Electrokinetic effect (EK) caused by long oceanic waves in porous water-saturated rocks of seabed and shore is examined theoretically. One possible reason for this effect is the motion of groundwater due to the volume deformation of porous rocks by oceanic waves coming on shore. The same mechanism is responsible for seismoelectric effect observed during seismic waves passage through ground-recording station. In this study, we examine another mechanism in which the wave-produced variable pressure on the seabed plays a role of a piston pushing seawater through the seabed rocks into sandy or porous rocks of the seashore thereby exciting the EK effect. To estimate this effect, we first consider a long gravity wave and then solve 2D‑problem on the pressure variations produced by this wave on the bottom. This solution is used to describe groundwater filtration in porous rocks subjected to the variable pressure of seawater. The EK current and telluric electric field in a porous medium are derivable through the pressure gradient of porous fluid. The amplitude of telluric electric field in a porous medium has been shown to decrease almost exponentially with distance from a shoreline. A penetration depth of the telluric field as a function of wave frequency in the range of 10‑100 mHz was analyzed. A role played by EK effect in the generation of ULF natural electromagnetic noise in coastal zone was discussed.
{"title":"Electrokinetic effect provided by long oceanic waves coming on shore","authors":"V. Surkov, V. Sorokin, Aleksey K. Yashchenko","doi":"10.4401/ag-8792","DOIUrl":"https://doi.org/10.4401/ag-8792","url":null,"abstract":"Electrokinetic effect (EK) caused by long oceanic waves in porous water-saturated rocks of seabed and shore is examined theoretically. One possible reason for this effect is the motion of groundwater due to the volume deformation of porous rocks by oceanic waves coming on shore. The same mechanism is responsible for seismoelectric effect observed during seismic waves passage through ground-recording station. In this study, we examine another mechanism in which the wave-produced variable pressure on the seabed plays a role of a piston pushing seawater through the seabed rocks into sandy or porous rocks of the seashore thereby exciting the EK effect. To estimate this effect, we first consider a long gravity wave and then solve 2D‑problem on the pressure variations produced by this wave on the bottom. This solution is used to describe groundwater filtration in porous rocks subjected to the variable pressure of seawater. The EK current and telluric electric field in a porous medium are derivable through the pressure gradient of porous fluid. The amplitude of telluric electric field in a porous medium has been shown to decrease almost exponentially with distance from a shoreline. A penetration depth of the telluric field as a function of wave frequency in the range of 10‑100 mHz was analyzed. A role played by EK effect in the generation of ULF natural electromagnetic noise in coastal zone was discussed.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"7 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84361089","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}
J. A. Lazzús, P. Vega-Jorquera, Rene Pacheco, L. Tamblay, M. Martínez-Ledesma, E. Ovalle, E. Carrasco, M. Bravo, C. Villalobos, I. Salfate, L. Palma-Chilla, A. Foppiano
The first report on the changes in meteorological parameters during the total solar eclipse of July 2, 2019, in La Serena (Chile), is presented. The event could be observed from morning time on the east of New Zealand, in the South Pacific Ocean, to sunset time in Chile. Several meteorological properties such as global radiation Rg, net radiation Rn, reflected radiation Rr (in Wm–2/min), air temperature (TA in °C), relative humidity (RH in %), wind speed amplitude (WS in ms–1), and wind speed direction (WD in degrees), were recorded with La Serena weather station SER (29.827°S, 71.261°W, 28 masl) at 1‑minute time resolution. Importantly, SER was located at 40 km from the axis of the umbra that covered 201 km of width, where it reached 100% darkness at a magnitude of 1.009 during a clear-sky day. Under these auspicious conditions, we observed a rate of changes in the drop of the radiation components of 3.1, 2.4, and 0.5 (Wm–2/min) for Rg, Rn, and Rr, respectively, with a 100% reduction in the components of surface solar radiation (0 Wm–2) during totality. In addition, all components showed a ~34% energy loss during the eclipse in comparison with the day before the event. Also, the rate of changes of –3.3 °C in TA, +11% in RH, –1.11 ms–1 in WS, and 180° to 340° for WD in total synchrony with the passing of the moon in front of the sun, reaching respective peaks at ~5 min lag with respect to totality. Thus, our results show a progressive change in all meteorological parameters in total synchrony with the eclipse’s phases caused by the passing of the moon in front of the sun.
