Fault Depth Research Articles

New source model for the 1771 Meiwa tsunami along the southern Ryukyu Trench inferred from high-resolution tsunami calculation

The 1771 Meiwa tsunami which struck the southern Ryukyu Islands (Sakishima Islands) had greater than 22 m run-up height, leaving about 12,000 casualties in its wake. At many places, the tsunami inundation or lack of inundation is well recorded in historical documents. Several tsunami source models have been proposed for this event using historical records as constraints of tsunami calculations. Nevertheless, the source model remains under discussion. This study re-evaluated the tsunami wave source model of the 1771 Meiwa tsunami using high-resolution (10 m mesh) bathymetric and topographical data for tsunami calculation, the latest historical record dataset, and seismological knowledge. Results demonstrated that a tsunami earthquake along the southern Ryukyu Trench was the likely cause of the 1771 event. However, it is noteworthy that assumption of a large slip with 30 m is necessary for a shallow and narrow region (fault depth = 5 km, fault width = 30 km, Mw = 8.49) of the plate boundary in the Ryukyu Trench, which is far larger than previously thought. This requirement of very large initial water level change at the source might involve not only the fault rupture along the plate boundary but also deformation by splay faults, inelastic deformation of unconsolidated sediments near the trench axis, and/or giant submarine landslides. Results also show that the effects of fault parameters on the run-up were quite different depending on the offshore coral reef width. This phenomenon strongly constrained the fault width to 30 km. Our tsunami ray tracing analysis further revealed the effects of bathymetry on tsunami propagation. It is noteworthy that meter-long huge tsunami boulders tend to be distributed along the specific coasts at which the tsunami was concentrated by bathymetric effects. This finding suggests that past tsunamis, including the 1771 event, might have affected the specific coral reefs on Sakishima Islands repeatedly, which is crucially important for understanding the heterogeneous distribution of tsunami boulders. This feature might also be useful to elucidate the effects of large tsunamis on the corals and reefs because a direct comparison of coral reefs that are damaged and not damaged by tsunami waves is testable in narrow areas in the case of the Sakishima Islands.

Age of folding in NW Lurestan arc across the Khanaqin fault by magnetostratigraphy on Aghajari growth strata, Zagros folded belt

The timing of deformation and the age of sediments in foreland basins are key information for reconstructing the tectonic history of orogenic belts. This study, utilized magnetostratigraphic techniques to determine the ages of ∼ 2.5 km-thick strata within the Zagros folded foreland basin in the flank of the NW-SE-trending Emam Hassan anticline, located above the N–S-trending Khanaqin blind basement fault. This fault separates the Lurestan arc in Iran from the Kirkuk embayment in Iraqi Kurdistan. These ages were combined with a detailed structural study to establish the timing of folding and integrate it into the regional framework of the Zagros folded belt. Magnetostratigraphic results indicate a Serravallian age at ∼ 13.4 Ma for the stratigraphic boundary between the Gachsaran Formation and the pre-growth Aghajari Formation, whereas the base of the Aghajari growth strata is Tortonian age (early Late Miocene) at ∼ 10 Ma. The mean sediment accumulation rate for the Aghajari Formation is ∼ 44 cm/kyr, with short peaks reaching up to 90 cm/kyr. Linear extrapolation of these rates proposes a younger age than ∼ 6.5 Ma (Messinian) for the base of the unconformable conglomerates of the Bakhtyari Formation. The Emam Hassan folding and related Gachsaran diapirism began ∼ 10 Ma and continued for at least 3.5 Myr until ∼ 6.5 Ma, coevally with the deposition of ∼ 1.3 km of the upper Aghajari Formation. Regional synthesis reveals that multi-detachment folding within the Lurestan arc propagates in-sequence towards the foreland. Although not the central focus of this study, our results, combined with the regional structural understanding, illustrate the potential 3-D structure at the depth of the seismogenic Khanaqin Fault, the source of the 2017 Mw 7.3 Sarpol-e Zahāb Earthquake.

