Seismic Noise Research Papers - Academia.edu (original) (raw)

2025, Astroparticle Physics

The gravitational wave detector VIRGO aims at extending the detection band down to a few Hertz by isolating the mirrors of the interferometer from seismic noise. This result is achieved by hanging each mirror through an elastic suspension (Superattenuator), designed to filter mechanical vibrations in all the degrees of freedom. An experimental upper limit of the mirror residual seismic noise at a few Hertz is provided in this paper. This is lower than the thermal noise floor, expected to limit the antenna sensitivity in the low frequency range.

2025

Vibration control assumes great importance in test bench design, especially when test frequencies vary in a very wide range. The aim of the paper is to illustrate the studies carried out for the design of the insulating foundations of two big test benches to be built in the FIAT Research Centre (CRF) in Turin. The benches, that will be located in a suitably modified existing building, are intended to be employed for comfort and fatigue tests on cars of different type and dimensions. Each bench is equipped with four actuators, able to act independently, producing load time histories whose frequency spectra can vary in a very general way between O and 200 Hz. The two benches, whose individual surface is about 20 m2, differ mainly on the degrees of freedom of each actuator: in the first bench the load direction is vertical, while in the second one the loads can act in any direction. To satisfy the wide set of design constraints a twin insulation system has been foreseen, using both pneumatic suspensions and elastomeric pads. In the paper, the theoretical analyses carried out are illustrated and the results are discussed, justifying the design choices.

2025, New Journal of Physics

The regularity of earthquakes, their destructive power, and the nuisance of ground vibration in urban environments, all motivate designs of defence structures to lessen the impact of seismic and ground vibration waves on buildings. Low frequency waves, in the range 1-10 Hz for earthquakes and up to a few tens of Hz for vibrations generated by human activities, cause a large amount of damage, or inconvenience; depending on the geological conditions they can travel considerable distances and may match the resonant fundamental frequency of buildings. The ultimate aim of any seismic metamaterial, or any other seismic shield, is to protect over this entire range of frequencies; the long wavelengths involved, and low frequency, have meant this has been unachievable to date. Notably this is scalable and the effects also hold for smaller devices in ultrasonics. There are three approaches to obtaining shielding effects: bragg scattering, locally resonant sub-wavelength inclusions and zerofrequency stop-band media. The former two have been explored, but the latter has not and is examined here. Elastic flexural waves, applicable in the mechanical vibrations of thin elastic plates, can be designed to have a broad zero-frequency stop-band using a periodic array of very small clamped circles. Inspired by this experimental and theoretical observation, all be it in a situation far removed from seismic waves, we demonstrate that it is possible to achieve elastic surface (Rayleigh) wave reflectors at very large wavelengths in structured soils modelled as a fully elastic layer periodically clamped to bedrock. We identify zero frequency stop-bands that only exist in the limit of columns of concrete clamped at their base to the bedrock. In a realistic configuration of a sedimentary basin 15 m deep we observe a zero frequency stop-band covering a broad frequency range of 0-30 Hz.

2025

Resolution for a local earthquake arrival time and ambient seismic noise tomography around the Eyjafjallajökull volcano Á. Benediktsdóttir (1), Ó. Guðmundsson (2), A. Tryggvason (2), R. Böðvarsson (2), B. Brandsdóttir (3), K. Vogfjörð... more

2025, Seismica 4(1)

Vibrations generated by anthropogenic activity propagate into the Earth's subsurface as highfrequency seismic waves. The COVID-19 pandemic, which prompted widespread adoption of prevention policies in 2020, including social distancing measures, stay-at-home orders, travel restrictions and lockdowns, provided a unique opportunity to investigate on a country-scale the impact of the pandemic restriction measures on seismic data. Greece, which implemented two strict nationwide lockdowns in March and November 2020, serves as a case study for examining the effects of the two national lockdown measures on highfrequency ambient seismic noise. We analyze seismic waveform data obtained exclusively from strong-motion seismic sensors deployed in urban areas across Greece. Our findings reveal a significant 43% reduction in seismic noise levels during the first lockdown and a slightly less, yet still substantial, reduction of 36% during the second lockdown. The most substantial daily reduction in seismic noise levels, exceeding 80%, occurred on Easter Sunday of 2020, during the first lockdown. The decrease in human activity during the 2020 lockdowns resulted in the most extensive and prolonged reduction in anthropogenic seismic noise ever recorded on a national scale in Greece. Our results highlight the effectiveness of strong-motion accelerograph stations in monitoring the effects of lockdown measures on seismic data. Notably, co-located acceleration and broadband sensors exhibited similar variations in high-frequency seismic noise. Furthermore, a strong correlation between high-frequency seismic noise and various categories of human mobility suggests the potential utility of accelerometers in long-term seismic monitoring of human activity.