{"title":"Changes in meteorological parameters during the total solar eclipse of 2 July 2019 in La Serena, Chile","authors":"J. A. Lazzús, P. Vega-Jorquera, Rene Pacheco, L. Tamblay, M. Martínez-Ledesma, E. Ovalle, E. Carrasco, M. Bravo, C. Villalobos, I. Salfate, L. Palma-Chilla, A. Foppiano","doi":"10.4401/ag-8623","DOIUrl":"https://doi.org/10.4401/ag-8623","url":null,"abstract":"The first report on the changes in meteorological parameters during the total solar eclipse of July 2, 2019, in La Serena (Chile), is presented. The event could be observed from morning time on the east of New Zealand, in the South Pacific Ocean, to sunset time in Chile. Several meteorological properties such as global radiation Rg, net radiation Rn, reflected radiation Rr (in Wm–2/min), air temperature (TA in °C), relative humidity (RH in %), wind speed amplitude (WS in ms–1), and wind speed direction (WD in degrees), were recorded with La Serena weather station SER (29.827°S, 71.261°W, 28 masl) at 1‑minute time resolution. Importantly, SER was located at 40 km from the axis of the umbra that covered 201 km of width, where it reached 100% darkness at a magnitude of 1.009 during a clear-sky day. Under these auspicious conditions, we observed a rate of changes in the drop of the radiation components of 3.1, 2.4, and 0.5 (Wm–2/min) for Rg, Rn, and Rr, respectively, with a 100% reduction in the components of surface solar radiation (0 Wm–2) during totality. In addition, all components showed a ~34% energy loss during the eclipse in comparison with the day before the event. Also, the rate of changes of –3.3 °C in TA, +11% in RH, –1.11 ms–1 in WS, and 180° to 340° for WD in total synchrony with the passing of the moon in front of the sun, reaching respective peaks at ~5 min lag with respect to totality. Thus, our results show a progressive change in all meteorological parameters in total synchrony with the eclipse’s phases caused by the passing of the moon in front of the sun.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"98 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90621342","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}
This study aims to determine Curie point depth (CPD), Heat flow and the boundaries of geological structures of Cyprus Island using EMAG2 magnetic data. CPD values were calculated by applying spectral analysis technique to magnetic anomaly map divided into 60 blocks (60x60 km2). Then, different thermal conductivity values (K=1, 1.5 and 2.5 Wm–1 K–1) and heat flow values were calculated using CPD values. CPD values ranged from 12.4 km to 28.18 km, and heat flow values were calculated between 20 and 50 mW/m2 for K=1. Shallow CPD values (CPD< 15km) were calculated in Polis, Morphou Bay, in the area between Larnaca and Famagusta and north of Kyrenia. Heat flow values are relatively high in these areas which can be researched in detail in terms of potential geothermal. In the final phase of the study, the boundaries of buried geological structures were determined by Analytic Signal (AS), Total Horizontal Derivative (THDR) and Tilt angle (TA) methods. Moho depth, Curie-Moho difference, 2D cross-correlation map of Moho and Curie depths and Earthquake distribution map are used for interpretation of the tectonic regime. Moho-Curie difference is roughly 0 and the 2D cross-correlation map produces higher (0.60-0.75) values in the southern part of the study area which might be evaluated as a passive crust. It is possible to say that few earthquakes are observed where the difference is around 0.
