Nelson Ricardo Coelho Flores Zuniga, Deyan Draganov, Ranajit Ghose
Abstract Using post‐critical reflection data, it is possible to obtain useful information that allows more reliable geological characterization of the subsurface. However, the strong distortion caused by the phase shift in post‐critical wavelets makes the use of post‐critical reflections rather challenging. For this reason, an approach which is capable of estimating the phase shift of each wavelet of a reflection event in a data‐driven manner is desirable. In this vein, in case the frequency spectrum of a wavelet can be correctly estimated, it is possible to estimate the instantaneous phase shift. In this work, we propose an approach which can perform such estimation based on spectral recomposition of seismic data. We design an inversion approach in order to reconstruct the seismic spectrum of the wavelets of a reflection event, which subsequently allows us to estimate the instantaneous phase of each wavelet of the near‐surface reflection events without performing prior velocity analysis and/or critical‐angle estimation. After finding the instantaneous phase for each wavelet of a reflection event, we show next how one can find the respective phase shifts that can then be corrected.
{"title":"Phase‐shift correction of seismic reflections by means of spectral recomposition","authors":"Nelson Ricardo Coelho Flores Zuniga, Deyan Draganov, Ranajit Ghose","doi":"10.1002/nsg.12271","DOIUrl":"https://doi.org/10.1002/nsg.12271","url":null,"abstract":"Abstract Using post‐critical reflection data, it is possible to obtain useful information that allows more reliable geological characterization of the subsurface. However, the strong distortion caused by the phase shift in post‐critical wavelets makes the use of post‐critical reflections rather challenging. For this reason, an approach which is capable of estimating the phase shift of each wavelet of a reflection event in a data‐driven manner is desirable. In this vein, in case the frequency spectrum of a wavelet can be correctly estimated, it is possible to estimate the instantaneous phase shift. In this work, we propose an approach which can perform such estimation based on spectral recomposition of seismic data. We design an inversion approach in order to reconstruct the seismic spectrum of the wavelets of a reflection event, which subsequently allows us to estimate the instantaneous phase of each wavelet of the near‐surface reflection events without performing prior velocity analysis and/or critical‐angle estimation. After finding the instantaneous phase for each wavelet of a reflection event, we show next how one can find the respective phase shifts that can then be corrected.","PeriodicalId":49771,"journal":{"name":"Near Surface Geophysics","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135647981","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Santin Ilaria, Roncoroni Giacomo, Forte Emanuele, Gutgesell Pietro, Pipan Michele
Abstract Scattering is often detected when ground‐penetrating radar (GPR) surveys are performed on glaciers at different latitudes and in various environments. This event is often seen as an undesirable feature on data, but it can be exploited to quantify the debris content in mountain glaciers through a dedicated scattering inversion approach. At first, we considered the possible variables affecting the scattering mechanisms, namely the dielectric properties of the scatterers, their size, shape and quantity, as well as the wavelength of the electromagnetic (EM) incident field to define the initial conditions for the inversion. Each parameter was independently evaluated with forward modelling tests to quantify its effect in the scattering mechanism. After extensive tests, we found that the dimension and the amount of scatterers are the crucial parameters. We further performed modelling randomizing the scatterer distribution and dimension, critically evaluating the stability of the approach and the complexity of the models. After the tests on synthetic data, the inversion procedure was applied to field datasets, acquired on the Eastern Gran Zebrù glacier (Central Italian Alps). The results show that even a low percentage of debris can produce high scattering. The proposed methodology is quite robust and able to provide quantitative estimates of the debris content within mountain glaciers in different conditions.
