S. Pondrelli, S. Salimbeni, P. Baccheschi, J. Confal, L. Margheriti
Over the years, seismic anisotropy characterization has become one of the most popular methods to study and understand the Earth’s deep structures. Starting from more than 20 years ago, considerable progress has been made to map the anisotropic structure beneath Italy and the Central Mediterranean area. In particular, several past and current international projects (such as RETREAT, CAT/SCAN, CIFALPS, CIFALPS-2, AlpArray) focused on retrieving the anisotropic structure beneath Italy and surrounding regions, promoting advances in the knowledge of geological and geodynamical setting of this intriguing area. All of these studies aimed at a better understanding the complex and active geodynamic evolution of both the active and remnant subduction systems characterising this region and the associated Apennines, Alps and Dinaric belts, together with the Adriatic and Tyrrhenian basins. The presence of dense high-quality seismic networks, permanently run by INGV and other institutions, and temporary seismic stations deployed in the framework of international projects, the improvements in data processing and the use of several and even more sophisticated methods proposed to quantify the anisotropy, allowed to collect a huge amount of anisotropic parameters. Here a collection of all measurements done on core refracted phases are shown and used as a measure of mantle deformation and interpreted into geodynamic models. Images of anisotropy identify well-developed mantle flows around the sinking European and Adriatic slabs, recognised by tomographic studies. Slab retreat and related mantle flow are interpreted as the main driving mechanism of the Central Mediterranean geodynamics.
{"title":"Peeking inside the mantle structure beneath the Italian region through SKS shear wave splitting anisotropy: a review","authors":"S. Pondrelli, S. Salimbeni, P. Baccheschi, J. Confal, L. Margheriti","doi":"10.4401/ag-8872","DOIUrl":"https://doi.org/10.4401/ag-8872","url":null,"abstract":"Over the years, seismic anisotropy characterization has become one of the most popular methods to study and understand the Earth’s deep structures. Starting from more than 20 years ago, considerable progress has been made to map the anisotropic structure beneath Italy and the Central Mediterranean area. In particular, several past and current international projects (such as RETREAT, CAT/SCAN, CIFALPS, CIFALPS-2, AlpArray) focused on retrieving the anisotropic structure beneath Italy and surrounding regions, promoting advances in the knowledge of geological and geodynamical setting of this intriguing area. All of these studies aimed at a better understanding the complex and active geodynamic evolution of both the active and remnant subduction systems characterising this region and the associated Apennines, Alps and Dinaric belts, together with the Adriatic and Tyrrhenian basins. The presence of dense high-quality seismic networks, permanently run by INGV and other institutions, and temporary seismic stations deployed in the framework of international projects, the improvements in data processing and the use of several and even more sophisticated methods proposed to quantify the anisotropy, allowed to collect a huge amount of anisotropic parameters. Here a collection of all measurements done on core refracted phases are shown and used as a measure of mantle deformation and interpreted into geodynamic models. Images of anisotropy identify well-developed mantle flows around the sinking European and Adriatic slabs, recognised by tomographic studies. Slab retreat and related mantle flow are interpreted as the main driving mechanism of the Central Mediterranean geodynamics.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"47 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77417568","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 Xiaojiang faults located in the SE margin of the Tibetan Plateau is a fault system of left-lateral strike-slip, striking NS, between the 2nd-order Sichuan-Yunnan block and the 1st-order South China block. The Xiaojiang faults and the surrounding areas are characterized by strong tectonic movements and intense seismic activities. Using seismic data from January 2013 to November 2020 recorded at the stations of the temporary QiaoJia seismic Array (QJ Array), deployed by the Institute of Geophysics, China Earthquake Administration, this study investigates the upper crustal anisotropy by the shear-wave splitting analysis on small local earthquakes, discusses the deformation patterns in the upper crust in the north segment of the Xiaojiang faults, evaluates the stress distribution in the study area, and analyzes its relationship with the regional tectonic structure. Adopting the data processing technique of shear-wave splitting, a total of 875 effective records were obtained at 50 stations. The mean direction of polarizations of fast shear-wave (PFS) is 162° ± 44° in the study areaand the mean normalized time-delay is 4.96 ± 2.38 ms/km. Based on the spatial distribution of the PFS and the regional geologic structure, the study area is divided into two zones: the zone N and the zone S. The PFS in the zone N is scattered, but the dominant PFS direction is in NNW, which is consistent with the direction of the regional maximum principal compressive stress. In the zone N, there are a few smaller local areas (i.e., subzones A, B, C, and D) in which the orientations of the PFS are quite different from the surrounding area. In the zone S, the dominant directions at most stations are in nearly NS, consistent with the strike of the Xiaojiang fault. It reveals the detailed spatial distribution of seismic anisotropy in the upper crust, as well as in situ principal compressive stress, indicating the influence of the regional stress, the complex tectonic environment, and maybe also the impact of the South China block. It also reveals that there also might be an upper-crust scale of tectonic line at near 26°20′N under Xiaojiang faults, which coincides with the north-south tectonic boundary in the lithospheric anisotropy.
