Pub Date : 2022-06-07DOI: 10.1080/08123985.2022.2067474
Shigeki Mizutani
The author proposes a new approach for analysing datasets of the differential curvature of a gravity-gradient tensor for density evaluation of the surface layer without a prior density assumption. The method, called the horizontal gravity-gradient stack–moving window correlation (HGGS-MWC) method, is based on a successive MWCs between the acquired data and the data of differential curvature responses of the surface layer calculated based on a digital elevation model. For improving the correlation, a HGGS processing method was devised and patented. It is applied to both datasets before the MWC processing. A point-source differential curvature response has the characteristic of forming a peculiar and symmetrical shape of a quadrant and distributing peaks and troughs over an underlying anomalous mass. These peaks and troughs are near or far away from their centre depending on the depth of the anomalous mass. This enables one to design a filter to enhance the responses of the surface layer. In addition, the HGGS processing affects both the contraction of the gravitational response and the attenuation of responses from deeper subsurface layers. The HGGS-MWC method leads to the production of values of the mass surface roughness ratio (MSR) in the wavenumber domain that are inherent to the measuring plane of surveys and determines the phase relation between the mass of the surface layer and the surface roughness. The MSR is a good indicator of whether a mass surplus or deficit relative to the regional average mass exists under a convex surface layer. Application to the observed datasets was performed in the area where serious landslides were triggered by the 2008 Iwate-Miyagi inland earthquake. Based on a flight height of 150 m, the mass variations of the surface layer, which is down to 300 m below the surface, are properly evaluated by analysing the wavelengths in the data mainly within the range of 270–650 m and perceivably up to 1,650 m. The specific areas can be delineated where low-density deposits, such as possible volcanic ashes and pumices associated with high water content, sit on high mountains with steep slopes. The information is useful for disaster prevention by playing a role in selecting potential areas for conducting further precise surveys. Regional density variations whose wavelengths are longer than 1,650 m remain unsolved and are an issue for future studies. With the issue solved, the results for the density distribution of the surface layer obtained by the HGGS-MWC method will serve for terrain corrections of the vertical gravity-gradient data and gravity data as well.
{"title":"Application of horizontal gravity-gradient stack for estimation of surface layer density in mountainous areas","authors":"Shigeki Mizutani","doi":"10.1080/08123985.2022.2067474","DOIUrl":"https://doi.org/10.1080/08123985.2022.2067474","url":null,"abstract":"The author proposes a new approach for analysing datasets of the differential curvature of a gravity-gradient tensor for density evaluation of the surface layer without a prior density assumption. The method, called the horizontal gravity-gradient stack–moving window correlation (HGGS-MWC) method, is based on a successive MWCs between the acquired data and the data of differential curvature responses of the surface layer calculated based on a digital elevation model. For improving the correlation, a HGGS processing method was devised and patented. It is applied to both datasets before the MWC processing. A point-source differential curvature response has the characteristic of forming a peculiar and symmetrical shape of a quadrant and distributing peaks and troughs over an underlying anomalous mass. These peaks and troughs are near or far away from their centre depending on the depth of the anomalous mass. This enables one to design a filter to enhance the responses of the surface layer. In addition, the HGGS processing affects both the contraction of the gravitational response and the attenuation of responses from deeper subsurface layers. The HGGS-MWC method leads to the production of values of the mass surface roughness ratio (MSR) in the wavenumber domain that are inherent to the measuring plane of surveys and determines the phase relation between the mass of the surface layer and the surface roughness. The MSR is a good indicator of whether a mass surplus or deficit relative to the regional average mass exists under a convex surface layer. Application to the observed datasets was performed in the area where serious landslides were triggered by the 2008 Iwate-Miyagi inland earthquake. Based on a flight height of 150 m, the mass variations of the surface layer, which is down to 300 m below the surface, are properly evaluated by analysing the wavelengths in the data mainly within the range of 270–650 m and perceivably up to 1,650 m. The specific areas can be delineated where low-density deposits, such as possible volcanic ashes and pumices associated with high water content, sit on high mountains with steep slopes. The information is useful for disaster prevention by playing a role in selecting potential areas for conducting further precise surveys. Regional density variations whose wavelengths are longer than 1,650 m remain unsolved and are an issue for future studies. With the issue solved, the results for the density distribution of the surface layer obtained by the HGGS-MWC method will serve for terrain corrections of the vertical gravity-gradient data and gravity data as well.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"1 - 20"},"PeriodicalIF":0.9,"publicationDate":"2022-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43295164","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}