{"title":"GPR modelling and inversion to quantify the debris content within ice","authors":"Santin Ilaria, Roncoroni Giacomo, Forte Emanuele, Gutgesell Pietro, Pipan Michele","doi":"10.1002/nsg.12274","DOIUrl":"https://doi.org/10.1002/nsg.12274","url":null,"abstract":"Abstract Scattering is often detected when ground‐penetrating radar (GPR) surveys are performed on glaciers at different latitudes and in various environments. This event is often seen as an undesirable feature on data, but it can be exploited to quantify the debris content in mountain glaciers through a dedicated scattering inversion approach. At first, we considered the possible variables affecting the scattering mechanisms, namely the dielectric properties of the scatterers, their size, shape and quantity, as well as the wavelength of the electromagnetic (EM) incident field to define the initial conditions for the inversion. Each parameter was independently evaluated with forward modelling tests to quantify its effect in the scattering mechanism. After extensive tests, we found that the dimension and the amount of scatterers are the crucial parameters. We further performed modelling randomizing the scatterer distribution and dimension, critically evaluating the stability of the approach and the complexity of the models. After the tests on synthetic data, the inversion procedure was applied to field datasets, acquired on the Eastern Gran Zebrù glacier (Central Italian Alps). The results show that even a low percentage of debris can produce high scattering. The proposed methodology is quite robust and able to provide quantitative estimates of the debris content within mountain glaciers in different conditions.","PeriodicalId":49771,"journal":{"name":"Near Surface Geophysics","volume":"85 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135323898","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. Onyebueke, M. Manzi, M. Rapetsoa, T. Kgarume, M. Westgate, R. Durrheim, Michelle Pienaar, M. Sihoyiya, Mvikeli Mpofu, M. Schoor, Phumlani Kubeka
Improving the exploration of deep‐seated mineral deposits and assessing the stability of the mine pillars require that geophysical techniques are deployed in a fast and cost‐effective manner with minimal environmental impact. This research presents results from in‐mine reflection seismic experiments and a Ground Penetrating Radar (GPR) survey conducted at Maseve platinum mine, South Africa. The research aims to develop and implement methods to image Platinum Group Metal (PGM) deposits and geological structures near mine tunnels and assess the stability of pillars. The seismic experiments were conducted using a sledgehammer source (10 lb), conventional cabled geophones (14 Hz), and a landstreamer with 4.5 Hz vertical component geophones. The GPR survey was conducted using a Noggin 500 GPR system with 500 MHz centre frequency. An image of the underlying orebody and geological structures down to 100 m from the mine tunnel floor (∼ 500 m below ground surface) was produced. We correlated the coherent reflections beneath the tunnel floor with a known Upper Group (UG2) PGM orebody. The final seismic section shows that the UG2 mineralisation is dissected by near‐vertical dykes, faults and fractures. These structures, faults in particular, are interpreted to have been active post‐mineralisation, implying that they may have contributed to the current complex geometry of the deposit. Four GPR profiles were collected around a stability pillar adjacent to the seismic lines. The radargram sections were processed to improve the S/N. The results show different patterns of fracturing and stress‐ induced structures. Perhaps, these fracturing were shown to be subvertical and constituted complex micro‐structures within the pillar, which could compromise the pillar stability and integrity. The study demonstrates that in‐mine seismic and GPR surveys can be cost‐effective and valuable for mineral exploration.This article is protected by copyright. All rights reserved
{"title":"Integration of In‐mine Seismic and GPR Surveys to Gain Advanced Knowledge of Bushveld Complex Orebodies","authors":"E. Onyebueke, M. Manzi, M. Rapetsoa, T. Kgarume, M. Westgate, R. Durrheim, Michelle Pienaar, M. Sihoyiya, Mvikeli Mpofu, M. Schoor, Phumlani Kubeka","doi":"10.1002/nsg.12270","DOIUrl":"https://doi.org/10.1002/nsg.12270","url":null,"abstract":"Improving the exploration of deep‐seated mineral deposits and assessing the stability of the mine pillars require that geophysical techniques are deployed in a fast and cost‐effective manner with minimal environmental impact. This research presents results from in‐mine reflection seismic experiments and a Ground Penetrating Radar (GPR) survey conducted at Maseve platinum mine, South Africa. The research aims to develop and implement methods to image Platinum Group Metal (PGM) deposits and geological structures near mine tunnels and assess the stability of pillars. The seismic experiments were conducted using a sledgehammer source (10 lb), conventional cabled geophones (14 Hz), and a landstreamer with 4.5 Hz vertical component geophones. The GPR survey was