2025, Journal of Seismology

In recent years, numerous induced seismic events have occurred in the proximity of the natural gas field in Northern Germany. To monitor the seismicity and to asses the seismic hazard potential, a local monitoring network was installed in the area. Focusing on the seismicity hazard assessment, a major challenge is the characterisation of potential site effects due to local soil characteristics. This is quantitatively performed by estimating the shear-wave velocity (V s ) variation with subsurface layer thickness. Such local effects can only be covered with a coarse spatial resolution due to the limited number of monitoring stations. Profiles were determined at three test sites (Langwedel, Walle and Bomlitz) by using a combined approach of small aperture 2D array ambient noise and small-scale active 1D measurements. The high-resolution frequency-wavenumber (HRFK), spatial autocorrelation (SPAC) and multichannel analysis of surface waves (MASW) methods were applied to the recorded ambient noise and active seismic data using various array sizes supplemented by the active measurements. This jointly allowed obtaining phase M. Fehr ( )

2025, Journal of Seismology

In recent years, the impact of wind turbines (WTs) on seismological stations has been noticed, since WT-induced ground motions perturbed the seismic background noise level at seismological monitoring sites. The resulting deterioration of the recording quality at seismic stations leads to a conflict between seismological network and WT operators. As a first step towards the solution of the conflict -or at least a peaceful coexistence -it is of paramount importance to understand the characteristics of seismic signals generated by WTs. For this study, a 6.5-week measurement campaign was conducted at a wind park (WP) consisting of five 2 MW turbines in North Rhine-Westphalia (Germany) with eleven mobile seismic stations installed at distances of 1-10 km from the WP. At each measurement point, power spectral density (PSD) spectra are calculated and correlated with different operating states of the WTs. Changes in the operating states of the WT are reflected in the noise level at the seismic stations with different distances to the WP. An analysis of the radiated frequencies from the WT foundation into the subsurface is carried out by performing shutdown and switch-on tests at the T. Neuffer ( )

2025, Journal of Seismology

2025

We have constructed a 3-D shear-wave velocity (Vs) model for the crust and uppermost mantle beneath the Middle East using Rayleigh wave records obtained from ambient-noise crosscorrelations and regional earthquakes. We combined one decade of data collected from 852 permanent and temporary broadband stations in the region to calculate group-velocity dispersion curves. A compilation of >54000 ray paths provides reliable group-velocity measurements for periods between 2 and 150 s. Path-averaged group velocities calculated at different periods were inverted for 2-D group-velocity maps. To overcome the problem of heterogeneous ray coverage, we used an adaptive grid parametrization for the group-velocity tomographic inversion. We then sample the period-dependent group-velocity field at each cell of a predefined grid to generate 1-D group-velocity dispersion curves, which are subsequently inverted for 1-D Vs models beneath each cell and combined to approximate the 3-D Vs structure of the area. The Vs model shows low velocities at shallow depths (5-10 km) beneath the Mesopotamian foredeep, South Caspian Basin, eastern Mediterranean and the Black Sea, in coincidence with deep sedimentary basins.

2025, Geophysical Journal International

We have constructed a 3-D shear wave velocity (Vs) model for the crust and uppermost mantle beneath the Middle East using Rayleigh wave records obtained from ambient-noise cross-correlations and regional earthquakes. We combined one decade of data collected from 852 permanent and temporary broad-band stations in the region to calculate group-velocity dispersion curves. A compilation of >54 000 ray paths provides reliable group-velocity measurements for periods between 2 and 150 s. Path-averaged group velocities calculated at different periods were inverted for 2-D group-velocity maps. To overcome the problem of heterogeneous ray coverage, we used an adaptive grid parametrization for the group-velocity tomographic inversion. We then sample the period-dependent group-velocity field at each cell of a predefined grid to generate 1-D group-velocity dispersion curves, which are subsequently inverted for 1-D Vs models beneath each cell and combined to approximate the 3-D Vs structure of the area. The Vs model shows low velocities at shallow depths (5-10 km) beneath the Mesopotamian foredeep, South Caspian Basin, eastern Mediterranean and the Black Sea, in coincidence with deep sedimentary basins. Shallow high-velocity anomalies are observed in regions such as the Arabian Shield, Anatolian Plateau and Central Iran, which are dominated by widespread magmatic exposures. In the 10-20 km depth range, we find evidence for a band of high velocities (>4.0 km s -1 ) along the southern Red Sea and Arabian Shield, indicating the presence of upper mantle rocks. Our 3-D velocity model exhibits high velocities in the depth range of 30-50 km beneath western Arabia, eastern Mediterranean, Central Iranian Block, South Caspian Basin and the Black Sea, possibly indicating a relatively thin crust. In contrast, the Zagros mountain range, the Sanandaj-Sirjan metamorphic zone in western central Iran, the easternmost Anatolian plateau and Lesser Caucasus are characterized by low velocities at these depths. Some of these anomalies may be related to thick crustal roots that support the high topography of these regions. In the upper mantle depth range, high-velocity anomalies are obtained beneath the Arabian Platform, southern Zagros, Persian Gulf and the eastern Mediterranean, in contrast to low velocities beneath the Red Sea, Arabian Shield, Afar depression, eastern Turkey and Lut Block in eastern Iran. Our Vs model may be used as a new reference crustal model for the Middle East in a broad range of future studies.

