Moho Depth Research Articles

INSIGHTS INTO THE MOHO DEPTH VARIATIONS AND CRUSTAL CHARACTERISTICS IN THE GUELMA–CONSTANTINE BASIN, NORTHEASTERN ALGERIA: A SHORT-PERIOD SEISMIC-RECEIVER-FUNCTION PERSPECTIVE

Teleseismic receiver functions (RF) were extracted from data collected at eight short-period, three-component seismic recording stations over the Guelma–Constantine Basin, northeastern Algeria, to improve the understanding of crustal structure and geodynamic processes. The H-κ stacking method was used to determine the Moho depths and average vP/vS ratios at each station. Careful linear inversion of RF was performed to determine the most appropriate average shear-wave and P-wave velocity profiles at each site. Both methods have yielded highly congruent results, with Moho depths showing robust correlations with previous seismological and geophysical studies. The previously observed pattern of the increasing Moho depth from north to south in the Tell Atlas has been confirmed. Furthermore, the identified transitional nature of the Moho in the Constantine Basin is consistent with a recent study. In addition, we identify a low-velocity zone (LVZ) at approximately 20 km depth within the southern Guelma Basin, confirming previous results in the Constantine Basin and suggesting an eastward elongation of the LVZ, at least into the southern periphery of the Guelma Basin. Examination of data from the northern tip of the Hammam Debbagh–Roknia NW–SE fault, the western boundary of the Guelma pull-apart basin, revealed a shallow Moho depth (22 km), less than the basin average depth of 25 km. The LVZ observed in the lower crust (12 km) suggests the presence of partial melts, consistent with gravimetric and chemical analyses of hydrothermal sources in the area. The extensional tectonic activity along this boundary, coupled with the low-viscosity zone and low average vP/vS ratio, is potentially associated with delamination processes. The effectiveness of our approach underscores its potential as a viable alternative or complementary method for investigating variations in the Moho depth.

The Distribution of Surface Heat Flow on the Tibetan Plateau Revealed by Data‐Driven Methods

AbstractSurface heat flow (SHF) serves as a vital parameter for assessing the heat transfer from deep Earth to the surface, which can provide crucial insights into internal geodynamic processes. As the “roof of the world,” the Tibetan Plateau and its tectonic evolution are highly important in terms of global climate change and geodynamic study. However, a comprehensive understanding of the SHF distribution across most regions of the Tibetan Plateau is limited due to sparse measurement data. To surmount this limitation, a spatially intelligent approach has been developed: The geographically neural network weighted regression with enhanced interpretability (EI‐GNNWR). This method integrates spatial heterogeneity and nonlinear interactions between geophysical and geological factors to predict the SHF distribution across the Tibetan Plateau. In this study, the EI‐GNNWR model is used to accurately predict SHF across the entire region. After evaluating the effectiveness and interpretability of the EI‐GNNWR model, our results demonstrate that medium to high SHF values are predominantly concentrated in the southern, northeastern, and southeastern sectors of the Tibetan Plateau. These observations suggest that the formation of zones with high SHF values may be strongly influenced by the Moho depth, ridges, topography, and average curvature of satellite gravity gradients. Especially, higher SHF values may indicate more profound geodynamic activities such as collisional orogeny, shear deformation zones, or lithospheric extension. These findings offer novel insights into the spatial patterns of SHF and deepen our understanding of the geothermal formation mechanisms driven by underlying tectonic activities.

Insights into the North Patagonian Massif Lower Crust: Petrology and Microstructure of Granulite Xenoliths

