Epicenter Research Articles

Lower-ionosphere anomalies prior to strong earthquakes that occurred in north-central mainland Greece on March 2021 as revealed by multi-method analysis of VLF sub-ionospheric propagation data

In this work we present the multi-method analysis of very low frequency (VLF) data, acquired by the radio receiver with call name UWA, located in Athens (Greece), in the University of West Attica, focusing on two strong ( ) earthquakes (EQs) that occurred in north-central mainland Greece sequentially, on 3 and 4 March 2021, with very close epicenters. Specifically, we used the data acquired from seven VLF transmitters located in Europe, North/North-West to UWA, and their propagation paths include the specific EQs epicenters. We analyzed these data using multiple analysis methods in order to investigate for possible EQ-related anomalies, taking also into account all the other possibly ionosphere-influencing extreme events that occurred during the studied period. Especially, we applied the “nighttime fluctuation method” (NFM), as well as, the “terminator time method” (TTM) in order to reveal any statistical anomaly in the nighttime amplitude recordings of VLF sub-ionospheric propagation data within 15 days before each one examined EQs. Also, we calculated the scalogram (wavelet power spectrum over time) using Morlet mother wavelet of the same nighttime data searching for possible imprints of wave-like structures during the same time period. In terms of criticality analysis, first we applied the “natural time” (NT) analysis method to the daily-valued NFM VLF propagation quantities, and subsequently applied the “method of critical fluctuations” (MCF) to the raw nighttime amplitude VLF recordings, to check for any criticality signatures up to two weeks before the examined EQs. Taking into account all the above-mentioned analysis results, we conclude that there are multiple indications that the lower ionosphere was indeed disturbed due to the preparation processes of the above-mentioned EQs, offering different types of seismogenic indications.

The crustal structure of the Longmenshan fault zone and its implications for seismogenesis: new insight from aeromagnetic and gravity data

Abstract. Although many geophysical models have been proposed in the Longmenshan fault zone (LFZ) and its surrounding areas, the deep structure of the seismic gap and its constraint of the Wenchuan and Lushan earthquakes remain uncertain. Based on the compiled aeromagnetic data and Bouguer gravity data, we have tried to create a more detailed and reasonable magnetic and density model using 2D forward modeling and 3D inversion and made the deep structure of the LFZ visible. The research shows that structure is heterogenous across the LFZ. The earthquake epicenters are located in regions with high-magnetic anomalies and gravity gradients that are associated with rigid blocks that were likely to accumulate stress. However, the seismic gap shows low-magnetic anomalies and transition of gravity anomalies related to a weak zone. The Sichuan Basin has two NE-trending banded high-magnetic blocks extending beneath the LFZ that firmly support the idea that the crust of the Sichuan Basin has subducted downward the LFZ. More importantly, the basement subducts to approximately 33 km west of the Wenchuan–Maoxian fault, with a low dip angle beneath the middle segment of the LFZ, whereas the distance decreases to approximately 17 and 19 km under the southern segment. Thus, the crust of the Sichuan Basin beneath the middle segment extends farther than that beneath the southern segment, with the seismic gap as the transition zone. Therefore, we propose that the structural heterogeneity of the basement on the western margin of the Sichuan Basin may be the main reason for the different focal mechanisms and geodynamics of the Wenchuan and Lushan earthquakes.

Statistical analysis of detected ionospheric anomalies with earthquake magnitudes: A case study of the New Zealand earthquakes of March 4, 2021

Statistical analysis of detected ionospheric anomalies with earthquake magnitudes was carried out on two seismic events of March 4, 2021, (M7.3 Gisborne and M8.1 Kermadec Earthquakes) to ascertain a possible link between observed perturbations and event size. GPS-TEC data were downloaded 20 days pre and 5 days post the events from stations within the epicenter of respective earthquakes. The data were statistically analyzed to detect unusual variations within the investigative window. The investigation revealed that the M7.3 Gisborne EQ shown two variations on –19 and –4 days; both being positive perturbations. However, five anomalies were detected for the M8.1 Kermadec EQ on –15, –11, –5, –3 and –2 days. With exception of the irregularities on –3 days, all others were positive anomalies. The observed anomalies were subjected to further scrutiny using the geomagnetic indices of Kernnifzer digit (kp) and disturbance storm time (Dst.) for geomagnetically induced perturbations while sunspot number and F 10.7 cm were used to monitor solar activities within this same period. The study suggested an increased in detected anomalies with earthquake magnitudes.

