Earthquake Preparation Research Articles

Modeling Locations with Enhanced Earth’s Crust Deformation during Earthquake Preparation near the Kamchatka Peninsula

In seismically active regions of the Earth, to which the Kamchatka peninsula refers, pre-seismic anomalies are recorded in different geophysical fields. One of such fields is the acoustic emission of rocks, the anomalies of which are recorded 1–3 days before earthquakes at the distance of the first hundreds of kilometers from their epicenters. Results of joint acoustic-deformation measurements showed that growth of geoacoustic radiation intensity occurs during the increase in the level of deformations in rock masses by more than one order compared to the background values. Simulation studies of the areas with increased deformation are realized to understand the causes of anomalous acoustic-deformation disturbance occurrences before strong earthquakes. The model is based on the assumption that the Earth’s crust in the first approximation can be considered as a homogeneous isotropic elastic half-space, and an earthquake source can be considered as a displacements along a rectangular fault plane. Based on these assumptions, deformation regions of Earth’s crust were modeled during the preparations of two earthquakes with local magnitudes ML≈5 occurred on the Kamchatka Peninsula in 2007 and 2009. The simulation results were compared for the first time with the data of a laser strainmeter-interferometer installed at the Karymshina observation site (52.83∘ N, 158.13∘ E). It was shown that, during the preparation of the both earthquakes, the Karymshina observation site was within the region of shear deformations ≈10−7, which exceeded the tidal ones by an order. On the whole, simulation results corresponded to the results of the natural observations. Construction of an adequate model for the generation of acoustic-deformation disturbances before strong earthquakes is topical for the development of an early notification system on the threat of catastrophic natural events.

Factors Associated with Knowledge of Evacuation Routes and Having an Emergency Backpack in Individuals Affected by a Major Earthquake in Piura, Peru.

Information on the prevention of earthquakes in Peru, a high-risk country, is still emerging. We determined the frequency and factors associated with knowledge of evacuation routes and the use of emergency backpacks in people affected by a major earthquake. A cross-sectional study using secondary data was conducted from August-December 2021 on people that experienced the 6.1 magnitude earthquake that occurred in Piura, Peru on 30 July 2021. The outcome was self-reported knowledge of evacuation routes and the use of emergency backpacks. The association with self-reported earthquake preparation training, use of sources of information on earthquakes, and sociodemographic variables was investigated. A total of 69.5% of participants knew evacuation routes, and 46.3% had an emergency backpack. A higher frequency of knowledge of evacuation routes was associated with previous training (PR: 1.47; 95% CI: 1.15-1.87), use of the media (PR: 1.35; 95% CI: 1.06-1.72), having received information from the COEN (PR: 1.19; 95% CI: 1.02-1.40), and with a greater number of household members (PR: 1.03; 95% CI: 1.01-1.06). There is a high frequency of knowledge of evacuation routes among participants. However, basic notions of prevention culture are still needed. This research contributes to policy development on earthquake preparation at the community level.

Sea temperature variation associated with the 2021 Haiti Mw 7.2 earthquake and possible mechanism

A catastrophic earthquake (magnitude Mw 7.2) occurred on 14 August 2021 in Haiti. Sea surface temperature (SST) and sea potential temperature (SPT) observed from satellites show pronounced changes prior to the main earthquake event. The changes are observed near the epicenter and the boundary of the Caribbean Plate. Here we have carried out a detailed analysis of ocean, atmosphere and land surface parameters (sea water salinity, chlorophyll-a, latent energy flux, sensible heat flux, specific humidity, air temperature, methane and land surface temperature) using multiple satellite data to understand the possible mechanism of sea temperature changes. The strong coupling among these geophysical and geochemical parameters has been found within 2-week prior to the 2021 Haiti Mw 7.2 earthquake due to the interaction between ocean/land and atmosphere during the last phase of earthquake preparation period caused by the tectonic movement. The spatiotemporal distribution pattern of anomalies is discussed in view of the focal mechanism of the earthquake event.

