Zohir Radi, Abdelkarim Yelles Chaouche, S. Guettouche, G. Bokelmann
Northern Algeria is a large region in the north-western of Africa, lying on the collision boundary between the African and Eurasian plates. Few studies on Lithosphere and Mantle deformation have been conducted in this region. To better understand the seismic anisotropy patterns beneath this area, we used data from 17 broadband stations installed in Tellian and the Saharan atlases using the SKS shear wave splitting method by processing hundreds of teleseismic events. To estimate the seismic anisotropy, two parameters were calculated, the fast polarization direction and the delay time for each station-event pair. The results show that the seismic anisotropy can be described by two main orientations, ENE-WSW follows the general trend of the Saharan Atlas, particularly in the central and western parts, and ESE-WNW follows the Hodna Mountains in south-eastern Algeria. Our results show that the anisotropy can be explained by single and heterogeneity in the anisotropic structure, where the measurements are very scattered, and the delay time and fast direction changed with the events backazimuth. In the ABSD, CBBR and CDCN stations, which lie in the arc between the Sahara Atlas and the Aurès Mountains, the origin hypothesis of the seismic anisotropy can be linked to the existence of a detached slab. Moreover, in ABZH, OKGL and EARB stations located in the Kabylide and Western regions, it can be associated with the Gibraltar slab. Both slabs sinking in the African margin mantle were previously imaged by seismic tomography. For the remaining stations, the single-layer best explains the observed seismic anisotropy from their regular fast polarization direction. The comparison of the obtained fast directions with GPS measurements shows that anisotropy fast axes are nearly perpendicular to the convergence direction between the African and Eurasia plates.
{"title":"Upper Mantle Anisotropy beneath Northern Algeria from Shear-Wave Splitting: Anisotropy beneath Northern Algeria","authors":"Zohir Radi, Abdelkarim Yelles Chaouche, S. Guettouche, G. Bokelmann","doi":"10.4401/ag-8839","DOIUrl":"https://doi.org/10.4401/ag-8839","url":null,"abstract":"Northern Algeria is a large region in the north-western of Africa, lying on the collision boundary between the African and Eurasian plates. Few studies on Lithosphere and Mantle deformation have been conducted in this region. To better understand the seismic anisotropy patterns beneath this area, we used data from 17 broadband stations installed in Tellian and the Saharan atlases using the SKS shear wave splitting method by processing hundreds of teleseismic events. To estimate the seismic anisotropy, two parameters were calculated, the fast polarization direction and the delay time for each station-event pair. The results show that the seismic anisotropy can be described by two main orientations, ENE-WSW follows the general trend of the Saharan Atlas, particularly in the central and western parts, and ESE-WNW follows the Hodna Mountains in south-eastern Algeria. Our results show that the anisotropy can be explained by single and heterogeneity in the anisotropic structure, where the measurements are very scattered, and the delay time and fast direction changed with the events backazimuth. In the ABSD, CBBR and CDCN stations, which lie in the arc between the Sahara Atlas and the Aurès Mountains, the origin hypothesis of the seismic anisotropy can be linked to the existence of a detached slab. Moreover, in ABZH, OKGL and EARB stations located in the Kabylide and Western regions, it can be associated with the Gibraltar slab. Both slabs sinking in the African margin mantle were previously imaged by seismic tomography. For the remaining stations, the single-layer best explains the observed seismic anisotropy from their regular fast polarization direction. The comparison of the obtained fast directions with GPS measurements shows that anisotropy fast axes are nearly perpendicular to the convergence direction between the African and Eurasia plates.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"12 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73994312","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}
N. O. Nfor, Ndikum Eric Ndoh, Marceline Motchongom Tingue, Vivian Ndfutu Nfor
In this study we propose a modified Burridge‐Knopoff model of earthquake fault, in which two tectonic plates are strongly coupled by nonlinear springs. By minimizing the effects of the veloci‐ ty‐weakening stick‐slip friction force between the masses and the moving surface, and in the limit of low amplitude oscillations; the system exhibits both stick‐slip and damped oscillatory motions as the values of some parameters are varied. Such motions usually characterize the dynamics of an earthquake fault, even though it is not always felt because of the low amplitude of vibrations. However when enough stress builds up in the subduction zones to overcome the frictional forces between tectonic plates, the oceanic rocks suddenly slip and there is violent release of energy at the epicentre. This outburst of energy simply signifies the generation of a very large amplitude and localized nonlinear wave. Such wave profile exactly fits the Peregrine solution of the damped/ forced nonlinear Schrodinger amplitude equation, derived from the modified one‐dimensional Burridge‐Knopoff equation of motion. In the regime of minimal or no frictional forces, these mon‐ ster waves suddenly appear and disappear without traces as shown by the numerical investigations. Our results strongly suggest that rogue waves emanates from the dynamics of nonlinearly coupled tectonic plates in subduction zones. This is further complemented by the fact that these giant waves were initially observed in Pacific and Atlantic oceans, which play hosts to the world’s largest oceanic subduction zones.
