Articles | Volume 12, issue 5
Solid Earth, 12, 1075–1085, 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article 17 May 2021
Research article | 17 May 2021
Seismic noise variability as an indicator of urban mobility during the COVID-19 pandemic in the Santiago metropolitan region, Chile
Javier Ojeda and Sergio Ruiz
Related subject area
Subject area: Crustal structure and composition | Editorial team: Seismics, seismology, geoelectrics, and electromagnetics | Discipline: SeismologyRelocation of earthquakes in the southern and eastern Alps (Austria, Italy) recorded by the dense, temporary SWATH-D network using a Markov chain Monte Carlo inversionTransversely isotropic lower crust of Variscan central Europe imaged by ambient noise tomography of the Bohemian MassifEvaluating seismic beamforming capabilities of distributed acoustic sensing arraysCrustal structure of southeast Australia from teleseismic receiver functionsSeismic monitoring of the Auckland Volcanic Field during New Zealand's COVID-19 lockdownUsing horizontal-to-vertical spectral ratios to construct shear-wave velocity profilesCrustal structures beneath the Eastern and Southern Alps from ambient noise tomographyIntroducing noisi: a Python tool for ambient noise cross-correlation modeling and noise source inversionDeep learning for fast simulation of seismic waves in complex mediaFault reactivation by gas injection at an underground gas storage off the east coast of SpainLithospheric image of the Central Iberian Zone (Iberian Massif) using global-phase seismic interferometryModeling active fault systems and seismic events by using a fiber bundle model – example case: the Northridge aftershock sequenceVisual analytics of aftershock point cloud data in complex fault systemsPassive processing of active nodal seismic data: estimation of VP∕VS ratios to characterize structure and hydrology of an alpine valley infillMonitoring of induced distributed double-couple sources using Marchenko-based virtual receiversER3D: a structural and geophysical 3-D model of central Emilia-Romagna (northern Italy) for numerical simulation of earthquake ground motionMigration of reflector orientation attributes in deep seismic profiles: evidence for decoupling of the Yilgarn Craton lower crustThe cross-dip correction as a tool to improve imaging of crooked-line seismic data: a case study from the post-glacial Burträsk fault, SwedenGreen's theorem in seismic imaging across the scalesNear-surface structure of the North Anatolian Fault zone from Rayleigh and Love wave tomography using ambient seismic noisePower spectra of random heterogeneities in the solid earthA multi-technology analysis of the 2017 North Korean nuclear testObtaining reliable source locations with time reverse imaging: limits to array design, velocity models and signal-to-noise ratios
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.
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.
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.
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.
Laura Ermert, Jonas Igel, Korbinian Sager, Eléonore Stutzmann, Tarje Nissen-Meyer, and Andreas Fichtner
Solid Earth, 11, 1597–1615,Short summary
We present an open-source tool to model ambient seismic auto- and cross-correlations with spatially varying source spectra. The modeling is based on pre-computed databases of seismic wave propagation, which can be obtained from public data providers. The aim of this tool is to facilitate the modeling of ambient noise correlations, which are an important seismologic observable, with realistic wave propagation physics. We present a description and benchmark along with example use cases.
Ben Moseley, Tarje Nissen-Meyer, and Andrew Markham
Solid Earth, 11, 1527–1549,Short summary
Simulations of seismic waves are very important; they allow us to understand how earthquakes spread and how the interior of the Earth is structured. However, whilst powerful, existing simulation methods usually require a large amount of computational power and time to run. In this research, we use modern machine learning techniques to accelerate these calculations inside complex models of the Earth.
Antonio Villaseñor, Robert B. Herrmann, Beatriz Gaite, and Arantza Ugalde
Solid Earth, 11, 63–74,Short summary
We present new earthquake focal depths and fault orientations for earthquakes that occurred in 2013 in the vicinity of an underground gas storage off the east coast of Spain. Our focal depths are in the range of 5–10 km, notably deeper than the depth of the gas injection (2 km). The obtained fault orientations also differ from the predominant faults at shallow depths. This suggests that the faults reactivated are deeper, previously unmapped faults occurring beneath the sedimentary layers.
Juvenal Andrés, Deyan Draganov, Martin Schimmel, Puy Ayarza, Imma Palomeras, Mario Ruiz, and Ramon Carbonell
Solid Earth, 10, 1937–1950,
Marisol Monterrubio-Velasco, F. Ramón Zúñiga, José Carlos Carrasco-Jiménez, Víctor Márquez-Ramírez, and Josep de la Puente
Solid Earth, 10, 1519–1540,Short summary
Earthquake aftershocks display spatiotemporal correlations arising from their self-organized critical behavior. Stochastical models such as the fiber bundle (FBM) permit the use of an analog of the physical model that produces a statistical behavior with many similarities to real series. In this work, a new model based on FBM that includes geometrical faults systems is proposed. Our analysis focuses on aftershock statistics, and as a study case we modeled the Northridge sequence.
Chisheng Wang, Junzhuo Ke, Jincheng Jiang, Min Lu, Wenqun Xiu, Peng Liu, and Qingquan Li
Solid Earth, 10, 1397–1407,Short summary
The point cloud of located aftershocks contains the information which can directly reveal the fault geometry and temporal evolution of an earthquake sequence. However, there is a lack of studies using state-of-the-art visual analytics methods to explore the data to discover hidden information about the earthquake fault. We present a novel interactive approach to illustrate 3-D aftershock point clouds, which can help the seismologist to better understand the complex fault system.
