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Keywords = high-frequency seismic radiation

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18 pages, 1727 KiB  
Article
Comparison of Backprojection Techniques for Rupture Propagation Modelling of the Mw = 7.8 Mainshock Earthquake near Kahramanmaras and the Mw = 7.5 Second-Largest Mainshock near Elbistan, Turkey, 2023
by Dimitrios Nikolopoulos, Mahmood Sultan, Aftab Alam, Demetrios Cantzos, Georgios Priniotakis, Michail Papoutsidakis, Farhan Javed, Georgios Prezerakos, Jamil Siddique, Muhammad Ali Shah, Muhammad Rafique and Panayiotis Yannakopoulos
Geosciences 2025, 15(4), 146; https://doi.org/10.3390/geosciences15040146 - 14 Apr 2025
Viewed by 307
Abstract
This paper utilises teleseismic Z-component data to investigate rupture propagation, extent, and velocity for two very destructive earthquakes in the East Anatolian Fault Zone (EAFZ): the Mw = 7.8 earthquake near Kahramanmaras and the largest (Mw = 7.5 s) aftershock [...] Read more.
This paper utilises teleseismic Z-component data to investigate rupture propagation, extent, and velocity for two very destructive earthquakes in the East Anatolian Fault Zone (EAFZ): the Mw = 7.8 earthquake near Kahramanmaras and the largest (Mw = 7.5 s) aftershock at Elbistan (both on 6 February 2023). The extent of the rupture is modelled with beamforming and multichannel signal classification. The teleseismic data are derived from agencies in USA and Canada. The rupture of the Mw = 7.8 earthquake is found to be bi-directional towards the northeast and southwest. Three rupture segments are identified for the Kahramanmaras earthquake between 34.5°–37.5° longitude and 37.0°–37.5° latitude, and another three are identified for the Elbistan earthquake between 36.5°–38.0° longitude and around 38.5° latitude. A total of 299 km is covered in 185 s with rupture velocities between 3.1 km/s and 3.4 km/s. Additionally, the mainshock’s splay and the second-largest aftershock’s rupture are also bidirectional, covering 150 km within 46 s. Five velocity segments are identified, three for the Kahramanmaras and two for the Elbistan earthquakes. Beamforming is efficient for identifying the velocity segments. The findings provide new insights on the evolution of the spatio-temporal rupture of the EAFZ and may serve as a basis for long-term earthquake hazard planning in the area. Full article
(This article belongs to the Special Issue Editorial Board Members' Collection Series: Natural Hazards)
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11 pages, 1519 KiB  
Article
Extraction of Tsunami Signals from Coupled Seismic and Tsunami Waves
by Linjian Song and Chao An
J. Mar. Sci. Eng. 2025, 13(3), 419; https://doi.org/10.3390/jmse13030419 - 24 Feb 2025
Viewed by 404
Abstract
The generation of an earthquake and a tsunami is a coupled process of radiating seismic waves and exciting tsunamis, and the two types of waves are simultaneously recorded by ocean-bottom pressure sensors. In order to constrain the earthquake source and evaluate the tsunami [...] Read more.
The generation of an earthquake and a tsunami is a coupled process of radiating seismic waves and exciting tsunamis, and the two types of waves are simultaneously recorded by ocean-bottom pressure sensors. In order to constrain the earthquake source and evaluate the tsunami hazards, it is necessary to separate the tsunami waves. It is traditional to apply a low-pass filter such that the seismic waves are filtered and the tsunami waves remain. However, filtering may also cause distortion of the tsunami waves. In this study, we first use the finite-element method to simulate the generation of seismic and tsunami waves and show that the coupling is a linear superposition of the two waves. We then propose a new method to extract the tsunami waves. First, a low-pass filter with relatively high cutoff frequency that does not affect the tsunami waves is adopted, so that only tsunami waves and low-frequency seismic waves remain. The low-frequency seismic waves satisfy a theoretical equation p=ρha (p pressure, ρ water density, h water depth, and a seafloor vertical acceleration), and they can be predicted and removed by utilizing the records of ocean-bottom acceleration. We demonstrate the procedure by numerical simulations and show that the method successfully extracts clean tsunami signals, which is important for earthquake source characterization and tsunami hazard assessment. Full article
(This article belongs to the Section Marine Hazards)
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18 pages, 1522 KiB  
Article
Frequency Response Extension Method of MET Vector Hydrophone Based on Dynamic Feedback Network
by Fang Bian, Ang Li, Hongyuan Yang, Fan Zheng, Dapeng Yang, Huaizhu Zhang, Linhang Zhang and Ruojin Li
Appl. Sci. 2025, 15(3), 1620; https://doi.org/10.3390/app15031620 - 5 Feb 2025
Cited by 1 | Viewed by 561
Abstract
Hydrophone is a key component of marine seismic exploration systems, divided into a scalar hydrophone and vector hydrophone. The electrochemical vector hydrophone has attracted much attention due to its high sensitivity and low-frequency detection capability. With the development of noise reduction technology, high-frequency [...] Read more.
