Seismic Anomalies Research Articles

Seismic Imaging Beneath Cascadia Shows Shallow Mantle Flow Patterns Guide Lower Mantle Upwellings

AbstractThe mantle transition zone (MTZ) plays an important role in modulating material transport between the upper mantle and the lower mantle. Constraining this transport is essential for understanding geochemical reservoirs, hydration cycles, and the evolution of the Earth. Slabs and hotspots are assumed to be the dominant locations of transport. However, the degree of material transport in other areas is debated. We apply P‐to‐S receiver functions to an amphibious data set from Cascadia to image the MTZ discontinuities beneath mid‐ocean ridges, a hotspot, and a subduction zone. We find a MTZ thinned by 10 ± 6 km beneath the ridges and by 8 ± 4 km beneath the base of the slab, closely resembling the 660 discontinuity topography. Depressions on the 410 discontinuity are smaller, 5 ± 2 km on average, focused in the north and the south and accompanied by supra‐410 discontinuity melt phases. The depressions occur away from locations of uplifted 660 discontinuity, but near slow seismic velocity anomalies imaged in the upper mantle. This suggests lower mantle upwellings occur beneath ridges and beneath the base of slabs but stall in the transition zone, with upper mantle convection determining upward material transport from the transition zone. Therefore, upper mantle dynamics play a larger role in determining transfer than typically assumed.

Application of fluid modulus inversion to complex lithology reservoirs in deep-water areas

It has been a challenge to distinguish between seismic anomalies caused by complex lithology and hydrocarbon reservoirs using conventional fluid identification techniques, leading to difficulties in accurately predicting hydrocarbon-bearing properties and determining oil-water contacts in reservoirs. In this study, we built a petrophysical model tailored to the deep-water area of the Baiyun Sag in the eastern South China Sea based on seismic data and explored the feasibility of the tri-parameter direct inversion method in the fluid identification of complex lithology reservoirs, offering a more precise alternative to conventional techniques. Our research found that the fluid modulus can successfully eliminate seismic amplitude anomalies caused by lithological variations. Furthermore, the seismic data-based direct inversion for fluid modulus can remove the cumulative errors caused by indirect inversion and the influence of porosity. We discovered that traditional methods using seismic amplitude anomalies were ineffective in detecting fluids, determining gas-water contacts, or delineating high-quality reservoirs. However, the fluid factor Kf, derived from solid-liquid decoupling, proved to be sensitive to the identification of hydrocarbon-bearing properties, distinguishing between high-quality and poor-quality gas zones. Our findings confirm the value of the fluid modulus in fluid identification and demonstrate that the tri-parameter direct inversion method can significantly enhance hydrocarbon exploration in deep-water areas, reducing associated risks.

Geodynamic reconstruction of offshore eastern Tunisia during the Cretaceous and Paleogene periods and its impact on hydrocarbon exploration

The analyses of structural, seismostratigraphic patterns and seismic anomalies were conducted using borehole and two-dimensional (2-D) seismic data to reconstruct the geodynamic evolution of offshore eastern Tunisia from the Cretaceous to the Paleogene times. Thirteen third-order sequences (S1 to S13) were identified, and several hiatuses were recognized, which were most likely related to the tectonic event associated with the convergence between Eurasian and African plates. Aptian buildups have also been recognized in the outer platform margin. The growth and distribution of these reefs are controlled by the uplift of fault blocks responsible for the relative sea-level fall which led to sub-aerial exposure and the development of a karstified carbonate platform. The structural features and the major tectonic events as well as the stratigraphic pattern, recognized in offshore eastern Tunisia, are related to the geodynamic evolution of the North African and western Mediterranean basins.The identification of several undrilled reef buildups with significant hydrocarbon potential could replenish the operators' portfolio.

