Mapping and modeling the heterogeneities distributed along the megathrust region in subduction zones is a key factor in understanding the seismic cycle and studying earthquake rupture behavior. Heterogeneities that control seismicity can be either structural, such as fractures or faulting, or compositional. The spatial resolution of Earth gravity field satellite-only models derived from the GOCE satellite ranges from 60 to 80 km at full degree/order, making them suitable for studying coseismic slips in large earthquakes (MW ≥ 8.0). In southern Peru, the Nazca Ridge subducts, a broad, smooth, and shallow seafloor relief that has been characterized as a seismic barrier. Using the vertical gravity gradient, we have mapped mass heterogeneities in this region, which appear to be spatially related to the seismogenic behavior. Positive and high relative values in the long-wavelength vertical gradient are associated with barriers to the propagation of seismic energy during large megathrust earthquakes (MW > 8.0). In contrast, low-vertical-gradient zones with an elliptical shape are qualitatively linked to asperities. These seismic barriers are associated with forearc strike-slip faults, while the asperities are linked to submarine basins. The positive gravity gradient mapped in the southern region of the subducted Nazca Ridge exhibits dual behavior: as a barrier to large earthquakes and as a seismic asperity for MW about 7 earthquakes.

In central-western Argentina, an early Paleozoic belt comprising mafic and ultramafic rocks spatially associated with metasedimentary successions is exposed along the western margin of the Argentine Precordillera. In this study, we integrate structural and geophysical datasets to constrain the three-dimensional geometry of the southern sector of the Precordillera mafic-ultramafic belt, with focus on in the Sierra de Bonilla area. Structural analysis in the Quebrada Santa Elena evidences polyphase ductile deformation with sinistral shear components, while gravity and magnetic modeling reveal pronouced density and magnetic susceptibility contrasts consistent with the presence of serpentinite lenses at depth. This work refines the understanding of the crustal architecture of the southern Precordillera and provides new insights into the accretionary processes active along the Gondwanan margin during the early Paleozoic.

The subduction of oceanic plate heterogeneities—drives profound tectonic and metallogenic modification of the overriding upper plates. Along the central Chile-Argentinean subduction margin, the collision of the Juan Fernández and Copiapó aseismic ridges and the adjacent Challenger fracture zone with the trench is the primary control on regional deformation. Through an integrated analysis of gravity fields and Moho depth—aided by upward continuation of spherical harmonics—we identify a previously unmapped aseismic ridge segment between these known features. This structure, here denominated the Huarpe ridge, lacks prominent bathymetry but exhibits a clear geophysical fingerprint: an isostatic anomaly indicating crustal overcompensation and a correlated flexure of the Moho. Our results demonstrate that the simultaneous subduction of these three buoyant ridges, together with the Challenger fracture zone, segments the outer rise of the Nazca plate, narrowing the Andean crustal root, and providing a mechanism for the Neogene to Recent uplift of the Greenvillian basement blocks in the Sierra de Maz, Umango, and Espinal ranges in the Western Sierras Pampeanas, representing an anomaly at the orogenic front area. In addition, we highlight the significant mineralization associated with hydrothermal and magmatic fluids related to the deformation imprinted by this ridge and the associated mantle magmas. In this process, the subducted plate adjacent to the oceanic ridge tears, inducing mantle decompression and partial melting of the oceanic crust, which metasomatizes the overlying mantle wedge and ultimately generates porphyry, gold, and volcanogenic massive sulfide deposits, among others. Notable examples include Pascua Lama (Cordillera Frontal, San Juan), San José (Precordillera, San Juan), Cerro Alumbre (Cordillera Frontal, San Juan), and Sierra de Maz (Western Sierras Pampeanas, San Juan). This study establishes that the Huarpe a-seismic ridge, together with the Challenger fracture zone, are first-order tectonic elements that actively shape the orogenic structure of the Andes and its associated metallogeny.