Hydrophone is a key component of marine seismic exploration systems, divided into a scalar hydrophone and vector hydrophone. The electrochemical vector hydrophone has attracted much attention due to its high sensitivity and low-frequency detection capability. With the development of noise reduction technology, high-frequency noise has been effectively suppressed, while low-frequency noise is still difficult to control, which has become a key issue in the monitoring of underwater target radiation noise. The traditional electrochemical vector hydrophone based on the molecular electron transfer (MET) principle is limited in the working bandwidth in the low-frequency band, which affects the detection capability of low-frequency radiation signals from underwater targets. In order to solve this problem, a frequency response extension method of a MET electrochemical vector hydrophone based on dynamic feedback network is proposed. By introducing a dynamic force balance negative feedback system based on a digital signal processor (DSP), the working bandwidth of the hydrophone is extended, and the detection capability of low-frequency signals is enhanced. At the same time, the system has field adjustability and can resist the long-term system frequency characteristic drift. Experimental results show that the proposed method effectively improves the frequency response performance of the electrochemical vector hydrophone, providing a new technical solution for its application in the monitoring of low-frequency radiation noise from underwater targets. Full article
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42 pages, 631 KiB  
Review
Electromagnetic and Radon Earthquake Precursors
by Dimitrios Nikolopoulos, Demetrios Cantzos, Aftab Alam, Stavros Dimopoulos and Ermioni Petraki
Geosciences 2024, 14(10), 271; https://doi.org/10.3390/geosciences14100271 - 14 Oct 2024
Cited by 4 | Viewed by 3422
Abstract
Earthquake forecasting is arguably one of the most challenging tasks in Earth sciences owing to the high complexity of the earthquake process. Over the past 40 years, there has been a plethora of work on finding credible, consistent and accurate earthquake precursors. This [...] Read more.
Earthquake forecasting is arguably one of the most challenging tasks in Earth sciences owing to the high complexity of the earthquake process. Over the past 40 years, there has been a plethora of work on finding credible, consistent and accurate earthquake precursors. This paper is a cumulative survey on earthquake precursor research, arranged into two broad categories: electromagnetic precursors and radon precursors. In the first category, methods related to measuring electromagnetic radiation in a wide frequency range, i.e., from a few Hz to several MHz, are presented. Precursors based on optical and radar imaging acquired by spaceborne sensors are also considered, in the broad sense, as electromagnetic. In the second category, concentration measurements of radon gas found in soil and air, or even in ground water after being dissolved, form the basis of radon activity precursors. Well-established mathematical techniques for analysing data derived from electromagnetic radiation and radon concentration measurements are also described with an emphasis on fractal methods. Finally, physical models of earthquake generation and propagation aiming at interpreting the foundation of the aforementioned seismic precursors, are investigated. Full article
(This article belongs to the Special Issue Precursory Phenomena Prior to Earthquakes (2nd Edition))
26 pages, 7612 KiB  
Review
Progress in Seismic Isolation Technology Research in Soft Soil Sites: A Review
by Xinqiang Yao and Bin Wu
Buildings 2024, 14(10), 3198; https://doi.org/10.3390/buildings14103198 - 8 Oct 2024
Viewed by 1723
Abstract
Soft soil sites can amplify the peak acceleration by a factor of 1.5 to 3.5 and exhibit the filtering effect on seismic waves. This effect results in the attenuation of high frequencies, amplification of low frequencies, and extension of the predominant period of [...] Read more.
