmonic–percussive separation algorithmsProbing environmental and tectonic changes underneath Ciudad de México with the urban seismic fieldTowards real-time seismic monitoring of a geothermal plant using Distributed Acoustic SensingConstraints on fracture distribution in the Los Humeros geothermal field from beamforming of ambient seismic noiseMapping the basement of the Cerdanya Basin (Eastern Pyrenees) using seismic ambient noiseUpper-lithospheric structure of northeastern Venezuela from joint inversion of surface-wave dispersion and receiver functionsA study on the effect of input data length on a deep-learning-based magnitude classifierQuantifying gender gaps in seismology authorshipMulti-array analysis of volcano-seismic signals at Fogo and Brava, Cape VerdeReflection imaging of complex geology in a crystalline environment using virtual-source seismology: case study from the Kylylahti polymetallic mine, FinlandRadial anisotropy and S-wave velocity depict the internal to external zone transition within the Variscan orogen (NW Iberia)The damaging character of shallow 20th century earthquakes in the Hainaut coal area (Belgium)Distributed acoustic sensing as a tool for subsurface mapping and seismic event monitoring: a proof of conceptSeismic monitoring of the STIMTEC hydraulic stimulation experiment in anisotropic metamorphic gneissTwo subduction-related heterogeneities beneath the Eastern Alps and the Bohemian Massif imaged by high-resolution P-wave tomographyOne-dimensional velocity structure modeling of the Earth's crust in the northwestern DinaridesA functional tool to explore the reliability of micro-earthquake focal mechanism solutions for seismotectonic purposesChangepoint detection in seismic double-difference data: application of a trans-dimensional algorithm to data-space explorationImaging structure and geometry of slabs in the greater Alpine area – a P-wave travel-time tomography using AlpArray Seismic Network data3D crustal structure of the Ligurian Basin revealed by surface wave tomography using ocean bottom seismometer dataBasin inversion: reactivated rift structures in the central Ligurian Sea revealed using ocean bottom seismometersMoho and uppermost mantle structure in the Alpine area from S-to-P converted wavesThe effect of 2020 COVID-19 lockdown measures on seismic noise recorded in RomaniaElastic anisotropies of deformed upper crustal rocks in the AlpsCOVID-19 lockdown effects on the seismic recordings in Central AmericaA revised image of the instrumental seismicity in the Lodi area (Po Plain, Italy)Seismic radiation from wind turbines: observations and analytical modeling of frequency-dependent amplitude decaysAccelerating Bayesian microseismic event location with deep learningPresent-day geodynamics of the Western Alps: new insights from earthquake mechanismsTeleseismic P waves at the AlpArray seismic network: wave fronts, absolute travel times and travel-time residualsStrain to ground motion conversion of distributed acoustic sensing data for earthquake magnitude and stress drop determinationSeismicity and seismotectonics of the Albstadt Shear Zone in the northern Alpine forelandRegional centroid moment tensor inversion of small to moderate earthquakes in the Alps using the dense AlpArray seismic network: challenges and seismotectonic insightsRelocation of earthquakes in the southern and eastern Alps (Austria, Italy) recorded by the dense, temporary SWATH-D network using a Markov chain Monte Carlo inversionSeismic noise variability as an indicator of urban mobility during the COVID-19 pandemic in the Santiago metropolitan region, ChileTransversely isotropic lower crust of Variscan central Europe imaged by ambient noise tomography of the Bohemian MassifEvaluating seismic beamforming capabilities of distributed acoustic sensing arraysUnprecedented quiescence in resource development area allows detection of long-lived latent seismicitySeismic monitoring of urban activity in Barcelona during the COVID-19 lockdownSeismic signature of the COVID-19 lockdown at the city scale: a case study with low-cost seismometers in the city of Querétaro, MexicoSeismicity during and after stimulation of a 6.1 km deep enhanced geothermal system in Helsinki, FinlandCharacterizing the oceanic ambient noise as recorded by the dense seismo-acoustic Kazakh networkCrustal structure of southeast Australia from teleseismic receiver functionsSeismic monitoring of the Auckland Volcanic Field during New Zealand's COVID-19 lockdownSeismic evidence of the COVID-19 lockdown measures: a case study from eastern Sicily (Italy)Sensing Earth and environment dynamics by telecommunication fiber-optic sensors: an urban experiment in Pennsylvania, USASeismic gaps and intraplate seismicity around Rodrigues Ridge (Indian Ocean) from time domain array analysisRupture-dependent breakdown energy in fault models with thermo-hydro-mechanical processesUsing horizontal-to-vertical spectral ratios to construct shear-wave velocity profilesCrustal structures beneath the Eastern and Southern Alps from ambient noise tomography
Zahra Zali, Theresa Rein, Frank Krüger, Matthias Ohrnberger, and Frank Scherbaum
Solid Earth, 14, 181–195,Short summary
Investigation of the global Earth's structure benefits from the analysis of ocean bottom seismometer (OBS) data that allow an improved seismic illumination of dark spots of crustal and mantle structures in the oceanic regions of the Earth. However, recordings from the ocean bottom are often highly contaminated by noise. We developed an OBS noise reduction algorithm, which removes much of the oceanic noise while preserving the earthquake signal and does not introduce waveform distortion.