Magmatism controls global oceanic transform fault topography

Oceanic transform faults play an essential role in plate tectonics. Yet to date, there is no unifying explanation for the global trend in broad-scale transform fault topography, ranging from deep valleys to shallow topographic highs. Using three-dimensional numerical models, we find that spreading-rate dependent magmatism within the transform domain exerts a first-order control on the observed spectrum of transform fault depths. Low-rate magmatism results in deep transform valleys caused by transform-parallel tectonic stretching; intermediate-rate magmatism fully accommodates far-field stretching, but strike-slip motion induces across-transform tension, producing transform strength dependent shallow valleys; high-rate magmatism produces elevated transform zones due to local compression. Our models also address the observation that fracture zones are consistently shallower than their adjacent transform fault zones. These results suggest that plate motion change is not a necessary condition for reproducing oceanic transform topography and that oceanic transform faults are not simple conservative strike-slip plate boundaries.

Influence of mantle plume on continental rift evolution: A case study of the East African rift system

Mantle plume is an essential component of the mantle convection system, and its influence on the geodynamics of continental rifts is of great significance for understanding the crust–mantle interaction. The East African Rift System, as the largest continental rift in the Cenozoic and in the initial stage, provides an excellent option for studying the interaction between the mantle plume and the continental crust. Based on the data such as GPS, seismic tomography, and global crustal model, a viscoelastic-plastic 2D thermodynamic numerical model is established to reconstruct the evolution of the Afar depression, Ethiopian Rift, and Kenyan Rift. By comparing the differences between the models of the Afar depression, Ethiopian Rift, and Kenyan Rift, the relationship between the mantle plume and pre-existing structures and their influence on the evolution of continental rifts are discussed. The results show that the mantle plume can increase the depth of the rift faults, concentrate the distribution of the faults, and strengthen the control of main faults on the rifts, allowing the possibility of narrow rifts. Pre-existing structures control the fault styles and symmetry of the rifts and also the morphology of the mantle plume.

Application of Regional Gravity and Magnetic Data in Yambajan and Gudui Geothermal Fields, Tibet

Yambajan geothermal field is the first wet steam field developed in the Chinese mainland. It is also the geothermal power station with the highest elevation in the world. It is rich in geothermal resources and its exploration and development level is relatively high. The Gudui geothermal field is the second largest geothermal display area in Tibet. It is rich in geothermal resources, second only to Yambajan Geothermal field, but its energy construction is relatively backward. In this paper, satellite gravity and aeromagnetic data are used to make a comprehensive comparative analysis of the two regions. The results show that they are both low gravity value areas and weak magnetic, and both of which are located on the fault zone. There is a very obvious relationship between the regional tectonic characteristics and the distribution law of hydrothermal activities, and the tectonic activities provide favorable conditions for the formation of hydrothermal activities. The fault depth in the south of the study area is deeper than that in the north, which is inferred to be caused by plate movement.

Coseismic and Early Postseismic Slip of the 2021 Mw 7.2 Nippes, Haiti, Earthquake: Transpressional Rupture of a Nonplanar Dipping Fault System

Abstract On 14 August 2021, an Mw 7.2 earthquake struck Nippes, Haiti, 11 yr after the devastating 2010 Mw 7.0 Port-au-Prince earthquake. This earthquake occurred in a remote region where the structure at the depth of the main boundary Enriquillo Plantain Garden fault (EPGF) is less known. Using Synthetic Aperture Radar imagery, we retrieve the coseismic and early postseismic deformation of the 2021 Haiti earthquake to constrain its fault geometry and slip distribution. Our modeling results show that the 2021 earthquake ruptured the high-angle Ravine du Sud fault and a bend fault ∼64° dipping to the north at depth. Although not only conclusive, the combination of coseismic and postseismic deformation, along with geomorphic features, and relocated aftershocks, suggest a nonplanar fault structure with significant variations in dip angles along both the depth and track of the EPGF in this region. East of the epicenter, we document a 25 km section along the EPGF that crept for ∼15 days. This distribution of aseismic slip utilizing stacked deformation indicates that only a small fraction of the accumulated strain near the surface was released during the earthquake, suggesting a high potential for seismic hazard in the region along the EPGF from the ruptured segment to the east, before reaching the 2010 rupture.