conducted using a Noggin 500 GPR system with 500 MHz centre frequency. An image of the underlying orebody and geological structures down to 100 m from the mine tunnel floor (∼ 500 m below ground surface) was produced. We correlated the coherent reflections beneath the tunnel floor with a known Upper Group (UG2) PGM orebody. The final seismic section shows that the UG2 mineralisation is dissected by near‐vertical dykes, faults and fractures. These structures, faults in particular, are interpreted to have been active post‐mineralisation, implying that they may have contributed to the current complex geometry of the deposit. Four GPR profiles were collected around a stability pillar adjacent to the seismic lines. The radargram sections were processed to improve the S/N. The results show different patterns of fracturing and stress‐ induced structures. Perhaps, these fracturing were shown to be subvertical and constituted complex micro‐structures within the pillar, which could compromise the pillar stability and integrity. The study demonstrates that in‐mine seismic and GPR surveys can be cost‐effective and valuable for mineral exploration.This article is protected by copyright. All rights reserved","PeriodicalId":49771,"journal":{"name":"Near Surface Geophysics","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41815583","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Papadopoulou Myrto, Malehmir Alireza, Markovic Magdalena, Berglund Johan
Seismic investigations were performed at a site in the southwest of Sweden where major quick‐clay landslides have occurred in the past. Given the potential high risk of the area and the presence of medium‐sized infrastructures, the site posed a need for detailed investigations in a wide depth range and in high resolution. A high‐fold seismic survey was designed and conducted along two profiles using 1–2 m receiver and shot spacing in order to retrieve both P‐ and S‐wavefield seismic images from vertical component data. The data were analyzed combining first‐break traveltime tomography and surface‐wave analysis as well as P‐ and S‐wavefield reflection seismic imaging. Using the first breaks, P‐wave velocity (VP) models were estimated, indicating the bedrock topography along the profiles and the sediment characteristics. The S‐wave velocity (Vs) models were estimated from the surface waves and indicated areas of low shear strength. Combined with VP and Vs models, this permits the estimation of VP/VS, a parameter that can indicate areas with high water content, significant for the detection of quick clays and possible liquefaction issues. The results are integrated with the P‐ and S‐wave reflection seismic images and compared with other geophysical investigations such as magnetic and gravity data that were collected along the profiles.This article is protected by copyright. All rights reserved
{"title":"High‐resolution P‐ and S‐wavefield seismic investigations of a quick‐clay site in southwest of Sweden","authors":"Papadopoulou Myrto, Malehmir Alireza, Markovic Magdalena, Berglund Johan","doi":"10.1002/nsg.12269","DOIUrl":"https://doi.org/10.1002/nsg.12269","url":null,"abstract":"Seismic investigations were performed at a site in the southwest of Sweden where major quick‐clay landslides have occurred in the past. Given the potential high risk of the area and the presence of medium‐sized infrastructures, the site posed a need for detailed investigations in a wide depth range and in high resolution. A high‐fold seismic survey was designed and conducted along two profiles using 1–2 m receiver and shot spacing in order to retrieve both P‐ and S‐wavefield seismic images from vertical component data. The data were analyzed combining first‐break traveltime tomography and surface‐wave analysis as well as P‐ and S‐wavefield reflection seismic imaging. Using the first breaks, P‐wave velocity (VP) models were estimated, indicating the bedrock topography along the profiles and the sediment characteristics. The S‐wave velocity (Vs) models were estimated from the surface waves and indicated areas of low shear strength. Combined with VP and Vs models, this permits the estimation of VP/VS, a parameter that can indicate areas with high water content, significant for the detection of quick clays and possible liquefaction issues. The results are integrated with the P‐ and S‐wave reflection seismic images and compared with other geophysical investigations such as magnetic and gravity data that were collected along the profiles.This article is protected by copyright. All rights reserved","PeriodicalId":49771,"journal":{"name":"Near Surface Geophysics","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48948154","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Lajaunie, J. Gance, P. Sailhac, J. Malet, S. Warden, H. Larnier