2025, Geosciences

To monitor the stability of a mountain slope in northern Italy, microseismic monitoring technique has been used since 2013. Locating microseismic events is a basic step of this technique. We performed a seismic tomographic survey on the mountain surface above the rock face to obtain a reliable velocity distribution in the rock mass for the localization procedure. Seismic travel-time inversion showed high heterogeneity of the rock mass with strong contrast in velocity distribution. Low velocities were found at shallow depth on the top of the rock cliff and intermediate velocities were observed in the most critical area of the rock face corresponding to a partially detached pillar. Using the 3D velocity model obtained from inversion, localization tests were performed based on the Equal Differential Time (EDT) localization method. The results showed hypocenter misfits to be around 15 m for the five geophones of the microseismic network and the error was significantly decreased compared...

2025, Frontiers in earth science

This study analyses the ambient noise field recorded by the seismic network, TREMBLE, in Bangladesh, operational since late 2016. Horizontal-vertical spectral ratios confirm the placement of stations on sediment, many situated on thick sedimentary columns, consistent with local geology. Noise across the broadband spectrum is systematically examined. A high amplitude local microseism (0.4-0.8 Hz) is recorded, originating near the coast and modulated by local tides. The secondary microseism (0.15-0.35 Hz) correlates strongly with wave height in the Bay of Bengal and varies with seasons, with greater power and higher horizontal amplitude in the monsoon season when the wave height is highest. The microseism increases in amplitude and decreases in frequency as a tropical depression moves inland. The primary microseism (∼0.07-0.08 Hz) exhibits no seasonal changes in power but display strong horizontal energy which changes with seasons. Low frequency (0.02-0.04 Hz) noise on the horizontal components has a 24-h periodicity, due to instrument tilt caused by atmospheric pressure changes. A station located next to the major Karnaphuli River shows elevated energy at ∼5 Hz correlated to periods of high rainfall. Anthropogenic noise (∼4-14 Hz) is stationdependent, demonstrating changing patterns in human activity, such as during Ramadan, national holidays and the COVID pandemic. Our work holds implications for seismic deployments, earthquake, and imaging studies, while providing insights into the interaction between the atmosphere, ocean, and solid Earth.

2025, Journal of Low Frequency Noise, Vibration and Active Control

The Virgo experiment, located near Pisa, Italy, is a large laser Michelson interferometer aiming at the first direct detection of gravitational waves. The interferometer monitors the relative distance of its mirrors placed at the ends of two 3 km-long perpendicular arms. The goal is to measure spectral differential variations of the arm lengths of 10−18 m/Hz1/2 in the frequency range from 10 Hz to 10 kHz. Avoiding spurious motions of the optical components is therefore essential to detect gravitational waves. Since the ground motion is 9 orders of magnitude larger than the arm length variations induced by gravitational waves, the seismic noise is the dominant low frequency noise source for terrestrial gravitational wave interferometers. The seismic isolation is obtained suspending the mirrors by an 8-meter tall chain of cascaded mechanical filters, called “Superattenuator” (SA). The Superattenuator is a passive device acting as a low pass filter in all six degrees of freedom, capabl...

2025, Classical and Quantum Gravity

An array of seismometers is being developed at the Sanford Underground Laboratory, the former Homestake mine, in South Dakota to study the properties of underground seismic fields and Newtonian noise, and to investigate the possible advantages of constructing a third-generation gravitational-wave detector underground. Seismic data were analyzed to characterize seismic noise and disturbances. External databases were used to identify sources of seismic waves: ocean-wave data to identify sources of oceanic microseisms and surface wind-speed data to investigate correlations with seismic motion as a function of depth. In addition, sources of events contributing to the spectrum at higher frequencies are characterized by studying the variation of event rates over the course of a day. Long-term observations of spectral variations provide further insight into the nature of seismic sources. Seismic spectra at three

2025, Scientific Reports

The Covid-19 pandemic created havoc and forced lockdowns in almost all the countries worldwide, to inhibit social spreading. In India as well, as a precautionary measure, complete and partial lockdowns were announced in phases during March 25 to May 31, 2020. The restricted human activities led to a drastic reduction in seismic background noise in the high frequency range of 1–20 Hz, representative of cultural noise. In this study, we analyse the effect of anthropogenic activity on the Earth vibrations, utilizing ambient noise recorded at twelve broadband seismographs installed in different environmental and geological conditions in Gujarat. We find that the lockdowns caused 1–19 dB decrease in seismic noise levels. The impact of restricted anthropogenic activities is predominantly visible during the daytime in urban areas, in the vicinity of industries and/or highways. A 27–79% reduction in seismic noise ground displacement (drms) is observed in daytime during the lockdown, in popu...