Pub Date : 2022-05-13DOI: 10.1080/08123985.2022.2072724
C. Yule, N. Rollet, M. Corkeron, J. Daniell
Mafic igneous units within sedimentary basins can be widespread and severely attenuate seismic reflection data. Attenuation obscures imaging of sub-igneous sedimentary units, impeding exploration in prospective and frontier basins. This study compared historical 2D seismic surveys and found two seismic acquisition parameters that have the greatest influence when imaging beneath mafic igneous rocks in offshore and onshore basins from Australia’s Northwest Shelf. These parameters were found by using a 3D model developed with integrated 2D seismic and well data in the Browse, North Carnarvon, Onshore and Offshore Canning basins. Simultaneously comparing the 2D seismic lines in 3D space revealed that the surveys with the longest, streamer length and the most receivers are the most effective at imaging beneath igneous units. Additionally, we identified potential depocenters obscured by igneous horizons from a regional basement map. These depocenters correlate with older basins that are infilled by pre-rift, Paleozoic sediment and capped by mafic igneous rocks formed during late Permian-Mesozoic rifting events. Much of the Northwest Shelf maintains a frontier status, but exploration outcomes can be improved. Therefore, maximising streamer length and number of receivers to future seismic surveys can result in more effective exploration opportunities in basins with known igneous occurrences.
{"title":"Seismic acquisition parameters to improve imaging beneath mafic igneous units: case study from Australia’s Northwest Shelf","authors":"C. Yule, N. Rollet, M. Corkeron, J. Daniell","doi":"10.1080/08123985.2022.2072724","DOIUrl":"https://doi.org/10.1080/08123985.2022.2072724","url":null,"abstract":"Mafic igneous units within sedimentary basins can be widespread and severely attenuate seismic reflection data. Attenuation obscures imaging of sub-igneous sedimentary units, impeding exploration in prospective and frontier basins. This study compared historical 2D seismic surveys and found two seismic acquisition parameters that have the greatest influence when imaging beneath mafic igneous rocks in offshore and onshore basins from Australia’s Northwest Shelf. These parameters were found by using a 3D model developed with integrated 2D seismic and well data in the Browse, North Carnarvon, Onshore and Offshore Canning basins. Simultaneously comparing the 2D seismic lines in 3D space revealed that the surveys with the longest, streamer length and the most receivers are the most effective at imaging beneath igneous units. Additionally, we identified potential depocenters obscured by igneous horizons from a regional basement map. These depocenters correlate with older basins that are infilled by pre-rift, Paleozoic sediment and capped by mafic igneous rocks formed during late Permian-Mesozoic rifting events. Much of the Northwest Shelf maintains a frontier status, but exploration outcomes can be improved. Therefore, maximising streamer length and number of receivers to future seismic surveys can result in more effective exploration opportunities in basins with known igneous occurrences.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"101 - 116"},"PeriodicalIF":0.9,"publicationDate":"2022-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49069723","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}
Karst cave is a sort of special and buried geological structure that was widely developed in the Permo-Carboniferous coal accumulation area of North China. It brings karst collapse and safety hazard in the mining industry. In this study, we propose a seismic structure-constrained inversion of controlled source audio-frequency magnetotelluric (CSAMT) data on a detailed survey and detection of karst caves. Instead of constrained by seismic impedance, the method in this study directly takes the seismic imaging results as structural constraints, which is different from the cross-gradient technique used by conventional structural constraints. First, the seismic migration section is divided according to the CSAMT inversion grid and applied pixel extraction for each grid. Clustering is carried out according to the structural information interpreted by the seismic migration section and the average pixel value of each cluster is calculated. Then the clustered results were used in the seismic structure-constrained inversion of CSAMT data based on cross-gradient technique. After that, as a karst cave model developed in limestone was established, the study compares the structure-constrained inversions with different clustering strategies shows a much more precision of karst cave detection than the method only applies CSAMT data. Moreover, experimental verification is provided in this study, which is for the detection of a suspected karst collapse column from Shandong Province, China. The comparison results further show that the structure-constrained inversion method proposed in this paper is applicable and may effectively improve the locating accuracy of karst caves.