Abstract The continental lower crust constitutes a key zone for understanding the mantle–crust magmatic and mechanical transfers, but its study is hampered by the paucity of lower crust samples. Here, we characterise the petrological, geochemical and petrophysical processes structuring the lower crust of the North Patagonian Massif (NPM; Argentina) using a suite of representative mafic granulite and websterite xenoliths. These xenoliths were entrained by alkaline lavas from five volcanic centres that erupted between the Oligocene and Pleistocene. Electron microprobe and Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICPMS) were used to obtain in situ geochemical data on the minerals, while microstructural data were obtained by Electron BackScatter Diffraction (EBSD). Both granulites and websterites display a granoblastic texture and sometimes a weak inherited magmatic layering. Mafic granulite xenoliths show a plagioclase + clinopyroxene ± orthopyroxene assemblage commonly associated with spinel or titanomagnetite. Websterite xenoliths show an association of clinopyroxene + orthopyroxene + spinel, along with accessory plagioclase. Mafic granulites and websterites have SiO2 contents ranging from 44 to 53 wt %, while their Mg# varies from 53 to 79. Clinopyroxenes are characterised by weak convex upward chondrite-normalised Rare Earth Elements - REE patterns (Light-REE </<< Mid-REE > Heavy-REE) which are similar to clinopyroxene phenocrysts and megacrysts from intra-plate basalts. Calculated liquid in equilibrium with clinopyroxene have similar REE patterns to those found in Cenozoic basalts from the NPM, suggesting that the xenolith suite represents evidence for underplating processes, possibly related to one of the magmatic events that have occurred in the NPM since the Permo-Trias. Mafic granulites and websterites show a weak mineral shape preferred orientation and an associated weak Crystal Preferred Orientation (CPO) related to the magmatic layering. Recorded plastic deformation is associated with the activation of both (100)[001] and (001)[100] slip systems in clinopyroxene, (100)[001] in orthopyroxene and (010)[001] in plagioclase. However, the activation of slip systems is generally not correlated with CPO in granulites, suggesting that the lower crust underwent subsolidus equilibration and weak plastic deformation in an inactive tectonic context, thereby preserving an inherited magmatic layering. Two-pyroxene (Fe–Mg) thermometer and pseudosection calculations define P–T conditions of the main paragenesis at 760°C to 1120°C and 7.2 to 10.3 kbar, which allows to define the Cenozoic geotherm of the NPM crust at 30°C/km and to reconsider the petrologic Moho depth at ca. 40 km.

Moho Depth and Crustal Velocity Structure Beneath Stations RTC and TAM from Teleseismic Receiver-Function Analysis

We apply the P-wave receiver-function technique to invert teleseismic data to investigate the S- wave velocity structure beneath stations RTC and TAM in West Africa. Teleseismic waveform receiver function analysis is a widely used technique for studying crustal structure beneath broadband seismic stations. Our results show that the crust beneath RTC is relatively complex with large velocity fluctuations. In the upper crust, a low velocity layer extends from 8 to 12 km deep. At Tamanrasset crustal structure east and west of the station differ. We find a high-velocity zone between 2 and 8 km to the east that we attribute to a high conductivity unit corresponding to intrusions described in the literature. We find no similar feature west of the station. Our velocity models for RTC and TAM are consistent with their differing tectonic environments. TAM, on a stable craton, displays a fairly homogeneous velocity structure while RTC, on thick sediments in an ocean-continent transition zone, has more heterogeneous structure. This structural difference is reflected as well by the depth to Moho, ~20 km at RTC and nearly 38 km at TAM, although both have gradational velocity increases with depth.

Crustal structure of the Bushveld complex, South Africa from 1D shear wave velocity models: Evidence for complex-wide crustal modification

Thirty-nine 1D shear wave velocity profiles, obtained by jointly inverting receiver functions and Rayleigh wave group velocities, are used to investigate the crustal structure of the Bushveld Complex in northern South Africa. Data from teleseismic earthquakes recorded on broadband seismic stations between 1997 and 1999 and 2015–2020 were used to compute P-wave receiver functions. Rayleigh wave group velocities between 5 and 30 s period were obtained from an ambient noise tomography and combined with group velocities between 30 and 60 s period from a published continental-scale surface wave tomography model. Moho depths of 45–47.5 km are found under the center of the complex compared to 40 km thick crust, on average, surrounding the complex, indicating ∼5–7 of crustal thickening. The bottom ∼10 km or more of the lower crust across much of the Bushveld Complex has a Vs ≥ 4.0 km/s, consistent with a mafic composition, whereas in most areas around the margins of the complex the thickness of the mafic lower crust is much less than 10 km. In the upper crust higher velocity structure (Vs > 3.6 km/s) above 15 km depth underlain by lower velocity structure is seen in many locations, suggesting the presence of mafic/ultramafic layering. These results favor the continuous-sheet model for the structure of the Bushveld Complex because the ensemble of 1D models is characterized by three diagnostic features consistent with that model: (1) thicker crust under the center of the complex than away from the complex; (2) a greater thickness of high-velocity (i.e., mafic) layering in the lower crust under the complex compared to away from the complex; (3) high-velocity (i.e., mafic/ultramafic) layering in the upper crust beneath much of the complex. The lack of upper crustal mafic/ultramafic layering beneath some parts of the complex is consistent with the post-emplacement tectonic and magmatic history of the complex.