2025, Advances in Geosciences

The purpose of this work is to study the subsoil structure of the Campi Flegrei area using both spectral ratios and array techniques applied to seismic noise. We have estimated the dispersion curves of Rayleigh waves by applying the Frequency-Wavenumber (f -k hereinafter) and Modified Spatial Autocorrelation (MSPAC) techniques to the seismic noise recorded by the underground short period seismic Array "ARF", by the broadband stations of the UNREST experiment and by the broadband stations of the seismic monitoring network of INGV -Osservatorio Vesuviano. We have performed the inversion of a dispersion curve (obtained averaging the f -k and MSPAC dispersion curves of seismic noise and single phase velocity values of coherent transient signals) jointly with the H /V spectral ratio of the broadband station CELG, to obtain a shear wave velocity model up to 2000 m depth. The best-fit model obtained is in a good agreement with the stratigraphic information available in the area coming from shallow boreholes and deep wells drilled for geothermal exploration. In active volcanic areas, such as Campi Flegrei, the definition of the velocity model is a crucial issue to characterize the physical parameters of the medium. Generally, a high quality characterization of the medium properties helps to separate the contributions of the volcanic source, path and site in the geophysical observables. Therefore, monitoring possible variations in time of such properties in general can help to recognize anomalies due to the volcano dynamics, i.e. fluid migration connected to the volcanic activity.

2025

The Mw 9.2 Sumatra earthquake of December 26, 2004, like other huge Earthquakes of the past, denotes the difficulty of the science to understand such extended seismic sources. In this work we intended to explain the project SISMOD that have as main purpose the deployment of a computational algorithm to perform the systematic and detailed study of extended seismic sources, independently its dimension and geometry. The method it will be structured to operate from a joint utilization of strong motions; teleseismic waveforms and geodetic data (GPS and InSAR)

2025, Civil Engineering Infrastructures Journal (CEIJ)

An effective earthquake (Mw 7.9) struck Alaska on 3 November, 2002. It ruptured 340 km along three faults namely, the Susitna Glacier, Denali and Totschunda faults in central Alaska. The earthquake was recorded at 23 stations in Alaska and the Peak Ground Acceleration (PGA) of 0.32g was recorded at station PS10, which was located 3 km from the fault rupture. In this study, strike-slip Denali fault has been considered for studying the characteristics of ground motions through modified semiempirical approach. The ground motion records of the 2002 Denali earthquake are generated through MATLAB code. The results revealed that modified semi-empirical approach is fairly good in agreement with observed ground motion records at all stations. A perfect match is observed between Fourier amplitude spectra of simulated and observed ground motions at PS09 and CARLO stations. A good match is observed between elastic response spectra of observed and simulated ground motions.

2025, Engineering Geology

The influence of underground cavities in assessing local seismic response was studied in some test sites in the urban area of Catania. The investigations were performed both in a natural cavity and in artificial tunnels, taking into account the near-surface geological features. Earthquake and ambient noise records were processed through spectral ratio techniques, investigating also on the possible directional effects. A set of 70 local and regional earthquakes was recorded by seismic stations deployed nearby a grotto located in the northern part of the town as well as in a reference site on the bedrock. As regards ambient noise measurements, about 30 recording sites were selected, locating the mobile stations inside the cavities as well as along short profiles crossing them. Spectral ratios coming out from performed measurements show that spectral peaks in the frequency range 3.0-7.0 Hz appear stable nearby the cavity, and show a tendency to be less pronounced at increasing distance from it. Moreover, the natural period of buildings erected nearby and over the considered cavity was evaluated to investigate on possible soil-structure interactions. The results so far obtained point out that the height of the cavities plays an important role. It appears evident that only cavities having height greater than about 4 m show significant H/V amplification peaks. Moreover, spectral ratios deriving from measurements performed inside the cavities show less pronounced spectral peaks than those obtained from measurements over and outside the cavities. Investigations about the interaction with nearby edifices show slight increments in the amplitude of spectral peaks representing the fundamental period of buildings located over the investigated grotto. Finally, our observations set into evidence a tendency toward a pronounced polarization of the ground motion that is parallel to the main axis of the grotto.

2025, Bruit sismique : nette diminution sur l’ensemble de la planète due au confinement COVID-19

Le fort ralentissement des activités humaines en raison de la pandémie de COVID-19, qualifié d’«anthropause» ressort d’un article publié dans la prestigieuse revue Science, dont le professeur en géophysique György Hetényi et son doctorant Shiba Subedi en FGSE sont co-auteurs au sein d’une importante équipe internationale. Ils y démontrent que les mesures de confinement visant à lutter contre la propagation du COVID-19 ont entraîné, entre le début et le milieu de l’année 2020, une réduction moyenne de 50% du bruit de fond observé dans le monde entier, une baisse sans précédent.

2025, Advances in Mechanical Engineering

This article aims to identify the dynamic characteristics (natural frequency in particular) of existing buildings by experimental methods, and then, to compare the results with those reflected by several code provisions and numerical analyses. To this end, ambient vibration tests were carried out on 40 existing concrete and steel buildings in order to obtain the natural frequency of such buildings. The results were then investigated as compared with those arising from several codes and standards, and also with those obtained from numerical analyses. It can be shown in this study that the test results are significantly different from those calculated based on the codes and standards. Moreover, the effect of in-fill walls on the fundamental natural frequency of such buildings is shown. The findings of this research can be used for model calibration and revision of the existing legislations.