Identification Of Shear Strain On The Surface Ground Of Wangi-Wangi Island, Southeast Sulawesi, Indonesia, Using Nakamura’s Technique and The Possibility Of Its Impacts

This research was conducted to determine the possible impact of an earthquake on the mainland of Wangi-Wangi Island based on the presence of shear strain on the surface ground (γ). The size of γ is obtained by multiplying the ground susceptibility index and the acceleration of basement ground or PGA using Nakamura’s technique. The data used are microtremor data and earthquake data from 1920 to 2020 sourced from the USGS. Microtremor data are obtained from the results of filtering ground vibration signals using a Band Pass Filter in the frequency range between 0.5 to 25 Hz. Ground vibration signals were recorded at 47 measurement points spread over the surface of Wangi-Wangi Island within 29.25 to 48.16 minutes. Furthermore, the microtremor data were processed using the HVSR (Horizontal to Vertical Spectral Ratio) method. The use of earthquake data must meet the requirements for a surface magnitude (MS) ≥ 5.0 SR and an earthquake epicenter depth (h) ≤ 45 km. The results obtained are the γ sizes of Wangi-Wangi Island in the order of 10-06 to 10-03. Based on the size distribution, it is known that the majority of the Wangi-Wangi Island area has the potential to experience cracks and land subsidence due to settlements if an earthquake occurs, and only a portion of the area is vibrating. In addition, it is also known that the mainland of Wangi-Wangi Island is not prone to landslides and liquefaction because γ<10-2.

Impact of earthquake’s epicenter distance to failure of the embankment – A seismic prediction

Cracks in clayey soil cause a reduction in the seismic loading capacity which can lead to structural failures. Seismic acceleration is the primary cause of crack propagation and damage to the earth's structure. This study investigated the impact of the earthquake's epicenter distance on the embankment model with a pre-existing crack in the embankment's core. The research adopted the numerical modeling method of soil categorized as a no-tensile material to explain displacement in selected points of the model using the extended finite element method (XFEM). Artificial Neural Networks (ANNs) were used to predict displacement obtained by XFEM. It was observed that the failure pattern and the maximum displacement time of the model change with the associated distance of the earthquake's epicenter. The key study objective is to understand the model's failure mode and introduce a new classification in earthquake damage prediction.

SEISMICITY of the CRIMEAN-BLACK SEA REGION in 2018–2019

The review of the Crimean-Black Sea region seismicity is made on the basis of seismic monitoring data from a regional network of 9 digital stations. The catalog includes information on 185 events with energy classes Kп=3.8–11.0. Maps of earthquake energy representativeness and epicenters of earthquakes are presented. A detailed description of the seismic situation in various districts of the region is given. The years 2018 and 2019 are characterized by moderate seismic activity in the region, which below than the long-term average one. The greatest activation of seismic processes was observed in 2018 in the Kerch-Anapa and Azov-Kuban districts. In the Kerch-Anapa district, three tangible earthquakes occurred. Their maximum observed intensity of I=4–5 is noted in seven settlements on the coast of the Caucasus. The released seismic energy in the Azov-Kuban district in 2018 significantly exceeded the 10-year (2010–2019) average value. The earthquake of the maximum class Kп=11.0, MW=4.2 was realized on October 15, 2018. Its source was in the central part of the Sea of Azov, at a depth h=6 km. On February 20, 2018 at 07 h00m a seismic event occurred on the eastern coast of the Sea of Azov. People felt it in the city of Primorsko-Akhtarsk with intensity of I=3–4. On the territory of the Crimean peninsula, two shocks were felt with the intensity of I=2 and I=3 in Sudak-Feodosiya and Yalta areas respectively. Solutions of focal mechanisms were obtained for the 7 strongest earthquakes from different districts of the region.