Moho depth model of South America from a machine learning approach

Crustal structure models play an important role in the characterization of seismogenic zones, in the regional delimitation of geological provinces and particularly, in understanding the genesis and evolution of sedimentary basins. Despite the increasing number of new seismic surveys and seismographic networks in South America, crustal thickness measurements are still scarce and irregularly sampled, reducing the resolution of crustal model maps. To overcome these challenges, a novel approach based on machine learning techniques is proposed, in order to explore higher resolution gravity datasets in the interpolation of crustal thickness measurement points obtained from previous seismic/seismological compilations. The algorithm used in this study is based on Gaussian processes prediction methods, which allowed inferring the depth of Moho to South America. The prediction error of the model obtained from the training and testing database was 3.48 km, which is compatible with the uncertainties derived from the H-k stacking analysis. The depth range varied from 69.8 km beneath the Andes to 4.3 km in oceanic regions. The average Moho depth for the South American Platform is 39.1 km, allowing a spatial correlation of deeper and shallower Moho regions with different types of continental basins. Compared to other models, the model resulting from this study presents fine-scale features highlighting the limits of the main tectonic domains and a good agreement with the suture zones. Overall, this study demonstrates the potential of applying machine learning tools in crustal-scale imaging using sparse datasets, providing new advances in Moho modeling of the South America, as well as new perspectives on its the history and tectonic evolution.

Contribution of Magnetotelluric inversion and potential field modeling to map the Gour Oumelalen deep geological Structure, Central Hoggar, Algeria

The Gour Oumelalen area is situated in the northern part of the Egere-Aleksod terrane (Central Hoggar, South of Algeria). This area is one of the best preserved Palaeoproterozoic and Archaean zones in Central Hoggar. The aim of this study based on a survey of 33 Magnetotelluric (MT) soundings, aeromagnetics and gravity data, is to investigate the crustal structure and its architecture beneath this area.As the first stage, we have determined dimensionality of the regional electric conductivity structure. For this purpose, we have used the impedance and phase tensor approaches. Our results suggest that the underling regional conductivity structure is complex. In the central part it presents a 3D geometry, and beyond, it is mainly 2D; with a strike direction oriented in the North-South direction. Thus, the MT data were inverted using the Occam's inversion algorithm (v.3); which is a powerful tool to modeling and inverting the 2-D MT data. The obtained geo-eletric models, show clearly a high resistive upper crust with a resistivity up to 1000 Ω m; overlies a conductive lower crust with a resistivity approximately less then 100 Ω m. Although, our resulting cross-sections confirm the major Precambrian faults, especially the Ounan shear zone, which is characterized by a high conductivity anomaly.At the second stage, using the joint modeling of gravity and magnetic data, we have characterized the different geological units. Although, our modeling reveals that the thicknesse of the upper crust is deeping toward the East, from 16 to 25 km. The Moho depth reaches an average value of 40 Km. Moreover, in the centre of the survey area, the Moho depth decreases and becomes equal to 20 Km. This uplifting of the upper mantle may corresponds to the high magnetic anomaly of the Tisseliline pluton. It seems also related to the magmatic intrusion along the Ounan Shear Zone.