2025, Frontiers in Earth Science

The Agung-Batur Volcanic Complex (ABVC), part of the Sunda volcanic arc, is the source of some of the most hazardous volcanic activity in Indonesia. The ABVC has undergone many small (VEI 1-2) eruptions since historical records began in the early 19th century, but Mt. Agung has experienced much larger (VEI 5) eruptions, both in the modern (1963) and historical (1843) eras, as well as several times during the past 2000-3000 years. The 1963 eruption caused more than 1000 deaths, and a more recent eruption in 2017 caused the evacuation of 140,000 people. Delineating the magma structure beneath ABVC is an important first step in understanding the physics of these eruptions. This paper presents the first local-scale study of Rayleigh wave group velocity structure and the seismic velocity structure beneath the ABVC using ambient seismic noise tomography. Seismic data were collected using 25 seismometers deployed across the ABVC during early January to March 2019. The local seismic network provides good resolution beneath both Mt. Agung and Mt. Batur. We obtained 158 Rayleigh Green's Functions, extracted by cross correlating noise simultaneously recorded at available station pairs. We used sub-space inversion to calculate group velocity at different periods and to estimate the lateral variations in group velocity for given periods. 2-D tomographic maps obtained from the inversion of the group velocity of Rayleigh waves clearly showed some pronounced velocity anomalies beneath the ABVC. We applied the Neighbourhood Algorithm (NA) technique to invert the Rayleigh wave dispersion curves to obtain shear wave velocity (Vs) vs. depth profiles. These profiles indicate a low Vs of about 1 km/s underlying the volcanic complex between Mt. Agung and Mt. Batur at depths up to 2 km, which we suggest is due to a combination of low-Vs volcanic deposits as well as a shallow hydrothermal fluids system associated with magma fluids and/or gases produced by magma intrusion at depths >7 km.

2025, Geophysical Journal International

In order to characterize the subsurface structure of the Jakarta Basin, Indonesia, a dense portable seismic broad-band network was operated by The Australian National University (ANU) and the Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG) between October 2013 and February 2014. Overall 96 locations were sampled through successive deployments of 52 seismic broad-band sensors at different parts of the city. Oceanic and anthropogenic noises were recorded as well as regional and teleseismic earthquakes. We apply regularized deconvolution to the recorded ambient noise of the vertical components of available station pairs, and over 3000 Green's functions were retrieved in total. Waveforms from interstation deconvolutions show clear arrivals of Rayleigh fundamental and higher order modes. The traveltimes that were extracted from group velocity filtering of fundamental mode Rayleigh wave arrivals, are used in a 2-stage Transdimensional Bayesian method to map shear wave structure of subsurface. The images of S wave speed show very low velocities and a thick basin covering most of the city with depths up to 1.5 km. These low seismic velocities and the thick basin beneath the city potentially cause seismic amplification during a subduction megathrust or other large earthquake close to the city of Jakarta.

2025, Boletin de Geología

Para contribuir con la microzonificación sísmica del área metropolitana de Mérida se realiza una caracterización geofísica del suelo, aplicando métodos de ruido sísmico ambiental, gravimetría y sísmica de refracción, entre otros. A partir de la técnica de ruido sísmico ambiental se obtienen periodos fundamentales que oscilan entre 0,2 y 2 segundos, los cuales presentan una buena correlación con los espesores de los sedimentos, obtenidos a partir de la gravimetría, y cuyos valores varían entre 12 y 130 m. La sísmica de refracción, a través de 62 perfiles sísmicos, establece modelos de velocidades tanto para las ondas P como para las ondas S de las capas más superficiales, hasta una profundidad máxima de 15 m. Todos estos resultados sirven de base para elaborar el mapa preliminar de microzonas sísmicas que clasifica el área metropolitana en tres partes: la zona 1-1 representada por velocidades de ondas de corte (Vs) desde 350 hasta 650 m/s y espesores de sedimentos entre 0 y 60 m; la zona 1-2 con velocidades Vs desde 350 hasta 650 m/s y espesores de sedimentos de más de 60 m y la zona 2-1 con velocidades Vs iguales ó mayores a 650 m/s y con espesores de sedimentos de 0 a 60 m.

2025

To contribute to the seismic microzonation of the Mérida metropolitan area, a geophysical characterization of the soil, applying methods of ambient seismic noise, gravity and seismic refraction, is performed. From the ambient seismic noise technique, fundamental periods ranging from 0.2 to 2 seconds are obtained, which have good correlation with the sediments thicknesses, obtained from gravimetry, that shows values ranging between 12 and 130 m. The seismic refraction, through 62 seismic profiles, establishes velocity models for the shallow layers up to a maximum depth of 15 m for both P and S waves. All these results provide a basis for a preliminary microzonation map that classifies the metropolitan area into three parts: the zone 1-1 with shear wave velocities from 350 to 650 m/s and sediments thicknesses between 0 and 60 m, the zone 1-2 with shear wave velocities from 350 to 650 m/s and sediments thicknesses greater than 60 m, and the area 2-1 with shear wave velocities equal to ...