Study of the electromechanical coupling process before the 2020 Ms 6.4 Yutian, China earthquake

The observation of electromechanical coupling might be used as an important tool to detect pre-seismic changes associated with the preparation of earthquakes. This paper attempts to study the electromechanical coupling process before the large earthquakes by using the load/unload response ratio (LURR) approach in which the geo-electric data and Benioff strain of small earthquakes were adopted as the data input. The variation of Coulomb failure stress induced by earth tides on the fault surface of the mainshock is applied to differentiate the loading and unloading stages. Using this technique, we test the geo-electric data recorded at the Hotan observatory near the epicenter of 2020 Yutian Ms 6.4 earthquake. Results show that the LURR time sequence fluctuated around 1.0 for many years and reached significant high peaks at the beginning of 2020. More importantly, this evolution correlates well with the LURR time series calculated by using the Benioff strain of small earthquakes within the circular region of 300 km radius centered at the epicenter. The underlying physics of the changes should be caused by the fluid infiltration derived from pre-seismic rock dilatancy. The corresponding volume variations in the crust could be found in the geophysical observation time series in the same neighborhoods.

Chemistry in earthquake: the active chemical role of liquid and supercritical waters in microfracturing at depth

The role of water in the nucleation process of an earthquake and its contribution to the mainshock is ascertained by many models in its physical part, as a factor capable of altering the balance of pressures and thus influencing the effective pressure. Assuming that water is present at depth, starting from the observation of its molecular structure at various crustal pressure and temperature conditions, the present paper analyses water’s chemical role in relation with the rock matrix, and its response during microfracturing. The creation of a network of new void spaces produces a decrease of the water pressure. Water may respond at molecular scale differently, depending on its aggregation state. Effectively depressurisation has a limited influence on the liquid water, only if it does not cause the transition to the vapour phase. Conversely, depressurisation causes an instantaneous variation in the intermolecular structure of supercritical water (SCW). Specifically, the nearly total disappearance of its ionic characteristics: that means the severe drop of solubility constants. At the same time, the already low viscosity decreases too: SCW intrudes easily into new fissures. When the microcracks tend to close, SCW reacquires adequate ionic characteristics for the rise in density (isothermal pressurisation); hence, an intense water rock interaction starts with freshly opened surfaces. This process influences actively the subcritical crack growth too, again with differences between liquid and SCW: last one participates only when reacquires density. Summarising, it is likely that water plays a fundamental and active role in determining the rock weakening, once earthquake preparation process begin with the development of microcracks are forming, perhaps playing an active role in determining the main rupture. With different modalities according to its aggregation state.

Analysis of Potential Precursory Pattern at Earth Surface and the Above Atmosphere and Ionosphere Preceding Two Mw ≥ 7 Earthquakes in Mexico in 2020–2021

AbstractComprehensive analyses of seismic precursory characteristics may provide evidence for the possible mechanisms of lithosphere‐atmosphere‐ionosphere coupling (LAIC). The integrated monitoring data from space and ground measurements makes it possible to reveal the potential earthquake precursory pattern obeying LAIC. In this paper, we study seismic precursors from air temperature data of the National Center for Environmental Prediction (NCEP), Global Navigation Satellite System (GNSS) based Total Electron Content (TEC) and electron density retrieved from Swarm satellite (Alpha) data in two Mw 7.0 earthquakes in Mexico in 2020–2021. We find seismic thermal anomalies can be identified from temperature variation in the lithosphere and atmosphere by improved tidal force fluctuant analysis (TFFA). The spatial‐temporal evolution of seismic thermal anomalies is significantly different from that of non‐seismic thermal anomalies. In addition, synergistic observations of the Swarm Alpha satellite and GNSS stations can provide more comprehensive information about perturbations in the ionosphere. The results show that anomalies originate along fault lineaments near the epicenter, leading to air pressure gradient and ionization process in the atmosphere, followed by ionospheric perturbations. Furthermore, composite anomalies of LAIC first appear around a month before earthquakes and tend to recur several times over earthquake preparation phases. Our study provides more evidence for understanding the characteristics of earthquake precursors.