Lithospheric resistivity structure of the Xuefeng Orogenic Belt and its implications for intracontinental deformation in South China

The Xuefeng Orogenic Belt (XFOB), located in the central part of the South China Block, is a typical Mesozoic intracontinental orogen in the central Jiangnan Orogenic Belt. By collecting magnetotelluric (MT) data across the XFOB, we obtained the resistivity structure of the lithosphere, which sheds light on the Mesozoic intracontinental orogenic processes in the XFOB. The resistivity structure reveals a low-resistivity body (<10 Ω∙m), beneath the XFOB, dipping southeast wards from a depth of 10 km to the bottom of the crust. This conductor is interpreted as a relic of the lower detachment zone, which coincides with low-density areas obtained from joint inversion of seismic models. It is believed to result from mineral fluids migrating along the thrust fault and squeezing sulfides into folds. Four low-resistivity bodies were identified at three extensional locations along the Jiangshan-Shaoxing Fault and at the Cili-Baojing Fault. The low-resistivity body (<10 Ω∙m) at the junction of the Shaoyang and the Hengyang Basin is located at the point where the Moho depth thins. The variation trend of the terrestrial heat flow values, with this low-resistivity body as the plate boundary, is consistent with the average variation of the terrestrial heat flow values within the block. We propose that the low-resistivity body under the Qidong-Yongzhou-Guilin fault conforms to the characteristics of the suture zone in the resistivity structure. Its existence indicates that the missing location of the Jiangshan-Shaoxing suture zone of the Yangtze and Cathaysia Block in the middle-southwest section of the South China Block is the Qidong-Yongzhou-Guilin fault. The Yangtze Block and the Hengyang Basin show high resistivity, the depth of which reaches 100 km and 40 km, respectively. Based on the resistivity model and geological data, the XFOB experienced Triassic compression, leading to basement decollement, thrusting, and nappe structures due to low-angle Paleo-Pacific Plate subduction. This compression also led to the uplift of the orogenic belt. Moreover, under the tension caused by the high-angle retreat of the Paleo-Pacific Plate, the Cretaceous extensional tectonics led to detachment along the thrust faults, forming half-graben and basin structures along the margins.

Lithospheric Folding Controls the Intracontinental Orogen of South China: Insight from Numerical Simulation

Abstract Orogenic processes worldwide have been attributed to various deformation mechanisms. However, the significance of lithospheric folding in these processes has often been overlooked and underestimated. Within the South China Block (SCB), a region marked by notable temporal and spatial variability in intracontinental deformation, the emergence of fold-and-thrust belts during the Paleozoic and Mesozoic periods has captured a scientific interest. The mechanisms governing the genesis of these belts remain a subject of debate, with no discernible subduction interface accounting for the extensive-scale fold-thrust deformation. Moreover, the SCB presents a substantial variation in lithospheric thickness, exceeding 100 km, offering a plausible mechanism for lithospheric folding. To interrogate this mechanism, we conducted lithospheric compression simulations via two-dimensional finite element methods, incorporating variable viscosity both laterally and vertically within the SCB. Our models elucidate that disparities in lithospheric strength beget distinctive deformational manifestation within the SCB. We observe that a weaker lithosphere tends to uplift, whereas a stronger lithosphere tends to subside during compression. Lithospheric strength also influences the Xuefengshan uplift and the spatial distribution of deformational features. In addition, lithospheric folding can account for crustal shortening and the presence of deep anomaly structures. A compelling correlation emerges between lithospheric folding and fluctuations in Moho depth and lithospheric thickness, suggesting its potential influence over the prolonged topographical evolution and shifts in depositional environments within the SCB. This study sheds new light on the role of lithospheric folding in the complex geodynamic history of the SCB and highlights its importance in understanding the broader context of orogenic processes worldwide.