{"title":"Seismic anisotropy in the upper crust around the north segment of Xiaojiang faults in the SE margin of Tibetan Plateau","authors":"Peng Wu, Yuan Gao, Lisheng Xu","doi":"10.4401/ag-8852","DOIUrl":"https://doi.org/10.4401/ag-8852","url":null,"abstract":"The Xiaojiang faults located in the SE margin of the Tibetan Plateau is a fault system of left-lateral strike-slip, striking NS, between the 2nd-order Sichuan-Yunnan block and the 1st-order South China block. The Xiaojiang faults and the surrounding areas are characterized by strong tectonic movements and intense seismic activities. Using seismic data from January 2013 to November 2020 recorded at the stations of the temporary QiaoJia seismic Array (QJ Array), deployed by the Institute of Geophysics, China Earthquake Administration, this study investigates the upper crustal anisotropy by the shear-wave splitting analysis on small local earthquakes, discusses the deformation patterns in the upper crust in the north segment of the Xiaojiang faults, evaluates the stress distribution in the study area, and analyzes its relationship with the regional tectonic structure. Adopting the data processing technique of shear-wave splitting, a total of 875 effective records were obtained at 50 stations. The mean direction of polarizations of fast shear-wave (PFS) is 162° ± 44° in the study areaand the mean normalized time-delay is 4.96 ± 2.38 ms/km. Based on the spatial distribution of the PFS and the regional geologic structure, the study area is divided into two zones: the zone N and the zone S. The PFS in the zone N is scattered, but the dominant PFS direction is in NNW, which is consistent with the direction of the regional maximum principal compressive stress. In the zone N, there are a few smaller local areas (i.e., subzones A, B, C, and D) in which the orientations of the PFS are quite different from the surrounding area. In the zone S, the dominant directions at most stations are in nearly NS, consistent with the strike of the Xiaojiang fault. It reveals the detailed spatial distribution of seismic anisotropy in the upper crust, as well as in situ principal compressive stress, indicating the influence of the regional stress, the complex tectonic environment, and maybe also the impact of the South China block. It also reveals that there also might be an upper-crust scale of tectonic line at near 26°20′N under Xiaojiang faults, which coincides with the north-south tectonic boundary in the lithospheric anisotropy.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"44 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79089883","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. Spingos, V. Kapetanidis, G. Michas, G. Kaviris, F. Vallianatos
The Eastern Gulf of Corinth (EGoC) is one of the most seismically active areas in Greece. It is monitored by local and regional seismic stations of the Hellenic Unified Seismic Network (HUSN). In 2020, a high-yield seismic sequence, lasting over five months, occurred at the Perachora peninsula. This provided a unique opportunity to investigate the anisotropic properties of the upper crust in the area, which lacks relevant studies. The sequence exhibited characteristics of a seismic swarm, with the strongest event having a magnitude of 3.7. In the herein analysis, we use recordings from suitable HUSN stations for two periods: (a) 2008 to 2019, a period of scarce seismicity, to identify background anisotropy and (b) the 2020 seismic swarm period. We used a fully automated method to measure shear-wave splitting properties. After considering a shear-wave window of 45° and several quality criteria, we determined a complex state of anisotropy, with NE-SW directions of polarization (𝜑) prevailing pre-2020, while a dominant WNW-ESE orientation was observed during the swarm (with secondary NE-SW and N-S trends). The spatial distribution of 𝜑 did not offer any strong correlation with local faults. Additionally, 𝜑 seemed to rotate in 2015 and 2020, with variations of normalized time-delays being present during the crisis. These observations, along with indications regarding fluid diffusion during the swarm, led us to hypothesize that shear-wave splitting in the EGoC is mainly driven by high pressure gradients. A better understanding of pre‑2020 seismicity and more local stations to record future seismicity would be required to further specify the connection between fluid processes and seismic anisotropy in the area.