SEISMICITY of the NORTH-EAST of RUSSIA in 2018–2019

The results of seismic monitoring of the Magadan region, Chukotka Autonomous Area and the shelf of adjacent Okhotsk, Chukchi, Bering and East Siberian seas are considered. There were 14 seismic stations working in the region. The catalog includes information about 644 earthquakes with energy classes KR=4.8–13.2. As usual, most of them (77 %) are localized in the Kolyma region (area № 2).The additional catalog contains information about 12 earthquakes in the Chukchi. The total seismic energy released within the region’s borders was ΣЕ=2.671013 J. The classification of Russian North-East earthquakes was performed using energy classes KR of T.G. Rautian’s scale. According to the earthquake energy representativeness map, the regional network of stations records without omissions the earthquakes with Kmin=7on the territory of Magadan region, with Kmin=8 in the Okhotsk sea and with Kmin=10 in the Chukchi. The strongest earthquake of 2018–2019 with KR=13.2 (MPSP=5.1, MS=4.0) occurred on July 5, 2019 in in the Kolyma area. 14 earthquakes with intensity I=2–5 of the Russian Seismic Intensity Scale (SIS-2017) were felt in North East settlements. Epicenters of Magadan region earthquakes were plotted on the tectonic zoning scheme. Most earthquakes are confined to the largest deep faults in the northwestern and sublatitudinal directions. All hypocenters are located within the earth's crust. The seismicity level of the North-East of Russia in 2018–2019 according to the “SOUS’09” scale was assessed as "background average one" for the observation period from 1968 to 2019. Spatially, all earthquakes in the North-East of Russia are traditionally concentrated in large seismogenic belts: Chersky, North-Okhotsk and Trans-Beringian.

SEISMICITY of YAKUTIA in 2018–2019

According to the information received from 20 stationary digital seismic stations of the Yakutia Branch of Geophysical Survey of the Russian Academy of Sciences, two-year (2018–2019) seismic monitoring of the territory of the Republic of Sakha (Yakutia) was carried out. During this time interval, more than 730 earthquakes with an energy class of KR≥7.2 (magnitude M≥1.8) were registered. During the previous two years, their number was 801. Manifestations of seismicity fixed the spatial position of the contact zones and their constituent blocks of known lithospheric plates: the Eurasian and North American plates in the northeastern and arctic regions, as well as the Eurasian and Amur plates – in the southern areas of Yakutia. The epicentral fields traced individual relief lineaments and identified active boundary structures combined into two large-scale seismic belts – BaikalStanovoy and Arctic-Asian. Their outlines are seen as bands of earthquake epicenters, elongated from the Olekma River to the Sea of Okhotsk in the south and as ensembles of separate groups and chains of earthquakes between the Laptev and Okhotsk Seas in the northeast and in the Arctic. Significant seismic activity has been detected in the northeast of the region – in the Olekminsk region and the Aldan Highlands (South Yakutia), as well as in the Yano-Oymyakon Highlands, the Chersky Ridge and the Laptev Sea. A map of epicenters was constructed for the entire territory of the region, where 12 districts were identified and an analysis of the seismotectonic situation in each of them was given. The map of Arctic earthquakes in the Lena River delta is considered separately. It is compiled according to the processing of digital seismograms obtained at 25 autonomous field stations installed in accordance with the Russian-German project "Seismicity and Neotectonics of the Laptev Sea Region" (SIOLA). In this area during 2016–2019 more than 2 thousand shocks of small energy classes KR≥7.2–10.7 (M≥1.8–3.7) were recorded within the depth interval of 1–36 km of the Earth's crust. The characteristics of the most seismically active local tectonic structures developed in this region are given.