{"title":"On the possibility of rogue wave generation based on the dynamics of modified Burridge-Knopoff model of earthquake fault","authors":"N. O. Nfor, Ndikum Eric Ndoh, Marceline Motchongom Tingue, Vivian Ndfutu Nfor","doi":"10.4401/ag-8856","DOIUrl":"https://doi.org/10.4401/ag-8856","url":null,"abstract":"In this study we propose a modified Burridge‐Knopoff model of earthquake fault, in which two tectonic plates are strongly coupled by nonlinear springs. By minimizing the effects of the veloci‐ ty‐weakening stick‐slip friction force between the masses and the moving surface, and in the limit of low amplitude oscillations; the system exhibits both stick‐slip and damped oscillatory motions as the values of some parameters are varied. Such motions usually characterize the dynamics of an earthquake fault, even though it is not always felt because of the low amplitude of vibrations. However when enough stress builds up in the subduction zones to overcome the frictional forces between tectonic plates, the oceanic rocks suddenly slip and there is violent release of energy at the epicentre. This outburst of energy simply signifies the generation of a very large amplitude and localized nonlinear wave. Such wave profile exactly fits the Peregrine solution of the damped/ forced nonlinear Schrodinger amplitude equation, derived from the modified one‐dimensional Burridge‐Knopoff equation of motion. In the regime of minimal or no frictional forces, these mon‐ ster waves suddenly appear and disappear without traces as shown by the numerical investigations. Our results strongly suggest that rogue waves emanates from the dynamics of nonlinearly coupled tectonic plates in subduction zones. This is further complemented by the fact that these giant waves were initially observed in Pacific and Atlantic oceans, which play hosts to the world’s largest oceanic subduction zones.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"93 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86208156","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 first model of two layers is presented to study the anisotropy pattern beneath Myanmar and Thailand using shear-wave splitting. Teleseismic activity recorded by 15 permanent broadband stations was analysed to investigate the anisotropy and to understand the flow direction in the mantle. The flow direction and speed were observed in the forms of fast polarisation direction (𝜙) and delay time (𝛿𝑡) between fast and slow components. The measurements showed that a two-layer model beneath stations better explicates the splitting observations than a single-layer model. The upper and lower layers were interpreted as lithosphere and asthenosphere in similar patterns and compared with GPS (Global Positioning System) velocity fields and strain rate fields. Two groups of 𝜙 can be classified and matched with West-Burma Terrane (WBT) and Shan-Thai Terrane (STT). The 𝜙 represents that West-Burma Terrane moves in a northward direction, Shan-Thai Terrane and Indo-China Terrane (ICT) move in a south-eastern direction, and West-Burma Terrane has less anisotropy of 𝜙 than Shan-Thai Terrane.