Altered crystalline catchments are complex to study and model, as they present multi‐scale properties that control their hydrogeological behavior and that are difficult to capture through a single geophysical imaging technique. Several volumes of interest must be sampled in order that both small‐scale (porosity, layering) and large‐scale (bedrock, weathering, faults) heterogeneities can be captured. We propose a geoelectrical model of the Strengbach catchment (Vosges Mountains, France), aiming at identifying the weathered structures and hydrogeological functioning of the aquifer. This is achieved through ERT and CSAMT measurements and the use of appropriate measurement setups. Meters‐scale shallow contrasts in the topsoil, catchment‐scale shallow contrasts (top 30 m) and large‐scale vertical contrasts (up to150 m) were resolved through this methodology. A structural interpretation is proposed, based on information provided by borehole measurements (gamma ray, optical images), analysis of sampled waters and geological mapping. The limits at depth of the weathered and fractured granite, not detected by ERT, are detected by CSAMT. The analysis showed that the weathering state of the granite controls, at first order, the electrical resistivity signal. Shallow geoelectrical signal (first 30 m) is particularly driven by surface conductivity hence by the clay content, whereas deep geoelectrical signal may arise from both the ionic content of pore waters and the clay content. A structural model is proposed and discussed. Geoelectrical contrasts revealed several qualities of weathered saprolite between the northern and the southern slopes. The inferred structural model and the distribution of weathered and unweathered crystalline units are considered for their respective effect on the hydrogeology, leading to the proposition of a new hydrogeological conceptual model of the catchment.This article is protected by copyright. All rights reserved
{"title":"Hydrogeological structure of a granitic mountain catchment inferred from multi‐method electrical resistivity datasets","authors":"M. Lajaunie, J. Gance, P. Sailhac, J. Malet, S. Warden, H. Larnier","doi":"10.1002/nsg.12268","DOIUrl":"https://doi.org/10.1002/nsg.12268","url":null,"abstract":"Altered crystalline catchments are complex to study and model, as they present multi‐scale properties that control their hydrogeological behavior and that are difficult to capture through a single geophysical imaging technique. Several volumes of interest must be sampled in order that both small‐scale (porosity, layering) and large‐scale (bedrock, weathering, faults) heterogeneities can be captured. We propose a geoelectrical model of the Strengbach catchment (Vosges Mountains, France), aiming at identifying the weathered structures and hydrogeological functioning of the aquifer. This is achieved through ERT and CSAMT measurements and the use of appropriate measurement setups. Meters‐scale shallow contrasts in the topsoil, catchment‐scale shallow contrasts (top 30 m) and large‐scale vertical contrasts (up to150 m) were resolved through this methodology. A structural interpretation is proposed, based on information provided by borehole measurements (gamma ray, optical images), analysis of sampled waters and geological mapping. The limits at depth of the weathered and fractured granite, not detected by ERT, are detected by CSAMT. The analysis showed that the weathering state of the granite controls, at first order, the electrical resistivity signal. Shallow geoelectrical signal (first 30 m) is particularly driven by surface conductivity hence by the clay content, whereas deep geoelectrical signal may arise from both the ionic content of pore waters and the clay content. A structural model is proposed and discussed. Geoelectrical contrasts revealed several qualities of weathered saprolite between the northern and the southern slopes. The inferred structural model and the distribution of weathered and unweathered crystalline units are considered for their respective effect on the hydrogeology, leading to the proposition of a new hydrogeological conceptual model of the catchment.This article is protected by copyright. All rights reserved","PeriodicalId":49771,"journal":{"name":"Near Surface Geophysics","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43405026","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Flooding, erosion, and increases in the water level in Lake Superior have contributed to changes in the stem location and width of the Grand Portage Creek. Those events threaten parts of the Grand Portage National Monument, a historically significant site on the North Shore of Lake Superior, Minnesota. We performed geophysical surveys to investigate these dynamic effects. We studied the near‐surface geological deposits, the mechanisms associated with creek stem dynamics, and sediment transport and deposition along the lakeshore in Grand Portage Bay. We deployed Ground Penetrating Radar (GPR), Sub Bottom Profiler (SBP), Side Scan Sonar (SSS), Geoprobe coring, and Van Veen Grab samplers and evaluated time‐lapse satellite images to assess the interaction of the Grand Portage Creek with the Grand Portage Bay. The onshore GPR surveys next to the national monument, the creek, and the shoreline showed the presence of a complex deposition with eroded ground surfaces and sediment layers across the creek valley. Results from the offshore geophysical campaigns and the interpretations of satellite images also document a heterogeneous deposition sequence environment with fine‐grained sediment deposits present south and southwest of the creek mouth. In addition, we documented an exposed boulder bed toward the east of the creek mouth that was exposed by the current and wave‐driven erosion process in the Grand Portage Bay. Time‐lapse satellite images and hydraulic current velocity simulations validate these observations and provide insight into how anthropogenic activities and natural events interact and might contribute to the long‐term stability of a site of historical and cultural importance.This article is protected by copyright. All rights reserved