The Analysis of Lithosphere–Atmosphere–Ionosphere Coupling Associated with the 2022 Luding Ms6.8 Earthquake

Taking the Luding Ms6.8 earthquake (EQ) on 5 September 2022 as a case study, we investigated the potential seismic anomalies of the ionosphere, infrared radiation, atmospheric electrostatic field (AEF), and hot spring ions in the seismogenic region. Firstly, we analyzed the multi-parameter anomalies in the ionosphere around the epicenter and found synchronous anomalous disturbances in the ground parameters, namely the global ionospheric map (GIM), GPS, TEC, and satellite parameters, such as the He+ and O+ densities on 26 August under relatively quiet solar–geomagnetic conditions (F10.7 < 120 SFU; Kp < 3; Dst > −30 nT; |AE| < 500 nT). Next, both the anomaly analysis of the infrared radiation and AEF, and the survey results of the Luding EQ scientific expedition on the hot spring ions showed pre-seismic anomalous variations at different time periods in the seismogenic region. The characteristics of Earth’s multi-sphere coupling anomalies in temporal evolution and spatial distribution were obvious, which validated the Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) mechanism. Finally, combining the analysis results and the LAIC mechanism, we suggested that the multi-sphere coupling anomalies were more likely associated with the Luding Ms6.8 EQ, and that the differential motion and the regional crustal stress accumulation between the Chuandian block and the Bayan Har block might have led to this EQ. Furthermore, remote sensing and ground-based monitoring technologies can play an important role in corroborating and compensating each other, while further study of the multi-sphere coupling mechanism will provide a clearer understanding of the seismogenic process for major EQs.

Tomographic Inversion Code Analysis Using Regularization Iteratively Reweighted Norm (Irn)

Indonesia is an area located in the ring of fire, which was formed as a result of the interaction between four plates, namely the Eurasian Plate on the south, the Eurasian Plate on the, the Philippine Plate, and the Pacific Plate on the northeast. The interaction between these plates causes Indonesia to have many active volcanoes and experience many geological natural disasters. In the tomographic inversion process, ill-condition problems are often found in matrix making. Therefore, a regularization technique is needed to obtain a consistent result. The regularization technique can be done using Matlab software with a package called IR Tools (Gazzola et al., 2018). In this research, inversion techniques are used in the form of Least Square and Iteratively Reweighted Norm (IRN). This study aims to analyze the tomographic inversion code with the regularization technique using the Iteratively Reweighted Norm (IRN). In this study, two types of data were used, synthetic data and real data. Based on the results, it shows that using the Least Square method has better where the resulting checkerboard is more than adequate to reconstruct the initial velocity and amplitude model, which is described more clearly and strongly. Based on the results of the real data inversion, it shows that there is a low Vp anomaly (red) in the lower area of Mt. Merapi and Mt Merbabu. Low seismic velocity anomalies are associated with magmatic zones, partial melting, or magma reservoirs. However, there is also a high seismic velocity anomaly (blue) associated with the subduction zone of the Indo-Australian Plate to the Eurasian Plate.

Early Result of Imaging 3D Seismic Velocity Structure In Central Java Using Double-Difference Tomography

Central Java is a part of the Sunda Arc and has relatively high seismicity due to the subduction zone between the Indo-Australian Plate and the Eurasian Plate. This study uses double-difference tomography to image the P and S wave 3D seismic velocity structures associated with tectonic patterns due to subduction zones. The data used comes from the earthquake catalogs of BMKG, BPPTKG, DOMERAPI, and MERAMEX, with a recording period from May 2004 to December 2020. The number of earthquakes that successfully relocated was 1930 from 1937 earthquakes recorded by 285 recording stations. The results of hypocentre relocation show that seismic activity in Central Java is relatively high and originates from geological structures, including subduction zones, back-thrust, and the Opak Fault. The tomogram results of the P and S wave velocity models support each other. The high seismic velocity anomaly is associated with the subduction zone of the Indo-Australian Plate to the Eurasian Plate with a maximum resolution of up to 100 km depth. Low seismic velocity anomalies are found at the Merapi-Lawu Anomaly (MLA), the Modern Volcanic Arc (MVA), the Sumbing-Sundoro-Dieng volcanic complex, the Banyumas-Cilacap sedimentary basin, and the Kendeng Basin. A low-velocity anomaly is found at a depth of about 40-50 km and a depth of 100 km, which is associated with the process of slab dehydration and partial melting. The inversion results show the impact of the Indo-Australian Plate subduction and the Eurasian Plate on volcanic activity, seismicity, and the geological structures developed in Central Java.