Near surface sediments introduce low frequency noise into gravity models

3D geologic modeling and mapping often relies on gravity modeling to identify key geologic structures, such as basin depth, fault offset, or fault dip. Such gravity models generally assume either homogeneous or spatially uncorrelated densities within modeled rock bodies and overlying sediments, with average densities typically derived from surface and drill-hole sampling. The noise contributed to the gravity anomaly by these density assumptions is zero in the homogeneous case and typically <200 μGal in the uncorrelated case. Rock bodies and sediments, however, show both a range of densities and spatial correlation of these densities, in both surface and drill-hole samples, and this correlation causes an increase in power in the low frequency content of the resulting gravity anomaly. Spatial correlation of densities can be modeled as a Gaussian random field (GRF), with the random field parameters derived from drill-hole and geologic map data. Data from alluvial fan sediments in southern Nevada indicate correlation lengths of up to 300 m in the vertical dimension and kilometers in the horizontal dimension. The resulting GRF density models show that the noise contributed to the measured gravity anomaly is of low frequency and can be several mGal in amplitude, contradicting the common attribution of lower frequencies to deeper sources. This low-frequency noise increases in power with an increase in sediment thickness. Its presence increases the ambiguity of interpretations of subsurface geologic body shape, such as basin analyses that attempt to quantify concealed basement fault depths, offsets, and dip angles. In the southwestern United States, where basin analyses are important for natural resource applications, such ambiguity increases the uncertainty of subsequent process modeling.

Focal Mechanism and Regional Fault Activity Analysis of 2022 Luding Strong Earthquake Constraint by InSAR and Its Inversion

On 5 September 2022, an Ms6.8 magnitude earthquake occurred in Luding County, Sichuan Province, China. Based on Sentinel-1 SAR images, this paper uses the D-InSAR approach to obtain the displacement field of the earthquake, invert the coseismic sliding distribution, and then calculate the static coulomb stress changes of the coseismic deformation on the aftershock distribution and surrounding faults. Further, the seismic structure is analyzed and discussed. The InSAR coseismic deformation field demonstrates that the maximum LoS displacement of the surface deformation caused by the Luding earthquake is about 15 cm. The Luding Ms 6.8 earthquake is dominated by the Moxi fault, which is a left-lateral strike-slip fault that ruptures along the NNW-SSE trend at about 160.3°, and the dip is 81°. The fault depth is mainly 5~15 km, the maximum sliding amount is about 174.8 cm, and the corresponding depth is 8.5 km. The seismic moment tensor obtained by inversion is 1.06 × 1019 Nm, Mw = 6.65. The Coulomb stress generated by the Luding earthquake on the northern end of the Anninghe fault zone exceeded the trigger threshold. The risk of the Anninghe fault’s future earthquake was greater, and continuous monitoring and risk assessment were required.

Efficient DCNN-LSTM Model for Fault Diagnosis of Raw Vibration Signals: Applications to Variable Speed Rotating Machines and Diverse Fault Depths Datasets

Bearings are the backbone of industrial machines that can shut down or damage the whole process when a fault occurs in them. Therefore, health diagnosis and fault identification in the bearings are essential to avoid a sudden shutdown. Vibration signals from the rotating bearings are extensively used to diagnose the health of industrial machines as well as to analyze their symmetrical behavior. When a fault occurs in the bearings, deviations from their symmetrical behavior can be indicative of potential faults. However, fault identification is challenging when (1) the vibration signals are recorded from variable speeds compared to the constant speed and (2) the vibration signals have diverse fault depths. In this work, we have proposed a highly accurate Deep Convolution Neural Network (DCNN)–Long Short-Term Memory (LSTM) model with a SoftMax classifier. The proposed model offers an innovative approach to fault diagnosis, as it obviates the need for preprocessing and digital signal processing techniques for feature computation. It demonstrates remarkable efficiency in accurately diagnosing fault conditions across variable speed vibration datasets encompassing diverse fault conditions, including but not limited to outer race fault, inner race fault, ball fault, and mixed faults, as well as constant speed datasets with varying fault depths. The proposed method can extract the features automatically from these vibration signals and, hence, are excellent to enhance the performance and efficiency to diagnose the machine’s health. For the experimental study, two different datasets—the constant speed with different fault depths and variable speed rotating machines—are considered to validate the performance of the proposed method. The accuracy achieved for the variable speed rotating machine dataset is 99.40%, while for the diverse fault dataset, the accuracy reaches 99.87%. Furthermore, the experimental results of the proposed method are compared with the existing methods in the literature as well as the artificial neural network (ANN) model.