Impact of mining-induced seismicity on land subsidence occurrence

Mining-induced seismicity can damage buildings and surface infrastructure and cause fatalities. It is a growing concern, owing to the sudden occurrence of seismic events, lack of effective prediction capabilities, and associated consequences. In this study, we analyzed 13 high-energy mining-induced earthquakes from 2016 to 2020 in Poland's Legnica-Glogow Copper District (LGCD), based on data recorded by the Induced Seismicity-European Plate Observing System (IS-EPOS). We used European Space Agency (ESA) Sentinel-1 Copernicus satellite radar images, to study the co-seismic subsidence in the region. Additionally, we employed volumetric point source approximation and a Bayesian inverse modeling scheme to estimate the location and strength of subsurface collapses from the land subsidence data. Finally, we correlated the geological constraints with the land subsidence and earthquake source parameters. The interferometric synthetic aperture radar (InSAR) displacement maps portrayed maximum line-of-sight (LOS) displacements of −144 mm and − 124 mm in ascending and descending images, respectively, with maximum land subsidence reaching −142 mm. Notably, only a few earthquakes with large magnitudes caused land subsidence. There was a significant correlation between earthquake magnitude and land subsidence; the greater the thickness of the loose Quaternary strata, the smaller the land subsidence. According to the inversion results, the focal depths of the collapses associated with the earthquakes were 437–669 m. However, the estimated collapse depths were situated above the mining exploitation fields, within the rigid Triassic rock layers. The associated collapse energy was 1.62 times greater than the seismic energy, indicating aseismic deformation in the field. Additionally, we observed spatial discrepancy between the location of the earthquake epicenters and the maximum land subsidence. Thus, our study can improve the current understanding of the impact of mining-induced seismicity, the occurrence of associated land subsidence, and seismic mechanisms in mining areas.

Multi‐Instrument Observations of Various Ionospheric Disturbances Caused by the 6 February 2023 Turkey Earthquake

AbstractIn this work, we investigate various types of ionospheric disturbances observed over Europe following the earthquake that occurred in Turkey on 6 February 2023. By combining observations from Doppler sounding systems, ionosondes, and GNSS receivers, we are able to discern different types of disturbances, propagating with different velocities and through different mechanisms. We can detect co‐seismic ionospheric disturbances close to the epicenter, as well as ionospheric signatures of acoustic waves propagating as a consequence of propagating seismic waves. Unlike the vast majority of past ionospheric co‐seismic disturbance studies that are primarily based on Total Electron Content variations, reflecting disturbances propagating around the F‐region peak, the focus of the present study is the manifestation of disturbances at different ionospheric altitudes by exploiting complementary ionospheric remote sensing techniques. This is particularly highlighted through ionospheric earthquake‐related signatures established as specific ionogram deformations known as multiple‐cusp signatures which appear as additional cusps at the base of the F‐region attributed to electron density irregularities generated by Rayleigh surface waves that generate acoustic waves propagating up to the ionosphere. Therefore this study underlines the advantage that multi‐instrument investigations offer in identifying the propagation of earthquake‐related ionospheric disturbances at different ionospheric altitudes and distances from the earthquake epicenter.

Apparent stress as an indicator of stress meta-instability: The 2021 MS6.4 Yangbi earthquake in Yunnan, China

Investigating spatiotemporal changes in crustal stress associated with major earthquakes has implications for understanding seismogenic processes. However, in individual earthquake cases, the characteristics of the stress after it reaches its maximum value are rarely discussed. In this study, we use the 2021 MS6.4 Yangbi earthquake in Yunnan, China and events of magnitudes ML ≥ 3.0 occurred in the surrounding area in the previous 11 years to investigate the spatiotemporal evolution of apparent stress. The results indicate that apparent stress began to increase in January 2015 and reached a maximum in January 2020. Apparent stress then remained at a high level until October 2020, after which it declined considerable. We suggest that the stress was in the accumulation stage from January 2015 to January 2020, and entered the meta-instability stage after October 2020. During the meta-instability stage, the zone of decreasing stress expanded continuously and the apparent stress increased around the Yangbi earthquake source region. These features are generally consistent with the results of laboratory rock stress experiments. We propose that apparent stress can be a good indicator for determining whether the stress at a specific location has entered the meta-instability stage and may become the epicenter of an impending strong earthquake.