The Boundary Areas Structure of the Malko-Petropavlovsk Fracture Zone from Local Seismic Tomography and Earthquake Foci Mechanisms Data

Abstract —This study continues analysis of the new seismic tomographic structure of the suprasubduction complex of the central zone of Kamchatka, obtained from the dense local networks data of 2018–2020, and is devoted to the analysis of the velocity structure in the Malko-Petropavlovsk fracture zone margins and around them. The seismic tomographic model involves about 98,000 P- and S-wave travel times from 2963 local earthquakes from August 2018 to July 2020. The resolution of this model makes it possible to trace the feeding systems of volcanoes of the South Kamchatka and East Volcanic Belt to the slab surface, as well as to identify subvertical structural faults. To construct the orientations of the compression and extension axes we used the foci mechanisms of 41 earthquakes with М ≥ 4.5 from the catalog of the International Seismological Center for the period 1979–2019. Along the Malko-Petropavlovsk fracture zone, the Avacha transform fault is clearly traced in the geometry and mutual arrangement of velocity anomalies almost throughout the entire depth of the model. Comparison of seismic anomalies with a map of the directions of the compression and extension axes distribution from the earthquake foci mechanisms showed the correlation between the change in the value of the velocity anomalies along the Avacha transform fault with the axes direction change by almost 180°. A near-surface low-velocity anomaly to the depths of 25–35 km was found along the western border of the Malko-Petropavlovsk zone under the southern tip of the Sredinny Ridge. This anomaly probably marks the axes junction zone boundary of the ancient volcanic front along the Sredinny Ridge and the modern active Eastern Volcanic Belt, which formed as a result of the Kronotsky paleoarc accretion. To the west from the Sredinny Ridge southern tip, another low-velocity anomaly was revealed. This anomaly was traced to a depth of ~150 km, has a contrasting southern boundary confirmed by the distribution of the compression and extension axes directions by the earthquake foci mechanisms and apparently marks the southern boundary of the West Kamchatka block.

Anomalies in Infrared Outgoing Longwave Radiation Data before the Yangbi Ms6.4 and Luding Ms6.8 Earthquakes Based on Time Series Forecasting Models

Numerous scholars have used traditional thermal anomaly extraction methods and time series prediction models to study seismic anomalies based on longwave infrared radiation data. This paper selected bidirectional long short-term memory (BILSTM) as the research algorithm after analyzing and comparing the prediction performance of five time series prediction models. Based on the outgoing longwave radiation (OLR) data, the time series prediction model was used to predict the infrared longwave radiation values in the spatial area of 5° × 5° at the epicenter for 30 days before the earthquake. The confidence interval was used as the evaluation criterion to extract anomalies. The examples of earthquakes selected for study were the Yangbi Ms6.4-magnitude earthquake in Yunnan on 21 May 2021 and the Luding Ms6.8-magnitude earthquake in Sichuan on 5 September 2022. The results showed that the observed values of the Yangbi earthquake 15 to 16 days before the earthquake (5 May to 6 May) exceeded the prediction confidence interval over a wide area and to a large extent. This indicates a strong and concentrated OLR anomaly before the Yangbi earthquake. The observations at 27 days (9 August), 18 days (18 August), and 8 days (28 August) before the Luding earthquake exceeded the prediction confidence interval in a local area and by a large extent, indicating a strong and scattered OLR anomaly before the Luding earthquake. Overall, the method used in this paper extracts anomalies in both spatial and temporal dimensions and is an effective method for extracting infrared longwave radiation anomalies.

Inferring the relationship between core-mantle heat flux and seismic tomography from mantle convection simulations

The heat flux pattern at Earth’s core-mantle boundary (CMB) imposes a heterogeneous boundary condition on core dynamics that may profoundly affect the geodynamo. Owing to the expected temperature dependence of seismic velocities, this pattern is classically approximated as proportional to the lowermost layer of seismic tomography models for the global mantle. Two biases however undermine such a simple linear relationship: 1) other contributions than thermal (compositional and mineralogical) influence seismic velocities and 2) the radial average is inherent to tomographic models whereas the local thermal state at the CMB is relevant for the heat flux. We analyze here simulations of thermochemical mantle convection where, owing to their spatial characteristics, specific mantle components are readily identified: hot thermochemical piles (TCPs), “normal” mantle (NM) and, when post-peroskite (pPv) is included, a cold region where this phase is present. Synthetic seismic velocities (i.e. from the mantle simulations) are then computed based on thermal, compositional and mineralogical sensitivities. A formalism to infer the CMB heat flux from these seismic shear velocity anomalies is derived. In this formalism, within each mantle population (i.e. TCPs, NM or pPv) the CMB heat flux vs. seismic anomalies follows a unique fitting function. The transition from one mantle population to another is marked by a jump in the seismic anomaly, i.e. a range of seismic anomalies in between two mantle populations corresponds to a similar CMB heat flux. Applying our formalism to the seismic anomalies from the mantle convection simulations provides far superior fits than the commonly used linear fits. The results highlight reduced negative heat flux anomalies beneath large low shear velocity provinces (LLSVPs), while positive heat flux anomalies are enhanced, both with respect to the classical linear interpretation.