Lithosphere Ionosphere Coupling Associated with Seismic Swarm in the Balkan Peninsula from ROB-TEC and GPS

With the rapid development of global navigation satellite systems (GNSS) and their increasingly wide range of applications in atmospheric science, total electron content (TEC) data are widely used in the theoretical study of layer coupling related to seismicity. This study detected and analyzed pre-earthquake ionospheric anomalies (PEIA) by using TEC data from the Royal Observatory of Belgium (ROB), and analyzed coseismic ionospheric disturbance (CID) with vertical TEC (VTEC) from the GPS stations in earthquake preparation areas. The results show that PEIA appear to increase continuously from 08:00–12:00 UT in the 3 days before a seismic swarm of Mw > 5.0. The ionosphere over the seismogenic zones exhibited large-scale anomalies when multiple seismogenic zones of the Balkan Peninsula spatially and temporally overlapped. Moreover, the TEC around the earthquake centers showed a positive anomaly lasting for 7 h. In a single seismogenic zone in Greece, the TEC around the earthquake center reached over +3.42 TECu. In addition, the CID observed from GPS stations shows that with the increase in the number of earthquakes, the ionosphere over the seismogenic area is more obviously disturbed, and after three strong earthquakes, TEC suddenly decreased over the seismogenic area and formed a phenomenon similar to an ionospheric hole. We conclude that a lithosphere–atmosphere–ionosphere coupling mechanism existed before the seismic swarm appeared in the Balkan Peninsula. Earthquake-induced VTEC anomalies occurred more frequently within a 3–10 day window before the earthquake. This phenomenon is particularly evident when multiple seismogenic zones overlap spatiotemporally.

Lineament analysis as a seismic precursor: The El Mayor Cucapah earthquake of April 4, 2010 (MW7.2), Baja California, Mexico

An earthquake called the MW7.2 “El Mayor Cucapah” earthquake on April 4, 2010 has been analyzed for seismic precursor. The changes in the lineament system concerning its pattern and time intervals were analyzed during the earthquake preparation period and occurrence using the automated lineament detection method. The Landsat 5 TM images were processed using LESSA and ADALGEO software obtaining similar results. The statistical analysis revealed the stress accumulation due to plate interaction during earthquake formation. The study shows that the number of extracted lineaments changes rapidly about 23 months before the earthquake, and the systems return to the initial stage after 23 months. Most lineaments coincide with the extension of the San Andreas Fault as NW direction is the dominant trend. Thus, it can be concluded that the featural changes within the Rose diagram corresponding to the different strokes direction along with oriented elongation lines as disclosed in the present study using satellite images could be identified as a mid-term and/or short-term precursors of the earthquake. However, even though the dynamism of the El Mayor Cucapah earthquake is found in the extracted lineaments, it is possible to isolate more significant earthquakes even if new ones appear near the zone. Moreover, using two algorithms for lineament detection allows for the tectonics to corroborate the obtained lineaments and dynamism.

Variability in the Statistical Properties of Continuous Seismic Records on a Network of Stations and Strong Earthquakes: A Case Study from the Kamchatka Peninsula, 2011–2021