{"title":"Two-layer model of anisotropy beneath Myanmar and Thailand revealed by shear-wave splitting","authors":"Kasemsak Saetang","doi":"10.4401/ag-8769","DOIUrl":"https://doi.org/10.4401/ag-8769","url":null,"abstract":"The first model of two layers is presented to study the anisotropy pattern beneath Myanmar and Thailand using shear-wave splitting. Teleseismic activity recorded by 15 permanent broadband stations was analysed to investigate the anisotropy and to understand the flow direction in the mantle. The flow direction and speed were observed in the forms of fast polarisation direction (𝜙) and delay time (𝛿𝑡) between fast and slow components. The measurements showed that a two-layer model beneath stations better explicates the splitting observations than a single-layer model. The upper and lower layers were interpreted as lithosphere and asthenosphere in similar patterns and compared with GPS (Global Positioning System) velocity fields and strain rate fields. Two groups of 𝜙 can be classified and matched with West-Burma Terrane (WBT) and Shan-Thai Terrane (STT). The 𝜙 represents that West-Burma Terrane moves in a northward direction, Shan-Thai Terrane and Indo-China Terrane (ICT) move in a south-eastern direction, and West-Burma Terrane has less anisotropy of 𝜙 than Shan-Thai Terrane.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"15 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78789127","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}
We present a review of the assessment of earthquake hazard in Italy, with special reference to the relationships between hazard models and building codes. After early attempts at hazard assessment in the 19th century, the 28 December 1908, Messina Straits earthquake prompted the inception of the first national seismic legislation, passed in early 1909. Nevertheless, the official building code started to be based on a truly scientific background only after 1980, when the catastrophic Irpinia (southern Italy) earthquake forced the qualified authority to accept a science-based assessment (statistics on the earthquake catalogue data) to support the implementation of the new national seismic zonation. Later on, between 1985 and 2000, the two basic components of seismic hazard assessment, namely the earthquake record and the distribution of earthquake sources, were greatly developed through investigations carried out by the Gruppo Nazionale Difesa dai Terremoti and by the Istituto Nazionale di Geofisica. Along with the improvement of basic data, the Italian seismological community started developing a new hazard model (PS4), based on the concept of seismotectonic probabilism, aimed at supplying the Italian Government with a solid reference frame for updating the seismic zonation and building code. Nevertheless, this goal was achieved only two decades later: on 31 October 2002 a moderate-size earthquake caused the death of 27 children and a teacher in a collapsed school of southern Italy, forcing the qualified authority to take a major step of modernization for the second time in 22 years. The entire Italian territory, including areas of rare and sparse seismicity, was subdivided into four seismic zones, mainly on the basis of PS4 results. In 2004, the Italian seismological community developed MPS04, a fully updated hazard model that was initially conceived only in view of updating the seismic zonation. In 2007, MPS04 was extended to provide design spectra for a new building code, which was finally adopted in 2009, following the disastrous L’Aquila (central Italy) earthquake. The experience of the European project for seismic hazard assessment named SHARE, completed in 2013, represented a step forward and put the basis for a new project, termed MPS19, designed specifically to provide a sound basis for updating the Italian building code.
我们提出了一项评估地震灾害在意大利，特别提到了灾害模型和建筑规范之间的关系。在19世纪的早期危险评估尝试之后，1908年12月28日，墨西拿海峡地震促使了第一个国家地震立法的开始，于1909年初通过。然而，直到1980年之后，官方建筑规范才开始基于真正的科学背景，当时灾难性的伊尔皮尼亚(意大利南部)地震迫使有资格的当局接受基于科学的评估(地震目录数据统计)，以支持新的国家地震带的实施。后来，在1985年至2000年间，地震灾害评估的两个基本组成部分，即地震记录和震源分布，通过Gruppo Nazionale Difesa dai Terremoti和instituto Nazionale di geofinica进行的调查得到了极大的发展。随着基础数据的改进，意大利地震学界开始基于地震构造概率的概念开发一种新的灾害模型(PS4)，旨在为意大利政府提供一个可靠的参考框架，以更新地震区划和建筑规范。然而，这一目标仅在二十年后就实现了:2002年10月31日，意大利南部一所倒塌的学校发生中等规模地震，造成27名儿童和一名教师死亡，迫使有资格的当局在22年内第二次采取重大的现代化步骤。整个意大利领土，包括罕见和稀疏地震活动的地区，被细分为四个地震带，主要是基于PS4的结果。2004年，意大利地震学界开发了MPS04，这是一个完全更新的危险模型，最初只是考虑到更新地震区划。2007年，MPS04被扩展到为新的建筑规范提供设计谱，该规范最终于2009年在灾难性的拉奎拉(意大利中部)地震之后被采用。2013年完成的欧洲地震风险评估项目SHARE的经验代表了向前迈出的一步，并为一个名为MPS19的新项目奠定了基础，该项目专门为更新意大利建筑规范提供了坚实的基础。