Depth-dependent seismic anomalies and potential asperity linked to fluid-driven crustal structure in Garhwal region, NW Himalaya

Characterizing the stress heterogeneity and crustal complexities are essential to understand the important aspects of rupture development and its propagation in a tectonically active region. We analyze a continuous seismic data (1999–2020) to estimate stress drops, b-value, fractal dimension (Dc) and focal mechanisms using a local network of 14 broadband stations. Seismic periodicity on a Himalayan major thrust above locked zone, involves long period of stress accumulation and interseismic strain. There exist a good spatio-temporal-depth correlation between the estimated results which indicates the positive anomaly at 12–14 km (stress transition) beneath the Chamoli region. Interestingly, this region shows maximum geodetic strain rate with comparatively high-stress drop, low coefficient friction value and very low b- (0.583 ± 0.02) and Dc- (1.20 ± 0.01) values. Majority of moderate to strong earthquakes and swarms activity have occurred in this region with maximum crustal accommodation. It is also observed that the significant temporal decrease in b-value always followed by moderate earthquakes. Here shallow crustal potential seismogenic asperity controls the earthquake's stress drop and rupture propagation. The observed correlations strongly support the evidence of entrapped fluid-faults interaction which alters pore pressure and generates numerous ruptures. Also, the role of pressurized entrapped fluids and roughness of fault-plane responsible for low friction zone and microseismicity. Continuous stress accumulation along the fault-plane within the asperity could release significant amount of energy in future.

Variable distribution of subducted oceanic crust beneath subduction regions of the lowermost mantle

Subducted oceanic crust (SOC) is one of the major sources of chemical heterogeneity in Earth's mantle. Previous geodynamic modeling studies have shown that SOC in the lowermost mantle could segregate from subducted slabs and accumulate on the core-mantle boundary (CMB). However, previous models are often simplified in a variety of ways that hinder a comprehensive understanding of the dynamics of SOC in the lowermost mantle. Here, I perform 3D high-resolution geodynamic models with single-sided subduction to study the dynamics of SOC in the lowermost mantle, with a focus on regions beneath subduction zones outside the large-low velocity provinces (LLVPs). I find that the ability of a thin (∼10 km) SOC to segregate from the slab is greatly controlled by the morphology of the slab. The segregation of SOC is much more efficient when the slab in the lowermost mantle is folded backward and extends beneath the subducting plate which allows the SOC to directly face or contact the CMB, than when the slab extends beneath the overriding plate with the SOC at the shallowest portion of the slab. The changes of slab morphology cause strong temporal and spatial variations in the distribution of SOC (1) at the CMB, (2) within 50 km above the CMB, and (3) at ∼50–300 km above the CMB, which, together with its variable degrees of mixing with other mantle materials, may explain the variations of seismic velocities, density, size, shape, and distribution of seismic anomalies in the lowermost mantle outside the LLVPs.

General features of multi-parameter anomalies of six moderate earthquakes occurred near Zhangbei-Bohai fault in China during the past decades

The great Zhangbei-Bohai fault (ZBF) is an important seismic active zone in Northeastern China, which intersects with another great fault, namely Tancheng-Lujiang fault (TLF), in the Central Bohai Sea. Most of the previous studies only investigated the earthquakes (EQs) happened in the west section of ZBF and anomalies appeared in the land area, but few researchers focused on the EQs happened in the east section of ZBF and studied the anomalies appeared above the Bohai Sea. Recently, we have investigated the disturbances on and above the Bohai Sea associated with the Zhangbei Mb5.6 EQ in 1998, whose epicenter located in the west section of ZBF, and found that there was seismicity induced gas release from submarine TLF. To study further the multi-parameter anomalies of EQs near ZBF during past decades and their relationship with ZBF and TLF, a scrutiny strategy for seismic anomaly in the sea area was proposed in this study. After comprehensive screening of EQs occurred near ZBF from 1998 to 2022 using multi-source remote sensing data, potential seismic anomalies including the anomalies of microwave brightness temperature and sea surface roughness on Bohai Sea were found correlated with 6 of the 23 investigated EQs, and there were commonly anomalies of CO and CH4 concentration in the atmosphere. All these seismic anomalies were found developing mainly along the TLF in Bohai Sea, and started usually before shocking, appeared co-seismically and in the next few days. Regional inconsistencies among the distribution of CO and CH4 anomalies could be owning to the specific underwater reservoir in the Bohai Bay Basin. Though analyzing the focal mechanism solutions of the selected EQ cases, we found that the seismic anomaly existed only when the TLF was in a stress state of tensile relaxation.