A study of spatiotemporal variability and synchronization effects in continuous seismic records (seismic noise) on a network of 21 broadband seismic stations on the Kamchatka Peninsula was carried out in connection with the occurrence of strong earthquakes, M = 7.2–8.3. Data of 1-min registrations of the vertical movements velocity Earth’s surface were used for constructing time series of daily values of the generalized Hurst exponent α*, singularity spectrum support width ∆α, wavelet-based spectral exponent β, and minimum normalized entropy of squared orthogonal wavelet coefficients En for all stations during the observation period 2011–2021. Averaged maps and time-frequency diagrams of the spectral measure of four noise parameters’ coherent behavior were constructed using data from the entire network of stations and by groups of stations taking into account network configuration, volcanic activity and coastal sea waves. Based on the distribution maps of noise parameters, it was found that strong earthquakes arose near extensive areas of the minimum values of α*, ∆α, β, and the En maximum values advance manifestation during several years. The time-frequency diagrams revealed increased amplitudes of the spectral measure of the coherent behavior of the 4-dimensional time series (synchronization effects) before three earthquakes with Mw = 7.5–8.3 over months to about one year according to observations from the entire network of stations, as well as according to data obtained at groups of continental and non-volcanic stations. A less-pronounced manifestation of coherence effects diagrams plotted from data obtained at coastal and volcanic groups of stations and is apparently associated with the noisiness in seismic records caused by coastal waves and signals of modern volcanic activity. The considered synchronization effects correspond to the author’s conceptual model of seismic noise behavior in preparation of strong earthquakes and data from other regions and can also be useful for medium-term estimates of the place and time of seismic events with Mw ≥ 7.5 in the Kamchatka.

Особенности динамики напряженно-деформированного состояния перед землетрясением M7.1 Риджкрест 2019 г. по результатам численного моделирования

The paper is concerned with the analysis of the simulated stress-strain state (SS) parameters of the earth's crust over the four-year period preceding the M7.1 2019 Ridgecrest earthquake in Southern California. SS parameters have been calculated using a detailed geomechanical model, taking into account an ongoing weak seismicity catalog data. Cyclic patterns are identified in the observed shear strain anomalies, with estimation of their spatial and temporal characteristics, and an attempt is made to track the influence of the local displacement direction and periodic migration of shear strain anomalies in the upper crust on the earthquake preparation. Finally, we discuss the role of the observed regularities in terms of existing models describing the earthquake preparation process.

A review of tidal triggering of global earthquakes

Earthquake prediction remains a challenging and difficult task for scientists all over the world. The tidal triggering of earthquakes is being proven by an increasing number of investigations, most of which have shown that earthquakes are positively correlated with tides, and thus, tides provide a potential tool for earthquake prediction, especially for imminent earthquakes. In this study, publications concerning the tidal triggering of earthquakes were compiled and analyzed with regard to global earthquakes, which were classified into three main types: tectonic, volcanic, and slow earthquakes. The results reveal a high correlation between tectonic earthquakes and tides (mainly for semidiurnal and diurnal tides; 14-day tides) before and after the occurrence of significant earthquakes. For volcanic earthquakes, observations of volcanoes on the seafloor and land indicate that volcanic earthquakes in near-shore volcanic areas and mid-ocean ridges have a strong correlation with tidal forces, mostly those with semidiurnal and diurnal periods. For slow earthquakes, the periodicity of the tremor duration is highly correlated with semidiurnal and diurnal tides. In conclusion, the tidal triggering of these three types of earthquakes makes a positive contribution to earthquake preparation and understanding the triggering mechanism, and thus, the prediction of these types of earthquakes should be investigated. However, there are still several inadequacies on this topic that need to be resolved to gain a definitiveanswer regarding the tidal triggering of all earthquakes. The main inadequacies are discussed in this paper from our point of view.

Application of the extreme gradient boosting method to quantitatively analyze the mechanism of radon anomalous change in Banglazhang hot spring before the Lijiang Mw 7.0 earthquake