{"title":"Shear-wave splitting patterns in Perachora (Eastern Gulf of Corinth, Greece)","authors":"I. Spingos, V. Kapetanidis, G. Michas, G. Kaviris, F. Vallianatos","doi":"10.4401/ag-8829","DOIUrl":"https://doi.org/10.4401/ag-8829","url":null,"abstract":"The Eastern Gulf of Corinth (EGoC) is one of the most seismically active areas in Greece. It is monitored by local and regional seismic stations of the Hellenic Unified Seismic Network (HUSN). In 2020, a high-yield seismic sequence, lasting over five months, occurred at the Perachora peninsula. This provided a unique opportunity to investigate the anisotropic properties of the upper crust in the area, which lacks relevant studies. The sequence exhibited characteristics of a seismic swarm, with the strongest event having a magnitude of 3.7. In the herein analysis, we use recordings from suitable HUSN stations for two periods: (a) 2008 to 2019, a period of scarce seismicity, to identify background anisotropy and (b) the 2020 seismic swarm period. We used a fully automated method to measure shear-wave splitting properties. After considering a shear-wave window of 45° and several quality criteria, we determined a complex state of anisotropy, with NE-SW directions of polarization (𝜑) prevailing pre-2020, while a dominant WNW-ESE orientation was observed during the swarm (with secondary NE-SW and N-S trends). The spatial distribution of 𝜑 did not offer any strong correlation with local faults. Additionally, 𝜑 seemed to rotate in 2015 and 2020, with variations of normalized time-delays being present during the crisis. These observations, along with indications regarding fluid diffusion during the swarm, led us to hypothesize that shear-wave splitting in the EGoC is mainly driven by high pressure gradients. A better understanding of pre‑2020 seismicity and more local stations to record future seismicity would be required to further specify the connection between fluid processes and seismic anisotropy in the area.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"33 1-2 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78211521","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 area of Damasi-Tyrnavos (Thessaloniki, Central Greece), in the vicinity of Larissa, was characterized by low seismic activity during the last decades. Two strong earthquakes of Mw = 6.3 and Mw = 6.0 The area of Damasi – Tyrnavos (Thessaly, Central Greece), in the vicinity of Larissa, was characterized occurred in early March 2021, followed by an intense aftershock sequence, related to WNW-ESE to NW-SE oriented faulting. This sequence was recorded by a dense local seismological network that provided a rich dataset and a unique opportunity to investigate upper crust shear-wave splitting for the first time in the study area. A fully automated technique, employing the eigenvalues method and cluster analysis, was implemented to measure the fast shear-wave polarization direction and the time-delay between the two split-shear-waves. This procedure yielded 655 results of adequate quality grade at 9 stations, after analyzing 1602 events and applying strict selection criteria, including the shear-wave window. The measured directions revealed a complex upper crust anisotropic regime. WNW-ESE to NW-SE, in accordance both with the APE model, being parallel to the local 𝜎 Hmax direction, and the strike of the fault planes. On the other hand, stations at the central part exhibit NNW-SSE and NNE-SSW anisotropy directions. An interesting feature is that the two northern stations are characterized by larger normalized time-delay values, possibly related to the migration of seismicity to the north during the initial stage of the seismic sequence.