Laura Ermert, Enrique Cabral-Cano, Estelle Chaussard, Dario Solano-Rojas, Luis Quintanar, Diana Morales Padilla, Enrique A. Fernandez-Torres, and Marine A. Denolle
Ciudad de México is built on a unique soil containing the clay-rich deposits of ancient lake Texcoco. Continuous, imperceptible shaking of these and deeper deposits by the traffic and other sources allows us to monitor changes in the subsurface seismic wave speed. Wave speed varies seasonally, likely due to temperature and rain effects; it temporarily drops after earthquakes, then starts to recover. Throughout the studied period, it increased on average, which may be related to soil compaction.
Jerome Azzola, Katja Thiemann, and Emmanuel Gaucher
Distributed Acoustic Sensing is applied to the micro-seismic monitoring of a geothermal plant. In this domain, the feasibility of managing the large flow of generated data and their suitability to monitor locally induced seismicity was yet to be assessed. The proposed monitoring system efficiently managed the acquisition, processing and saving of the data over a 6-month period. This testing period proved that the monitoring concept advantageously complements more classical monitoring networks.
Heather Kennedy, Katrin Löer, and Amy Gilligan
Solid Earth, 13, 1843–1858,Short summary
The energy transition is an important topic for benefiting the future; thus renewable energy is required to reach net-zero carbon emission goals. Geothermal energy, heat from the ground, can be used in this transition. Therefore, geothermal fields need to be characterized as much as possible to allow for increased productivity within these fields. This study involves and looks at potential fractures within a geothermal field at depth to help increase the overall understanding of this field.
Jordi Diaz, Sergi Ventosa, Martin Schimmel, Mario Ruiz, Albert Macau, Anna Gabàs, David Martí, Özgenç Akin, and Jaume Vergés
We assess the capability of multiple methods based on the interpretation of seismic noise to map the basement of the Cerdanya basin, located in the eastern Pyrenees. Basement depths estimations retrieved from the different approaches are consistent, with maximum depths reaching 700 m close to the Têt Fault bounding the basin to the east. Our results prove that seismic noise analysis using high-density networks is an excellent tool to improve the geological characterisation of sedimentary basins.
Roberto Cabieces, Mariano S. Arnaiz-Rodríguez, Antonio Villaseñor, Elizabeth Berg, Andrés Olivar-Castaño, Sergi Ventosa, and Ana M. G. Ferreira
Solid Earth, 13, 1781–1801,Short summary
This paper presents a new 3D shear-wave velocity model of the lithosphere of northeastern Venezuela, including new Moho and Vp / Vs maps. Data were retrieved from land and broadband ocean bottom seismometers from the BOLIVAR experiment.