The southern Kamchatka Peninsula lies along the southeastern margin of the Okhotsk microplate; a region identified with high seismic potential. This segment of the megathrust hosted the historic Great Kamchatka earthquake (Mw = 9.0) in 1952, one of the four largest ever instrumentally recorded. On July 29, 2025, an Mw = 8.8 earthquake ruptured a similar portion of the megathrust through shallow reverse faulting, which is characteristic of subduction zones. In this study, we investigate the coseismic slip behavior of this event along the Kuril-Kamchatka subduction zone by directly modeling gravity data from the GOCE satellite mission. Finite-fault models from different data sources indicate that the rupture propagated entirely southwestward. Most of these models showed that deformation was distributed across distinct patches, with the highest slip occurring to the southwest of the epicenter, mainly between 50° and 51° N, coinciding with a low anomaly of the vertical gravity gradient (Tzz). Spectral coherency between a coseismic slip distribution model and Tzz showed a correlation of about 90%. A saddle-point in the Tzz variation at 53° N marks an important seismic barrier that also constrained previous great megathrust earthquakes. The northeastern termination of foreshock and aftershock activity further supports this. Another seismic barrier was inferred at 51° N by comparing Tzz to coseismic slip and to kinematic rupture models. Our results show that the Tzz effectively maps major asperities and barriers, in agreement to the degree of interseimic coupling, as found in previous studies of other great megathrust events around the world. We conclude that the density distribution mapped from satellite GOCE indicates a primary factor controlling seismic segmentation. We also propose the Tzz as a first-order proxy for seismic hazard assessment, as well as for constraining locking and finite-fault models that require a priori information on megathrust structure.

This research covers the study of the first month of data from a local seismological network deployed after the MW 6.4, January 18, 2021, San Juan earthquake, over the central Chilean-Pampean flat slab. Almost 1000 seismic events were detected in the first month after the MW 6.4 earthquake occurred, with ML magnitude ranging from −0.2 to 4.3. The majority of the seismic events were relocated at a depth of around 14 km and distributed in a northeast–southwest direction. The focal mechanism solutions obtained represent the rupture main process with one of their nodal planes according to the epicentral distribution, from which we can define the rupture dip to 61°. On the other hand, quickly after the MW 6.4 earthquake occurred, a nearby region at shallower depths became activated, from which Differential Synthetic Aperture Radar Interferometry results show vertical movements. In the epicentral area and concordance with the northeast–southwest rupture region, we found a low of the analytical signal which extends in the same strike by approximately 80 km to the most populated region in the San Juan Province. Considering the closeness of the greatest earthquakes that shocked the eastern sector of the San Juan Province to the subducted Juan Fernandez Ridge track, and the direction of the rupture process, we infer its influence as one of the significant factors that contributes to the high seismic activity in this region.

Using information from the Earth magnetic anomaly model (EMAG2), gravity (global vertical gravity gradient), Geoid (Eigen6C4), and heat flow, complemented with seismological data (NEIC), we were able to analyze sublithospheric and lithospheric processes beneath the South American plate in the Central Andes where the Nazca Plate experiences a strong transition from horizontal, from the Chilean-Pampean flat subduction zone in the south to steep in the north beneath the southern Altiplano, a region characterized by delamination. This section of the Nazca Plate presents several heterogeneities, such as the transform Challenger Fault Zone, and three aseismic volcanic chains originated in hot spots, the Juan Fernandez Ridge, Copiapo Ridge, and Taltal Ridge that were signaled as sources for subducted plate tearings, abnormal heat flow, volatile injection and asthenospheric upwellings from tomographic and volcanological studies. Besides, associated sub-lithospheric viscosity drop has been linked to lithospheric delamination. Geoid residuals confirm the existence of thinned sectors of the over-thickened southern Altiplano crust, in coincidence with low seismicity and high heat flow zones at the site of subduction of the Challenger fault zone and Copiapo and Taltal aseismic Ridges, which supports former proposals of subducted slab tearings at these heterogeneities controlling lithospheric drippings and retro arc volcanism.

Knowledge of the lithospheric structure is key to understanding the seismotectonic characteristics of convergent margins. In this study, we provide a robust one-dimensional velocity model for the Anelo region, located within the Neuquen extensional basin in Argentina, with the aim of illuminating the lithospheric characteristics of the back-arc region of the southern central Andes. Data from a temporary network of broadband stations operational from October 2014 to March 2020 was utilized. We employed two distinct seismological techniques for obtaining models with varying resolutions at multiple scales and depths. On the one hand, upper thin layers were obtained by the inversion of a model based on hypocenters from local earthquakes, and on the other, we calculated receiver functions to estimate thicker and deeper layers. By combining both methods we were able to obtain a joint and accurate velocity model, a crucial tool for conducting seismicity studies in the region and achieving precise determinations of earthquake locations. Moreover, the analysis of velocity variations offers valuable insights into the complex lithospheric structure beneath the study area, shedding light on the poorly understood seismotectonic activity in the Andean retroarc. We suggest that the presence of a weakened or hot lithospheric mantle beneath the southern Neuquen Basin may be linked to the Payenia mantle anomaly. This anomaly likely softens the upper plate, concentrating deformation and intraplate seismicity, as documented in the vicinity of the study area.