{"title":"Geophysical surveys and satellite imaging for the evaluation of near‐surface terrain dynamic ‐ a case study on Grand Portage, MN, USA","authors":"Jeong-Mo Lee, D. Fratta","doi":"10.1002/nsg.12267","DOIUrl":"https://doi.org/10.1002/nsg.12267","url":null,"abstract":"Flooding, erosion, and increases in the water level in Lake Superior have contributed to changes in the stem location and width of the Grand Portage Creek. Those events threaten parts of the Grand Portage National Monument, a historically significant site on the North Shore of Lake Superior, Minnesota. We performed geophysical surveys to investigate these dynamic effects. We studied the near‐surface geological deposits, the mechanisms associated with creek stem dynamics, and sediment transport and deposition along the lakeshore in Grand Portage Bay. We deployed Ground Penetrating Radar (GPR), Sub Bottom Profiler (SBP), Side Scan Sonar (SSS), Geoprobe coring, and Van Veen Grab samplers and evaluated time‐lapse satellite images to assess the interaction of the Grand Portage Creek with the Grand Portage Bay. The onshore GPR surveys next to the national monument, the creek, and the shoreline showed the presence of a complex deposition with eroded ground surfaces and sediment layers across the creek valley. Results from the offshore geophysical campaigns and the interpretations of satellite images also document a heterogeneous deposition sequence environment with fine‐grained sediment deposits present south and southwest of the creek mouth. In addition, we documented an exposed boulder bed toward the east of the creek mouth that was exposed by the current and wave‐driven erosion process in the Grand Portage Bay. Time‐lapse satellite images and hydraulic current velocity simulations validate these observations and provide insight into how anthropogenic activities and natural events interact and might contribute to the long‐term stability of a site of historical and cultural importance.This article is protected by copyright. All rights reserved","PeriodicalId":49771,"journal":{"name":"Near Surface Geophysics","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47364883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Qingjie Yang, Bing Zhou, Marcus Engsig, M. Won, M. Riahi, M. Al-khaleel, S. Greenhalgh
Derivatives of the displacement tensor with respect to the independent model parameters of the subsurface, also called Fréchet derivatives (or sensitivity kernels), are a key ingredient for seismic full‐waveform inversion with a local‐search optimization algorithm. They provide a quantitative measure of the expected changes in the seismograms due to perturbations of the subsurface model parameters for a given survey geometry. Since 2.5‐D wavefield modeling involves a real point source in a 2‐D geological model with 3D (spherical) wave properties, it yields synthetic data much closer to the actual practical field data than the commonly used 2‐D wave simulation does, which uses an unrealistic line source in which the waves spread cylindrically. Based on our recently developed general 2.5‐D wavefield modeling scheme, we apply the perturbation method to obtain explicit analytic expressions for the derivatives of the displacement tensor for 2.5‐D/2‐D frequency‐domain seismic full‐waveform inversion in general viscoelastic anisotropic media. We then demonstrate the numerical calculations of all these derivatives in two common cases: (i) viscoelastic isotropic and (ii) viscoelastic tilted transversely isotropic (TTI) solids. Examples of the differing sensitivity patterns for the various derivatives are investigated and compared for four different homogeneous models involving 2‐D and 2.5‐D modeling. Also, the numerical results are verified against the analytic solutions for homogeneous models. We further validate the numerical derivatives in a 2‐D heterogeneous viscoelastic TTI case by conducting a synthetic data experiment of frequency‐domain full‐waveform inversion to individually recover the twelve independent model parameters (density, dip angle, five elastic moduli, and five corresponding Q‐factors) in a simple model comprising an anomalous square box target embedded in a uniform background. Another 2.5‐D multi‐target model experiment presenting impacts from four common seismic surveying geometries validates the Fréchet derivatives again.This article is protected by copyright. All rights reserved