GEODYNAMIC REGIMES IN THE LAPTEV SEA REGION ACCORDING TO THE LATEST SEISMOLOGICAL DATA

The results of the analysis of focal mechanisms and the general distribution of earthquake epicenters in the Laptev Sea region were presented. For four groups of clusters of events with known focal mechanisms, the directions of the principal stress axes were calculated by the formal stress inversion method. The distributions of earthquake epicenters and crustal thickness were compared. It has been revealed that, according to seismological data, the prolongation of the extension axis of the Gakkel Ridge on the Laptev Sea shelf is currently located in the vicinity of the group of extension detachments, which is extended along the eastern boundary of the Anisin, Zarya, and Belkovsko-Svyatonossky rift chains. The older extension axis, located along the group detachments marking the eastern boundary of the Ust-Lena and Omoloy rift systems, and continuing the axis of the Gakkel Ridge, is currently much less active, realizing residual stresses near its intersection with the Khatanga-Lomonosov fault zone in the northwestern parts of the shelf and with the Lena-Taimyr zone of boundary uplifts – in the southwestern. Near the Lena delta extension axes are oriented along the Olenekskaya and Bykovskaya channels and the border of the Siberian Platform, forming the extension conditions in the eastern part and the strike-slip regime in the western part of the vicinity of the Lena delta.

Development of an Improved Decision Support Tool for Geothermal Site Selection in Nigeria Based on Comprehensive Criteria

Geothermal resource assessment is crucial for the rural electrification of Nigeria. A comprehensive set of criteria was used to appraise promising geothermal sites in Nigeria. The evaluation of the sites was performed using the multi-criteria decision analysis (MCDA) method and taking into account evidence of a wide range of criteria from a set of geological, geophysical, well log, environmental, remote sensing, and geochemical datasets to appraise promising geothermal sites and to add to the current debate on the needed criteria for geothermal development. To gather relevant data, various sources such as bottom-hole temperature (BHT) data from different boreholes and oil and gas wells, aeromagnetic maps, reduced-to-the-pole, magnetic, heat flow, seismic, and geothermal gradient data from aerogravity maps, Bouguer anomaly maps, earthquake epicenter maps, satellite images, and geological maps were obtained from the literature. A case study of the thirty-six states of Nigeria, including the federal capital territory, Abuja (FCT), was conducted to illustrate how these criteria would reveal the technical aspect of the geothermal energy situation. A model was developed to show that the application of a wide range of criteria to the six datasets identified and analyzed in this study reveals that the datasets complement each other and should not be used independently. It can be found from the overall suitability map that more than 20% of the study area is suitable for geothermal energy development. It can also be observed from the map that some of the promising sites in Nigeria may include but are not limited to Bauchi, FCT, Taraba, Ebonyi, Adamawa, Oyo, and Nasarawa states in Nigeria. The opportunities for the further application of the approach are discussed, including the use of the model to help policymakers decide where to invest in the future.

Structural Heterogeneity Controlled Rupture Process of the 2021 Mw 7.1 Fukushima, Japan, Earthquake Revealed by Joint Inversion of Seismic and Geodetic Data

Abstract We determined the rupture model of the 2021 Mw 7.1 Fukushima earthquake near northeastern Japan in this study and adopted this model to investigate the cause of this earthquake and its aftershocks. The rupture model was obtained through joint inversion of teleseismic, strong-motion and geodetic data. It is shown that the slips were predominantly distributed on the southwest side of the earthquake epicenter, indicating a unilateral rupture event. We observed that the seismic moment was released in three time periods, producing four slip patches on the fault plane. Through comparison, we demonstrated that our joint inversion model was more reliable in describing the rupture process of the Fukushima earthquake than the automatic inversion models determined using only strong-motion data. By jointly analyzing the slip distribution and seismic velocity structure, we found a good correlation between the slip patches and VP/VS anomalies, suggesting that structural heterogeneities along the fault zone played a critical role in controlling the rupture process of the Fukushima earthquake. In addition, most aftershocks were located in the region characterized by small slips and high VP/VS, and we demonstrated that they were caused by stress changes due to the presence of fluids and the rupture of the mainshock.