{"title":"Seismic structure-constrained inversion of CSAMT data for detecting karst caves","authors":"Laifu Wen, Jiulong Cheng, Sitong Yang, Fei Li, Awei Liu, Yanli Yang","doi":"10.1080/08123985.2022.2065916","DOIUrl":"https://doi.org/10.1080/08123985.2022.2065916","url":null,"abstract":"Karst cave is a sort of special and buried geological structure that was widely developed in the Permo-Carboniferous coal accumulation area of North China. It brings karst collapse and safety hazard in the mining industry. In this study, we propose a seismic structure-constrained inversion of controlled source audio-frequency magnetotelluric (CSAMT) data on a detailed survey and detection of karst caves. Instead of constrained by seismic impedance, the method in this study directly takes the seismic imaging results as structural constraints, which is different from the cross-gradient technique used by conventional structural constraints. First, the seismic migration section is divided according to the CSAMT inversion grid and applied pixel extraction for each grid. Clustering is carried out according to the structural information interpreted by the seismic migration section and the average pixel value of each cluster is calculated. Then the clustered results were used in the seismic structure-constrained inversion of CSAMT data based on cross-gradient technique. After that, as a karst cave model developed in limestone was established, the study compares the structure-constrained inversions with different clustering strategies shows a much more precision of karst cave detection than the method only applies CSAMT data. Moreover, experimental verification is provided in this study, which is for the detection of a suspected karst collapse column from Shandong Province, China. The comparison results further show that the structure-constrained inversion method proposed in this paper is applicable and may effectively improve the locating accuracy of karst caves.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"55 - 67"},"PeriodicalIF":0.9,"publicationDate":"2022-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42356500","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}
Pub Date : 2022-04-07DOI: 10.1080/08123985.2022.2058393
Yan Zhang, Chunying Gu, Jiayue Yang, Suyi Li
The magnitude versus offset (MVO) curve, a type of frequency domain marine controlled-source electromagnetic data, is the most common way to identify electromagnetic anomalies in oil and gas reservoirs. However, in actual exploration, it can be difficult to identify the boundary of the high resistance anomaly when there are response signals of multiple emission frequencies. Also, the noise would reduce the accuracy of manually detecting electromagnetic anomalies. The robustness of the bidirectional long short-term memory (LSTM) network is relatively strong, and the LSTM neural network would get the most out of the sequence information of the data for feature extraction purposes and to achieve automatic classification and identification. Therefore, this paper proposes a method of using bidirectional LSTM to solve the problem of anomaly identification in marine controlled-source electromagnetic data. The LSTM unit was applied to establish anomaly identification models of single-layer LSTM, two-layer LSTM, and bidirectional LSTM, respectively. In this paper, theoretical data were calculated by a one-dimensional uniform layered medium model, and the synthetic noise data were constructed by adding random noise with different signal-to-noise ratios. The three types of models were trained, verified, and tested, respectively, to compare the accuracy of electromagnetic anomaly identification. According to the comparison, a conclusion can be drawn that the bidirectional LSTM model suggests the best manifestation of learning the characteristics of the sample. Its electromagnetic anomaly identification accuracy reached 100% in the theoretical dataset and 79.58% in the synthetic noise dataset.