{"title":"Numerical Fréchet derivatives of the displacement tensor for 2.5‐D frequency‐domain seismic full‐waveform inversion in viscoelastic TTI media","authors":"Qingjie Yang, Bing Zhou, Marcus Engsig, M. Won, M. Riahi, M. Al-khaleel, S. Greenhalgh","doi":"10.1002/nsg.12265","DOIUrl":"https://doi.org/10.1002/nsg.12265","url":null,"abstract":"Derivatives of the displacement tensor with respect to the independent model parameters of the subsurface, also called Fréchet derivatives (or sensitivity kernels), are a key ingredient for seismic full‐waveform inversion with a local‐search optimization algorithm. They provide a quantitative measure of the expected changes in the seismograms due to perturbations of the subsurface model parameters for a given survey geometry. Since 2.5‐D wavefield modeling involves a real point source in a 2‐D geological model with 3D (spherical) wave properties, it yields synthetic data much closer to the actual practical field data than the commonly used 2‐D wave simulation does, which uses an unrealistic line source in which the waves spread cylindrically. Based on our recently developed general 2.5‐D wavefield modeling scheme, we apply the perturbation method to obtain explicit analytic expressions for the derivatives of the displacement tensor for 2.5‐D/2‐D frequency‐domain seismic full‐waveform inversion in general viscoelastic anisotropic media. We then demonstrate the numerical calculations of all these derivatives in two common cases: (i) viscoelastic isotropic and (ii) viscoelastic tilted transversely isotropic (TTI) solids. Examples of the differing sensitivity patterns for the various derivatives are investigated and compared for four different homogeneous models involving 2‐D and 2.5‐D modeling. Also, the numerical results are verified against the analytic solutions for homogeneous models. We further validate the numerical derivatives in a 2‐D heterogeneous viscoelastic TTI case by conducting a synthetic data experiment of frequency‐domain full‐waveform inversion to individually recover the twelve independent model parameters (density, dip angle, five elastic moduli, and five corresponding Q‐factors) in a simple model comprising an anomalous square box target embedded in a uniform background. Another 2.5‐D multi‐target model experiment presenting impacts from four common seismic surveying geometries validates the Fréchet derivatives again.This article is protected by copyright. All rights reserved","PeriodicalId":49771,"journal":{"name":"Near Surface Geophysics","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45142895","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Glaciers generate seismic waves due to calving and fracturing, and recording and following event classification can be used to monitor glacier dynamics. Our aim with this study is to analyze seismic data acquired at the seabed and on land in front of Nordenskiöldbreen on Svalbard during 8 days in October 2020. The survey included 27 ocean bottom nodes, each equipped with three geophones and a hydrophone, and 101 land‐based geophones. The resulting data contain numerous seismic P‐, S‐, and Scholte wave events throughout the study period, as well as non‐seismic gravity waves. The recording quality strongly depends on receiver type and location, especially for the latter wave types. Our results demonstrate that hydrophones at the seabed are advantageous to record gravity waves, and that Scholte waves are only recorded close to the glacier. The Scholte waves are used to estimate the near‐surface S‐wave profile of the seabed sediments, and the gravity wave amplitudes are converted to wave height at the surface. We further discuss possible source mechanisms for the recorded events and present evidence that waves from earthquakes, calving, and brittle fracturing of the glacier and icebergs are all represented in the data. The interpretation is based on frequency content, duration, seismic velocities, and onset (emergent/impulsive), and supported by source localization which we show is challenging for this dataset. In conclusion, our study demonstrates the potential of using seismic for detecting glacier‐related events and provides valuable knowledge about the importance of survey geometry, particularly the advantages of including seabed receivers in the vicinity of the glacier.This article is protected by copyright. All rights reserved