Thin-skinned and thick-skinned tear faults in central Tarim Basin

Currently, the interpretation scheme for strike slip faults in the central Tarim Basin does not typically take into account the depth of tear faults. This paper specifically explores this aspect, focusing on two tear faults (Nos. 4 and 7) to examine the thick-skinned and thin-skinned systems in the area. By utilizing high-resolution seismic data, we discovered that No. 4 Fault is a thick-skinned tear fault whereas No. 7 Fault is a thin-skinned tear fault. Additionally, we have calculated the strata shortening data for both Nos. 4 and 7 Faults to further our understanding of these systems. For No. 4 Fault, we observed shortening differences between the western and eastern sections in both the supra- and sub-salt strata, whereas for No. 7 Fault, we observed shortening differences only in the supra-salt strata. We demonstrated that under the action of thrusting, a tear fault could penetrate the salt layer if there is a shortening difference in the different positions of the sub-salt strata. A lack of shortening difference in the sub-salt strata implies that a tear fault should be thin-skinned which cannot penetrate the salt layer, even though the sub-salt strata may be deformed during thrusting.

Characteristics of consecutive tsunamis and resulting tsunami behaviors in southern Taiwan induced by the Hengchun earthquake doublet on 26 December 2006

Abstract. Consecutive ML 7.0 submarine earthquakes occurred offshore of the Hengchun Peninsula, Taiwan, on 26 December 2006. A small tsunami was generated and recorded at tide gauge stations. This important event attracted public interest, as it was generated by an earthquake doublet and produced a tsunami risk for Taiwan. This study analyzed tide gauge tsunami waveforms and numerical simulations to understand the source characteristics and resulting behaviors of tsunamis. The maximum wave heights at the three nearest stations were 0.08 m (Kaohsiung), 0.12 m (Dongkung), and 0.3 m (Houbihu), and only Houbihu recorded the first wave crest as the largest. The tsunami duration was 3.9 h at Dongkung and over 6 h at Kaohsiung and Houbihu. Spectral analyses detected dominant periodic components of spectral peaks on the tsunami waveforms. The period band from 13.6–23.1 min was identified as the tsunami source spectrum, and the approximate fault area for the consecutive tsunamis was estimated to be 800 km2, with central fault depths of 20 km (first earthquake, Mw 7.0) and 33 km (second earthquake, Mw 6.9). The focal mechanisms of the first earthquake, with a strike of 319∘, dip of 69∘, and rake of −102∘, and the second earthquake, with a strike of 151∘, dip of 48∘, and rake of 0∘, could successfully reproduce the observed tsunami waveforms. Numerical simulations suggested that the tsunami waves were coastally trapped on the south coast of Taiwan during the tsunami's passage. The trapped waves propagated along the coast as edge waves, which repeatedly reflected and refracted among the shelves, interfered with incoming incident wave, and resonated with the fundamental modes of the shelves, amplifying and continuing the tsunami wave oscillation. These results elucidated the generation and consequential behaviors of the 2006 tsunami in southern Taiwan, contributing essential information for tsunami warning and coastal emergency response in Taiwan to reduce disaster risk.

Contemporary Velocity Field for Turkey Inferred from Combination of a Dense Network of Long Term GNSS Observations

The Anatolia?Aegean domain represents a broad plate boundary zone, with the deformation accommodated by major faults bounding quasi-low deforming units. First-order features of this deformation were obtained in the form of a GNSS-derived velocity field. During the last decade, the accuracy of velocity solutions was improved, and the expansion of continuous networks increased spatial resolution. Nonetheless, an accurate representation of the deformation field requires interstation distances much lower than the locking depth of nearby faults, which has not yet been satisfied. The basis for creating a precise and accurate velocity field is uniform processing of the time series recorded both in the campaign and permanent GNSS stations, at once and for a single reference system. Although for Anatolia the data density has increased 6-fold since the landmark work of Reilinger et al. (2006), this crucial integration has not been made. We aim to fill this gap by analyzing the data and providing a uniform velocity solution. In this study, we processed the time series of 836 stations, of which 178 are published for the first time. With a period of up to 28 years, we present the most accurate velocity field with increased spatial and temporal resolution and homogeneity. We used the improved coverage of the velocity field to calculate strain accumulation on the North and East Anatolian Faults. Modelled slip rates vary between 20 and 26 mm/yr and 9.7 and 11 mm/yr for the North and East Anatolian faults, respectively. The data can better constrain the kinematics of continental deformation, provide accurate boundary conditions for dynamic models, and help test outstanding hypotheses about the kinematics of the Anatolia-Aegean domain.