{"title":"A high resistivity anomaly identification method for marine controlled-source electromagnetic data","authors":"Yan Zhang, Chunying Gu, Jiayue Yang, Suyi Li","doi":"10.1080/08123985.2022.2058393","DOIUrl":"https://doi.org/10.1080/08123985.2022.2058393","url":null,"abstract":"The magnitude versus offset (MVO) curve, a type of frequency domain marine controlled-source electromagnetic data, is the most common way to identify electromagnetic anomalies in oil and gas reservoirs. However, in actual exploration, it can be difficult to identify the boundary of the high resistance anomaly when there are response signals of multiple emission frequencies. Also, the noise would reduce the accuracy of manually detecting electromagnetic anomalies. The robustness of the bidirectional long short-term memory (LSTM) network is relatively strong, and the LSTM neural network would get the most out of the sequence information of the data for feature extraction purposes and to achieve automatic classification and identification. Therefore, this paper proposes a method of using bidirectional LSTM to solve the problem of anomaly identification in marine controlled-source electromagnetic data. The LSTM unit was applied to establish anomaly identification models of single-layer LSTM, two-layer LSTM, and bidirectional LSTM, respectively. In this paper, theoretical data were calculated by a one-dimensional uniform layered medium model, and the synthetic noise data were constructed by adding random noise with different signal-to-noise ratios. The three types of models were trained, verified, and tested, respectively, to compare the accuracy of electromagnetic anomaly identification. According to the comparison, a conclusion can be drawn that the bidirectional LSTM model suggests the best manifestation of learning the characteristics of the sample. Its electromagnetic anomaly identification accuracy reached 100% in the theoretical dataset and 79.58% in the synthetic noise dataset.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"21 - 32"},"PeriodicalIF":0.9,"publicationDate":"2022-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49380998","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}
Pub Date : 2022-03-28DOI: 10.1080/08123985.2022.2053777
G. Leucci, L. De Giorgi, I. Ditaranto, I. Miccoli, G. Scardozzi
The results of the geophysical surveys carried out in the city of Ugento, specifically in the St. Antonio area and into the Medieval Castle, are presented in this paper. The aim of this study is to integrate the results of Ground-Penetrating Radar and Electrical Resistivity Tomography surveys in order to support archaeological investigations aimed at the elaboration of a detailed archaeological map of the Messapian, Roman and Medieval settlement. Indeed, the obtained data were jointly analysed with archaeological data already known and were georeferenced on the general plans of the site in order to obtain an overall view of the anomalies detected by geophysical instrumentation and related to buried ancient structures. In particular, the geophysical surveys carried out in the St. Antonio area made it possible to reconstruct a stretch of the Messapian city walls and nearby necropolis, while the investigations inside the Castle allowed for the acquisition of very interesting data about previous phases dated to the Middle Ages (and maybe also the Messapian or Roman ages) and about the geo-morphological characteristics of the site.