本研究旨在利用EMAG2磁资料确定塞浦路斯岛的居里点深度(CPD)、热流和地质构造边界。将磁异常图划分为60块(60x60 km2)，应用波谱分析技术计算CPD值。然后利用CPD值计算不同的导热系数值(K= 1,1.5和2.5 Wm-1 K - 1)和热流值。当K=1时，CPD值为12.4 ~ 28.18 km，热流值为20 ~ 50 mW/m2。在Polis, Morphou Bay, Larnaca和Famagusta之间以及Kyrenia北部地区，计算了浅CPD值(CPD< 15km)。这些地区的热流值相对较高，可以从地热潜力方面进行详细研究。在研究的最后阶段，通过分析信号(AS)、总水平导数(THDR)和倾角(TA)方法确定了埋藏地质构造的边界。利用莫霍深度、居里-莫霍差、二维莫霍-居里深度互相关图和地震分布图解释构造格局。Moho-Curie差值大致为0,2D互相关图在研究区南部产生较高的值(0.60-0.75)，可评价为被动地壳。可以说，在差值为0左右的地方观测到的地震很少。
{"title":"Estimation of Curie-Point Depths and Heat Flow from Spectral Analysis of EMAG2 Magnetic Data in Cyprus Island","authors":"E. Pamuk, Ilkin Özsöz","doi":"10.4401/ag-8741","DOIUrl":"https://doi.org/10.4401/ag-8741","url":null,"abstract":"This study aims to determine Curie point depth (CPD), Heat flow and the boundaries of geological structures of Cyprus Island using EMAG2 magnetic data. CPD values were calculated by applying spectral analysis technique to magnetic anomaly map divided into 60 blocks (60x60 km2). Then, different thermal conductivity values (K=1, 1.5 and 2.5 Wm–1 K–1) and heat flow values were calculated using CPD values. CPD values ranged from 12.4 km to 28.18 km, and heat flow values were calculated between 20 and 50 mW/m2 for K=1. Shallow CPD values (CPD< 15km) were calculated in Polis, Morphou Bay, in the area between Larnaca and Famagusta and north of Kyrenia. Heat flow values are relatively high in these areas which can be researched in detail in terms of potential geothermal. In the final phase of the study, the boundaries of buried geological structures were determined by Analytic Signal (AS), Total Horizontal Derivative (THDR) and Tilt angle (TA) methods. Moho depth, Curie-Moho difference, 2D cross-correlation map of Moho and Curie depths and Earthquake distribution map are used for interpretation of the tectonic regime. Moho-Curie difference is roughly 0 and the 2D cross-correlation map produces higher (0.60-0.75) values in the southern part of the study area which might be evaluated as a passive crust. It is possible to say that few earthquakes are observed where the difference is around 0.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"13 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80324305","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}
Seismic anisotropy inside the Earth’s interior, especially in the upper and lowermost mantle, is commonly studied measuring shear wave splitting. This is mostly done by the determination of the splitting parameters the fast polarization direction and the time delay as well as the splitting intensity. The applied techniques highly relay on the correct temporal alignment of the single traces (vertical, north, east or Z, N, E components, respectively) of an earthquake relative to each other. Mixing wrongly aligned recording components would result in misleading and wrong data representations, including the particle motions in both the ZNE and the ray (LQT) coordinate systems and waveforms in the LQT coordinate system. The main pitfall in this context is that start and end times of the single traces in general differ due to data storage details. Unfortunately, especially the code of the widely used MATLAB based shear wave splitting software package SplitLab contains an error source causing a wrong relative temporal alignment of the input seismograms. This effect distorts splitting signals or simulates non-existing ones. We show examples and offer a remedy.
{"title":"On the effects of wrongly aligned seismogram components for shear wave splitting analysis","authors":"Yvonne Fröhlich, M. Grund, J. Ritter","doi":"10.4401/ag-8781","DOIUrl":"https://doi.org/10.4401/ag-8781","url":null,"abstract":"Seismic anisotropy inside the Earth’s interior, especially in the upper and lowermost mantle, is commonly studied measuring shear wave splitting. This is mostly done by the determination of the splitting parameters the fast polarization direction and the time delay as well as the splitting intensity. The applied techniques highly relay on the correct temporal alignment of the single traces (vertical, north, east or Z, N, E components, respectively) of an earthquake relative to each other. Mixing wrongly aligned recording components would result in misleading and wrong data representations, including the particle motions in both the ZNE and the ray (LQT) coordinate systems and waveforms in the LQT coordinate system. The main pitfall in this context is that start and end times of the single traces in general differ due to data storage details. Unfortunately, especially the code of the widely used MATLAB based shear wave splitting software package SplitLab contains an error source causing a wrong relative temporal alignment of the input seismograms. This effect distorts splitting signals or simulates non-existing ones. We show examples and offer a remedy.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"59 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80529159","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}
Improving the vertical resolution is one of the significant tasks for seismic data processing. Most traditional resolution-enhancement techniques assume that the seismic wavelet is time-invariant. However, the seismic wavelet varies with seismic wave propagation in the subsurface. To solve this issue, a new spectral-modeling method is proposed to extract the time-varying wavelet using improved generalized S-transform (IGST) and higher-order Fourier series. The IGST based on modified time-window function can effectively improve the resolution of the time-frequency (t-f) spectrum. The high-order Fourier series is used to fit on the logarithm t-f spectrum and achieve the high-precision time-varying wavelet. The proposed method is composed of four steps in the implementation. Firstly, the seismic data is decomposed by the IGST and converted to the logarithm t-f domain. Secondly, the time-varying wavelet spectrum is modeled at each time sample using a higher-order Fourier series. Thirdly, the boxcar smoothing method is used to smooth the time-varying wavelet spectrum and extract the time-varying wavelet with Hilbert transform. Finally, using the time-varying wavelet spectrum to spectrally balance seismic data to flatten the seismic response. Synthetic and field data examples demonstrate the feasibility of the proposed method in improving the signal-to-noise ratio and enhancing the vertical resolution.