Soft soil sites can amplify the peak acceleration by a factor of 1.5 to 3.5 and exhibit the filtering effect on seismic waves. This effect results in the attenuation of high frequencies, amplification of low frequencies, and extension of the predominant period of ground motion. Consequently, soft soil sites have a more pronounced impact on isolation buildings constructed on them. The seismic isolation structure design typically involves assuming rigid foundation for calculations. However, the soil properties can significantly impact the dynamic response of the structure, affecting factors such as input ground motion, changes in vibration characteristics, radiation energy dissipation, and material damping energy dissipation. Therefore, neglecting these influences and relying solely on the rigid foundation assumption for calculations can lead to significant errors in the final seismic response analysis of the structure. Currently, there are numerous LNG storage tanks, museums, and other isolation buildings constructed on soft soil sites. Therefore, research on seismic isolation measures for soft soil sites holds significant practical importance. In light of this, this paper, firstly, provides a systematic summary of seismic isolation strategies and engineering applications for soft soil sites. Secondly, it further discusses advancements in research on the dynamic interactions of soil–isolated structures, covering analytical methods, numerical investigations, and experimental studies on soft soil sites. Lastly, the paper concludes with insights on current research progress and prospects for further studies. Full article
(This article belongs to the Section Building Structures)
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18 pages, 1578 KiB  
Review
The Generation of Seismogenic Anomalous Electric Fields in the Lower Atmosphere, and Its Application to Very-High-Frequency and Very-Low-Frequency/Low-Frequency Emissions: A Review
by Masashi Hayakawa, Yasuhide Hobara, Koichiro Michimoto and Alexander P. Nickolaenko
Atmosphere 2024, 15(10), 1173; https://doi.org/10.3390/atmos15101173 - 30 Sep 2024
Cited by 2 | Viewed by 927
Abstract
The purpose of this paper is, first of all, to review the previous works on the seismic (or earthquake (EQ)-related) direct current (DC) (or quasi-stationary) electric fields in the lower atmosphere, which is likely to be generated by the conductivity current flowing in [...] Read more.
The purpose of this paper is, first of all, to review the previous works on the seismic (or earthquake (EQ)-related) direct current (DC) (or quasi-stationary) electric fields in the lower atmosphere, which is likely to be generated by the conductivity current flowing in the closed atmosphere–ionosphere electric circuit during the preparation phase of an EQ. The current source is electromotive force (EMF) caused by upward convective transport and the gravitational sedimentation of radon and charged aerosols injected into the atmosphere by soil gasses during the course of the intensification of seismic processes. The theoretical calculations predict that pre-EQ DC electric field enhancement in the atmosphere can reach the breakdown value at the altitudes 2–6 km, suggesting the generation of a peculiar seismic-related thundercloud. Then, we propose to apply this theoretical inference to the observational results of seismogenic VHF (very high frequency) and VLF/LF (very low frequency/low frequency) natural radio emissions. The formation of such a peculiar layer initiates numerous chaotic electrical discharges within this region, leading to the generation of VHF electromagnetic radiation. Earlier works on VHF seismogenic radiation performed in Greece have been compared with the theoretical estimates, and showed a good agreement in the frequency range and intensity. The same idea can also be applied, for the first time, to seismogenic VLF/LF lightning discharges, which is completely the same mechanism with conventional cloud-to-ground lightning discharges. In fact, such seismogenic VLF/LF lightning discharges have been observed to appear before an EQ. So, we conclude in this review that both seismogenic VHF radiation and VLF/LF lightning discharges are regarded as indirect evidence of the generation of anomalous electric fields in the lowest atmosphere due to the emanation of radioactive radon and charged aerosols during the preparation phase of EQs. Finally, we have addressed the most fundamental issue of whether VHF and VLF/LF radiation reported in earlier works is either of atmospheric origin (as proposed in this paper) or of lithospheric origin as the result of microfracturing in the EQ fault region, which has long been hypothesized. This paper will raise a question regarding this hypothesis of lithospheric origin by proposing an alternative atmospheric origin outlined in this review. Also, the data on seismogenic electromagnetic radiation and its inference on perturbations in the lower atmosphere will be suggested to be extensively integrated in future lithosphere–atmosphere–ionosphere coupling (LAIC) studies. Full article
(This article belongs to the Section Upper Atmosphere)
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14 pages, 3543 KiB  
Article
Geomagnetic Disturbances and Pulse Amplitude Anomalies Preceding M > 6 Earthquakes from 2021 to 2022 in Sichuan-Yunnan, China
by Xia Li, Rui Qu, Yingfeng Ji, Lili Feng, Weiling Zhu, Ye Zhu, Xiaofeng Liao, Manqiu He, Zhisheng Feng, Wenjie Fan, Chang He, Weiming Wang and Haris Faheem
Sensors 2024, 24(13), 4280; https://doi.org/10.3390/s24134280 - 1 Jul 2024
Viewed by 1374
Abstract
Compelling evidence has shown that geomagnetic disturbances in vertical intensity polarization before great earthquakes are promising precursors across diverse rupture conditions. However, the geomagnetic vertical intensity polarization method uses the spectrum of smooth signals, and the anomalous waveforms of seismic electromagnetic radiation, which [...] Read more.