Two-step classification of highly mixed oil in the Qikou Sag (Bohai Bay Basin, China): Implications for origin, maturity, and biodegradation

Mixing of crude oil leads to unpredictable changes in the property and composition of mixtures, bringing uncertainties to petroleum production. Therefore, it is crucial to reveal the origin, maturity, and biodegradation of mixed oil during the exploration stage. Here we address these issues using the highly-mixed oil from the Qikou Sag (Bohai Bay Basin, eastern China) after a two-step classification. Firstly, the highly-mixed oil was classified into two groups (groups I and II) according to their physical property (API gravity and sulfur content), molecular composition, and gas chromatograms of saturated hydrocarbons. Secondly, the group I oil was further divided into two sub-groups (groups I-1 and I-2) based on the principal component analysis (PCA) and hierarchical cluster analysis (HCA) of biomarkers (including n-alkanes, isoprenoids, terpenoids, and steroids). The group I oil is non-biodegraded, in which the group I-1 oil from deep reservoirs is a mixture of hydrocarbons from three sets of source rock, whereas the group I-2 oil from shallow reservoirs is mixed by hydrocarbons from five sets of source rock. Maturity parameters of biomarkers suggest that the group I oil is thermally mature. The group II oil was slightly (PM 1–2) to severely (PM 4+) biodegraded, as indicated by low API gravity, high percentages of asphaltenes and NSO, high ratios of Pr/n-C17 and Ph/n-C18, and the assignment of UCM and 25-norhopane. The burial depth of reservoirs and secondary faults (formed after the Neogene) are the primary controlling factors for the biodegradation. Our results demonstrate that the two-step classification facilitates the grouping of highly mixed oil, which provides a basis for indicating their origin, maturity, and biodegradation. The results also provide guidance for regional petroleum exploration and production.

Thrust faulting on Venus: Tectonic modeling of the Vedma Dorsa Ridge Belt

Radar images from the Magellan mission reveal compressional ridge belts transecting several low-lying plains on Venus, including Atalanta, Vinmara, Lavinia, and Rusalka/Llorona/Vellamo Planitiae. Vedma Dorsa is an ∼1800 km long ridge belt with 0.5–1 km of relief in Llorona/Vellamo Planitiae. We analyze sections of the ridge belt that have an asymmetric topographic cross section, indicative of deep thrust faulting and shallow folding as the dominant formation mechanisms. We perform elastic dislocation and Monte Carlo tectonic modeling of thrust faulting at several locations along Vedma Dorsa to constrain the fault displacement (D), depth of faulting (z), and fault dip (θ). We find that the models are consistent with blind thrust faulting and folding as the dominant mechanism for producing Vedma, with preferred fault parameters of D ∼ 1–2 km, z ∼ 10–25 km, and θ ∼ 25–30°. The results support an upper fault tip >3 km below the surface (blind fault), and a change in dip at depth. Our preferred models and the additional fault complexities supported at each site suggest that this section of Vedma is an intermediate structure between lobate scraps and fold and thrust belts, incorporating morphometric aspects from both classifications. Observations of terrestrial fault depths and the best-fitting depth of faulting from our models lead to an estimated heat flux of 16–39 mW m−2 at the time of Vedma Dorsa's formation, consistent with formation over a cold, downwelling region of the mantle.

Geoelectrical model of geothermal spring in Ie Jue Seulawah deriving from 2D VLF-EM and DC resistivity methods

Seulawah Agam is one of the volcanic areas in Aceh province, Indonesia, which planned for a powerplant constriction with an energy capacity expected to be approximately 230 MWe. This volcano has seven manifestations in the form of craters, hot water, and heated soil. The hydrothermal system in this volcano is controlled by a fault system which acts as a medium for the entry and exit of fluids. Therefore, understanding the local geology is required for geothermal power plant development, especially for the determination area for injection and production wells. In this research, we use the Very Low-Frequency Electromagnetic (VLF-EM) methods combined with electrical resistivity tomography data on the Ie Jue manifestation area to determine the shallow structure related to the manifestation. The VLF was made for 4 profiles with 700 m length for each VLF-EM profile and 300 m for electrical resistivity lines. We utilized the Karous Hjelt filter for qualitative interpretation, while Occam's algorithm was applied for 2D inversion of data for quantitative analysis of VLF-EM data. Based on the current density model, several vertical conductive anomalies can be well demonstrated at a distance of 300-400 m from the four VLF profiles. The conductive anomaly can also be seen in the resistivity data from the electrical resistivity. The results of the Occam model show that the depth of faults and fractures is seen at 30 m depth with low resistivity (below 100 Ωm). This anomaly is generally associated with outcrops in the field, such as fumarole and warm ground on the east side of the manifestation area. In addition, the 2D inversion model of VLF also shows the contrast of several fracture zones as a place for fluid to enter and exit the Seulawah volcano. Therefore, based on our result, it can be summed up that this method is effectively applied to geothermal in high terrain areas such as in Indonesia and can be used to suggest safe locations for injection wells and production of geothermal drilling.