2025, Bulletin of the Seismological Society of America

Ambient seismic-noise correlation is a powerful tool for extracting the seismic core phases that propagate through the interior of the Earth. In this study, we present and refine the root-mean-square-stacking method to extract stable core phases (e.g., PcP, ScS, PcS/ScP, and PKiKP) from within the Central Alborz region, Iran, using empirical Green's functions. Our studies on the extracted core phases using empirical Green's functions indicated that the ambient seismic noise method is independent from global seismicity (M ≥ 5:5). We also show that, by dividing ambient seismic records into shorter (i.e., 2700 s) and overlapping (70%) time windows, before the cross-correlation procedure, we can improve the quality and stability of the empirical Green's functions generated. Consequently, 73 days (equivalent to 22% of the total time period for the dataset) of nonconsecutive ambient seismic-noise time windows have been used to retrieve core-phase empirical Green's functions in a 5-10 s period band.

2025, Engineering Seismology, Geotechnical and Structural Earthquake Engineering

2025, The European Physical Journal Special Topics

Summary of the long term data taking, related to one of the proposed next generation ground-based gravitational detector’s location is presented here. Results of seismic and infrasound noise, electromagnetic attenuation and cosmic muon radiation measurements are reported in the underground Matra Gravitational and Geophysical Laboratory near Gyöngyösoroszi, Hungary. The collected seismic data of more than two years is evaluated from the point of view of the Einstein Telescope, a proposed third generation underground gravitational wave observatory. Applying our results for the site selection will significantly improve the signal to noise ratio of the multi-messenger astrophysics era, especially at the low frequency regime.

2025, Symposium on the Application of Geophysics to Engineering and Environmental Problems 2006

Studies for urban hazard or resource assessment often take place in densely populated areas characterized by considerable cultural noise. These site conditions can severely compromise seismic reflection data quality. We have collected vibroseis and hammer (weight drop) seismic reflection data in a range of geologic conditions to image stratigraphy and structures in the upper one km along regional highways, city streets, and power line access roads. In addition to the challenges of safety and outreach, acquisition efforts along busy streets and highways often encounter poor receiver coupling and largeamplitude coherent noise from traffic and power lines. Although higher quality seismic reflection data may be obtained by simply choosing alternate sites with less cultural noise, modifications to the acquisition and processing steps can minimize the effects of cultural noise and poor coupling where profiling is most relevant. Flagging crews, flyers and public announcements assist with outreach and safety concerns, and the local news media are often enthusiastic about publicizing geologic studies. Recording long-record vibroseis data reduces the effects of noise by itself, but data quality can be further optimized by recording uncorrelated, unstacked data and applying precorrelation amplitude adjustments and filters. Recording individual hammer shots likewise allows gains or mutes to normalize or remove traffic noise prior to vertical stacking. Large numbers of receiver channels allow attenuation of random noise and velocity filtering to remove coherent noise. Because ground roll and normal moveout (NMO) corrections minimize near-surface coverage, asymmetric source-receiver geometry allows for additional near-surface fold while muting large amplitude ground roll and NMO stretch. Source and geophone coupling on road shoulders can degrade signal quality due to variable materials and topography, but these problems are often addressed with static corrections. Our experience is that high-quality seismic data can be obtained in noisy urban areas, but many recorded channels and a careful attention to acquisition and processing procedures can significantly improve the results.

2025

In June 2001, during the project "Estudio Cortical de Caracas" (ECCAR) a total of 8 seismic wide angle profiles were measured in the Caracas metropolitan region, extending between the towns of Caraballeda (a the coast) and Ocumare del Tuy (50 km south). The main subject of the ECCAR project was to determine the sediment thickness and derive the seismic velocities in order to obtain new subsoil information for the Seismic Microzoning Project of the metropolitan region of Caracas. In the south of Caracas, a superficial layer of 10 - 15 m in thickness and a Vp velocity of 1.8 km/s is underlain by a layer with a velocity of 2.1-2.4 km/s and a maximum thickness of 380 m, corresponding these units to the alluvial sediments of the Caracas valley. Below, a layer with a velocity of 3.8 km/s corresponds to the slightly meteorized rocks of the Las Mercedes and Las Brisas Schists. Below 700 m in depth, velocities increase to 5.1 km/s, which is associated to the same metamorphic units,...

2025

improve the dissipation term . While overall scores have improved significantly, large biases still exist in some regions. Recent work on the wave dissipation (ARDHUIN et al., 2008), resulted in a new formulation of the dissipation, thanks to tracking swells by ROS (Radar Aperture Synthesis). This paper presents an evaluation of various formulations discussed here, through the joint use of in situ data and remote sensed data for the year 2007.

2025, GEOPHYSICS

The presence of noise in towed marine seismic data is a long-standing problem. The various types of noise present in marine seismic records are never truly random. Instead, seismic noise is more complex and often challenging to attenuate in seismic data processing. Therefore, we have examined a wide range of real data examples contaminated by different types of noise including swell noise, seismic interference noise, strumming noise, passing vessel noise, vertical particle velocity noise, streamer hit and fishing gear noise, snapping shrimp noise, spike-like noise, cross-feed noise, and streamer-mounted device noise. The noise examples investigated focus only on data acquired with analog group forming. Each noise type is classified based on its origin, coherency, and frequency content. We then determine how the noise component can be effectively attenuated through industry-standard seismic processing techniques. In this tutorial, we avoid presenting the finest details of either the ...