Megha Chakraborty, Wei Li, Johannes Faber, Georg Rümpker, Horst Stoecker, and Nishtha Srivastava
Solid Earth, 13, 1721–1729,Short summary
Earthquake magnitude is a crucial parameter in defining its damage potential, and hence its speedy determination is essential to issue an early warning in regions close to the epicentre. This study summarises our findings in an attempt to apply deep-learning-based classifiers to earthquake waveforms, particularly with respect to finding an optimum length of input data. We conclude that the input length has no significant effect on the model accuracy, which varies between 90 %–94 %.
Laura Anna Ermert, Maria Koroni, and Naiara Korta Martiartu
We investigated gender and authorship in seismology by analyzing author names of peer-reviewed articles. Seismology continues to be a male-dominated field, although the representation of female authors has been increasing from 2010 to 2020. Gender gaps appear for single authors, authors in high-impact journals, and highly productive authors. We hope to draw the attention of the seismological community to these issues and motivate leaders in the field to take action in order to support diversity.
Carola Leva, Georg Rümpker, and Ingo Wölbern
Solid Earth, 13, 1243–1258,Short summary
The seismicity of Fogo and Brava, Cape Verde, is dominated by volcano-tectonic earthquakes in the area of Brava and volcanic seismic signals, such as hybrid events, on Fogo. We locate these events using a multi-array analysis, which allows the localization of seismic events occurring outside the network and of volcanic signals lacking clear phases. We observe exceptionally high apparent velocities for the hybrid events located on Fogo. These velocities are likely caused by a complex ray path.
Michal Chamarczuk, Michal Malinowski, Deyan Draganov, Emilia Koivisto, Suvi Heinonen, and Sanna Rötsä
Solid Earth, 13, 705–723,Short summary
In passive seismic measurement, all noise sources from the environment, such as traffic, vibrations caused by distant excavation, and explosive work from underground mines, are utilized. In the Kylylahti experiment, receivers recorded ambient noise sources for 30 d. These recordings were subjected to data analysis and processing using novel methodology developed in our study and used for imaging the subsurface geology of the Kylylahti mine area.
Jorge Acevedo, Gabriela Fernández-Viejo, Sergio Llana-Fúnez, Carlos López-Fernández, Javier Olona, and Diego Pérez-Millán
Solid Earth, 13, 659–679,Short summary
The NW Iberian Peninsula provides one of the most complete Variscan sections in Europe, showing the transition between a sedimentary domain with folds and thrust and a metamorphic domain with igneous intrusions. By processing the seismic ambient noise recorded by several seismograph networks in this area, new 3-D S-wave velocity and radial anisotropy models were created. These models reveal the limit between the two domains, delineating the core of the large western European Variscan Belt.
Thierry Camelbeeck, Koen Van Noten, Thomas Lecocq, and Marc Hendrickx
Solid Earth, 13, 469–495,Short summary
Over the 20th century, shallow damaging seismicity occurred in and near the Hainaut coal mining area in Belgium. We provide an overview of earthquake parameters and impacts, combining felt and damage testimonies and instrumental measurements. Shallower earthquakes have a depth and timing compatible with mining activity. The most damaging events occurred deeper than the mines but could still have been triggered by mining-caused crustal changes. Our modelling can be applied to other regions.
Nicola Piana Agostinetti, Alberto Villa, and Gilberto Saccorotti
Solid Earth, 13, 449–468,Short summary
Sensing the Earth is a fundamental operation for the future where georesources, like geothermal energy and CO2 underground storage, will become important tools for addressing societal challenges. The development of networks of optical fibre cables gives the possibility of a sensing grid with an unprecedented spatial coverage. Here, we investigate the potential of using portions of a optical fibre cable as a standard seismometer for exploring the subsurface and monitoring georesources.
Carolin M. Boese, Grzegorz Kwiatek, Thomas Fischer, Katrin Plenkers, Juliane Starke, Felix Blümle, Christoph Janssen, and Georg Dresen
Solid Earth, 13, 323–346,Short summary
Hydraulic stimulation experiments in underground facilities allow for placing monitoring equipment close to and surrounding the stimulated rock under realistic and complex conditions at depth. We evaluate how accurately the direction-dependent velocity must be known for high-resolution seismic monitoring during stimulation. Induced transient deformation in rocks only 2.5–5 m apart may differ significantly in magnitude and style, and monitoring requires sensitive sensors adapted to the frequency.