{"title":"Shear-wave splitting perspectives from the intense aftershock sequence of Damasi – Tyrnavos","authors":"G. Kaviris","doi":"10.4401/ag-8848","DOIUrl":"https://doi.org/10.4401/ag-8848","url":null,"abstract":"The area of Damasi-Tyrnavos (Thessaloniki, Central Greece), in the vicinity of Larissa, was characterized by low seismic activity during the last decades. Two strong earthquakes of Mw = 6.3 and Mw = 6.0 The area of Damasi – Tyrnavos (Thessaly, Central Greece), in the vicinity of Larissa, was characterized occurred in early March 2021, followed by an intense aftershock sequence, related to WNW-ESE to NW-SE oriented faulting. This sequence was recorded by a dense local seismological network that provided a rich dataset and a unique opportunity to investigate upper crust shear-wave splitting for the first time in the study area. A fully automated technique, employing the eigenvalues method and cluster analysis, was implemented to measure the fast shear-wave polarization direction and the time-delay between the two split-shear-waves. This procedure yielded 655 results of adequate quality grade at 9 stations, after analyzing 1602 events and applying strict selection criteria, including the shear-wave window. The measured directions revealed a complex upper crust anisotropic regime. WNW-ESE to NW-SE, in accordance both with the APE model, being parallel to the local 𝜎 Hmax direction, and the strike of the fault planes. On the other hand, stations at the central part exhibit NNW-SSE and NNE-SSW anisotropy directions. An interesting feature is that the two northern stations are characterized by larger normalized time-delay values, possibly related to the migration of seismicity to the north during the initial stage of the seismic sequence.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"48 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83381573","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}
G. Rümpker, A. Kaviani, F. Link, M. Reiss, A. Komeazi
We assess the capabilities of different observables for the inversion of core-refracted shear waves (XKS phases) to uniquely resolve the anisotropic structure of the upper mantle. For this purpose, we perform full-waveform calculations for relatively simple, canonical models of upper-mantle anisotropy. The models are characterized by two and four domains of different anisotropic properties. Specifically, we assume hexagonal symmetry with arbitrarily chosen strength of the anisotropy and orientation of the horizontal fast axis. XKS waveforms, generated from plane-wave initial conditions, traverse through anisotropic models and are recorded at the surface by a single station (in case of vertical variations) and by a dense station profile across the laterally and vertically varying structure. In addition to waveforms, we consider the effects of anisotropic variations on apparent splitting parameters and splitting intensity. The results show that, generally, it is not possible to fully resolve the anisotropic parameters of a given model, even if complete waveforms (under noisefree conditions and for the complete azimuthal range) are considered. This is because waveforms for significantly different anisotropic models can be indistinguishable. However, inversions of both waveforms and apparent splitting parameters lead to similar models that exhibit systematic variations of anisotropic parameters. These characteristics may be exploited to better constrain the inversions. The results also show that splitting intensity holds some significant drawbacks: First, even from measurements over a wide range of back-azimuth, there is no characteristic signature that would indicate depth variations of anisotropy. Secondly, identical azimuthal variations of splitting intensity for different anisotropic structures do not imply that the corresponding split waveforms are also similar. Thus, fitting of observed and calculated splitting intensities could lead to anisotropic models that are incompatible with the observed waveforms. We conclude that (bandlimited) XKS-splitting inversions and related tomographic schemes, even if based on complete waveforms, are not sufficient to fully resolve the heterogeneous anisotropic structures of the upper mantle and that combinations with alternative methods, based on e.g., receiver-function splitting, P-wave travel-time deviations, or surface waves, are required.