2025

Misclassified nonearthquake seismic events like quarry blasts can contaminate the earthquake catalog. The local earthquakes sometimes have similar features as the quarry blasts, which makes manual discrimination difficult and unreliable. Thus, we propose to use the compact convolutional transformer (CCT) and capsule neural network to discriminate between earthquakes and quarry blasts. First, we extract 60 s three-channel seismograms, that is, 10 and 50 s before and after the P-wave arrival time. Then, we transform the time-series data into a time-frequency domain (scalogram) using the continuous wavelet transform. Afterward, we utilize the CCT network to extract the most significant features from the input scalograms. The capsule neural network is utilized to extract the spatial relation between the extracted features using the routing-by-agreement approach (dynamic routing). The capsule neural network extracts different digit vectors for the earthquake and the quarry blast classes, allowing a robust classification accuracy. The proposed algorithm is evaluated using the seismic dataset recorded by the Egyptian Seismic Network. The dataset is divided into 80% for training and 20% for testing. Although the dataset is unbalanced, the proposed algorithm shows promising results. The testing accuracy of the proposed algorithm is 97.31%. The precision, recall, and F1-score are 97.23%, 98.83%, and 98.02%, respectively. In addition, the proposed algorithm outperforms the traditional deep learning models, for example, convolutional neural network, ResNet, VGG, and AlexNet networks. Finally, the proposed method is demonstrated to enjoy a high-generalization ability through a real-time monitoring experiment.

2025, Scientific Reports

The analysis of the background noise in seismic networks has proved to be a powerful tool not only to acquire new insights on the crustal structure, but also to monitor different natural and anthropogenic processes. We show that data acquired during controlled source experiments can also be a valuable tool to monitor such processes, in particular when using high-density deployments. Data from a wide-angle reflection and refraction seismic profile in the central-northwest part of Iberia is used to identify signals related to aircrafts, road traffic, quarry blasts, wind blow, rainfall or thunders. The most prominent observations are those generated by a helicopter and an airplane flying following trajectories subparallel to the profile, which are tracked along 200 km with a spatial resolution of 350 m, hence providing an exceptional dataset. Other highlights are the observation of the Doppler effect on signals generated by moving cars and the high-density recording of acoustic waves g...

2025, Applied Sciences

The Trans-Mexican Volcanic Belt (TMVB), located in central Mexico, is an area for which low to moderate seismic risk is considered. This is based on the limited instrumental data available, even though large historical earthquakes have damaged some urban centers in the past. However, site effects is an aspect that must be considered in estimating risk, because there are some instances of important amplifications that have been documented with serious effects. In this work, ambient noise and earthquake records from 90 seismic permanent and temporary stations are used to analyze site response in the TMVB. The results obtained show a heterogeneous range in the value of the fundamental frequency. When possible, a comparison was made of the results obtained from ambient noise and earthquake records. In almost all these comparisons, no significant differences were observed in terms of the fundamental frequency. However, there were some stations with a flat average HVSR ambient noise curve...

2025

In this study, short-period noise characteristics at BURAR station were investigated by applying both power spectral density estimation (PSD) and frequency-wavenumber (f-k) array technique. Regular recording of noise spectra for 60 seconds time window sampled at every six hours has been performed over one-year period. F-k analysis estimates were calculated for 9 frequency bandwidths between 0.1 and 16 Hz. The

2025, Bulletin of the Seismological Society of America

Seismic investigations are mainly limited by seismic noise. Two microbarometers have been installed in the seismic vault of two different GEOSCOPE stations, one at SSB and the other at TAM. All vertical components and most of the horizontal components show a significant correlation with pressure. In order to correct the seismic signals from the atmospheric pressure noise, a transfer function between the pressure data and the seismic data is inverted. Results show that, after correction, the noise levels reached on the horizontal components are similar between the two stations, and the vertical components display noise levels below the low-noise model as defined by Peterson (1993). This technique reduces part of the noise and allows detection of small earthquakes and a better extraction of normal modes. The analysis of the lowest normal modes of the Earth excited by the MS = 8.2 Macquarie Island earthquake is given to illustrate the perspectives of the method.