Radon concentration in groundwater is affected by meteorological and seismo-tectonic factors and is sensitive indicators of crustal stress. While previous studies have focused on the mechanisms of periodic and precursory radon anomalies, few have quantitatively assessed their influences, and compared their rates of change under normal and earthquake conditions. This study constructs four models to analyze the mechanisms of radon variation under natural and seismic conditions using the Extreme Gradient Boosting method: 1) the multi-year dynamic variation model, 2) the maximal radon concentration model, 3) the minimum radon concentration model, and 4) the precursory anomaly model. The feature relative importance of external factors influencing radon concentration in groundwater are estimated. The optimized extreme gradient boosting model estimated the feature importance of spring discharge (SD), water temperature (WT), precipitation (P), barometric pressure (BP), and antecedent radon (AR) to be 23.79%, 22.16%, 9.81%, 18.8% and 25.44%, respectively. Thus, SD is the most important influence on radon variation under normal conditions. For radon variation during the earthquake preparation period, the feature relative importance indicates significant changes in WT (increasing from 22.16% to 27.70%) and SD (decreasing from 23.79% to 17.99%). Although WT was the most important predictor in the precursory anomaly model, its effect on radon solubility is insufficient to explain the radon anomalies prior to the Lijiang Mw 7.0 earthquake. Analysis of the precursory mechanisms of these radon anomalies in terms of SD, WT, P, BP, and radon emanation found that radon anomalies are most likely caused by increases in radon emanation due to the earthquake-induced formation of microfractures in rock.

Earthquake Response for Students with Different Severe Degrees of Disabilities: An Investigation of the Special Education Classes in Primary Schools in Taipei.

Taipei has been ranked as the most vulnerable city to a wider combination of risks. Although the Special Education Law addresses the consideration of disaster preparedness for students with disabilities enrolling in Special Education Schools, more attention needs to be given to the far larger number of students with disabilities enrolling in normal schools. These schools need to consider the care for students with different types and severe degrees of disabilities. The aim of the research is to investigate challenges of earthquake preparation and response for students with different severe degrees of disabilities who enrol in the special education classes in general primary schools. The objectives of the research include the following: (1) investigating the challenges and requirements for support of students with different severe degrees of disabilities; (2) examining the need and support for students with different degrees of disabilities during the earthquake response process; and (3) exploring the best practice in the curriculum building for students with different severity of disabilities. The purposive sampling was used to select four primary schools in Taipei as participant groups in the research. The research team used semi-structured interviews to interview eight participants: one special education class teacher and one administrator of each school were invited. Findings include the following: (1) ensuring the appropriate design of physical environment for earthquake response in schools, including rapid response, evacuation, and assembly points for students with different severe degrees of disabilities; (2) proposing suitable staff to student ratio to be planned for the response phase; (3) identifying the appropriate individualised curriculum and learning objectives to suit students with different severe degrees of disabilities.

Potential utilization of air temperature, total electron content, and air relative humidity as possible earthquake precursors: A case study of Mexico M7.4 earthquake

This study examines ionospheric total electron content (TEC) perturbations from six International Global Navigation Satellite System stations (GNSS) including GUAT-Guatemala, SSIA-El Salvador, INEG-Mexico, MANA-Nicaragua, MDO1-United States of America, and BOGT- Colombia for several days around the occurrence of a major earthquake (M 7.4 and depth 20.0 km) in Mexico, June 23, 2020 at 10:29 Local Time (LT). The INEG station in the North-Northwest of the epicenter at a distance of about 936 km indicated a positive TEC anomaly on June 18, 2020, which can be possibly viewed as an earthquake precursor due to its occurrence during a quiet geomagnetic storm and inactive solar activity. Study findings reveal that other TEC perturbations may not be related to the earthquake, because they appeared during geomagnetic activities. Moreover, the atmospheric parameters have significant and synchronous deviations from the earthquake epicenter on June 13, 2020. The highest atmospheric chemical potential (ACP) is about 0.010 eV, atmospheric air temperature has positive deviation of 3.937 °C at 15:00 LT, the lowest atmospheric relative humidity has negative deviation of 25.387% at 13:00 LT and outgoing longwave radiation (OLR) 27.58 W m−2. Observations validate that in the earthquake preparation zone, variations in atmospheric air temperature and relative humidity reach at peak value during 10 days prior to the impending earthquake event with the later perturbations in the ionosphere.