{"title":"Testing observables for teleseismic shear-wave splitting inversions: ambiguities of intensities, parameters, and waveforms","authors":"G. Rümpker, A. Kaviani, F. Link, M. Reiss, A. Komeazi","doi":"10.4401/ag-8870","DOIUrl":"https://doi.org/10.4401/ag-8870","url":null,"abstract":"We assess the capabilities of different observables for the inversion of core-refracted shear waves (XKS phases) to uniquely resolve the anisotropic structure of the upper mantle. For this purpose, we perform full-waveform calculations for relatively simple, canonical models of upper-mantle anisotropy. The models are characterized by two and four domains of different anisotropic properties. Specifically, we assume hexagonal symmetry with arbitrarily chosen strength of the anisotropy and orientation of the horizontal fast axis. XKS waveforms, generated from plane-wave initial conditions, traverse through anisotropic models and are recorded at the surface by a single station (in case of vertical variations) and by a dense station profile across the laterally and vertically varying structure. In addition to waveforms, we consider the effects of anisotropic variations on apparent splitting parameters and splitting intensity. The results show that, generally, it is not possible to fully resolve the anisotropic parameters of a given model, even if complete waveforms (under noisefree conditions and for the complete azimuthal range) are considered. This is because waveforms for significantly different anisotropic models can be indistinguishable. However, inversions of both waveforms and apparent splitting parameters lead to similar models that exhibit systematic variations of anisotropic parameters. These characteristics may be exploited to better constrain the inversions. The results also show that splitting intensity holds some significant drawbacks: First, even from measurements over a wide range of back-azimuth, there is no characteristic signature that would indicate depth variations of anisotropy. Secondly, identical azimuthal variations of splitting intensity for different anisotropic structures do not imply that the corresponding split waveforms are also similar. Thus, fitting of observed and calculated splitting intensities could lead to anisotropic models that are incompatible with the observed waveforms. We conclude that (bandlimited) XKS-splitting inversions and related tomographic schemes, even if based on complete waveforms, are not sufficient to fully resolve the heterogeneous anisotropic structures of the upper mantle and that combinations with alternative methods, based on e.g., receiver-function splitting, P-wave travel-time deviations, or surface waves, are required.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"20 1 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83875919","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}
A new crustal 1D layered model for Albania has been determined. The data used consist of P and S readings from 108 evenly distributed and well located earthquakes using the Albanian Seismic Network and nearby seismic stations. The method used was to relocate the data using many thousand models, which were varied in a systematic way in a wide range around a start model determined from currently available models. The model with the lowest average travel time residual RMS was then selected as a final model. Tests with synthetic data showed this to be a robust method. With the dataset, the average RMS was reduced from 0.69s, using the current model, to 0.56s using the start model and to 0.49s using the final model. The new hypocenters were also found to be closer to a set of well located ISC hypocenters than the original locations. The final model found is: Depth to interface (km) P-velocity (km/s) 0 5.5 12 6.0 23 6.3 41 7.7 with a Vp/Vs=1.81. This final model is different from the currently used model in Albania and should therefore represent a significant improvement for earthquake location.
{"title":"1D crustal structure of Albania region","authors":"E. Dushi, J. Havskov","doi":"10.4401/ag-8805","DOIUrl":"https://doi.org/10.4401/ag-8805","url":null,"abstract":"A new crustal 1D layered model for Albania has been determined. The data used consist of P and S readings from 108 evenly distributed and well located earthquakes using the Albanian Seismic Network and nearby seismic stations. The method used was to relocate the data using many thousand models, which were varied in a systematic way in a wide range around a start model determined from currently available models. The model with the lowest average travel time residual RMS was then selected as a final model. Tests with synthetic data showed this to be a robust method. With the dataset, the average RMS was reduced from 0.69s, using the current model, to 0.56s using the start model and to 0.49s using the final model. The new hypocenters were also found to be closer to a set of well located ISC hypocenters than the original locations. The final model found is: Depth to interface (km) P-velocity (km/s) 0 5.5 12 6.0 23 6.3 41 7.7 with a Vp/Vs=1.81. This final model is different from the currently used model in Albania and should therefore represent a significant improvement for earthquake location. ","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"66 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86028083","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 study the effects of seismic coupling, friction, viscous, and inertia on earthquake nucleation based on a two-body spring-slider model in the presence of thermal- pressurized slip-dependent friction and viscosity. The stiffness ratio of the system to represent seismic coupling is the ratio of coil spring K between two sliders and the leaf spring L between a slider and the background plate and denoted by s=K/L. The s is not a significant factor in generating the nucleation phase. The masses of the two sliders are m1 and m2, respectively. The frictional and viscous effects are specified by the static friction force, fo, the characteristic displacement, Uc, and viscosity coefficient, h, respectively. Numerical simulations show that friction and viscosity can both lengthen the natural period of the system and viscosity increases the duration time of motion of the slider. Higher viscosity causes lower particle velocities than lower viscosity. The ratios g=h2/h1, f=fo2/fo1, y=Uc2/Ucl, and m=m2/m1 are four important factors in influencing the generation of a nucleation phase. When s>0.17, g>1, 1.15>f>1, y<1, and m<30, simulation results exhibit the generation of nucleation phase on slider 1 and the formation of P wave on slider 2. The results are consistent with the observations and suggest the possibility of generation of nucleation phase on a sub-fault. Results exhibit independence of P wave at slider 2 on the shape and duration time of nucleation phase at slider 1.