{"title":"The assessment of earthquake hazard in Italy: a review","authors":"D. Slejko, G. Valensise, C. Meletti, M. Stucchi","doi":"10.4401/ag-8863","DOIUrl":"https://doi.org/10.4401/ag-8863","url":null,"abstract":"We present a review of the assessment of earthquake hazard in Italy, with special reference to the relationships between hazard models and building codes. After early attempts at hazard assessment in the 19th century, the 28 December 1908, Messina Straits earthquake prompted the inception of the first national seismic legislation, passed in early 1909. Nevertheless, the official building code started to be based on a truly scientific background only after 1980, when the catastrophic Irpinia (southern Italy) earthquake forced the qualified authority to accept a science-based assessment (statistics on the earthquake catalogue data) to support the implementation of the new national seismic zonation. Later on, between 1985 and 2000, the two basic components of seismic hazard assessment, namely the earthquake record and the distribution of earthquake sources, were greatly developed through investigations carried out by the Gruppo Nazionale Difesa dai Terremoti and by the Istituto Nazionale di Geofisica. Along with the improvement of basic data, the Italian seismological community started developing a new hazard model (PS4), based on the concept of seismotectonic probabilism, aimed at supplying the Italian Government with a solid reference frame for updating the seismic zonation and building code. Nevertheless, this goal was achieved only two decades later: on 31 October 2002 a moderate-size earthquake caused the death of 27 children and a teacher in a collapsed school of southern Italy, forcing the qualified authority to take a major step of modernization for the second time in 22 years. The entire Italian territory, including areas of rare and sparse seismicity, was subdivided into four seismic zones, mainly on the basis of PS4 results. In 2004, the Italian seismological community developed MPS04, a fully updated hazard model that was initially conceived only in view of updating the seismic zonation. In 2007, MPS04 was extended to provide design spectra for a new building code, which was finally adopted in 2009, following the disastrous L’Aquila (central Italy) earthquake. The experience of the European project for seismic hazard assessment named SHARE, completed in 2013, represented a step forward and put the basis for a new project, termed MPS19, designed specifically to provide a sound basis for updating the Italian building code.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"46 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84892146","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}
Ayça Çırmık, F. Doğru, Oya Ankaya Pamukçu, Başak Turguz, A. Bonforte
Ground deformation monitoring of active volcanoes is used routinely to determine phases of vol‐ cano unrest and can provide insights in the evolving plumbing system of a volcano and the influence local tectonics structures have on the volcano tectonic evolution of the volcanic edifice. Volcanic deformation analysis can be performed using velocity and direction measurements of the ground surface using Global Navigation Satellite System (GNSS). In this study, we perform two‐dimen‐ sional deformation analyses of pre‐ and post‐eruptive phases with the scope of determining the strain before and after an eruptive phase at Mt. Etna Volcano (southern Italy) during 2004‐2006. In order to do so, we analyse the GNSS displacement data from Mt. Etna between 2004‐2005 and 2005‐2006 using the dedicated SSPX software. The extention, dilation and rotation maps of the study area were determined. The contraction and volumetric decrease concomitant the 2004‐2005 effusive eruptive period and extension and volumetric increase for the 2005‐2006 data series were observed. The deformation on the northeast part of Mt. Etna Volcano, which showed different characteristics with respect to its surroundings, was thought to be conditioned by the dynamic of the Pernicana fault system. Additionally, Complete Spherical Bouguer (CSB) gravity anomaly and the gravity gradient tensors were calculated giving insight on the subsurface structures of Mt. Etna Volcano and its surroundings.