Terrigenic helium in brackish groundwaters of Kuwait, probable influences from hydrocarbon resources

The presence of helium in groundwater can shed light on its age, migration patterns, and potential recharge locations. The 4He, 3He/4He, 20Ne, and major ions concentrations in groundwater samples were analysed. He concentration in groundwaters of the Kuwait group aquifers ranged from 3.82 × 10−8 to 1.33x−6 cm3STP/g and that of Dammam formation ranged from 9.97 × 10−8 to 1.62 × 10−6 cm3STP/g. The distribution of He was inferred to be influenced by geological structures and it was found that He decreased with Cl concentration and δ18O with few exceptions. The δ18O signatures reflect mixing between aquifers. The higher He fluxes were recorded during the Last Glacial Maximum, but they rose steadily over time. Most of the north Kuwait samples, dating from 1650 to 348 yBP, had a tritiogenic component similar to the present atmosphere, as indicated by RA (Air normalized He ratios) values, which was inferred to be due to the decay of tritium derived from meteoric impact. Magnitude 2–4 earthquake epicenters occurred more frequently in areas with lower RA values. Lateral flow was predominant with insitu (He derived from rock matrix along the flow) and exogenous sources (vertical upward cross formational flow, atmospheric input and from hydrocarbon reservoirs). Groundwater samples near oil fields were found to contain more terrigenic He, suggesting its migration to shallow waters through fault planes. The presence of more He in brackish groundwater at a shallow depth may be indicative of an abundant source beneath. He excess (Heex) and air corrected He excess (ΔHe%) are indicators of non-neuclogenic and radiogenic He sources, such as the exsolution from adjoining hydrocarbon fields through structurally weaker planes.

Tectonic Aspects of the East Anatolian 06.02.2023 Earthquake in Turkey

Abstract—During the East Anatolian earthquake with Mw = 7.8, which occurred on February 6, 2023 at 1:17 UTC, the 361 km long segment of the NE-trending East Anatolian active left-lateral fault zone (EAFZ) was activated. A left-lateral displacement took place at a distance of 318 km on formed seismic ruptures. Its maximum magnitude of 8.5 m is registered northward of the earthquake epicenter. To the northeast, the displacement of several meters is maintained over a significant length of the activated segment and is accompanied by uplift of the south-eastern side of the ruptured zone at up to 1.5 m. To the southwest of the maximum displacement area, the strike slip decreases from it at shorter distances compared to the northeastern part and the vertical component varies, although the southeastern side is mostly uplifted. In the terminal southwest, the strike slip is replaced by normal faults, gaping fractures, and other manifestations of transverse extension, which are accompanied by landslides and are mainly secondary seismic dislocations. Left lateral slip also occurred at the northern ends of the western and eastern branches of the Dead Sea Transform (DST), adjacent to the EAFZ from the south. Despite the fact that the energy distribution of numerous aftershocks along the EAFZ is generally proportional to the distribution of offsets on seismic ruptures, the slip on the EAFZ occurred during and immediately after the main shock. In the northern part of the DST, a significant decrease in the amount of energy released by strong earthquakes during the last centuries has been established. We consider that the tectonic stress accumulated in the northern part of the DST became the important geodynamic source of the East Anatolian 02.06.2023 earthquake.

Diachronous Quaternary Development of the Jiayuguan Fault and Implications for Strain Compartmentalization and Modern Earthquake Hazards in the NW Hexi Corridor, China

AbstractThe NNW‐trending Jiayuguan Fault (JYGF) is an actively developing thrust fault that delimits the SW margin of Jiayuguan, a major industrial city in the northwestern Hexi Corridor, China. In this study, we document the geometry, kinematics, and slip rates of the JYGF based on analysis of satellite imagery, low‐altitude photogrammetry, field observations, paleo‐seismic trenching, and Quaternary dating. The JYGF hanging‐wall contains a NE‐vergent asymmetric anticline of Cretaceous redbeds unconformably overlain by faulted, tilted and folded alluvial fan and fluvial terrace surfaces. Subsidiary fault scarps are associated with anticlinal flexure and contractional strain. The vertical uplift and crustal shortening rates are both ∼0.1 mm/a since ∼420 ka and geomorphic markers and dated landforms indicate southeastward fault propagation and hanging‐wall uplift from the Heishan toward the modern Beida River channel. The NW end of the fault appears to connect with the Altyn‐Tagh‐Heishan‐Jinta'Nanshan sinistral strike‐slip fault array suggesting that the JYGF is one of several parallel, splay faults that transfer strike‐slip motion to active folding and thrusting in the region. We relocate the 1992 Ms 5.4 earthquake epicenter using the NonLinLoc method and suggest that the JYGF may link southeastward with Quaternary‐active faults and folds in the Wenshushan. A seismic rupture along the total fault length of 25–40 km for the JYGF‐Wenshushan deforming belt corresponds to a potential earthquake magnitude in the 6.6–7.0 range. Compartmentalized faulting and folding in the NW–most Hexi Corridor defines a triangular block of active deformation where NE‐directed contractional deformation of the Qilian Shan foreland interacts with E‐W left‐lateral displacement along the Altyn‐Tagh‐Heishan‐Jinta'Nanshan sinistral strike‐slip system.