Evolution of the transtensional Barreirinhas pull-apart system in the Brazilian Equatorial margin and its correlation with the African conjugate counterpart

The Barreirinhas pull-apart system encompasses marginal basins in divergent and transform margin segments in the central sector of the Brazilian Equatorial Margin and its African conjugate counterpart. This ancient pull-apart system evolved through transtensional strike-slip motion within a highly heterogeneous crystalline basement affected by multiple rift phases. The geometry and development of pull-apart structural elements during the final rifting phase before continental breakup and the mechanisms and extent to which they were influenced by preexisting crustal heterogeneities are comprehensively addressed using an extensive database of potential field (magnetic and gravity) and 2D seismic reflection data. We also assess the lithospheric thermomechanical conditions and their influence on transtensional extension throughout Curie Point Depth, Heat Flow, and Moho depth, derived from potential field data and published seismological models. Plate reconstruction of Brazilian and African equatorial margins based on gravity patterns and comparison with sandbox analog models allow a 3D synoptic model to reveal the Barreirinhas pull-apart system evolution during the Equatorial Atlantic opening. During the rift phase I, the location of major grabens was controlled by favorably oriented Neoproterozoic shear zones, while the cooler, stronger, and thicker crust beneath cratonic areas formed the western barrier to strike-slip rift activity during rift phase II. This same geological domain anchored the onset of the pull-apart system in the last rift phase III, whose principal displacement zones developed along the extensive oceanic fracture zones linked by sigmoidal fault systems. Toward the end of the rift phase, a large asymmetric lozangle to a lazy-Z-shaped, pull-apart basin developed above low overlapping ∼90°, releasing stepover in oblique transtensional strike-slip motion.

Seismic observations of Nazca-plate crustal thicknesses providing constraints for a first-order asthenospheric-mantle potential-temperature anomalies assessment

The Nazca plate is populated with several magmatic tracks exhibiting complex morphologies responding to time-dependent positioning of spreading centers (East Pacific Rise, Cocos-Nazca). Mantle plumes beneath the Nazca plate are/were located on- or off-ridge (with ridge being spreading center), modulating the resulting hotspot-tracks’ crustal thickness accordingly. We use published seismic observational constraints of Moho depths to study asthenospheric-mantle potential-temperature anomalies (ΔTp) beneath the Nazca plate. We use a simple thermodynamics formulation for adiabatic cooling and decompression melting, and a depth-dependent, static analytical description presenting different options for hydrated-solidus-liquidus curves up to 8 GPa-lithostatic pressure as a function of bulk water content in the peridotite source. The calculated Tp-anomalies are relative to an average Nazca crust (∼6 km thick) formed at the East Pacific Rise with source hydration levels of about 0.01 wt%. As active-upwelling perturbing passive MOR environments, on-ridge plumes added mass (lower crustal intrusion, surface extrusion) to young crust creating OIB hotspot-tracks whose mean crustal thicknesses (≤18 km) are consistent with inferred ΔTp range-values of [-100, 75] °C (Iquique Ridge), [-50, 130] °C (Nazca Ridge), and [-20, 150] °C (Carnegie Ridge south), considering conservative bulk water contents of 0.005–0.08 wt%. The Juan Fernández OIB hotspot track was formed by an off-ridge active-upwelling plume impinging under a 27 Myr-old oceanic lithosphere with ∼7 km-thick pre-existing crust. Currently, the track presents 4-5 km-high isolated volcanic edifices and about 1 km crustal root, totaling about 12–13 km aggregate melt thickness, and suggesting ΔTp range-values of [-20, 160] °C.

Along-strike forearc and subducted upper slab structure beneath north Chile: Slow slip implications

We evaluate the lateral variation of the lithospheric structure beneath the forearc of the North Chile subduction zone along strike, extending from Iquique to Valparaiso, to understand a possible seismic structure that hosts deep slow earthquakes by comparing the deep slow slip areas around 60 km depth, using receiver function and inversion method. Relative differences are investigated in seismic velocities around the plate interface, especially underlying the mantle wedge, the upper part of the subducted oceanic crust, and the oceanic mantle along the subduction strike. We estimate and compare the thickness and velocity of subducted oceanic crust, slab top, subducted oceanic Moho, continental Moho, and wedge mantle velocity beneath the seismic stations. The oceanic crustal thickness range from ∼5 to 10 km respectively, and the oceanic Moho depth is ∼40 km–∼90 km. It was observed that the disparities in velocities were more pronounced near the south of the Iquique zone (18°S-25°S), with high subducting oceanic crust velocities. These discrepancies in velocities could be regarded as the presence of fluids from subducted ridges and seamounts, which might alter seismicity in the area, including slow slip.