Compelling evidence has shown that geomagnetic disturbances in vertical intensity polarization before great earthquakes are promising precursors across diverse rupture conditions. However, the geomagnetic vertical intensity polarization method uses the spectrum of smooth signals, and the anomalous waveforms of seismic electromagnetic radiation, which are basically nonstationary, have not been adequately considered. By combining pulse amplitude analysis and an experimental study of the cumulative frequency of anomalies, we found that the pulse amplitudes before the 2022 Luding M6.8 earthquake show characteristics of multiple synchronous anomalies, with the highest (or higher) values occurring during the analyzed period. Similar synchronous anomalies were observed before the 2021 Yangbi M6.4 earthquake, the 2022 Lushan M6.1 earthquake and the 2022 Malcolm M6.0 earthquake, and these anomalies indicate migration from the periphery toward the epicenters over time. The synchronous changes are in line with the recognition of previous geomagnetic anomalies with characteristics of high values before an earthquake and gradual recovery after the earthquake. Our study suggests that the pulse amplitude is effective for extracting anomalies in geomagnetic vertical intensity polarization, especially in the presence of nonstationary signals when utilizing observations from multiple station arrays. Our findings highlight the importance of incorporating pulse amplitude analysis into earthquake prediction research on geomagnetic disturbances. Full article
(This article belongs to the Collection Seismology and Earthquake Engineering)
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19 pages, 7201 KiB  
Article
Study on Seismic Source Parameter Characteristics of Baihetan Reservoir Area in the Lower Reaches of the Jinsha River
by Jing Shi, Cuiping Zhao, Zhousheng Yang and Lisheng Xu
Water 2024, 16(10), 1370; https://doi.org/10.3390/w16101370 - 11 May 2024
Cited by 1 | Viewed by 977
Abstract
The source parameters of earthquakes (stress drop, corner frequency, seismic moment, source size, radiant energy, etc.) provide important information about the source features, the state of stress, and the mechanism of earthquake rupture dynamics. Using the digital observation data obtained from a high-density [...] Read more.
The source parameters of earthquakes (stress drop, corner frequency, seismic moment, source size, radiant energy, etc.) provide important information about the source features, the state of stress, and the mechanism of earthquake rupture dynamics. Using the digital observation data obtained from a high-density seismic monitoring network deployed in the Baihetan reservoir area of the lower Jinsha River, we obtained Brune source parameters of the 459 earthquakes ranging in magnitude ML 1.50~4.70. The results revealed seismic moments M0 within the range of 2.03 × 1012~1.45 × 1016 N·m, corner frequencies fc between 2.00 and 10.00 Hz, and source dimensions varying from 130.00 to 480.00 m, with stress drops spanning from 0.12 to 61.24 MPa. It is noteworthy that the majority of the earthquakes had stress drops less than 10.00 MPa, with as much as 73.30% of these events having stress drops within the range of 0.10 to 2.00 MPa. We found that stress drop, corner frequency, and source size in the study area exhibited positive correlations with earthquake magnitude. Earthquakes occurring at shallower depths for the same magnitude tended to have smaller stress drops and corner frequencies, but larger rupture scales. During the first 2 years of impoundment with significant water level fluctuation, earthquakes beneath or near the reservoir released higher stress drops relative to pre-reservoir conditions, with average stress drops significantly elevated from 5.52 to 13.562 Mpa for events above ML3 since the impoundment. The radiated energy released by earthquakes with magnitudes below ML3.0 are significantly more than before impoundment, indicating that earthquakes of similar magnitudes in the reservoir area may produce greater intensity and perceptibility following the impoundment. According to our result, the triggered seismicity will continue to be active under annual regulation changes in the water level of the Baihetan Dam at high elevations in future years. Full article
(This article belongs to the Special Issue Safety Evaluation of Dam and Geotechnical Engineering, Volume II)
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15 pages, 2384 KiB  
Article
Time Domain Source Parameter Estimation of Natural and Man-Induced Microearthquakes at the Geysers Geothermal Field
by Valeria Longobardi, Sahar Nazeri, Simona Colombelli, Raffaele Rea, Grazia De Landro and Aldo Zollo
Energies 2023, 16(3), 1121; https://doi.org/10.3390/en16031121 - 19 Jan 2023
Cited by 3 | Viewed by 2401
Abstract
Water injection in geothermal areas is the preferential strategy to sustain the natural production of geothermal resources. In this context, monitoring microearthquakes is a fundamental tool to track changes in the reservoirs in terms of soil composition, response to injections, and resource exploitation [...] Read more.