{"title":"Exploring the Kinematic Structure of Mount Etna Volcano (Sicily, Italy) by Deformation Analysis and Gravity Gradient Tensors","authors":"Ayça Çırmık, F. Doğru, Oya Ankaya Pamukçu, Başak Turguz, A. Bonforte","doi":"10.4401/ag-8719","DOIUrl":"https://doi.org/10.4401/ag-8719","url":null,"abstract":"Ground deformation monitoring of active volcanoes is used routinely to determine phases of vol‐ cano unrest and can provide insights in the evolving plumbing system of a volcano and the influence local tectonics structures have on the volcano tectonic evolution of the volcanic edifice. Volcanic deformation analysis can be performed using velocity and direction measurements of the ground surface using Global Navigation Satellite System (GNSS). In this study, we perform two‐dimen‐ sional deformation analyses of pre‐ and post‐eruptive phases with the scope of determining the strain before and after an eruptive phase at Mt. Etna Volcano (southern Italy) during 2004‐2006. In order to do so, we analyse the GNSS displacement data from Mt. Etna between 2004‐2005 and 2005‐2006 using the dedicated SSPX software. The extention, dilation and rotation maps of the study area were determined. The contraction and volumetric decrease concomitant the 2004‐2005 effusive eruptive period and extension and volumetric increase for the 2005‐2006 data series were observed. The deformation on the northeast part of Mt. Etna Volcano, which showed different characteristics with respect to its surroundings, was thought to be conditioned by the dynamic of the Pernicana fault system. Additionally, Complete Spherical Bouguer (CSB) gravity anomaly and the gravity gradient tensors were calculated giving insight on the subsurface structures of Mt. Etna Volcano and its surroundings.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"8 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76480852","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. Buttinelli, F. Maesano, D. Sopher, Fabio Feriozzi, S. Maraio, F. Mazzarini, L. Improta, R. Vallone, F. Villani, R. Basili
In recent decades, geological modeling has significantly evolved, relying on the growing potential of hardware and software to manage and integrate vast datasets of 2D-3D geophysical underground data. Therefore, digitization and integration with other forms of data can often improve understanding of geological systems, even when using so-called vintage or historical data. Seismic reflection data have been extensively acquired mainly for hydrocarbon exploration since the 60s generating large volumes of data. Typically, these data have been for private commercial use and are relatively unavailable for research. However, with time, large volumes of vintage seismic reflection data in many countries worldwide are now becoming publicly available through time-based de-classification schemes. Such data have a great potential for modern-day geo-research, unleashing opportunities to improve geological understanding through re-interpretation with modern methods. However, a downside of these vintage data is that they are often only available in analog (paper, raster) format. The vectorization of these data then constitutes an essential step for unlocking their research potential. In 2018 INGV established the SISMOLAB-3D infrastructure, which is mainly devoted to analyzing digital subsurface data, such as seismic reflection profiles and well-logs, to build 2D-3D geological models, principally for seismotectonics, seismic hazard assessment, and geo-resources applications. In this contribution, we discuss the robustness of the WIGGLE2SEGY code, firstly published by Sopher in 2018, focusing on examples from different tectonic and geodynamic contexts within Italian territory. We applied the SEG-Y conversion method to onshore and offshore raster seismic profiles related to ceased exploration permits, comparing the results with other published archives of SEG-Y data obtained from the conversion of vintage data. Such an approach results in digital SEG-Y files with unprecedented quality and detail. The system- atic application of this method will allow the construction of a comprehensive dataset of digital SEG-Y seismic profiles across Italy, thereby expanding and sharing the INGV SISMOLAB-3D port- folio with the scientific community to foster innovative and advanced scientific analysis.
{"title":"Revitalizing vintage seismic reflection profiles by converting into SEG-Y format: case studies from publicly available data on the Italian territory","authors":"M. Buttinelli, F. Maesano, D. Sopher, Fabio Feriozzi, S. Maraio, F. Mazzarini, L. Improta, R. Vallone, F. Villani, R. Basili","doi":"10.4401/ag-8883","DOIUrl":"https://doi.org/10.4401/ag-8883","url":null,"abstract":"In recent decades, geological modeling has significantly evolved, relying on the growing potential of hardware and software to manage and integrate vast datasets of 2D-3D geophysical underground data. Therefore, digitization and integration with other forms of data can often improve understanding of geological systems, even when using so-called vintage or historical data. Seismic reflection data have been extensively acquired mainly for hydrocarbon exploration since the 60s generating large volumes of data. Typically, these data have been for private commercial use and are relatively unavailable for research. However, with time, large volumes of vintage seismic reflection data in many countries worldwide are now becoming publicly available through time-based de-classification schemes. Such data have a great potential for modern-day geo-research, unleashing opportunities to improve geological understanding through re-interpretation with modern methods. However, a downside of these vintage data is that they are often only available in analog (paper, raster) format. The vectorization of these data then constitutes an essential step for unlocking their research potential. In 2018 INGV established the SISMOLAB-3D infrastructure, which is mainly devoted to analyzing digital subsurface data, such as seismic reflection profiles and well-logs, to build 2D-3D geological models, principally for seismotectonics, seismic hazard assessment, and geo-resources applications. In this contribution, we discuss the robustness of the WIGGLE2SEGY code, firstly published by Sopher in 2018, focusing on examples from different tectonic and geodynamic contexts within Italian territory. We applied the SEG-Y conversion method to onshore and offshore raster seismic profiles related to ceased exploration permits, comparing the results with other published archives of SEG-Y data obtained from the conversion of vintage data. Such an approach results in digital SEG-Y files with unprecedented quality and detail. The system- atic application of this method will allow the construction of a comprehensive dataset of digital SEG-Y seismic profiles across Italy, thereby expanding and sharing the INGV SISMOLAB-3D port- folio with the scientific community to foster innovative and advanced scientific analysis.