2025

Gunungapi Marapi, Sumatera Barat berada pada tingkat aktivitas level II (status Waspada) sejak Agustus 2011 hingga sekarang. Data sinyal gempabumi vulkanik Agustus-September 2013 yang meliputi sinyal gempabumi Vulkano-Tektonik (VT) dan Tornillo telah diolah untuk mengetahui keberadaan lokasi serta nilai faktor kualitas (Q factor) dari titik-titik hiposenter. Lokasi hiposenter diperoleh dengan menggunakan metode Geiger. Nilai faktor kualitas (Q factor) diperoleh dari perkalian nilai frekuensi dominan dengan phi (π) dan dibagi dengan perkalian koefisien atenuasi terhadap kecepatan perambatan medium oleh gelombang P. Lokasi hiposenter dari gempabumi VT dengan jumlah data 24 event dari 4 stasiun seismik yang tersebar pada sisi barat laut puncak Gunungapi Marapi yang memiliki kedalaman 1.855 m sampai 4.642 m. Data sinyal Tornillo berjumlah 20 event yang terekam pada satu stasiun seismik, dengan komponen vertikal. Untuk sinyal Tornillo, nilai koefisien atenuasi 0,17-0,73 dB/λ dan asumsi kecepatan rambat medium 2,84 km/s. Untuk gempabumi VT, nilai koefisien atenuasi 0,16-0,4 dB/λ dan asumsi kecepatan rambat medium berada antara nilai 2,36-2,84 km/s. Nilai Q factor dari gempabumi VT berada pada rentang 14-38 λ/dB dan dari sinyal Tornillo berada pada rentang 9-40 λ/dB. Litologi umum yang diperoleh dari nilai Q factor dapat diklasifikasikan sebagai batuan sedimen (Q= 20-200 λ/dB), batulempung (Q= 20-70 λ/dB), dan batuan dengan gas dalam rongga (Q= 5-50 λ/dB).

2025

2025, Bulletin of the Seismological Society of America

2025, Near Surface Geophysics

ABSTRACTIn this study, 20 hours of ambient seismic noise recorded from a small‐scale inter‐station distance was used to obtain near‐surface shear wave velocity structures at a local test site in Tehran (Iran). High‐resolution group velocity dispersion curves using fundamental mode of surface waves were calculated for all possible combinations of station pairs at frequencies ranging from 1 Hz to 25 Hz. Unlike most previous studies regarding ambient seismic noise, which observe very little coherent noise at frequencies larger than 1 Hz, the empirical Green’s functions were extracted using a root‐mean‐square stacking method showing more coherent signals. Our results indicate that ambient seismic noise is a viable technique at a frequency range of 1 Hz–25 Hz even when different sensor types are present. One‐dimensional VSV and VSH models from the near surface were then assessed by inverting the calculated Rayleigh and Love waves’ dispersion measurements. We observed that the calculated ...

2025, Seismological Research Letters

2025, Geophysical Journal International

In this study, we present an application of the ambient noise tomography (ANT) to study the near-surface geological structures of the metropolitan Tehran/Iran region. Short-period fundamental mode Rayleigh wave Green's functions were estimated using cross-correlations of the vertical component of the ambient noise from 2009 October to 2011 May using a variety of seismic sensors, for example, accelerometers and seismometers, deployed in the Tehran area. Standard common low frequency processing procedures were applied to the cross-correlations, and shorter time-windows comprising 10-min segments were used in the processing step to enhance the time resolution of the signal in the frequency range of interest (1-10 s). Stacking was also conducted using the rms of the estimated empirical Green's functions. Our results demonstrate that ambient seismic noise tomography is a viable technique at periods of 1-10 s in length, even when different sensor types are present. Analysis of the empirical Green's functions indicates that the dominant sources of ambient seismic noise originated from the same origin, and no significant seasonal or spatial variations in the ambient noise sources were observed. Multiple-filter analysis was used to extract the group velocities from the estimated empirical Green's functions, which were then inverted to image the spatially varying dispersion at periods of lengths between 1 and 7 s using tomographic inversion of the traveltimes estimated for each frequency. The resulting group velocity maps show high correlations with known geological and tectonic features of the study region. In general, most of the Tehran basin, with certain exceptions, could be clearly resolved with low group velocities, whereas the mountain ranges were found to be correlated with high group velocities. In the Tehran basin, for 2 and 3 s periods, the low-velocity zone deepens towards the south-southwest, which reflects thicker sediments in the southern part of the basin than in the north. This feature has also been observed in other geological studies. The Vs models also show that bedrock depth varies between 400 and 1400 m from north to south within the Tehran basin. At longer periods main faults are associated with abrupt transitions between regions of high-to low-velocity anomalies. In general, our results indicate that ANT can be a flexible and effective approach for studying near-surface heterogeneity using short-period surface wave data.

2025, Geophysical Journal International

We analysed background surface waves in seismic ambient noise by cross-correlating continuous records of eight ocean bottom seismometers and nine differential pressure gauges deployed in the northwestern Pacific Ocean by the PLATE project. After estimating the clock delay and instrumental phase responses of differential pressure gauges by using cross-correlation functions, we measured average phase velocities in the area of the array for the fundamental-, first higher-and second higher-mode Rayleigh waves, and the fundamental-mode Love waves at a period range of 3-40 s by waveform fitting. We then measured phase-velocity anomalies of fundamental-mode and first higher-mode Rayleigh waves for each pair of stations at a period range of 5-25 s, and corrected the effect of variation in water-depths. The seismic anomalies imply the presence of strong azimuthal anisotropy beneath the eastern part of array. The direction of maximum velocity is approximately N35 • E in the fossil seafloor spreading direction perpendicular to magnetic lineations from the ancient triple junction at this location. The peak-to-peak intensity of shear-wave velocity anisotropy in the mantle is ∼7 per cent.