{"title":"Can the Nucleation Phase be Generated on a Sub-fault Linked to the Main Fault of an Earthquake?","authors":"Jeen-Hwa Wang","doi":"10.4401/ag-8833","DOIUrl":"https://doi.org/10.4401/ag-8833","url":null,"abstract":"We study the effects of seismic coupling, friction, viscous, and inertia on earthquake nucleation based on a two-body spring-slider model in the presence of thermal- pressurized slip-dependent friction and viscosity. The stiffness ratio of the system to represent seismic coupling is the ratio of coil spring K between two sliders and the leaf spring L between a slider and the background plate and denoted by s=K/L. The s is not a significant factor in generating the nucleation phase. The masses of the two sliders are m1 and m2, respectively. The frictional and viscous effects are specified by the static friction force, fo, the characteristic displacement, Uc, and viscosity coefficient, h, respectively. Numerical simulations show that friction and viscosity can both lengthen the natural period of the system and viscosity increases the duration time of motion of the slider. Higher viscosity causes lower particle velocities than lower viscosity. The ratios g=h2/h1, f=fo2/fo1, y=Uc2/Ucl, and m=m2/m1 are four important factors in influencing the generation of a nucleation phase. When s>0.17, g>1, 1.15>f>1, y<1, and m<30, simulation results exhibit the generation of nucleation phase on slider 1 and the formation of P wave on slider 2. The results are consistent with the observations and suggest the possibility of generation of nucleation phase on a sub-fault. Results exhibit independence of P wave at slider 2 on the shape and duration time of nucleation phase at slider 1.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134939695","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 paper aims to delineate buried faults in Izmir city and its surroundings, western Turkey using aeromagnetic and seismological data. In this context, the geophysical data processing techniques including reduced‑to‑pole transform (RTP), power spectrum analysis, high-pass filter and second vertical derivative method (SVD) have been applied to the total field aeromagnetic data of the study area. First, to remove the undesirable effects caused by the dipolar nature of the Earth field, RTP transform has been applied to those data. Second, the average depths of the regional and residual sources in the region have been calculated as 16.84 km and 3.75 km, respectively using power spectrum analysis. After, to emphasize the effects of the residual anomalies, the high-pass filter has been applied to the RTP data. Finally, the second vertical derivative method (SVD) has applied to the filtered data for delineating the uncovering buried faults and their lineaments in the eastern part of the Aegean extension. The results from those methods show five major fault zones that could cause devastating earthquakes in the area. Especially, the study reveals for the first time that one of these faults which lies from Doganbey to the city center of Izmir in the literature actually reaches out to Manisa city in the NE direction. As a result, these lineaments can be evaluated as traces of buried faults could be an important clue in predicting earthquake potential. A comparison of seismicity map and the heat flow map shows that the region (between Cesme and Seferihisar) represented with a low b‑value has a high potential earthquake. The spatial distribution of the earthquakes, b‑values and heat flow values in the depths may be related to the existence thin lithospheric mantle. Furthermore, the region represented by strong aeromagnetic anomalies may be considered to be magmatic material arising from the magma filling inside the strike-slip faults. The fault structure observed on the SVD map are also important for the geothermal energy potential of the region as well.