{"title":"Improved generalized S-transform deconvolution for non-stationary seismic data","authors":"Chao Sun, D. He, Shen Lijun, Liang Sun","doi":"10.4401/ag-8761","DOIUrl":"https://doi.org/10.4401/ag-8761","url":null,"abstract":"Improving the vertical resolution is one of the significant tasks for seismic data processing. Most traditional resolution-enhancement techniques assume that the seismic wavelet is time-invariant. However, the seismic wavelet varies with seismic wave propagation in the subsurface. To solve this issue, a new spectral-modeling method is proposed to extract the time-varying wavelet using improved generalized S-transform (IGST) and higher-order Fourier series. The IGST based on modified time-window function can effectively improve the resolution of the time-frequency (t-f) spectrum. The high-order Fourier series is used to fit on the logarithm t-f spectrum and achieve the high-precision time-varying wavelet. The proposed method is composed of four steps in the implementation. Firstly, the seismic data is decomposed by the IGST and converted to the logarithm t-f domain. Secondly, the time-varying wavelet spectrum is modeled at each time sample using a higher-order Fourier series. Thirdly, the boxcar smoothing method is used to smooth the time-varying wavelet spectrum and extract the time-varying wavelet with Hilbert transform. Finally, using the time-varying wavelet spectrum to spectrally balance seismic data to flatten the seismic response. Synthetic and field data examples demonstrate the feasibility of the proposed method in improving the signal-to-noise ratio and enhancing the vertical resolution.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"41 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90730411","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}
Sheng Liu, Shuanggen Jin, Songbai Xuan, Xiangqun Liu
Non-uniqueness, low computational efficiency and large memory requirements are main issues for geophysical data inversion. In this paper, we propose an efficient algorithm for 3D correlationanalysis joint inversion of gravity and magnetic data with high accuracy and low computation effort. Firstly, since the number of the observed field data is smaller than the number of inverted parameters, the calculations of the correlation-analysis for joint inversion of gravity and magnetic data in model space (MS) are transformed into the equivalent calculations in data space (DS), which can reduce the dimensions of the calculation domain, improve the computation efficiency and reduce the non-uniqueness. Then, an improved conjugate gradient (ICG) method is employed for the optimization algorithm, which can facilitate the use of stable functions with sparse factors and improve the accuracy of the inversion. The inversion performed by the combined DS-ICG method for synthetic data tests shows the calculation effort can be effectively reduced, and the issues with non-uniqueness are improved. Finally, the test by real field data can delineate the distribution of underground geological bodies, which illustrates the strong stability and good applicability of our extended method.