Electromagnetic Umbrella Modeling of Mega Meteorological Anomaly Disasters and Large Earthquake Associations

In this paper, we briefly analyze four reasons for the generation of large outbursts of positively charged particle fluxes in the Earth's interior during the gestation period of large earthquakes, and propose a physical mechanism for the formation of an EMB (electromagnetic umbrella) model of the difference between the concentration of positive and negative charged particle fluxes, which can be used to explain the relationship between a mega-meteorological catastrophic event and the generation of excessive charged particle fluxes from the lithosphere prior to the large earthquakes. Causality. We compare some historical records of major earthquakes of magnitude 7.5 around the world, and find that the correlation between mega-meteorological hazard events and large earthquakes has a good fit. Based on this statistic, in this paper, we take three large earthquakes, Wenchuan, May 12, 2008, Fukushima, Japan, March 11, 2011, and Turkey, Feb. 6, 2023, as case studies, to explore the way to assist in locating the epicenter of major earthquakes by reverse tracking method using the major meteorological disaster events.

A Cloud-IoT Architecture for Latency-Aware Localization in Earthquake Early Warning.

An effective earthquake early warning system requires rapid and reliable earthquake source detection. Despite the numerous proposed epicenter localization solutions in recent years, their utilization within the Internet of Things (IoT) framework and integration with IoT-oriented cloud platforms remain underexplored. This paper proposes a complete IoT architecture for earthquake detection, localization, and event notification. The architecture, which has been designed, deployed, and tested on a standard cloud platform, introduces an innovative approach by implementing P-wave "picking" directly on IoT devices, deviating from traditional regional earthquake early warning (EEW) approaches. Pick association, source localization, event declaration, and user notification functionalities are also deployed on the cloud. The cloud integration simplifies the integration of other services in the architecture, such as data storage and device management. Moreover, a localization algorithm based on the hyperbola method is proposed, but here, the time difference of arrival multilateration is applied that is often used in wireless sensor network applications. The results show that the proposed end-to-end architecture is able to provide a quick estimate of the earthquake epicenter location with acceptable errors for an EEW system scenario. Rigorous testing against the standard of reference in Italy for regional EEW showed an overall 3.39 s gain in the system localization speed, thus offering a tangible metric of the efficiency and potential proposed system as an EEW solution.

Joint inversion of Rayleigh group and phase velocities for S-wave velocity structure of the 2021 MS6.0 Luxian earthquake source area, China

On September 16, 2021, a MS6.0 earthquake struck Luxian County, one of the shale gas blocks in the Southeastern Sichuan Basin, China. To understand the seismogenic environment and its mechanism, we inverted a fine three-dimensional S-wave velocity model from ambient noise tomography using data from a newly deployed dense seismic array around the epicenter, by extracting and jointly inverting the Rayleigh phase and group velocities in the period of 1.6–7.2 s. The results showed that the velocity model varied significantly beneath different geological units. The Yujiasi syncline is characterized by low velocity at depths of ∼ 3.0–4.0 km, corresponding to the stable sedimentary layer in the Sichuan Basin. The eastern and western branches of the Huayingshan fault belt generally exhibit high velocities in the NE-SW direction, with a few local low-velocity zones. The Luxian MS6.0 earthquake epicenter is located at the boundary between the high- and low-velocity zones, and the earthquake sequences expand eastward from the epicenter at depths of 3.0–5.0 km. Integrated with the velocity variations around the epicenter, distribution of aftershock sequences, and focal mechanism solution, it is speculated that the seismogenic mechanism of the main shock might be interpreted as the reactivation of pre-existing faults by hydraulic fracturing.