Slip Rate of Kumering Fault in Lampung Province Calculated from GPS Data from 2007 to 2021

Kumering Fault in Lampung Province is a segment of SFZ that was tectonically active region that had generates large earthquakes. The earthquake hazard around Kumering Fault can be estimated by understanding slip rate of Kumering Fault. This research aim is to estimate slip rate of Kumering Fault by using GPS data from 2007 to 2021. GPS data used in this research are 6 periodic GPS sites and 1 continuous Sumatran GPS Array site. GPS data is processed to obtain daily solution coordinates which are used to calculate velocity by using least-square method of linear regression. Fault parallel velocities are calculated to estimate slip rate and locking depth of Kumering Fault. The The process to obtain slip rate is using grid-search method by finding best fit velocities for all GPS sites. The velocities of GPS sites indicate Sundaland Plate movement. Fault parallel velocities shows the typical movement of right-lateral Kumering Fault. The slip rate of Kumering Fault estimated from this study is 18.2 ± 10 mm/year while the locking depth of the Kumering Fault is 17 ± 3 km. It proves that SFZ is rigid block. However, building more GPS sites in area study is mandatory to obtain better result.

Probabilistic tsunami hazard analysis for western Makran coasts, south-east Iran

Makran subduction zone, along the southern coasts of Iran and Pakistan, has a wide potential seismogenic zone and may be capable of generating large magnitude (M ~ 9) tsunamigenic earthquakes. Considering ambiguities exist in tsunamigenic source characterization for subduction megathrusts like Makran, where detailed geologic, seismic, and geodetic data are insufficient, the probabilistic tsunami hazard analysis (PTHA) is the most prevalent approach to handle uncertainties and estimate more reliable tsunami hazard. Here, PTHA is performed for the coastal region of the western Makran, south-eastern Iran. Using the logic tree approach, we have considered the uncertainty of maximum seismic magnitude, earthquake occurrence model, continuity of seismic zone, seismic coupling coefficient, rupture depth, presence or absence of splay faults, fault locations, and fault slip distribution in PTHA calculation for the western Makran region. We have derived uniform tsunami hazard maps for two return periods of 475 and 2475 years for two confidence levels, the mean and the 84th percentile. Ground subsidence effects are also evaluated in a probabilistic manner. According to the PTHA results, Chabahar and Sirik towns are at the highest and lowest tsunami risk, respectively.

Observation and Study of Lithospheric Magnetic Anomalies on Profile SD in Mongolia

To understand the deep tectonic environment at the origin of strong earthquakes along the northern section of the North-South seismic belt and the central continental block of Mongolia, large-scale gravity and geomagnetic surveys and rock sample collection were carried out along the Suhbaatar-Ulaanbaatar-Dalandzadgad profile in Mongolia. The spatial distribution characteristics of the lithospheric magnetic field at 160 geomagnetic measuring points along the profile were then systematically analyzed and summarized. Based on the composition of the lithospheric magnetic field from different sources at different depths combined with the regional geological structure and collected rock sample lithology, the lithospheric magnetic field was further decomposed into different components—the basement, middle layer, and shallow surface—by the upward continuation method. The results show that these components have obvious zoning characteristics and that the lithospheric magnetic field distribution of the Suhbaatar-Ulaanbaatar-Dalandzadgad profile is related to the geological structure, rock lithology, seismic activity, natural remanent magnetization, and magnetic susceptibility. Many destructive earthquakes have occurred in the area where the lithospheric magnetic field changes dramatically, the lithologies are dominantly igneous, and the magnetic susceptibility and natural remanent magnetization are high. In contrast, the lithologies in the area with moderate variation in the lithospheric magnetic field are mostly sedimentary, the magnetic susceptibility and natural remanent magnetization are low, and destructive earthquakes are rare. Since the lithospheric magnetic field reflects the magnetic characteristics of the rocks above the Curie interface, its spatial distribution not only corresponds to the geological structure but also predicts the depth and location of faults. Therefore, it is significant to carry out geomagnetic surveys and rock sampling to analyze the characteristics of geological structures and research regional seismicity.