{"title":"3-D data-space joint inversion of gravity and magnetic data using a correlation-analysis constraint","authors":"Sheng Liu, Shuanggen Jin, Songbai Xuan, Xiangqun Liu","doi":"10.4401/ag-8750","DOIUrl":"https://doi.org/10.4401/ag-8750","url":null,"abstract":"Non-uniqueness, low computational efficiency and large memory requirements are main issues for geophysical data inversion. In this paper, we propose an efficient algorithm for 3D correlationanalysis joint inversion of gravity and magnetic data with high accuracy and low computation effort. Firstly, since the number of the observed field data is smaller than the number of inverted parameters, the calculations of the correlation-analysis for joint inversion of gravity and magnetic data in model space (MS) are transformed into the equivalent calculations in data space (DS), which can reduce the dimensions of the calculation domain, improve the computation efficiency and reduce the non-uniqueness. Then, an improved conjugate gradient (ICG) method is employed for the optimization algorithm, which can facilitate the use of stable functions with sparse factors and improve the accuracy of the inversion. The inversion performed by the combined DS-ICG method for synthetic data tests shows the calculation effort can be effectively reduced, and the issues with non-uniqueness are improved. Finally, the test by real field data can delineate the distribution of underground geological bodies, which illustrates the strong stability and good applicability of our extended method.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"64 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82788698","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}
Ghazaleh Rasaneh, Alireza Hajian, M. Hodhodi, Roohollah Kimiae, S. Gambino
The Seismic Amplitude Ratio Analysis method (SARA) was applied to data recorded six days before the May 13, 2008 eruption of Mt. Etna to test its potential as a forecasting attribute. By using this method, the magma migration path, as well as the seismic migration, can be determined with the amplitude of continuous data recorded at least at one pair of stations from a seismic network near the eruption site. Due to the sudden changes in the seismic amplitude ratio calculated for each pair of stations, the seismic migration trend, as well as the magma path at depths, were detected before the main eruption. The start and end times of the seismic swarms were also determined. The standard practice to achieve similar results is to use volcanic tremors, which must be pre-selected thus reducing efficiency and increasing the time needed. By using the whole seismic signal, the method provides a simpler semi-automated alternative, especially for a seismic event or places where it is not possible to record tremors continuously. This simple method is useful to reduce uncertainties relative to hazardous magma propagation during volcanic unrest, as it helps improve the accuracy of locating seismic swarms and determining the direction of magma movement at depth before the eruption. We also analyzed the amplitude ratio trend using Mann-Kendall and Sen's estimator test. The results of these tests confirmed a positive and increasing trend from the day before the eruption in most pairs of stations.
{"title":"Monitoring magma migration at Mt. Etna using the Seismic Amplitude Ratio Analysis method","authors":"Ghazaleh Rasaneh, Alireza Hajian, M. Hodhodi, Roohollah Kimiae, S. Gambino","doi":"10.4401/ag-8807","DOIUrl":"https://doi.org/10.4401/ag-8807","url":null,"abstract":"The Seismic Amplitude Ratio Analysis method (SARA) was applied to data recorded six days before the May 13, 2008 eruption of Mt. Etna to test its potential as a forecasting attribute. By using this method, the magma migration path, as well as the seismic migration, can be determined with the amplitude of continuous data recorded at least at one pair of stations from a seismic network near the eruption site. Due to the sudden changes in the seismic amplitude ratio calculated for each pair of stations, the seismic migration trend, as well as the magma path at depths, were detected before the main eruption. The start and end times of the seismic swarms were also determined. The standard practice to achieve similar results is to use volcanic tremors, which must be pre-selected thus reducing efficiency and increasing the time needed. By using the whole seismic signal, the method provides a simpler semi-automated alternative, especially for a seismic event or places where it is not possible to record tremors continuously. This simple method is useful to reduce uncertainties relative to hazardous magma propagation during volcanic unrest, as it helps improve the accuracy of locating seismic swarms and determining the direction of magma movement at depth before the eruption. We also analyzed the amplitude ratio trend using Mann-Kendall and Sen's estimator test. The results of these tests confirmed a positive and increasing trend from the day before the eruption in most pairs of stations.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"21 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81464397","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}
Michail Ravnalis, Ch. Kkallas, C. Papazachos, B. Margaris, C. Papaioannou
We apply a stochastic simulation approach for the simultaneous modeling of macroseismic data and strong ground motion records for several shallow strong earthquakes (M ≥ 6.0) that occurred in the Aegean area from 1980 to 1995 Alkyonides (1981, M6.7), Kalamata (1986, M6.0), Kozani (1995, M6.6) and Aigio (1995, M6.4). The application is semi-automatic, as several of the selected input parameters for the stochastic simulation modeling were automatically calibrated using a priori information (e.g., magnitude, stress parameter, site effects). Other parameters (e.g., fault type, depth) were pre‑determined, based on published information, most of which are usually derived during standard earthquake analysis. The validity and reliability of this approach was examined, to test if this method could be applied either in a fully automated manner, or for the study of source properties of historical earthquakes. While the results obtained from the semi-automated simulations were satisfactory, they also suggest that it is not possible to achieve the same level of reliability and robustness when modeling complicated seismic sequences, as e.g., is the case of the Alkyonides earthquake (1981, M6.7).