Jaroslava Plomerová, Helena Žlebčíková, György Hetényi, Luděk Vecsey, Vladislav Babuška, and AlpArray-EASI and AlpArray working groups
Solid Earth, 13, 251–270,Short summary
We present high-resolution tomography images of upper mantle structure beneath the E Alps and the adjacent Bohemian Massif. The northward-dipping lithosphere, imaged down to ∼200 km beneath the E Alps without signs of delamination, is probably formed by a mixture of a fragment of detached European plate and the Adriatic plate subductions. A detached high-velocity anomaly, sub-parallel to and distinct from the E Alps heterogeneity, is imaged at ∼100–200 km beneath the southern part of the BM.
Gregor Rajh, Josip Stipčević, Mladen Živčić, Marijan Herak, Andrej Gosar, and the AlpArray Working Group
Solid Earth, 13, 177–203,Short summary
We investigated the 1-D velocity structure of the Earth's crust in the NW Dinarides with inversion of arrival times from earthquakes. The obtained velocity models give a better insight into the crustal structure and show velocity variations among different parts of the study area. In addition to general structural implications and a potential for improving further work, the results of our study can also be used for routine earthquake location and for detecting errors in seismological bulletins.
Guido Maria Adinolfi, Raffaella De Matteis, Rita de Nardis, and Aldo Zollo
Solid Earth, 13, 65–83,Short summary
We propose a methodology useful to evaluate (1) the reliability of a focal mechanism solution inferred by the inversion of seismological data and (2) the performance of a seismic network, operated to monitor natural or induced seismicity, to assess focal mechanism solutions. As a test case, we studied the focal mechanism reliability by using synthetic data computed for ISNet, a local seismic network monitoring the Irpinia fault system (southern Italy).
Nicola Piana Agostinetti and Giulia Sgattoni
Solid Earth, 12, 2717–2733,Short summary
One of the present-day challenges for geoscientists is tackling the big data revolution. An ever-growing amount of data needs to be processed and data are subjectively handled before using them to make inferences on the Earth’s interior. But imposing subjective decisions on the data might have strong influences on the final outputs. Here we present a totally novel and automatic application for screening the data and for defining data volumes that are consistent with physical hypotheses.
Marcel Paffrath, Wolfgang Friederich, Stefan M. Schmid, Mark R. Handy, and the AlpArray and AlpArray-Swath D Working Group
Solid Earth, 12, 2671–2702,Short summary
The Alpine mountain belt was formed by the collision of the Eurasian and African plates in the geological past, during which parts of the colliding plates sank into the earth's mantle. Using seismological data from distant earthquakes recorded by the AlpArray Seismic Network, we have derived an image of the current location of these subducted parts in the earth's mantle. Their quantity and spatial distribution is key information needed to understand how the Alpine orogen was formed.
Felix N. Wolf, Dietrich Lange, Anke Dannowski, Martin Thorwart, Wayne Crawford, Lars Wiesenberg, Ingo Grevemeyer, Heidrun Kopp, and the AlpArray Working Group
Solid Earth, 12, 2597–2613,Short summary
The Ligurian Sea opened ~30–15 Ma during SE migration of the Calabrian subduction zone. Using ambient seismic noise from stations on land and at the ocean bottom, we calculated a 3D shear-velocity model of the Ligurian Basin. In keeping with existing 2D studies, we find a shallow crust–mantle transition at the SW basin centre that deepens towards the northeast, Corsica, and the Liguro-Provençal coast. We observe a separation of SW and NE basins. We do not observe high crustal vP/vS ratios.
Martin Thorwart, Anke Dannowski, Ingo Grevemeyer, Dietrich Lange, Heidrun Kopp, Florian Petersen, Wayne C. Crawford, Anne Paul, and the AlpArray Working Group
Solid Earth, 12, 2553–2571,Short summary
We analyse broadband ocean bottom seismometer data of the AlpArray OBS network in the Ligurian Basin. Two earthquake clusters with thrust faulting focal mechanisms indicate compression of the rift basin. The locations of seismicity suggest reactivation of pre-existing rift structures and strengthening of crust and uppermost mantle during rifting-related extension. Slightly different striking directions of faults may mimic the anti-clockwise rotation of the Corsica–Sardinia block.