{"title":"Determination of buried active faults and earthquake potential for Izmir and its surroundings (western Turkey) using aeromagnetic anomalies and seismological data","authors":"Ezgi Erbek-Kiran, A. Ateş, M. Dolmaz","doi":"10.4401/ag-8871","DOIUrl":"https://doi.org/10.4401/ag-8871","url":null,"abstract":"The paper aims to delineate buried faults in Izmir city and its surroundings, western Turkey using aeromagnetic and seismological data. In this context, the geophysical data processing techniques including reduced‑to‑pole transform (RTP), power spectrum analysis, high-pass filter and second vertical derivative method (SVD) have been applied to the total field aeromagnetic data of the study area. First, to remove the undesirable effects caused by the dipolar nature of the Earth field, RTP transform has been applied to those data. Second, the average depths of the regional and residual sources in the region have been calculated as 16.84 km and 3.75 km, respectively using power spectrum analysis. After, to emphasize the effects of the residual anomalies, the high-pass filter has been applied to the RTP data. Finally, the second vertical derivative method (SVD) has applied to the filtered data for delineating the uncovering buried faults and their lineaments in the eastern part of the Aegean extension. The results from those methods show five major fault zones that could cause devastating earthquakes in the area. Especially, the study reveals for the first time that one of these faults which lies from Doganbey to the city center of Izmir in the literature actually reaches out to Manisa city in the NE direction. As a result, these lineaments can be evaluated as traces of buried faults could be an important clue in predicting earthquake potential. A comparison of seismicity map and the heat flow map shows that the region (between Cesme and Seferihisar) represented with a low b‑value has a high potential earthquake. The spatial distribution of the earthquakes, b‑values and heat flow values in the depths may be related to the existence thin lithospheric mantle. Furthermore, the region represented by strong aeromagnetic anomalies may be considered to be magmatic material arising from the magma filling inside the strike-slip faults. The fault structure observed on the SVD map are also important for the geothermal energy potential of the region as well. ","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"30 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89744231","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. Oros, M. Popa, D. Paulescu, A. Plăcintă, C. Ghita
We present a refined and the most complete catalogue of the focal mechanisms for the Intra-Carpathian region of Romania. It contains the high-quality solutions computed for 1217 earthquakes recorded between 1909 and 2018. Primary data gathered from the original seismograms and seismic bulletins have been used to compute the source parameters and focal mechanisms solutions. The focal mechanisms have been obtained using the HASH method by the polarities and S/P amplitudes ratios inversion. Our catalogue provides data necessary for the investigation of the contemporary stress field at different scales with high spatial and temporal resolution. We determined the stress field characteristics through formal inversion of focal mechanisms and also computed the reactivation potential of the active fault systems using the Win‑Tensor program. The stress field is heterogeneous, with SHmax significantly deviating from the first-order stress field direction and also with strong local variations in the stress regime.