{"title":"Semi-automated stochastic simultaneous simulation of macroseismic information and strong ground motion records for recent strong earthquakes of the Aegean area","authors":"Michail Ravnalis, Ch. Kkallas, C. Papazachos, B. Margaris, C. Papaioannou","doi":"10.4401/ag-8636","DOIUrl":"https://doi.org/10.4401/ag-8636","url":null,"abstract":"We apply a stochastic simulation approach for the simultaneous modeling of macroseismic data and strong ground motion records for several shallow strong earthquakes (M ≥ 6.0) that occurred in the Aegean area from 1980 to 1995 Alkyonides (1981, M6.7), Kalamata (1986, M6.0), Kozani (1995, M6.6) and Aigio (1995, M6.4). The application is semi-automatic, as several of the selected input parameters for the stochastic simulation modeling were automatically calibrated using a priori information (e.g., magnitude, stress parameter, site effects). Other parameters (e.g., fault type, depth) were pre‑determined, based on published information, most of which are usually derived during standard earthquake analysis. The validity and reliability of this approach was examined, to test if this method could be applied either in a fully automated manner, or for the study of source properties of historical earthquakes. While the results obtained from the semi-automated simulations were satisfactory, they also suggest that it is not possible to achieve the same level of reliability and robustness when modeling complicated seismic sequences, as e.g., is the case of the Alkyonides earthquake (1981, M6.7).","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"24 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83972187","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}
Volumetric strain signal recorded by the Sacks-Evertson strainmeter has a very high resolution and can measure small strain changes (down to 10–9) accompanying volcanic processes. However, different disturbing components perturb the recorded strain signal. These disturbances can mask ultra-small strain changes related to volcano activity and thus need to be filtered in order to accurately monitor volcano deformation. We developed the software STRALERT (STRain and wArning signaLs in nEar Real-Time) to provide both the recorded and the filtered strain signals in near real-time to the Surveillance Room of the “Istituto Nazionale di Geofisica e Vulcanologia – Osservatorio Etneo” which monitors the Etna activity. The software encloses a modified version of the code BAYTAP-G for filtering the incoming signal from the continuously running strainmeter at Etna. Thanks to the appropriate and robust signal filtering, STRALERT is capable to provide anefficient estimate of transient strain changes, which concur in tracing volcano deformation and detecting the onset and the conclusion of eruptive events. Our findings demonstrate the important contribution of STRALERT for volcano surveillance operations.
由Sacks-Evertson应变仪记录的体积应变信号具有非常高的分辨率，可以测量伴随火山过程的小应变变化(低至10-9)。然而，不同的干扰分量会干扰记录的应变信号。这些干扰可以掩盖与火山活动有关的超微小应变变化，因此需要过滤，以便准确监测火山变形。我们开发了STRALERT (STRain and wArning signaLs in nEar Real-Time)软件，为监测埃特纳火山活动的“Istituto Nazionale di Geofisica e Vulcanologia - observatorio Etneo”监测室提供记录和过滤的近实时应变信号。该软件包含了代码BAYTAP-G的修改版本，用于过滤来自埃特纳连续运行的应变仪的输入信号。由于适当和鲁棒的信号滤波，STRALERT能够提供瞬态应变变化的有效估计，这与跟踪火山变形和探测喷发事件的开始和结束是一致的。我们的发现证明了STRALERT对火山监测行动的重要贡献。
{"title":"Near real-time filtering of high precision borehole strainmeter signals for volcano surveillance","authors":"L. Carleo, A. Bonaccorso, G. Currenti, A. Sicali","doi":"10.4401/ag-8787","DOIUrl":"https://doi.org/10.4401/ag-8787","url":null,"abstract":"Volumetric strain signal recorded by the Sacks-Evertson strainmeter has a very high resolution and can measure small strain changes (down to 10–9) accompanying volcanic processes. However, different disturbing components perturb the recorded strain signal. These disturbances can mask ultra-small strain changes related to volcano activity and thus need to be filtered in order to accurately monitor volcano deformation. We developed the software STRALERT (STRain and wArning signaLs in nEar Real-Time) to provide both the recorded and the filtered strain signals in near real-time to the Surveillance Room of the “Istituto Nazionale di Geofisica e Vulcanologia – Osservatorio Etneo” which monitors the Etna activity. The software encloses a modified version of the code BAYTAP-G for filtering the incoming signal from the continuously running strainmeter at Etna. Thanks to the appropriate and robust signal filtering, STRALERT is capable to provide anefficient estimate of transient strain changes, which concur in tracing volcano deformation and detecting the onset and the conclusion of eruptive events. Our findings demonstrate the important contribution of STRALERT for volcano surveillance operations.