Anomalous elastic properties of mudrocks bounding reservoirs with high concentrations of naturally occurring CO2

Very high concentrations of CO2 have been encountered in solution as carbonic acid in hydrocarbon reservoirs in parts of the Greater Sarawak Basin, offshore Borneo, Malaysia. Concentrations can exceed 80%. Anomalous features in 3D seismic data also are found in areas with high CO2 concentrations. These features appear as halos around reservoirs, cutting across stratigraphy and indicating a hardening of the nonreservoir rocks within the envelope of the halo. These halos can extend for hundreds of meters above and below a reservoir. Elastic log data from wells that pass through and adjacent to these seismic anomalies indicate that mudrocks within the anomalies have higher densities and velocities than would be predicted from locally derived compaction trends. Combinable magnetic resonance measurements indicate that the anomalous properties are the result of lower-than-expected capillary-bound microporosities. It is proposed that carbonic acid in the reservoir fluids diffuses into the bounding rocks, causing a loss of porosity. The amount of porosity lost depends on the clay content of the mudrock and the initial level of compaction, with shallower, more clay-rich shales able to lose more porosity. The anomalous seismic signatures result from a sharp transition (over approximately 5 m) at the diagenetic front between normal and altered rocks. The alteration can significantly change the amplitude variation with offset response of the reservoirs and therefore the ability to correctly predict fluid phase and reservoir quality. No anomalies are observed when the concentration of CO2 in the reservoir is less than 10% but always present when CO2 exceeds 20%. Therefore, it is possible to map the general distribution of high CO2 concentration from seismic data. There is no indication that the scale, amplitude, or shape of the anomalies gives an indication of the concentration of CO2.

Three-dimensional magnetotelluric inversion for the characterization of the Sol de Mañana high-enthalpy geothermal field, Bolivia

We describe the three-dimensional magnetotelluric modeling results of Laguna Colorada - Sol de Mañana geothermal field in SW Bolivia. It is located near Laguna Colorada in the foothills of the Western Cordillera of the Andes and at the margin of the Altiplano-Puna Magma Body (APMB), which is characterized by a vast electrical conductivity anomaly and corresponding seismic anomalies in the mid and deep crust. The magnetotelluric (MT) data comprising 70 stations were modeled by a 3-D inversion. The final model shows a broad conductor at a few hundred meters in depth, which we interpret as the confining cap layer. Beneath, equally widespread, a layer of intermediate resistivity marks the high-temperature hydrothermal reservoir. Detailed interpretation of MT data with information from existing wells suggests a potential for a high-enthalpy geothermal field.

Grain size reduction by plug flow in the wet oceanic upper mantle explains the asthenosphere's low seismic Q zone

The prominent seismic low-velocity zone (LVZ) in the oceanic low-viscosity asthenosphere is approximately coincident with the low seismic Q zone (LQZ; a zone of high seismic attenuation). Small olivine grain sizes could link these seismic and rheological properties because they reduce viscosity, seismic velocity and seismic Q. Because rock deformation reduces grain sizes, the asthenosphere's seismic properties can place constraints on asthenospheric flow. To determine dominant flow patterns, we develop a self-consistent analytical 1-D channel flow model that accounts for upper mantle rheology and its dependence on flow-modified grain-sizes, water content, and melt fraction, for flow driven by both surface plate motions (Couette flow) and/or horizontal pressure gradients (Poiseuille flow). We find that Couette flow dominates if the upper mantle is dry, and plug flow (a Poiseuille flow for power law rheology) dominates if it is weakened by wet conditions. A plug flow configuration spanning the upper 670 km of the mantle best explains the LQZ in the asthenosphere, and can be attributed to significant grain-size reduction due to extensive shearing across the asthenosphere. This flow configuration also explains high seismic Q values below the asthenosphere associated with minimal shear deformation and large grain sizes above the mantle transition zone. We suggest that the asthenospheric LQZ and LVZ seismic anomalies can be largely explained by grain-size variations associated with plug flow in the wet upper mantle.