Water injection in geothermal areas is the preferential strategy to sustain the natural production of geothermal resources. In this context, monitoring microearthquakes is a fundamental tool to track changes in the reservoirs in terms of soil composition, response to injections, and resource exploitation with space and time. Therefore, refined source characterization is crucial to better estimate the size, source mechanism, and rupture process of microearthquakes, as they are possibly related to industrial activities, and to identify any potential variation in the background seismicity. Standard approaches for source parameter estimation are ordinarily based on the modelling of Fourier displacement spectra and its characteristic parameters: the low-frequency spectral level and corner frequency. Here, we apply an innovative time domain technique that uses the curves of P-wave amplitude vs. time along the seismogram. This methodology allows estimation of seismic moment, source radius, and stress release from the plateau level and the corner time of the average logarithm of P-wave displacement versus time with the assumption of a triangular moment rate function, uniform rupture speed, and a constant/frequency-independent Q-factor. In the current paper, this time domain methodology is implemented on a selected catalog of microearthquakes consisting of 83 events with a moment magnitude ranging between 1.0 and 1.5 that occurred during a 7-year period (2007–2014) of fluid extraction/injection around Prati-9 and Prati-29 wells at The Geysers geothermal field. The results show that the time domain technique provides accurate seismic moment (moment magnitude) and rupture duration/radius estimates of microearthquakes down to the explored limit (M 1) while accounting for the anelastic attenuation effect in the radiated high-frequency wavefield. The retrieved source radius vs. moment scaling is consistent with a self-similar, constant stress drop scaling model, which proves an appropriate attenuation correction and the validity of the assumed, triangular moment rate function for microearthquake ruptures. Two alternative mechanical models are proposed to explain the observed difference (about two orders of magnitude) in the retrieved average stress release estimates between the time and frequency domain methods. We argue that the two quantities may not refer to the same physical quantity representing the stress release of earthquake ruptures. Either the smaller stress release values from the time domain method may indicate a larger fracture area (by a factor of 20) radiating the observed P-waveforms than the one estimated from the corner frequencies, or the frequency domain estimate is a proxy for dynamic stress release while the time domain is more representative of the static release. The latter is associated with a much lower dynamic friction value than static friction value at the fault during the rupture process. Full article
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15 pages, 4952 KiB  
Article
Nonlinear Soliton-like Oscillations and Waves during Geomaterial Destruction Based on Electromagnetic Radiation Signals
by Victor Dmitrievich Borisov
Foundations 2022, 2(3), 798-812; https://doi.org/10.3390/foundations2030054 - 19 Sep 2022
Cited by 1 | Viewed by 1635
Abstract
The work is devoted to the results of processing electromagnetic radiation signals obtained during laboratory loading of marble and diabase samples using a technique for determining the parameters of microcracks, developed and published by the author earlier. As a result of such processing, [...] Read more.
The work is devoted to the results of processing electromagnetic radiation signals obtained during laboratory loading of marble and diabase samples using a technique for determining the parameters of microcracks, developed and published by the author earlier. As a result of such processing, certain patterns were found in the nature of the evolution of the oscillatory process ensemble of microcracks. For example, solitary non-linear waves almost always preceded a sequence of High Frequency traces. Equations for straight lines approximating High Frequency traces in logarithmic coordinates, close to the equation of the Gutenberg–Richter law. Due to the similarity of seismic processes at different scale levels, the results of modeling at the microscale level can be used to describe seismic processes at the macroscale level, for example, to study the processes occurring immediately before destruction and at the time of destruction in order to search for repeatability and regularities. The regularities obtained can be used in the development of a predictive criterion that makes it possible to predict the time of one or another geophysical (seismic) event. Full article
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