Spatial Distribution of Tremor Episodes From Long‐Term Monitoring in the Northern Cascadia Subduction Zone

AbstractLarge bursts of non‐volcanic tremor (“major” tremor episodes) correlated with geodetic deformation recur regularly in the Cascadia subduction zone and are often called episodic tremor and slip (ETS). Minor episodes of tremor between ETS are ubiquitous but have been understudied. This paper assesses time‐invariant characteristics of tremor episodes of all sizes within northern Cascadia. We derive a catalog of tremor episodes ranging in size from 10 to &gt;13,000 tremor events using the results of 17 years of tremor monitoring. Minor episodes represent ∼96% of all 896 tremor episodes and their occurrence varies on 10‐km scales. Using estimates for the depth of the forearc Moho and subducting slab, we observe an association between the location of the forearc mantle corner (FMC) and tremor occurrence that leads to along‐dip modality. Bimodality, present in southern Washington and Vancouver Island, represents the segmentation of major and minor episodes up‐dip and down‐dip of the FMC, respectively. Unimodality, present in Puget Sound, results when the FMC is located near the down‐dip edge of the ETS zone and no segmentation occurs. We also use our extensive tremor episode catalog alongside three‐dimensional regional tomographic velocity models to reassess the relationship between tremor activity and low Vp/Vs signatures in the forearc. We do not find a correlation between tremor episode recurrence intervals and Vp/Vs, contrary to some previous work, suggesting that controls on silica precipitation in the forearc crust are not dominant controls of tremor episode recurrence, or that the association is not widely observable.

Crustal thicknesses in Uruguay from joint inversion of receiver functions and surface wave dispersion

The development of a seismic network in Uruguay in recent years has enabled studies of crustal structure in a region with few seismological studies of this type. In this work, we update the crustal thicknesses and Vp/Vs ratios calculated by H-k stack and present S-wave velocity models based on joint inversion of receiver functions and Rayleigh wave group velocity dispersion curves.Some interesting results are the presence of a lower crust with a high S-wave velocity of 4.1 km/s below one of the stations located on the Río de la Plata Craton and the existence of a transitional Moho in Uruguay's northernmost station on the Paraná Basin, perhaps suggesting the presence of localized underplated material. A relatively thick crust, 41.8 km, compared to surrounding stations, was found beneath the Sierra Ballena Shear Zone in the Dom Feliciano Belt. We confirm the decrease in crustal thickness when approaching the oceanic coast, reaching a Moho depth of 36.3 km in SE Uruguay. Finally, the calculated Poisson's ratio allows inferring a crust of felsic to intermediate composition beneath most of Uruguay.

Lithospheric structure of the Paraná, Chaco-Paraná, and Pantanal basins: Insights from ambient noise and earthquake-based surface wave tomography

To investigate the lithospheric seismic structure of southern South America beneath the Paraná, Chaco-Paraná, and Pantanal basins, we measure two distinct sets of dispersion curves of Rayleigh waves: the first corresponds to 25,986 phase velocity dispersion curves in the period range 5–50 s, extracted from cross-correlation of the ambient noise between pairs of stations and thus sensitive mainly to crustal structure; the second set is derived from group velocities extracted from earthquake recordings, resulting in 33,888 dispersion curves with periods ranging from 8 to 200 s, allowing us to probe deeper Earth structure. From these data sets, we derive two independent S-wave velocity models following a two-step inversion procedure, resulting in a crustal and a lithospheric mantle model with depths extending up to 50 and 200 km, respectively. Features imaged in our crustal model include low velocity anomalies in agreement with the surface position of the major sedimentary basins and high velocity anomalies within fold-thrust provinces and the basement of the Pantanal basin. In the uppermost mantle, we identify high velocities in the region of the Paraná basin, São Francisco and Amazonian cratons, and Luiz Alves block, and a low velocity feature beneath the Pantanal basin, which suggests a potentially thinner lithosphere under the basin. We also illuminate a strong velocity gradient boundary between the eastern border of the Pantanal basin with the Paraná basin, from crustal to lithospheric mantle depths, which seems to delineate the western and southern borders of the Paraná basin, coinciding with the Western Paraná Suture. Additionally, we construct a Moho depth proxy map for the study area, which has an overall good agreement with previous results, except for a thicker crust beneath the southern Chaco-Paraná basin. This area, together with a thicker crust counterpart in the Paraná basin, has a remarkable correlation with the position of a volcanic layer related to the Paraná Magmatic Province, which leads us to suggest that magmatic processes played an important role in the south Chaco-Paraná basin as well.