Sedimentary deformation relating to episodic seepage in the last 1.2 million years: a multi-scale seismic study from the Vestnesa Ridge, eastern Fram Strait

Seafloor hydrocarbon seepage is a natural fluid release process that occurs worldwide on continental shelves, slopes, and in deep oceanic basins. The Vestnesa sedimentary ridge in the eastern Fram Strait hosts a deep-water gas hydrate system that became charged with hydrocarbons ∼2.7 Ma and has experienced episodic seepage along the entire ridge until a few thousand years ago, when seepage activity apparently ceased in the west but persisted in the east. Although it has been documented that faults and fractures play a key role in feeding the seeps with thermogenic gases, the mechanisms controlling seepage periodicity remain poorly understood. Here we integrate high-resolution P-cable 3D seismic and Chirp data to investigate the spatial and temporal evolution of high-resolution fractures and fluid flow features in the west of the Vestnesa Ridge. We characterize sediment deformation using a fracture density seismic attribute workflow revealing two highly deformed stratigraphic intervals and associated small-scale pockmarks (<20 m diameter). Chronostratigraphic constraints from the region show that these two highly deformed intervals are influenced by at least three major climatic and oceanic events during the last 1.2 million years: the Mid-Pleistocene Transition (∼1.25–0.7 Ma), the penultimate deglaciation (∼130 ka) and the last deglaciation (Heinrich Stadial 1: ∼16 ka). These periods of deformation appear associated with seismic anomalies potentially correlated with buried methane-derived authigenic carbonate and have been sensitive to shifts in the boundary of the free gas-gas hydrate interface. Our results show shifts (up to ∼30 m) in the depth of the base of the gas hydrate stability zone (GHSZ) associated with major changes in ocean bottom water temperatures. This ocean-driven effect on the base of the GHSZ since the Last Glacial Maximum coincides with the already highly deformed Mid-Pleistocene Transition sedimentary interval and likely enhanced deformation and gas leakage along the ridge. Our results have implications for understanding how glacial cycles impact fracture formation and associated seepage activity.

3-D crustal shear wave velocity model derived from full-waveform tomography for Central Honshu Island, Japan

SUMMARY We present a crustal shear wave (S-wave) velocity model for central Japan that accurately captures the previously mapped geology and lithology of the region. We perform a full-waveform tomographic inversion using a large seismic data volume that was recorded by the dense, permanent seismic monitoring network that spans the Japan Islands to resolve the seismic structure beneath central Honshu Island. The inversion reduces the time–frequency phase misfit by 16.4 and 6.7 per cent in the 20–50-s and 10–30-s period ranges, respectively. We infer that the resolved seismic velocity anomalies in our inversion reflect a range of subsurface features, including volcanic fluids, dehydration fluids from the subducted crust and sedimentary basins. In contrast to previous S-wave velocity models of the same region, which have been based primarily on first-arrival tomography, our S-wave velocity model is based on the explicit computation of the full seismic wavefield. This approach makes our model more suitable for modelling seismic wavefields in the 10–50-s period range and enables high-resolution imaging of the subsurface.

Mapping crustal structure across southern Australia using seismic ambient noise tomography

The rocks of southern Australia record over three billion years of Earth’s evolution, but the basement geology is veiled by sediment. Geophysical data are needed to unveil the geology. The 2018–2022 Lake Eyre Basin and 2020–2022 AusArray SA seismic arrays expand seismic coverage in South Australia. In conjunction with permanent and preceding temporary arrays, we extracted Rayleigh wave dispersion data from ambient noise recordings at a total of 501 seismic stations spanning the transition from Precambrian to Phanerozoic Australia. These data were used to develop Rayleigh wave phase velocity maps of southern Australia at periods 3–20s, and in turn, a shear wave velocity model to 20km depth. At upper-crustal depths, low velocity structure tracks Phanerozoic sedimentary accumulations. The Moyston Fault, regarded as the boundary between the Delamerian and Lachlan Orogens, has an intermittent expression in the shear velocity model: it has no obvious expression at depths shallower than ∼10km, but in the mid-crust is marked by a velocity contrast in southern Victoria and a velocity contrast tracing the southern edge of the Darling Basin in western New South Wales. An arcuate velocity contrast characterising the western edge of deep, sediment-filled troughs of the Darling Basin is a candidate for the transition from Precambrian to Phanerozoic crust. Fluid derived from neotectonic metamorphic devolatilization and/or remnant hydrated mantle is our preferred hypothesis for explaining seismicity and coincident seismic and conductivity anomalies in the mid-to-lower crust beneath the Ikara–Flinders Ranges. Our model suggests that the Olympic Dam and Carrapateena IOCG deposits reside above the margin of a mid-crustal low seismic velocity zone. We surmise that this might reflect past metalliferous fluid movement associated with the Olympic Cu-Au Province, akin to low reflectivity and low resistivity zones evident in 2D reflection seismic and magnetotelluric profiles, respectively.