Gravity and electrical resistivity analysis of deep and shallow structures related to aquifers within the Jeffara Plain, southeast Tunisia

The aquifers under the Jeffara Plain in southeastern Tunisia is a complex aquifer system consisting of interconnected shallow and deep aquifers within Triassic and younger sediments. The extent of the aquifers is only roughly known, so a gravity and electrical resistivity analysis was undertaken to aid for determining the aquifers extent. The gravity analysis consisted of creating a residual gravity anomaly map, a power spectrum analysis to determine the depth to density sources and a 3D Euler deconvolution analysis to locate lineaments and the depth of density sources. The gravity analysis was used to infer the location and depth of faults and thicker portions of the aquifer containing sediments The electrical resistivity survey was used to characterize the geometry and the depth of deep and shallow aquifers surrounding Medenine city. The residual gravity anomaly map identified a series of northwest-trending gravity minima related to grabens. The Euler deconvolution determined faults can be classified into deep faults (˃ 2.5 km depth) that these associated with the Medenine fault and nearly determined offshoots that trend north-northeast, shallow (0.5–1.0 km) and near surface faults (<0.5 km). The shallow and the near-surface faults involve Upper Cretaceous and younger sediments and trend in a variety of directions. The electrical resistivity models indicate that the shallow aquifers are approximately 20 m thick and the deep aquifer is found below 25 m in depth and is at least 30 m thick. The shallow aquifers were found on all four models but the deep aquifer was found only on two profiles. The location of both the shallow and deep aquifers were affected by faults inferred by the electrical resistivity data and these faults were correlated with lineaments determined by the gravity analysis. This shows that the shallow/near surface faults are important conduits between the shallow and deep aquifers. The most important fault was the Medenine and its newly deduced offshoots as the electrical resistivity models indicate that these faults act as a barrier for the deep aquifer. Based on both the gravity analysis and the electrical resistivity models, the extent of the deep aquifer can be extended further to the east than was previously known.

Results of geological and geophysical study of the deep structure of Angara and Trans-Baikal mantle plumes and their connection with mineral deposits.

The purpose of the article is to consider the issues of geological and geophysical interpretation of the data of balloon and satellite magnetic measurements along the regional profile crossing the territory of the Angara-Baikal region. In order to conduct scientific research along the regional Trans-Siberian geological and geophysical profile A-B the author used various geological and geophysical materials including the magnetic field digital data measured by the MAGSAT artificial Earth satellite and a balloon; data on the values of the electrical resistivity in the mantle of this region; geothermal data; seismic data on the location of earthquake hypocenters in the area of the profile under investigation. The research methods involved multilevel measurements of satellite and balloon magnetic fields, which significantly expanded the possibilities of geological and geophysical interpretation of the data obtained. The conducted study revealed that the geological and geophysical interpretation of multilevel aeromagnetic data allows for a reasonably accurate determination of the location coordinates and lithospheric penetration depth of tectonic faults associated with the Angara and Trans-Baikal mantle plumes, which are of significant interest in terms of exploration of coal and uranium deposits. The spatial and depth characteristics of tectonic faults obtained from balloon and satellite data are confirmed by a set of analyzed independent geophysical data: magnetotelluric sounding, geothermy, seismology and other geophysical methods. In conclusion it should be noted that the author has demonstrated the application possibility of satellite and balloon magnetic surveys for the study of the deep structure of the Angara and Trans-Baikal mantle plumes. In addition, it was found out that according to balloon and satellite magnetic data, large deep tectonic faults in the lithosphere (Barguzinsky, Ikatsky, Tukolamsky, Tungirsky) can be identified, which also allow marking various subhorizontal boundaries of lithospheric layers in the location area of the Angara and Trans-Baikal mantle plumes using special points of the magnetically active zones of these faults. The practical significance of the conducted research is in the identification of the spatial relationship between the location of the Angara mantle plume and coal deposits of the Irkutsk basin, as well as uranium deposits in the zone of the Trans-Baikal mantle plume.