Deep Electrical Structure of the Langshan Mountain-Linhe Basin Area on the Northwest Edge of the Ordos Block, China

A series of fault depression structures have developed around the Ordos Block. The Langshan Mountain-Linhe Basin area (LLA), located on the northwest edge of the Ordos Block, is a typical, normal tension fault system. A geological survey shows that the Langshan Piedmont fault (LPF) in this area has a large slip rate and indicates risk of earthquake preparation. Broadband magnetotelluric (MT) exploration research was recently carried out across the LLA in the NW–SE direction, and the three-dimensional deep electrical structure thus obtained revealed that the LPF in the LLA is an evident electrical boundary zone on the whole crustal scale and is the main boundary fault of the primary structural block of the Alxa and Ordos Blocks. The MT results also show that the Linhe Basin and Ordos Block belong to the same tectonic basement. The Linhe and Dengkou faults belong to the internal faults of the Ordos Block. The upper crust of the Langshan Mountain on the west side of LPF is characterized by high-resistivity, the middle and lower crust have a low-resistivity layer, and the Linhe Basin on the east side has a Cenozoic low-resistivity sedimentary layer of approximately 10 km thick, which reveals that the Linhe Basin is a faulted basin with sedimentary thickness around the Ordos Block. This indicates that the LLA has experienced continuous and strong tension, normal fault depression sedimentary activities since the Cenozoic era. The current Global Positioning System velocity field shows that there is an apparent NW–SE acceleration zone in the LLA. The leveling data indicate that Linhe Basin shows a subsidence trend relative to the Ordos Block, indicating that the area is undergoing continuous NW–SE tension and faulting. It is speculated that there is a risk of earthquake preparation in the LPF.

Pronounced Changes in Thermal Signals Associated with the Madoi (China) M 7.3 Earthquake from Passive Microwave and Infrared Satellite Data

Thermal variations in surface and atmosphere observed from multiple satellites prior to strong earthquakes have been widely reported ever since seismic thermal anomalies were discovered three decades ago. These thermal changes are related to stress accumulation caused by the tectonic activities in the final stage of earthquake preparation. In the present paper, we focused on the thermal changes associated with the 2021 Madoi M 7.3 earthquake in China and analyzed the temporal and spatial evolution of the Index of Microwave Radiation Anomaly (IMRA) and the Index of Longwave Radiation Anomaly (ILRA) based on 8-year microwave brightness temperature (MWBT) and 14-year outgoing longwave radiation (OLR) data collected by satellites. We also explored their responses in different tectonic units (seismogenic fault zone and active tectonic block). Our results indicated that the enhanced IMRA was distributed along the seismogenic fault since mid-February and reappeared for a longer time and with stronger intensity in March and April 2021. The pronounced enhancement in the ILRA was observed within one month over Bayan Har tectonic and adjacent blocks. The higher ILRA over the tectonic blocks in the southern Tibet Plateau at the beginning of 2021 could be associated with the regional stress accumulation, as proven by the occurrences of two moderate earthquakes during this period.

On the influence of deep seismicity on the preparation of large earthquakes in the South-Asian region

The change dynamics in the creepex parameter over time and its comparison with changes in other earthquake parameters (magnitude and depth) is used to test the thesis about the influence on strong crustal events from deep processes associated with the transformation and movement of matter in the upper mantle using the example of the seismicity of the South-Asian region.

Gravity changes caused by crustal fluids invasion: A perspective from finite element modeling