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"36 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75099359","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}
Here, we report a Spatio-temporal analysis of the frequency magnitude distribution of earthquakes (b-value) before the 28th April 2021 (Mw 6.4) earthquake event observed in northeast India. To esti- mate the average b-value for the study region, a data set of 750 earthquake events with magnitude Mw ≥ 3.9 is extracted from the homogenous part of the earthquake catalog (1950-2021) documented by the United States Geological Survey (USGS) and International seismological center (ISC) in the region. For spatial analysis of the disparities in b-value, the whole study region is subdivided into 16 square grids of dimension 1o×1o and the b-value is calculated for each subsection. In congruence with other studies, this work yields b-values ranging from 0.66 to 1.25. After the calculation of the b-value for each grid, it is observed that the grid with the epicentral location of the 28th April 2021 (6.4) earthquake has a low b-value. Accordingly, the spatial correlation and aberrant pattern between b-value and focal depth have been comprehensively explored. It is observed that the b-value sig- nificantly dips within a depth range of ~15-35 km which implicates high-stress accumulation and crustal homogeneity. The depth-wise variation in b-value infers the antithetical relationship between b-value and crustal stress. Mostly interplate earthquakes are observed in the study region; thereby hinting at intense seismicity at the upper crust.
{"title":"Spatio-temporal analysis of b-value prior to 28 April 2021 Assam Earthquake and implications thereof","authors":"V. Sarma, Dipok K. Bora, Rajib Biswas","doi":"10.4401/ag-8802","DOIUrl":"https://doi.org/10.4401/ag-8802","url":null,"abstract":"Here, we report a Spatio-temporal analysis of the frequency magnitude distribution of earthquakes (b-value) before the 28th April 2021 (Mw 6.4) earthquake event observed in northeast India. To esti- mate the average b-value for the study region, a data set of 750 earthquake events with magnitude Mw ≥ 3.9 is extracted from the homogenous part of the earthquake catalog (1950-2021) documented by the United States Geological Survey (USGS) and International seismological center (ISC) in the region. For spatial analysis of the disparities in b-value, the whole study region is subdivided into 16 square grids of dimension 1o×1o and the b-value is calculated for each subsection. In congruence with other studies, this work yields b-values ranging from 0.66 to 1.25. After the calculation of the b-value for each grid, it is observed that the grid with the epicentral location of the 28th April 2021 (6.4) earthquake has a low b-value. Accordingly, the spatial correlation and aberrant pattern between b-value and focal depth have been comprehensively explored. It is observed that the b-value sig- nificantly dips within a depth range of ~15-35 km which implicates high-stress accumulation and crustal homogeneity. The depth-wise variation in b-value infers the antithetical relationship between b-value and crustal stress. Mostly interplate earthquakes are observed in the study region; thereby hinting at intense seismicity at the upper crust.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"93 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76960946","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}
Electric currents flowing in the atmospheric global electric circuit (GEC) are closed by ionospheric currents. The physical and mathematical approach to simulate the ionospheric potential which drives these currents has been described in our previous papers. Only the internal electric fields and currents generated by thunderstorms are studied, and without any magnetospheric current sources or generators. The atmospheric conductivity profiles with altitude are empirically determined, and the topography of the Earth’s surface is taken into account. A two-dimensional approximation of the ionospheric conductor is based on the high conductivity along the geomagnetic field; the Pedersen and Hall conductivities are calculated using empirical models. The potentials in the E- and F-layers of the ionosphere are considered to be constant along each magnetic field line. The main progress in comparison with previous versions of the model is obtained through applying the global distribution of thunderstorms obtained from the ground-based World Wide Lightning Location Network. Under typical conditions for July, under low solar activity in 2008, at 18:00 UTC, the calculated maximum potential difference in the ionosphere is 54 V. This newest version of our model contains the equatorial electrojets. There are day-time electrojets, the strengths of which are up to 65 A, and night-time ones (of up to 40 A), while the total current flowing in the GEC is taken to be equal to 1.43 kA in our model to satisfy the Carnegie curve, i.e. the diurnal variation of the vertical electric field at ground level with UTC. The maximum of the electric potential is shifted from Africa to South-East Asia in the new model. The equatorial electrojets also change their position, direction and intensity.