Rainer Kind, Stefan M. Schmid, Xiaohui Yuan, Benjamin Heit, Thomas Meier, and the AlpArray and AlpArray-SWATH-D Working Groups
Solid Earth, 12, 2503–2521,Short summary
A large amount of new seismic data from the greater Alpine area have been obtained within the AlpArray and SWATH-D projects. S-to-P converted seismic phases from the Moho and from the mantle lithosphere have been processed with a newly developed method. Examples of new observations are a rapid change in Moho depth at 13° E below the Tauern Window from 60 km in the west to 40 km in the east and a second Moho trough along the boundary of the Bohemian Massif towards the Western Carpathians.
Bogdan Grecu, Felix Borleanu, Alexandru Tiganescu, Natalia Poiata, Raluca Dinescu, and Dragos Tataru
Solid Earth, 12, 2351–2368,Short summary
The lockdown imposed in Romania to prevent the spread of COVID-19 has significantly impacted human activity across the country. By analyzing the ground vibrations recorded at seismic stations, we were able to monitor the changes in human activity before and during the lockdown. The reduced human activity during the lockdown has also provided a good opportunity for stations sited in noisy urban areas to record earthquake signals that would not have been recorded under normal conditions.
Ruth Keppler, Roman Vasin, Michael Stipp, Tomás Lokajícek, Matej Petruzálek, and Nikolaus Froitzheim
Solid Earth, 12, 2303–2326,Short summary
Rocks in mountain belts have been deformed during continental collision causing a certain alignment of the minerals referred to as crystallographic preferred orientation (CPO). Minerals have anisotropic properties: the velocity of seismic waves travelling through them is direction dependent. This leads to anisotropy of the rocks. We measured the CPO of common rocks within the Alps. With this data and known anisotropic properties of the minerals we calculated the seismic anisotropy of the rocks.
Mario Arroyo-Solórzano, Diego Castro-Rojas, Frédérick Massin, Lepolt Linkimer, Ivonne Arroyo, and Robin Yani
Solid Earth, 12, 2127–2144,Short summary
We present the first seismic noise variation levels during COVID-19 in Central America using 10 seismometers. We study the impact of the seismic noise reduction on the detectability of earthquakes and on the felt reports. Our results show maximum values (~50 % decrease) at seismic stations near airports and densely inhabited cities. The decrease in seismic noise improved earthquake locations and reports. Seismic noise could also be useful to verify compliance with lockdown measures.
Laura Peruzza, Alessandra Schibuola, Maria Adelaide Romano, Marco Garbin, Mariangela Guidarelli, Denis Sandron, and Enrico Priolo
Solid Earth, 12, 2021–2039,Short summary
In weakly seismic or poorly monitored areas, the uncritical use of earthquake catalogues can be misleading. This is the case for a central sector in the Po Valley, where the Northern Apennines and Southern Alps collide. We collect and reprocess the available instrumental data of about 300 earthquakes from 1951 to 2019. The seismicity is weak, deeper than expected, and far from some existing human activities carried out underground. The potential tectonic causative sources are still unknown.
Fabian Limberger, Michael Lindenfeld, Hagen Deckert, and Georg Rümpker
Solid Earth, 12, 1851–1864,Short summary
Frequency-dependent amplitude decays of seismic signals induced by wind turbines are determined from (up to) 6 months of continuous recordings measured along an 8 km profile located at a wind farm in Bavaria, Germany. The radiation pattern and amplitude decay of the induced signals are accounted for by an analytical approach that includes path and source effects. This approach is generalized to predict the characteristic seismic radiation patterns of arbitrary wind farm configurations.