Gravity changes related to large earthquake preparation are reported in broad seismogenic source regions, and crustal fluids may change the gravity potential and trigger earthquakes. However, what is the major factors affecting crustal fluids movement in the upper 10 km of the continental crust and altering the gravity potential is still poorly understood. In this study, we evaluated the gravity changes caused by invasion of crustal fluids into the depth of 6–10 km using finite element based numerical modeling. We conducted a series of numerical experiments to investigate the influences of permeability distribution, the fluid source, and the invasion depth on gravity changes. The sensitivity analysis and comparison results suggest that the invasion of high-pressure fluids increases fluid density and produces positive gravity changes within a decade. Fluid pressure is the key factor for the variations of fluid density, while temperature exerts a minor influence. Consistent with the dissipation of fluid pressure, the corresponding gravity changes are fast (>3 μGal/year) in the first 2–3 years of fluid invasion and become increasingly slow later. Therefore, the first few years are the more suitable time for monitoring the gravity changes caused by crustal fluids invasion. The fluid-related gravity changes are positively correlated to the porosity and permeability of rocks adjacent to the fluid source, the salinity and the scale of crustal fluids, and the initial temperatures, and are negatively correlated to the invasion depth. Transient invasion of crustal fluids can be detected by means of the high precision gravity observation under certain conditions subjected to the initial geological characteristics of the continental crust and the geochemical evolution of the fluid sources.

Stress State in the Source Region of Mw2.2 Earthquake in a Deep Gold Mine in South Africa Determined from Borehole Cores

In December 2007, an Mw2.2 earthquake occurred in a gabbroic dike at 3.3 km depth in a deep gold mine in South Africa. The fore- and aftershock activity was analyzed in an effort to understand the preparation and generation processes of earthquakes; these findings have already been published. The present paper focuses on the stress state in the source region of the mainshock. A 90-m-long borehole across the mainshock fault was drilled ~ 1.5 years after the mainshock and logged by an optical televiewer. The fault can be identified by severe damage to the borehole wall at the point where the borehole intersected the aftershock cluster. Except for a 10-m section in the hanging wall of the fault, borehole cores were fully recovered. Borehole breakout (BO) and core disking (CD) were found to occur. Two stress measurement techniques [Deformation Rate Analysis (DRA) and Diametrical Core Deformation Analysis (DCDA)] were applied to the borehole cores. By combining their results with occurrence criteria for BO and CD, the principal stress state in the source region of the mainshock was determined. The principal directions in the hanging wall of the fault were nearly identical to the virgin stress state, while it was significantly disturbed in the footwall. The vertical stresses were 106 MPa and 40 MPa in the hanging wall and footwall, respectively. The significant difference in the vertical stress between the two sides of the fault can be explained by the stress redistribution associated with a nonuniform slip on a nonplanar fault.

Developing a Deep Learning-Based Detector of Magnetic, Ne, Te and TEC Anomalies from Swarm Satellites: The Case of Mw 7.1 2021 Japan Earthquake

Since the appearance and evolution of earthquake ionospheric precursors are expected to show a nonlinear and complex behaviour, the use of nonlinear predictor models seems more appropriate. This paper proposes a new approach based on deep learning as a powerful tool for extracting the nonlinear patterns from a time series of ionospheric precursors. A Long Short-Term Memory (LSTM) network as a type of Recurrent Neural Network (RNN) was used to investigate 52 six-month time series, deduced from the three Swarm satellite (Alpha (A), Bravo (B) and Charlie (C)) measurements, including electron density (Ne), electron temperature (Te), magnetic scalar and vector (X, Y, Z) components, Slant and Vertical Total Electron Content (STEC and VTEC), for day and night periods around the time and location of a seismic event. This new approach was tested on a strong Mw = 7.1 earthquake in Japan on 13 February 2021, at 14:07:50 UTC by comparing the results with two implemented methods, i.e., Median and LSTM methods. Furthermore, clear anomalies are seen by a voting classification method 1, 6, 8, 13, 31 and 32 days before the earthquake. A comparison with atmospheric data investigation is further provided, supporting the lithosphere–atmosphere–ionosphere coupling (LAIC) mechanism as a suitable theory to explain the alteration of upper geolayers in the earthquake preparation phase. In other words, using multi-method and multi-precursor analysis applied to 52 time series and also to the orbit-by-orbit investigation, the observed anomalies on the previous day and up to 32 days before the event in normal solar and quiet geomagnetic conditions could be considered as a striking hint of the forthcoming Japan earthquake.