{"title":"WWLLN Data Used to Model the Global Ionospheric Electric Field Generated by Thunderstorms","authors":"V. Denisenko, M. Rycroft","doi":"10.4401/ag-8821","DOIUrl":"https://doi.org/10.4401/ag-8821","url":null,"abstract":"Electric currents flowing in the atmospheric global electric circuit (GEC) are closed by ionospheric currents. The physical and mathematical approach to simulate the ionospheric potential which drives these currents has been described in our previous papers. Only the internal electric fields and currents generated by thunderstorms are studied, and without any magnetospheric current sources or generators. The atmospheric conductivity profiles with altitude are empirically determined, and the topography of the Earth’s surface is taken into account. A two-dimensional approximation of the ionospheric conductor is based on the high conductivity along the geomagnetic field; the Pedersen and Hall conductivities are calculated using empirical models. The potentials in the E- and F-layers of the ionosphere are considered to be constant along each magnetic field line. The main progress in comparison with previous versions of the model is obtained through applying the global distribution of thunderstorms obtained from the ground-based World Wide Lightning Location Network. Under typical conditions for July, under low solar activity in 2008, at 18:00 UTC, the calculated maximum potential difference in the ionosphere is 54 V. This newest version of our model contains the equatorial electrojets. There are day-time electrojets, the strengths of which are up to 65 A, and night-time ones (of up to 40 A), while the total current flowing in the GEC is taken to be equal to 1.43 kA in our model to satisfy the Carnegie curve, i.e. the diurnal variation of the vertical electric field at ground level with UTC. The maximum of the electric potential is shifted from Africa to South-East Asia in the new model. The equatorial electrojets also change their position, direction and intensity.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"24 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82820630","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}
I. Tiryakioglu, Kaan Çalişkan, C. O. Yigit, K. Hastaoglu, F. Poyraz, T. Baybura, E. Gurlek, Ç. Özkaymak
In this research, the aim was to examine the aseismic surface deformations that occurred in the Bolvadin district center with a precise leveling technique. For this purpose, a geodetic leveling network consisting of eight profiles and 81 benchmarks was installed in the region, and five campaigns of precise leveling measurements were performed between 2016-2020. As a result of the evaluations of the leveling measurements, deformations over time were calculated at each benchmark. In consequence of the evaluation of the five campaign measurements, the deformation amount increased continuously from 2016 to 2020. When the adjusted height differences between 2019‑2020 were examined, it was observed that the deformation amount of the previous years doubled. Additionally, deformation rates between –20 and –90 mm/year were estimated using the Kalman filtering methods. According to the current data obtained, the total vertical displacement amount has reached approximately 1 m and the deformation continues today.