A translithospheric magmatic system revealed beneath Changbaishan volcano

Abstract Changbaishan volcano (CBV), located on the border between China and North Korea, has undergone violent eruptions since the Oligocene, making it one of the most captivating and explosive volcanoes on Earth. However, the lack of precise characterization regarding the magmatic system makes it difficult to decipher its eruption risk and mechanism, despite its significant size and past devastating effects. In this study, we employed newly developed teleseismic receiver function techniques, including Ps and Sp waves, to construct a lithospheric structure model beneath the CBV region. The results show a thick crust (~37 km) and a weak, thin lithosphere under the CBV, with a low-amplitude width of 80 km at the Moho depth and 200 km at the depth of the lithosphere-asthenosphere boundary. These features depict the seismological response of a translithospheric magmatic system beneath the CBV, where hot upwelling material rises through the lithospheric mantle, underplates at the base of the crust, and forms the magma chamber(s) at shallow depth. Such magmatic system features can be taken as a unifying paradigm for large volcanic regions worldwide.

Crustal thickness variations beneath Egypt through gravity inversion and forward modeling: linking surface thermal anomalies and Moho topography

This study aims to quantify the topography of the Moho boundary, the lower crust and uppermost mantle contact of Egypt, in order to estimate the crustal thickness variation and its link to the distribution of thermal anomalies under Egypt. This is accomplished by modeling satellite gravity, supported by the passive seismic constraints throughout Egypt. However, when estimating the thickness of the crust in Egypt using just seismic data, substantial uncertainty and deviation are produced due to the sparsely dispersed stations. Integrating seismic and gravity data minimizes uncertainty and improves estimate accuracy. The investigation is broken down into four stages, the first involving utilizing the Sentinel-3B satellite to create land surface temperature maps. The subsequent steps consist of gravity and seismic data adjustments, inversion and forward modeling. We used seismically restricted nonlinear inversion to look at Goco06s satellite gravity data to model the Moho’s topographic surface. The data gathered from deep seismic refraction and receiver functions adjusted the analyzed data. The inversion process relies on the adapted Bott's approach and Tikhonov regularization, using the assumption of the sphericity of the Earth planet. Reference values for depth of Moho and density contrast were set at 35 km and 500 kg/m3, respectively. The average statistical difference for Moho depth between gravity-based model and seismic data is − 0.10 km. Through forward gravity modeling, five gravity profiles were chosen and interpreted in 2.5D models. The results indicated that the Moho depth in the south varies from 35 to 39 km and decreases in the north and the Mediterranean. In upper Egypt, the highest Moho depth is 39 km. The depth varies beneath the Sinai Peninsula as it is about 35 km in its south, reaches 30 km in the northern portion, and ranges along the Red Sea’s Rift Margin from 29 to 32 km. Moreover, the final model shows the relation between Moho coincides with the surface temperature anomalies approved by satellite images and hot springs. The model reveals a correlation between Moho discontinuity and surface temperature anomalies, revealing the highest geothermal potential in a rectangular area in central Egypt, between latitudes 25°N and 30°N, based on satellite imagery and hot springs distribution.