{"title":"Ground-penetrating radar and electrical resistivity tomography surveys aimed at the knowledge of the Messapian and Medieval settlement of Ugento (southern Apulia, Italy)","authors":"G. Leucci, L. De Giorgi, I. Ditaranto, I. Miccoli, G. Scardozzi","doi":"10.1080/08123985.2022.2053777","DOIUrl":"https://doi.org/10.1080/08123985.2022.2053777","url":null,"abstract":"The results of the geophysical surveys carried out in the city of Ugento, specifically in the St. Antonio area and into the Medieval Castle, are presented in this paper. The aim of this study is to integrate the results of Ground-Penetrating Radar and Electrical Resistivity Tomography surveys in order to support archaeological investigations aimed at the elaboration of a detailed archaeological map of the Messapian, Roman and Medieval settlement. Indeed, the obtained data were jointly analysed with archaeological data already known and were georeferenced on the general plans of the site in order to obtain an overall view of the anomalies detected by geophysical instrumentation and related to buried ancient structures. In particular, the geophysical surveys carried out in the St. Antonio area made it possible to reconstruct a stretch of the Messapian city walls and nearby necropolis, while the investigations inside the Castle allowed for the acquisition of very interesting data about previous phases dated to the Middle Ages (and maybe also the Messapian or Roman ages) and about the geo-morphological characteristics of the site.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"33 - 54"},"PeriodicalIF":0.9,"publicationDate":"2022-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42904062","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}
Pub Date : 2022-03-28DOI: 10.1080/08123985.2022.2053778
Dongliang Zhang, C. Tsingas, T. Fei
This paper presents a new algorithm to generate edge detection images using a migrated image. The key idea is that discontinuity response are comprised of all dip angle ranges and thus after F-K filtering, they can exist in both images with negative-only and positive-only dips. However, reflection responses can only exist in either image with negative-only dips or image with positive-only dips. Applying multiplication imaging condition (MIC) to two images with opposite dips can generate an edge detection image. This method can be easily extended to 3D cases. More specifically, two strategies are proposed. The first one involves applying a 3D F-K filter to calculate four components with different dip and azimuth angles, then multiplying the decomposed four components to generate the final edge detection image. The other one consists of splitting the 3D data volume into 2D sections and then applying the 2D methodology to generate the edge detection image. Both synthetic and real data tests will be employed in 2D and 3D to demonstrate the validity of edge detection using MIC.
{"title":"Edge detection using multiplication imaging conditions","authors":"Dongliang Zhang, C. Tsingas, T. Fei","doi":"10.1080/08123985.2022.2053778","DOIUrl":"https://doi.org/10.1080/08123985.2022.2053778","url":null,"abstract":"This paper presents a new algorithm to generate edge detection images using a migrated image. The key idea is that discontinuity response are comprised of all dip angle ranges and thus after F-K filtering, they can exist in both images with negative-only and positive-only dips. However, reflection responses can only exist in either image with negative-only dips or image with positive-only dips. Applying multiplication imaging condition (MIC) to two images with opposite dips can generate an edge detection image. This method can be easily extended to 3D cases. More specifically, two strategies are proposed. The first one involves applying a 3D F-K filter to calculate four components with different dip and azimuth angles, then multiplying the decomposed four components to generate the final edge detection image. The other one consists of splitting the 3D data volume into 2D sections and then applying the 2D methodology to generate the edge detection image. Both synthetic and real data tests will be employed in 2D and 3D to demonstrate the validity of edge detection using MIC.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"68 - 78"},"PeriodicalIF":0.9,"publicationDate":"2022-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48426514","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}
The spectral-element method (SEM), which combines the flexibility of the finite element method (FEM) with the accuracy of spectral method, has been successfully applied to simulate seismic wavefields in geological models on different scales. One kind of SEMs that adopts orthogonal Legendre polynomials is widely used in seismology community. In the SEM with orthogonal Legendre polynomials, the Gauss-Lobatto-Legendre (GLL) quadrature rule is employed to calculate the integrals involved in the SEM leading to a diagonal mass matrix. However, the GLL quadrature rule can exactly approximate only integrals with a polynomial degree below 2N-1 (N is the interpolation order in space) and cannot exactly calculate those of polynomials with degree 2N involved in the mass matrix. Therefore, the error of the mass matrix originating from inexact numerical integration may reduce the accuracy of the SEM. To improve the SEM accuracy, we construct a least-squares objective function in terms of numerical and exact integrals to increase the accuracy of the GLL quadrature rule. Then, we utilise the conjugate gradient method to solve the objective function and obtain a set of optimal quadrature weights. The optimal mass matrix can be obtained simultaneously by utilising the GLL quadrature rule with optimal integration weights. The improvement in the numerical accuracy of the SEM with an optimal mass matrix (OSEM) is demonstrated by theoretical analysis and numerical examples.