Alessio Spurio Mancini, Davide Piras, Ana Margarida Godinho Ferreira, Michael Paul Hobson, and Benjamin Joachimi
Solid Earth, 12, 1683–1705,Short summary
The localization of an earthquake is affected by many uncertainties. To correctly propagate these uncertainties into an estimate of the earthquake coordinates and their associated errors, many simulations of seismic waves are needed. This operation is computationally very intensive, hindering the feasibility of this approach. In this paper, we present a series of deep-learning methods to produce accurate seismic traces in a fraction of the time needed with standard methods.
Marguerite Mathey, Christian Sue, Colin Pagani, Stéphane Baize, Andrea Walpersdorf, Thomas Bodin, Laurent Husson, Estelle Hannouz, and Bertrand Potin
Solid Earth, 12, 1661–1681,Short summary
This work features the highest-resolution seismic stress and strain fields available at the present time for the analysis of the active crustal deformation of the Western Alps. In this paper, we address a large dataset of newly computed focal mechanisms from a statistical standpoint, which allows us to suggest a joint control from far-field forces and from buoyancy forces on the present-day deformation of the Western Alps.
Marcel Paffrath, Wolfgang Friederich, and the AlpArray and AlpArray-SWATH D Working Groups
Solid Earth, 12, 1635–1660,Short summary
Using the AlpArray seismic network, we have determined highly accurate travel times of P waves from over 370 major global earthquakes between 2015 and 2019, which shall be used for a tomography of the mantle beneath the greater Alpine region. Comparing with theoretical travel times of a standard reference earth model, we receive very stable patterns of travel-time differences across the network which provide evidence of varying subduction behaviour along the strike of the Alpine orogen.
Itzhak Lior, Anthony Sladen, Diego Mercerat, Jean-Paul Ampuero, Diane Rivet, and Serge Sambolian
Solid Earth, 12, 1421–1442,Short summary
The increasing use of distributed acoustic sensing (DAS) inhibits the transformation of optical fibers into dense arrays of seismo-acoustic sensors. Here, DAS strain records are converted to ground motions using the waves' apparent velocity. An algorithm for velocity determination is presented, accounting for velocity variations between different seismic waves. The conversion allows for robust determination of fundamental source parameters, earthquake magnitude and stress drop.
Sarah Mader, Joachim R. R. Ritter, Klaus Reicherter, and the AlpArray Working Group
Solid Earth, 12, 1389–1409,Short summary
The Albstadt Shear Zone, SW Germany, is an active rupture zone with sometimes damaging earthquakes but no visible surface structure. To identify its segmentations, geometry, faulting pattern and extension, we analyze the continuous earthquake activity in 2011–2018. We find a segmented N–S-oriented fault zone with mainly horizontal and minor vertical movement along mostly NNE- and some NNW-oriented rupture planes. The main horizontal stress is oriented NW and due to Alpine-related loading.
Gesa Maria Petersen, Simone Cesca, Sebastian Heimann, Peter Niemz, Torsten Dahm, Daniela Kühn, Jörn Kummerow, Thomas Plenefisch, and the AlpArray and AlpArray-Swath-D working groups
Solid Earth, 12, 1233–1257,Short summary
The Alpine mountains are known for a complex tectonic history. We shed light onto ongoing tectonic processes by studying rupture mechanisms of small to moderate earthquakes between 2016 and 2019 observed by the temporary AlpArray seismic network. The rupture processes of 75 earthquakes were analyzed, along with past earthquakes and deformation data. Our observations point at variations in the underlying tectonic processes and stress regimes across the Alps.
Azam Jozi Najafabadi, Christian Haberland, Trond Ryberg, Vincent F. Verwater, Eline Le Breton, Mark R. Handy, Michael Weber, and the AlpArray and AlpArray SWATH-D working groups
Solid Earth, 12, 1087–1109,Short summary
This study achieved high-precision hypocenters of 335 earthquakes (1–4.2 ML) and 1D velocity models of the Southern and Eastern Alps. The general pattern of seismicity reflects head-on convergence of the Adriatic Indenter with the Alpine orogenic crust. The relatively deeper seismicity in the eastern Southern Alps and Giudicarie Belt indicates southward propagation of the Southern Alpine deformation front. The derived hypocenters form excellent data for further seismological studies, e.g., LET.