{"title":"A refined catalogue of focal mechanisms for the Intra‑Carpathian region of Romania: implications for the stress field and seismogenic features assessment","authors":"E. Oros, M. Popa, D. Paulescu, A. Plăcintă, C. Ghita","doi":"10.4401/ag-8387","DOIUrl":"https://doi.org/10.4401/ag-8387","url":null,"abstract":"We present a refined and the most complete catalogue of the focal mechanisms for the Intra-Carpathian region of Romania. It contains the high-quality solutions computed for 1217 earthquakes recorded between 1909 and 2018. Primary data gathered from the original seismograms and seismic bulletins have been used to compute the source parameters and focal mechanisms solutions. The focal mechanisms have been obtained using the HASH method by the polarities and S/P amplitudes ratios inversion. Our catalogue provides data necessary for the investigation of the contemporary stress field at different scales with high spatial and temporal resolution. We determined the stress field characteristics through formal inversion of focal mechanisms and also computed the reactivation potential of the active fault systems using the Win‑Tensor program. The stress field is heterogeneous, with SHmax significantly deviating from the first-order stress field direction and also with strong local variations in the stress regime.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"31 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88203781","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}
Satellite thermal remote sensing is widely used to detect and quantify the high-temperature vol- canic features produced during an eruption, e.g. released radiative power. Some space agencies provide Fire Radiative Power (FRP) Products to characterize any thermal anomaly around the world. In particular, Level-2 FRP Products of the Visible Infrared Imaging Radiometer Suite (VIIRS) and the Sea and Land Surface Temperature Radiometer (SLSTR) are freely available online and they allow to monitor high-temperature volcanic features related to the dynamics of volcanic activity. Here, we propose the FastVRP platform developed in Google Colab to process automatically the FRP Products provided by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) space agencies. FastVRP was designed to monitor the volcanic radiative power (VRP) related to eruptive activity of Mt. Etna (Sicily, Italy). We compared the quality of these FRP Products during a number of recent paroxysmal lava fountains occurred at Etna volcano between February and March 2021. We highlighted the advantages and the limits of each sensor in monitor- ing intense volcanic eruptions lasting a few hours. Furthermore, we combine the mid-high spatial/ low temporal resolution VIIRS and SLSTR with the low spatial-high temporal resolution SEVIRI (Spinning Enhanced Visible and Infrared Radiometer Imager) to improve estimates of the energies released from each paroxysmal episode. In particular, we propose a fitting approach to enhance the accuracy of SEVIRI low spatial-high temporal resolution measurements exploiting the few acqui- sitions from VIIRS and SLSTR high spatial-low temporal resolution during lava fountain cooling phase. We validated the radiative power values forecasted from VIIRS and SLSTR with the radiative power values retrieved using MODIS (Moderate Resolution Imaging Spectroradiometer) sensor.
{"title":"The FastVRP automatic platform for the thermal monitoring of volcanic activity using VIIRS and SLSTR sensors: FastFRP to monitor volcanic radiative power","authors":"F. Torrisi, E. Amato, C. Corradino, C. Del Negro","doi":"10.4401/ag-8823","DOIUrl":"https://doi.org/10.4401/ag-8823","url":null,"abstract":"Satellite thermal remote sensing is widely used to detect and quantify the high-temperature vol- canic features produced during an eruption, e.g. released radiative power. Some space agencies provide Fire Radiative Power (FRP) Products to characterize any thermal anomaly around the world. In particular, Level-2 FRP Products of the Visible Infrared Imaging Radiometer Suite (VIIRS) and the Sea and Land Surface Temperature Radiometer (SLSTR) are freely available online and they allow to monitor high-temperature volcanic features related to the dynamics of volcanic activity. Here, we propose the FastVRP platform developed in Google Colab to process automatically the FRP Products provided by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) space agencies. FastVRP was designed to monitor the volcanic radiative power (VRP) related to eruptive activity of Mt. Etna (Sicily, Italy). We compared the quality of these FRP Products during a number of recent paroxysmal lava fountains occurred at Etna volcano between February and March 2021. We highlighted the advantages and the limits of each sensor in monitor- ing intense volcanic eruptions lasting a few hours. Furthermore, we combine the mid-high spatial/ low temporal resolution VIIRS and SLSTR with the low spatial-high temporal resolution SEVIRI (Spinning Enhanced Visible and Infrared Radiometer Imager) to improve estimates of the energies released from each paroxysmal episode. In particular, we propose a fitting approach to enhance the accuracy of SEVIRI low spatial-high temporal resolution measurements exploiting the few acqui- sitions from VIIRS and SLSTR high spatial-low temporal resolution during lava fountain cooling phase. We validated the radiative power values forecasted from VIIRS and SLSTR with the radiative power values retrieved using MODIS (Moderate Resolution Imaging Spectroradiometer) sensor.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"6 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84195220","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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