{"title":"Spectral-element method with an optimal mass matrix for seismic wave modelling","authors":"Shaolin Liu, Dinghui Yang, Xi-wei Xu, Wenshuai Wang, Xiaofan Li, Xueli Meng","doi":"10.1080/08123985.2022.2043126","DOIUrl":"https://doi.org/10.1080/08123985.2022.2043126","url":null,"abstract":"The spectral-element method (SEM), which combines the flexibility of the finite element method (FEM) with the accuracy of spectral method, has been successfully applied to simulate seismic wavefields in geological models on different scales. One kind of SEMs that adopts orthogonal Legendre polynomials is widely used in seismology community. In the SEM with orthogonal Legendre polynomials, the Gauss-Lobatto-Legendre (GLL) quadrature rule is employed to calculate the integrals involved in the SEM leading to a diagonal mass matrix. However, the GLL quadrature rule can exactly approximate only integrals with a polynomial degree below 2N-1 (N is the interpolation order in space) and cannot exactly calculate those of polynomials with degree 2N involved in the mass matrix. Therefore, the error of the mass matrix originating from inexact numerical integration may reduce the accuracy of the SEM. To improve the SEM accuracy, we construct a least-squares objective function in terms of numerical and exact integrals to increase the accuracy of the GLL quadrature rule. Then, we utilise the conjugate gradient method to solve the objective function and obtain a set of optimal quadrature weights. The optimal mass matrix can be obtained simultaneously by utilising the GLL quadrature rule with optimal integration weights. The improvement in the numerical accuracy of the SEM with an optimal mass matrix (OSEM) is demonstrated by theoretical analysis and numerical examples.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"53 1","pages":"683 - 693"},"PeriodicalIF":0.9,"publicationDate":"2022-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49096024","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}
Pub Date : 2022-03-02DOI: 10.1080/08123985.2022.2043125
Jitender Kumar, K. Sain
Empirical mode decomposition (EMD) is an effective tool for signal analysis that splits the data into individual modes, called the intrinsic mode functions, which are associated with symmetric and narrow-band waveform ensuring that the instantaneous frequencies are smooth and positive. However, some negative features encumber its direct application namely the mode mixing and splitting, aliasing and endpoint artefacts. Two variants, ensemble EMD (EEMD) and complete ensemble EMD (CEEMD) have been recently introduced to overcome these problems. We intend to show the application of the EMD for demarcating the zones of gas-hydrates and free-gas bearing sediments. Gas-hydrates are ice-like crystalline substances that occur in shallow sediments along the outer continental margins and in the permafrost regions, and are considered as viable major future energy resources of the world. Gas-hydrates in marine environment are generally identified by an anomalous reflector, known as the bottom simulating reflector, on seismic section. The present study demonstrates that the EMD can be effectively utilised in demarcating the zones of gas-hydrates and free-gas bearing sediments with a field example in the Mahanadi basin of the eastern Indian margin.