Javier Ojeda and Sergio Ruiz
Solid Earth, 12, 1075–1085,Short summary
In Santiago, Chile, the lockdown imposed due to COVID-19 was recorded by seismological instruments. This analysis shows temporal changes in the surface vibrations controlled by lockdown phases, mobility, and epidemiological factors. Our findings suggest that
dynamic lockdownand the early deconfinement in April 2020 caused an increase in mobility and therefore virus transmission. We propose that seismic networks could be used to monitor urban mobility as a new proxy in public policies.
Jiří Kvapil, Jaroslava Plomerová, Hana Kampfová Exnerová, Vladislav Babuška, György Hetényi, and AlpArray Working Group
Solid Earth, 12, 1051–1074,Short summary
This paper presents a high-resolution 3-D shear wave velocity (vS) model of the Bohemian Massif crust imaged from high-density data and enhanced depth sensitivity of tomographic inversion. The dominant features of the model are relatively higher vS in the upper crust than in its surrounding, a distinct intra-crustal interface, and a velocity decrease in the lower part of the crust. The low vS in the lower part of the crust is explained by the anisotropic fabric of the lower crust.
Martijn P. A. van den Ende and Jean-Paul Ampuero
Solid Earth, 12, 915–934,Short summary
Distributed acoustic sensing (DAS) is an emerging technology that measures stretching of an optical-fibre cable. This technology can be used to record the ground shaking of earthquakes, which offers a cost-efficient alternative to conventional seismometers. Since DAS is relatively new, we need to verify that existing seismological methods can be applied to this new data type. In this study, we reveal several issues by comparing DAS with conventional seismometer data for earthquake localisation.
Rebecca O. Salvage and David W. Eaton
Solid Earth, 12, 765–783,Short summary
Small earthquakes in Alberta and north-east British Columbia have been previously ascribed to industrial activities. The COVID-19 pandemic forced almost all these activities to stop for ~ 4 months. However, unexpectedly, earthquakes still occurred during this time. Some of these earthquakes may be natural and some the result of earthquakes > M6 occurring around the world. However, ~ 65 % of the earthquakes detected may be the remnants of previous fluid injection in the area (
Jordi Diaz, Mario Ruiz, and José-Antonio Jara
Solid Earth, 12, 725–739,Short summary
During the COVID-19 pandemic lockdown, the city of Barcelona was covered by a network of 19 seismometers. The results confirm that the quieting of human activity during lockdown has resulted in a reduction of seismic vibrations. The different lockdown phases in Barcelona are recognized consistently at most of the seismic stations. Our contribution demonstrates that seismic noise can be used as a free and reliable tool to monitor human activity in urban environments.
Raphael S. M. De Plaen, Víctor Hugo Márquez-Ramírez, Xyoli Pérez-Campos, F. Ramón Zuñiga, Quetzalcoatl Rodríguez-Pérez, Juan Martín Gómez González, and Lucia Capra
Solid Earth, 12, 713–724,Short summary
COVID-19 pandemic lockdowns in countries with a dominant informal economy have been a greater challenge than in other places. This motivated the monitoring of the mobility of populations with seismic noise throughout the various phases of lockdown and in the city of Querétaro (central Mexico). Our results emphasize the benefit of densifying urban seismic networks, even with low-cost instruments, to observe variations in mobility at the city scale over exclusively relying on mobile technology.
Maria Leonhardt, Grzegorz Kwiatek, Patricia Martínez-Garzón, Marco Bohnhoff, Tero Saarno, Pekka Heikkinen, and Georg Dresen
Solid Earth, 12, 581–594,
Alexandr Smirnov, Marine De Carlo, Alexis Le Pichon, Nikolai M. Shapiro, and Sergey Kulichkov
Solid Earth, 12, 503–520,Short summary
Seismic and infrasound methods are techniques used to monitor natural events and explosions. At low frequencies, band signal can be dominated by microbaroms and microseisms. The noise observations in the Kazakh network are performed and compared with source and propagation modeling. The network is dense and well situated for studying very distant source regions of the ambient noise. The prospects are opening for the use of ocean noise in solid Earth and atmosphere tomography.