Michael Behm, Feng Cheng, Anna Patterson, and Gerilyn S. Soreghan
Solid Earth, 10, 1337–1354,Short summary
New acquisition styles for active seismic source exploration provide a wealth of additional quasi-passive data. We show how these data can be used to gain complementary information about the subsurface. Specifically, we process an active-source dataset from an alpine valley in western Colorado with both active and passive inversion schemes. The results provide new insights on subsurface hydrology based on the ratio of P-wave and S-wave velocity structures.
Joeri Brackenhoff, Jan Thorbecke, and Kees Wapenaar
Solid Earth, 10, 1301–1319,Short summary
Earthquakes in the subsurface are hard to monitor due to their complicated signals. We aim to make the monitoring of the subsurface possible by redatuming the sources and the receivers from the surface of the Earth to the subsurface to monitor earthquakes originating from small faults in the subsurface. By using several sources together, we create complex earthquake signals for large-scale faults sources.
Peter Klin, Giovanna Laurenzano, Maria Adelaide Romano, Enrico Priolo, and Luca Martelli
Solid Earth, 10, 931–949,Short summary
Using geological and geophysical data, we set up a 3-D digital description of the underground structure in the central part of the Po alluvial plain. By means of computer-simulated propagation of seismic waves, we were able to identify the structural features that caused the unexpected elongation and amplification of the earthquake ground motion that was observed in the area during the 2012 seismic crisis. The study permits a deeper understanding of the seismic hazard in alluvial basins.
Andrew J. Calvert and Michael P. Doublier
Solid Earth, 10, 637–645,Short summary
Deep (> 40 km) seismic reflection surveys are acquired on land along crooked roads. Using the varying azimuth between source and receiver, the true 3-D orientation of crustal structures can be determined. Applying this method to a survey over the ancient Australian Yilgarn Craton reveals that most reflectors in the lower crust exhibit a systematic dip perpendicular to those in the overlying crust, consistent with lateral flow of a weak lower crust in the hotter early Earth 2.7 billion years ago.
Ruth A. Beckel and Christopher Juhlin
Solid Earth, 10, 581–598,Short summary
Scandinavia is crossed by extensive fault scarps that have likely been caused by huge earthquakes when the ice sheets of the last glacial melted. Due to the inaccessibility of the terrain, reflection seismic data have to be collected along crooked lines, which reduces the imaging quality unless special corrections are applied. We developed a new correction method that is very tolerant to noise and used it to improve the reflection image of such a fault and refine its geological interpretation.
Kees Wapenaar, Joeri Brackenhoff, and Jan Thorbecke
Solid Earth, 10, 517–536,Short summary
The earthquake seismology and seismic exploration communities have developed a variety of seismic imaging methods for passive- and active-source data. Despite the seemingly different approaches and underlying principles, many of these methods are based in some way or another on the same mathematical theorem. Starting with this theorem, we discuss a variety of classical and recent seismic imaging methods in a systematic way and explain their similarities and differences.
George Taylor, Sebastian Rost, Gregory A. Houseman, and Gregor Hillers
Solid Earth, 10, 363–378,Short summary
We constructed a seismic velocity model of the North Anatolian Fault in Turkey. We found that the fault is located within a region of reduced seismic velocity and skirts the edges of a geological unit that displays high seismic velocity, indicating that this unit could be stronger than the surrounding material. Furthermore, we found that seismic waves travel fastest in the NE–SW direction, which is the direction of maximum extension for this part of Turkey and indicates mineral alignment.
Solid Earth, 10, 275–292,Short summary
Recent seismological observations clarified that the velocity structure of the crust and upper mantle is randomly heterogeneous. I compile reported power spectral density functions of random velocity fluctuations based on various types of measurements. Their spectral envelope is approximated by the third power of wavenumber. It is interesting to study what kinds of geophysical processes created such a power-law spectral envelope at different scales and in different geological environments.
Peter Gaebler, Lars Ceranna, Nima Nooshiri, Andreas Barth, Simone Cesca, Michaela Frei, Ilona Grünberg, Gernot Hartmann, Karl Koch, Christoph Pilger, J. Ole Ross, and Torsten Dahm
Solid Earth, 10, 59–78,Short summary
On 3 September 2017 official channels of the Democratic People’s Republic of Korea announced the successful test of a nuclear device. This study provides a multi-technology analysis of the 2017 North Korean event and its aftermath using a wide array of geophysical methods (seismology, infrasound, remote sensing, radionuclide monitoring, and atmospheric transport modeling). Our results clearly indicate that the September 2017 North Korean event was in fact a nuclear test.
Claudia Werner and Erik H. Saenger
Solid Earth, 9, 1487–1505,Short summary
Time reverse imaging is a method for locating quasi-simultaneous or low-amplitude earthquakes. Numerous three-dimensional synthetic simulations were performed to discover the influence of station distributions, complex velocity models and high noise rates on the reliability of localisations. The guidelines obtained enable the estimation of the localisation success rates of an existing station set-up and provide the basis for designing new arrays.
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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.
In Santiago, Chile, the lockdown imposed due to COVID-19 was recorded by seismological...