{"title":"Empirical mode decomposition approach for delineating gas-hydrates and free gas in Mahanadi offshore, eastern Indian margin","authors":"Jitender Kumar, K. Sain","doi":"10.1080/08123985.2022.2043125","DOIUrl":"https://doi.org/10.1080/08123985.2022.2043125","url":null,"abstract":"Empirical mode decomposition (EMD) is an effective tool for signal analysis that splits the data into individual modes, called the intrinsic mode functions, which are associated with symmetric and narrow-band waveform ensuring that the instantaneous frequencies are smooth and positive. However, some negative features encumber its direct application namely the mode mixing and splitting, aliasing and endpoint artefacts. Two variants, ensemble EMD (EEMD) and complete ensemble EMD (CEEMD) have been recently introduced to overcome these problems. We intend to show the application of the EMD for demarcating the zones of gas-hydrates and free-gas bearing sediments. Gas-hydrates are ice-like crystalline substances that occur in shallow sediments along the outer continental margins and in the permafrost regions, and are considered as viable major future energy resources of the world. Gas-hydrates in marine environment are generally identified by an anomalous reflector, known as the bottom simulating reflector, on seismic section. The present study demonstrates that the EMD can be effectively utilised in demarcating the zones of gas-hydrates and free-gas bearing sediments with a field example in the Mahanadi basin of the eastern Indian margin.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"88 - 100"},"PeriodicalIF":0.9,"publicationDate":"2022-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45313172","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}
Pub Date : 2022-02-07DOI: 10.1080/08123985.2022.2031966
Atef M Abu Donia
Granitoid intrusions traditionally form a focus for geothermal heat exploration, as granite is a major host for Heat-Producing Elements (HPE; U, Th & K). Airborne spectral gamma-ray data for the study area highlight variations in HPE abundances in granitic rock units, indicating variation in the Radioactive Heat Production (RHP) values of these rocks. The computed arithmetic means of RHP for granitic rocks range from 0.96 µWm−3 for tonalite-quartz diorite to 1.10 µWm−3 for granodiorite, followed by a gradual increase to 1.52 µWm−3 for monzogranite and 2.51 µWm−3 for alkali-feldspar granite. The major control on the distribution of U and Th elements in the granitoid rocks appears to have been primarily of magmatic differentiation and is reflected in the linear correlation between these elements. Besides, subsequent post-magmatic hydrothermal fluids play their important roles in remobilization of profitable secondary U-mineralizations to be trapped and enrichment in the alkali-feldspar granitic rocks.
{"title":"Role of uranium redistribution in radioactive heat production of granitic rocks, Northern Eastern Desert, Egypt","authors":"Atef M Abu Donia","doi":"10.1080/08123985.2022.2031966","DOIUrl":"https://doi.org/10.1080/08123985.2022.2031966","url":null,"abstract":"Granitoid intrusions traditionally form a focus for geothermal heat exploration, as granite is a major host for Heat-Producing Elements (HPE; U, Th & K). Airborne spectral gamma-ray data for the study area highlight variations in HPE abundances in granitic rock units, indicating variation in the Radioactive Heat Production (RHP) values of these rocks. The computed arithmetic means of RHP for granitic rocks range from 0.96 µWm−3 for tonalite-quartz diorite to 1.10 µWm−3 for granodiorite, followed by a gradual increase to 1.52 µWm−3 for monzogranite and 2.51 µWm−3 for alkali-feldspar granite. The major control on the distribution of U and Th elements in the granitoid rocks appears to have been primarily of magmatic differentiation and is reflected in the linear correlation between these elements. Besides, subsequent post-magmatic hydrothermal fluids play their important roles in remobilization of profitable secondary U-mineralizations to be trapped and enrichment in the alkali-feldspar granitic rocks.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"53 1","pages":"694 - 709"},"PeriodicalIF":0.9,"publicationDate":"2022-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47574100","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}
Pub Date : 2022-01-25DOI: 10.1080/08123985.2022.2027730
Shangbin Liu, Yongxin Wang, Huaifeng Sun, Yang Yang
This paper focuses on low computational efficiency in simulated annealing (SA) inversion of Transient Electromagnetic (TEM) data. Asynchronous multiple Markov chains (MMC) parallel strategy is a very promising SA acceleration method, which can be accelerated almost linearly. However, this method also reduces the accuracy of the solution. To overcome this problem, we added the solution set strategy to the asynchronous MMC parallel simulated annealing (PSA) algorithm for the first time. In this new algorithm, each thread independently searches for direction and exchanges data with the solution set in the shared memory. We used both the synthetic and field data to test the new algorithm. The synthetic data tests showed that the MMC PSA results are better than those of the original MMC PSA. We analyzed the efficiency of the new algorithm. Compared with the sequential VFSA, the maximum speedup of the new algorithm is approximately 10 times. The field data test also showed that the improved MMC PSA algorithm has good practicability. These tests demonstrate that the improved algorithm is effective, showing that its convergence speed is greatly improved without reducing the accuracy.
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