{"title":"Case study of combined marine and land‐based passive seismic surveying in front of Nordenskiöldbreen outlet glacier, Adolfbukta, Svalbard","authors":"H. M. Stemland, B. Ruud, T. Johansen","doi":"10.1002/nsg.12266","DOIUrl":"https://doi.org/10.1002/nsg.12266","url":null,"abstract":"Glaciers generate seismic waves due to calving and fracturing, and recording and following event classification can be used to monitor glacier dynamics. Our aim with this study is to analyze seismic data acquired at the seabed and on land in front of Nordenskiöldbreen on Svalbard during 8 days in October 2020. The survey included 27 ocean bottom nodes, each equipped with three geophones and a hydrophone, and 101 land‐based geophones. The resulting data contain numerous seismic P‐, S‐, and Scholte wave events throughout the study period, as well as non‐seismic gravity waves. The recording quality strongly depends on receiver type and location, especially for the latter wave types. Our results demonstrate that hydrophones at the seabed are advantageous to record gravity waves, and that Scholte waves are only recorded close to the glacier. The Scholte waves are used to estimate the near‐surface S‐wave profile of the seabed sediments, and the gravity wave amplitudes are converted to wave height at the surface. We further discuss possible source mechanisms for the recorded events and present evidence that waves from earthquakes, calving, and brittle fracturing of the glacier and icebergs are all represented in the data. The interpretation is based on frequency content, duration, seismic velocities, and onset (emergent/impulsive), and supported by source localization which we show is challenging for this dataset. In conclusion, our study demonstrates the potential of using seismic for detecting glacier‐related events and provides valuable knowledge about the importance of survey geometry, particularly the advantages of including seabed receivers in the vicinity of the glacier.This article is protected by copyright. All rights reserved","PeriodicalId":49771,"journal":{"name":"Near Surface Geophysics","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45638470","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ground penetrating radar (GPR) is regulated regarding emission limits for ultra‐wideband (UWB) in a number of jurisdictions. The definitions of these regulations employ concepts and terminology that are more suited to traditional narrow band radio transmitters. Further, the emissions limits were based on limited quantitative factual information and have resulted in stringent limitations on GPR technology advancement. Factual theoretical and experimental information on the emissions from actual GPR devices is not generally available and the relationship with regulatory requirements is poorly understood by users. This information gap must be filled if a compelling argument for less stringent emissions levels is to be mounted in the future. Moreover, the current regulations have the potential to trigger further review of emission limits in the future which could be detrimental to the use of GPR. In this paper, we present the basic steps entailed in translating impulse time‐domain GPR instrument behaviour into ‘regulatory’ parameters. To achieve this, we also employ three‐dimensional (3D) finite‐difference time‐domain (FDTD) numerical modelling to simulate the transient electromagnetic (EM) field variation around dipole antennas placed on the surface of a half‐space or at a height over it to illustrate the dependency on sensor height and ground permittivity. The ultimate goal is to establish the foundation for more sensible rule making, if and when, the regulatory standards come under scrutiny for revision and further user understanding.This article is protected by copyright. All rights reserved
{"title":"Relating GPR System Parameters to Regulatory Emissions Limits","authors":"A. P. Annan, N. Diamanti, J. Redman","doi":"10.1002/nsg.12264","DOIUrl":"https://doi.org/10.1002/nsg.12264","url":null,"abstract":"Ground penetrating radar (GPR) is regulated regarding emission limits for ultra‐wideband (UWB) in a number of jurisdictions. The definitions of these regulations employ concepts and terminology that are more suited to traditional narrow band radio transmitters. Further, the emissions limits were based on limited quantitative factual information and have resulted in stringent limitations on GPR technology advancement. Factual theoretical and experimental information on the emissions from actual GPR devices is not generally available and the relationship with regulatory requirements is poorly understood by users. This information gap must be filled if a compelling argument for less stringent emissions levels is to be mounted in the future. Moreover, the current regulations have the potential to trigger further review of emission limits in the future which could be detrimental to the use of GPR. In this paper, we present the basic steps entailed in translating impulse time‐domain GPR instrument behaviour into ‘regulatory’ parameters. To achieve this, we also employ three‐dimensional (3D) finite‐difference time‐domain (FDTD) numerical modelling to simulate the transient electromagnetic (EM) field variation around dipole antennas placed on the surface of a half‐space or at a height over it to illustrate the dependency on sensor height and ground permittivity. The ultimate goal is to establish the foundation for more sensible rule making, if and when, the regulatory standards come under scrutiny for revision and further user understanding.This article is protected by copyright. All rights reserved","PeriodicalId":49771,"journal":{"name":"Near Surface Geophysics","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46216476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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