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"19 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91221126","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 recent decades, Interferometric Synthetic Aperture Radar (InSAR) has progressed as an effective and reliable tool for monitoring the surface deformations of the earth. Despite the potential of this method for deformation monitoring, the quality description of InSAR timeseries in terms of precision and noise structure and, consequently, the precision description of the InSAR-derived parameters (e.g., displacement and its velocity) are still somewhat ambiguous. In this paper, we propose a data-derived methodology that directly estimates the precision and noise structure of the final InSAR products, using Least Squares Variance Component Estimation (LS-VCE). Note that due to the spatial correlation among adjacent coherent pixels and adjacent acquisitions, a multivariate LS-VCE model should be applied. We used the proposed method on deformation timeseries derived from the Sentine-l data over city of Tehran, Iran. The results show that applying the multivariate LS-VCE method in our case study improves the results by about 50% compared with the case where the noise parameters are not considered. In addition, the results confirm that InSAR timeseries are highly correlated in time and space. Particularly, the spatial correlation between a series of neighbouring targets for the noise components is significant and gradually decreases with increasing arc length. It should be noted that the observed spatial correlation should be differentiated from the well-known spatial correlation imposed by atmospheric components. In fact, due to the atmosphere filtering step, the noise structure of the final results will be different from the statistical characteristics of a raw atmospheric signal. The proposed methodology is not case study dependent and can be used as an appropriate approach to provide the precision (as a quality descriptor) of the timeseries InSAR products.
{"title":"Assessment of noise in InSAR timeseries using least squares variance component estimation","authors":"S. Babaee, M. Hossainali, Sami Samie Esfahany","doi":"10.4401/ag-8766","DOIUrl":"https://doi.org/10.4401/ag-8766","url":null,"abstract":"In recent decades, Interferometric Synthetic Aperture Radar (InSAR) has progressed as an effective and reliable tool for monitoring the surface deformations of the earth. Despite the potential of this method for deformation monitoring, the quality description of InSAR timeseries in terms of precision and noise structure and, consequently, the precision description of the InSAR-derived parameters (e.g., displacement and its velocity) are still somewhat ambiguous. In this paper, we propose a data-derived methodology that directly estimates the precision and noise structure of the final InSAR products, using Least Squares Variance Component Estimation (LS-VCE). Note that due to the spatial correlation among adjacent coherent pixels and adjacent acquisitions, a multivariate LS-VCE model should be applied. We used the proposed method on deformation timeseries derived from the Sentine-l data over city of Tehran, Iran. The results show that applying the multivariate LS-VCE method in our case study improves the results by about 50% compared with the case where the noise parameters are not considered. In addition, the results confirm that InSAR timeseries are highly correlated in time and space. Particularly, the spatial correlation between a series of neighbouring targets for the noise components is significant and gradually decreases with increasing arc length. It should be noted that the observed spatial correlation should be differentiated from the well-known spatial correlation imposed by atmospheric components. In fact, due to the atmosphere filtering step, the noise structure of the final results will be different from the statistical characteristics of a raw atmospheric signal. The proposed methodology is not case study dependent and can be used as an appropriate approach to provide the precision (as a quality descriptor) of the timeseries InSAR products.","PeriodicalId":50766,"journal":{"name":"Annals of Geophysics","volume":"38 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80967504","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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