Characteristic identification of seismogenic electromagnetic anomalies based on station electromagnetic impedance

The main components of seismo-electromagnetic research are the deep underground electromagnetic seismogenic environment, electromagnetic field changes at different stages of the seismogenic process, and the physical mechanism and change rules of electromagnetic properties of the earth’s interior. Traditional electric and magnetic methods mainly analyze the single field change of the geoelectric field, geomagnetic field, or resistivity at frequencies less than 1 Hz. These do not include the extremely low-frequency band that is sensitive to seismic events, so it is difficult to obtain the characteristics of time-spatial variations and propagation characteristics precursors. In comparison, magnetotelluric stations observe magnetotelluric fields containing seismogenic-induced electromagnetic disturbances, and the observation frequency band is wide. In this paper, the three-dimensional numerical simulation method is used to calculate the magnetotelluric apparent resistivity anomaly generated by resistivity changes in the seismogenic zone, and the forward algorithm of arbitrarily orientated dipole source in layered earth is used to simulate the response of low-frequency pre-earthquake electromagnetic radiation. The magnetotelluric response including seismogenic resistivity anomaly and pre-earthquake electromagnetic radiation is obtained using the field component composition method. The frequency characteristics and spatial distribution characteristics of apparent resistivity anomalies are systematically analyzed, and the results are of important significance for the observation, data processing, and identification and analysis of seismic electromagnetic anomalies in different seismogenic processes.

Study of the Preparation Phase of Turkey’s Powerful Earthquake (6 February 2023) by a Geophysical Multi-Parametric Fuzzy Inference System

On 6 February 2023, a powerful earthquake at the border between Turkey and Syria caused catastrophic consequences and was, unfortunately, one of the deadliest earthquakes of the recent decades. The moment magnitude of the earthquake was estimated to be 7.8, and it was localized in the Kahramanmaraş region of Turkey. This article aims to investigate the behavior of more than 50 different lithosphere–atmosphere–ionosphere (LAI) anomalies obtained from satellite data and different data services in a time period of about six months before the earthquake to discuss the possibility of predicting the mentioned earthquake by an early warning system based on various geophysical parameters. In this study, 52 time series covering six months of data were acquired with: (i) three identical satellites of the Swarm constellation (Alpha (A), Bravo (B) and Charlie (C); and the analyzed parameters: electron density (Ne) and temperature (Te), magnetic field scalar (F) and vector (X, Y and Z) components); (ii) the Google Earth Engine (GEE) platform service data (including ozone, water vapor and surface temperature), (iii) the Giovanni data service (including the aerosol optical depth (AOD), methane, carbon monoxide and ozone); and (iv) the USGS earthquake catalogue (including the daily seismic rate and maximum magnitude for each day), around the location of the seismic event from 1 September 2022 to 17 February 2023, and these were analyzed. The results show that the number of seismic anomalies increased since about 33 days before the earthquake and reached a peak, i.e., the highest number, one day before. The findings of implementing the proposed predictor based on the Mamdani fuzzy inference system (FIS) emphasize that the occurrence of a powerful earthquake could be predicted from about nine days to one day before the earthquake due to the clear increase in the number of seismo-LAI anomalies. However, this study has still conducted a posteriori, knowing the earthquake’s epicenter and magnitude. Therefore, based on the results of this article and similar research, we emphasize the urgency of the creation of early earthquake warning systems in seismic-prone areas by investigating the data of different services, such as GEE, Giovanni and various other global satellite platforms services, such as Swarm. Finally, the path toward earthquake prediction is still long, and the goal is far, but the present results support the idea that this challenging goal could be achieved in the future.