{"title":"The velocity of aseismic surface deformations between 2016‑2020 detected by precise leveling surveys of the Akşehir Simav Fault System in the Bolvadin district, western Anatolia","authors":"I. Tiryakioglu, Kaan Çalişkan, C. O. Yigit, K. Hastaoglu, F. Poyraz, T. Baybura, E. Gurlek, Ç. Özkaymak","doi":"10.4401/ag-8784","DOIUrl":"https://doi.org/10.4401/ag-8784","url":null,"abstract":"In this research, the aim was to examine the aseismic surface deformations that occurred in the Bolvadin district center with a precise leveling technique. For this purpose, a geodetic leveling network consisting of eight profiles and 81 benchmarks was installed in the region, and five campaigns of precise leveling measurements were performed between 2016-2020. As a result of the evaluations of the leveling measurements, deformations over time were calculated at each benchmark. In consequence of the evaluation of the five campaign measurements, the deformation amount increased continuously from 2016 to 2020. When the adjusted height differences between 2019‑2020 were examined, it was observed that the deformation amount of the previous years doubled. Additionally, deformation rates between –20 and –90 mm/year were estimated using the Kalman filtering methods. According to the current data obtained, the total vertical displacement amount has reached approximately 1 m and the deformation continues today.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"35 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75689798","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}
In Turkey, two official seismology centers, Bogazici University Kandilli Observatory and Earthquake Research Institute Regional Earthquake-Tsunami Monitoring Center (KOERI-RETMC) and Republic of Turkey Prime Ministry Disaster Emergency Management Authority (AFAD) announce and share seismic catalogs with the public and international services. According to their seismic network distribution, together with different crustal models and calculation algorithms, obtaining earthquake parameters (location, depth, etc.) could differ between these two centers, especially, affecting source types of the low-magnitude events. Both low-magnitude tectonic events and artificial quakes that originating from open-pit quarry are catalogued by the seismology centers. These two centers announce different source types for the seismic events; therefore, this study focuses on the reliable identification of the micro-seismic events. Magnitude Ml<2.4 177 seismic events commonly identified in KOERI-RETMC and AFAD catalogs are used. Due to the differences between KOERI-RETMC and AFAD seismic catalogs, the “first determination” (FD) was needed to start the discrimination analyses. Then, waveforms of the station SEYD and SEDI are operated by KOERI-RETMC and AFAD were analyzed with four methods (Amplitude Ratio, Complexity, Short Time Fourier Transform and Corner Frequency-Power Spectrum) and two statistical approaches (linear and quadratic discriminant functions) with the use and comparison with FD. Finally, station-based weightings are obtained with all techniques, and the source types of all events are calculated in percent. Generally, the success rates of the methods are calculated over 90%. The reliability increases with the co-usage of many analyses and the application of method-based weighting. Hence, many methods should be used to reliably determine the source types of micro-seismic events. Both centers should make more detailed analyses to identify micro-seismic events and share their reliable and revised catalogs.
{"title":"Refining micro-seismic catalogs around Seydişehir, Turkey","authors":"Evrim Yavuz","doi":"10.4401/ag-8736","DOIUrl":"https://doi.org/10.4401/ag-8736","url":null,"abstract":"In Turkey, two official seismology centers, Bogazici University Kandilli Observatory and Earthquake Research Institute Regional Earthquake-Tsunami Monitoring Center (KOERI-RETMC) and Republic of Turkey Prime Ministry Disaster Emergency Management Authority (AFAD) announce and share seismic catalogs with the public and international services. According to their seismic network distribution, together with different crustal models and calculation algorithms, obtaining earthquake parameters (location, depth, etc.) could differ between these two centers, especially, affecting source types of the low-magnitude events. Both low-magnitude tectonic events and artificial quakes that originating from open-pit quarry are catalogued by the seismology centers. These two centers announce different source types for the seismic events; therefore, this study focuses on the reliable identification of the micro-seismic events. Magnitude Ml<2.4 177 seismic events commonly identified in KOERI-RETMC and AFAD catalogs are used. Due to the differences between KOERI-RETMC and AFAD seismic catalogs, the “first determination” (FD) was needed to start the discrimination analyses. Then, waveforms of the station SEYD and SEDI are operated by KOERI-RETMC and AFAD were analyzed with four methods (Amplitude Ratio, Complexity, Short Time Fourier Transform and Corner Frequency-Power Spectrum) and two statistical approaches (linear and quadratic discriminant functions) with the use and comparison with FD. Finally, station-based weightings are obtained with all techniques, and the source types of all events are calculated in percent. Generally, the success rates of the methods are calculated over 90%. The reliability increases with the co-usage of many analyses and the application of method-based weighting. Hence, many methods should be used to reliably determine the source types of micro-seismic events. Both centers should make more detailed analyses to identify micro-seismic events and share their reliable and revised catalogs.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"87 27 Pt 1 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84049391","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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