Earthquake Detectability and Depth Resolution with Dense Arrays in Long Beach, California: Further Evidence for Upper-Mantle Seismicity within a Continental Setting

Abstract The Newport–Inglewood fault (NIF) is a slowly deforming fault cutting through a thin continental crust with a normal geothermal; yet it hosts some of the deepest earthquakes in southern California. The nucleation of deep earthquakes in such a continental setting is not well understood. Moreover, the deep seismogenic zone implies that the maximum NIF earthquake magnitude may be larger than expected. Here, we quantify the resolution of the Long Beach (LB) and the Extended Long Beach (ELB) dense arrays used to study deep NIF seismicity. Previous study of the regional catalog and of downward-continued LB array data found NIF seismicity extending into the upper mantle beneath LB. Later studies, which analyzed the ELB raw data, found little evidence for such deep events. To resolve this inconsistency, we quantify the array’s microearthquake detectability and resolution power via analysis of pre- and postdownward migrated LB seismograms and benchmark tests. Downward migration focuses energy onto the source region and deamplifies the surface noise, thus significantly improving detectability and resolution. The detectability is also improved with the increase in the array aperture-to-source-depth ratio. The LB array maximum aperture is only 20% larger than the ELB aperture, yet its resolution for deep (&amp;gt;20 km) events is improved by about a factor of two, suggesting that small changes to the array geometry may yield significant improvement to the resolution power. Assuming a constant aperture, we find the LB array maintain resolution with 1% of its sensors used for backprojection. However, the high-sensor density is essential for improving the signal-to-noise ratio. Analysis of the regional and array-derived NIF catalogs together with newly acquired Moho depths beneath the NIF suggests that mantle seismicity beneath LB may be a long-lived feature of this fault.

Uncertainty Quantification in Radial Anisotropy Models Based on Transdimensional Bayesian Inversion of Receiver Functions and Surface-Wave Dispersion: Case Study Sri Lanka

ABSTRACT In geophysical inference problems, quantification of data uncertainties is required to balance the data-fitting ability of the model and its complexity. The transdimensional hierarchical Bayesian approach is a powerful tool to evaluate the level of uncertainty and determine the complexity of the model by treating data errors and model dimensions as unknown. In this article, we take account of the uncertainty through the whole procedure, thus developing a two-step fully Bayesian approach with coupled uncertainty propagation to estimate the crustal isotropic and radial anisotropy (RA) model based on Rayleigh and Love dispersion as well as receiver functions (RFs). First, 2D surface-wave tomography is applied to determine period-wise ambient noise phase velocity maps and their uncertainty for Rayleigh and Love waves. Probabilistic profiles of the isotropic average VS and RA as a function of depth are then derived at station sites by inverting the local surface-wave dispersion and model errors and RFs jointly. The workflow is applied to a temporary seismic broadband array covering all of Sri Lanka. The probabilistic results enable us to effectively quantify the uncertainty of the final RA model and provide robust inferences. The shear-wave velocity results show that the range of Moho depths is between 30 and 40 km, with the thickest crust (38–40 km) beneath the central Highland Complex. Positive RA (VSH&amp;gt;VSV) observed in the upper crust is attributed to subhorizontal alignment of metamorphic foliation and stretched layers resulting from deformation. Negative RA (VSV&amp;gt;VSH) in the midcrust of central Sri Lanka may indicate the existence of melt inclusions and could result from the uplift and folding process. The positive RA in the lower crust could be caused by crustal channel flow in a collision orogeny.

Gravity Modelling Insights into Crustal Structure: Moho Depth and Subsurface Structures in Central Sulawesi

Abstract The present study examines the underlying structures and Moho depth’s geological implications in Central Sulawesi. Comprehending the underlying features of this area is essential for evaluating seismic risks and geological mechanisms. From the World Gravity Map 2012 (WGM 2012), we used a 2D radially-averaged power spectrum analysis of Bouguer gravity anomalies. The Moho depth is around 31 km in the northwest and northeast, with significant fluctuations in the middle and eastern regions. Although the northeastern and northwestern regions have similar depths, the center region has a lower Moho depth. On the other hand, the Palu-Koro Fault limit is marked by the eastern area, which corresponds to the Matano Fault, mirroring the center region. Furthermore, substantial orogenesis inside the Eastern Tokorondo Complex is suggested by Moho depth thinning, especially in the central, eastern, and southern portions. Our research emphasizes Central Sulawesi’s complicated geological structures, marked by variable Moho depth and underlying formations. With implications for earthquake risk assessment and hazard reduction, these insights advance our knowledge of the region’s geological processes.