Mohammed Bello, David G. Cornwell, Nicholas Rawlinson, Anya M. Reading, and Othaniel K. Likkason
Solid Earth, 12, 463–481,Short summary
In this study, ground motion caused by distant earthquakes recorded in southeast Australia is used to image the structure of the crust and underlying mantle. This part of the Australian continent was assembled over the last 500 million years, but it remains poorly understood. By studying variations in crustal properties and thickness, we find evidence for the presence of an old microcontinent that is embedded in the younger terrane and forms a connection between Victoria and Tasmania.
Kasper van Wijk, Calum J. Chamberlain, Thomas Lecocq, and Koen Van Noten
Solid Earth, 12, 363–373,Short summary
The Auckland Volcanic Field is monitored by a seismic network. The lockdown measures to combat COVID-19 in New Zealand provided an opportunity to evaluate the performance of seismic stations in the network and to search for small(er) local earthquakes, potentially hidden in the noise during "normal" times. Cross-correlation of template events resulted in detection of 30 new events not detected by GeoNet, but there is no evidence of an increase in detections during the quiet period of lockdown.
Andrea Cannata, Flavio Cannavò, Giuseppe Di Grazia, Marco Aliotta, Carmelo Cassisi, Raphael S. M. De Plaen, Stefano Gresta, Thomas Lecocq, Placido Montalto, and Mariangela Sciotto
Solid Earth, 12, 299–317,Short summary
During the COVID-19 pandemic, most countries put in place social interventions, aimed at restricting human mobility, which caused a decrease in the seismic noise, generated by human activities and called anthropogenic seismic noise. In densely populated eastern Sicily, we observed a decrease in the seismic noise amplitude reaching 50 %. We found similarities between the temporal patterns of seismic noise and human mobility, as quantified by mobile-phone-derived data and ship traffic data.
Tieyuan Zhu, Junzhu Shen, and Eileen R. Martin
Solid Earth, 12, 219–235,Short summary
We describe the Fiber Optic foR Environmental SEnsEing (FORESEE) project in Pennsylvania, USA, the first continuous-monitoring distributed acoustic sensing (DAS) fiber array in the eastern USA. With the success of collecting 1 year of continuous DAS recordings using nearly 5 km of telecommunication fiber underneath the university campus, we conclude that DAS along with telecommunication fiber will potentially serve the purpose of continuous near-surface seismic monitoring in populated areas.
Manvendra Singh and Georg Rümpker
Solid Earth, 11, 2557–2568,Short summary
Using seismic array methods, 63 events were located in the Rodrigues–CIR region, not reported by any global network, most of them being off the ridge axis. The lack of seismicity along this section of the CIR, as observed from global data and this study, can possibly be attributed to the presence of partially molten mantle beneath Rodrigues Ridge. The results will be of interest for a broad range of geoscientists interested in the tectonic evolution of Indian Ocean and plume–crust interaction.
Valère Lambert and Nadia Lapusta
Solid Earth, 11, 2283–2302,
Janneke van Ginkel, Elmer Ruigrok, and Rien Herber
Solid Earth, 11, 2015–2030,Short summary
Knowledge of subsurface velocities is key to understand how earthquake waves travel through the Earth. We present a method to construct velocity profiles for the upper sediment layer on top of the Groningen field, the Netherlands. Here, the soft-sediment layer causes resonance of seismic waves, and this resonance is used to compute velocities from. Recordings from large earthquakes and the background noise signals are used to derive reliable velocities for the deep sedimentary layer.
Ehsan Qorbani, Dimitri Zigone, Mark R. Handy, Götz Bokelmann, and AlpArray-EASI working group
Solid Earth, 11, 1947–1968,Short summary
The crustal structure of the Eastern and Southern Alps is complex. Although several seismological studies have targeted the crust, the velocity structure under this area is still not fully understood. Here we study the crustal velocity structure using seismic ambient noise tomography. Our high-resolution models image several velocity anomalies and contrasts and reveal details of the crustal structure. We discuss our new models of the crust with respect to the geologic and tectonic features.
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