The earthquake potential of the segment known as the Shumagin gap, located along the southwestern Alaska convergent margin, has been debated for over 40 years. This portion of the megathrust has not experienced a historically great earthquake with a magnitude (Mw) greater than Mw = 8.0, or at least none has been recorded in the instrumental era, exhibiting a moderate to low slip deficit. On 22 July 2020, an Mw = 7.8 thrust-fault earthquake ruptured a deeper portion of the megathrust along the eastern edge of the Shumagin Gap. Aftershocks following this event, including an Mw = 7.6 strike-slip earthquake on 19 October 2020, delineated an approximate north-south fault zone. Later, on 29 July 2021, an Mw = 8.2 thrust-fault earthquake ruptured the Semidi segment to the East. In this work, we examined the coseismic behavior of the Shumagin gap and adjacent Semidi segment along the Alaska margin from direct and inverse models obtained from satellite-derived gravity data. The distribution of the vertical gravity gradient shows a saddle point topography along the Shumagin Gap where the aftershocks of the July 2020 Mw = 7.8 earthquake concentrated in a nest. The gravity disturbance and the inverse model of mass anomalies also show an along-strike segmentation. Anomalous mass inferred along the Shumagin Gap, is consistent with the seismicity, focal mechanisms, and recently published works, suggesting that this segment hosts a seismic barrier (along-strike) that limits earthquakes with magnitudes Mw > 8.0. On the other hand, an across-strike (along-dip) segmentation is inferred from Tzz, which is consistent with vertical motion models. Comparison of the interplate coupling and b-values distribution to the vertical gravity gradient, allowed mapping main asperities in the region suggesting that the area to the west of the Shumagin gap could host a great megathrust earthquake in the future.

The Precordillera fold-thrust belt, situated within the Pampean flat-subduction segment (27 degrees-33 degrees S), is characterised by enigmatic transversal structures which extend and influence deformation patterns, the full extent of which is yet to be fully elucidated. The Northern Pie de Palo Lineament represents a key example, and has been proposed to play a pivotal role in the development and structural control of the Precordillera. In any case, this lineament has not been subjected to a comprehensive study, which has led to ongoing debate regarding its structural control, persistence, and morphology. This study was therefore focused on this structure, employing multiple geophysical methodologies, including aeromagnetic and gravimetric techniques. This approach enabled the first visualization of the full extension and fault zone of the North Pie de Palo Lineament, which crosses the entire Precordillera fold-thrust belt in a transverse direction. Consequently, it can be posited that this structure would have exerted a conditioning influence on the thermo-mechanical state of the Andean lithosphere, enabled the uplift of mafic bodies and thus influenced the Neogene deformation of the Precordillera fold and thrust belt. The confirmation and characterization of this major structure open new perspectives on the interaction of deepseated transversal structures with fold belts during the evolution of the southern central Andes.

In central-western Argentina, an Early Paleozoic belt including mafic-ultramafic bodies and marine metasedimentary rocks occurs along the western margin of the Precordillera and in the eastern Frontal Cordillera. In this paper, we present the analysis of aeromagnetic data and its processing focused on mapping geological limits, structures and the relation at depth of the southern Precordillera. With this main objective were applied filtering algorithms, reduction to the pole, tilt derivative, analytical signal, and particularly, the use of Improved Logistic Function (IL) as a new method of edge detection, in combination with the inversion map obtained from the Magnetization Vector Inversion (MVI) method. The results allow us to describe at depth the main trend of the Southern Precordillera Mafic Ultramafic Belt as two separated bocks, one in Peñasco and another in Cerro (Co.) Cortaderas, passing through Cerro (Co.) Pozos with a possible NNE-SSW direction. The combination of this techniques also can be used as prospecting guide to Pb-Zn-Ag vein deposits and High sulfidation Au-Epitermal deposits.

The Cretaceous-Cenozoic General Levalle rift basin (GLB) in Central Argentina, near 900 km east from the modern Chile-Peru trench, is an exploratory hydrocarbon frontier located within an intracratonic setting. The basin is 4.5 km deep and can be divided into three major evolutionary stages, synrift, intermediate and postrift. To date, the basin subsidence has not been yet addressed. We particularly made emphasis on the postrift sequence given that records of thousands of metres of Cretaceous and Cenozoic Strata and tectonic and thermal events are not known to account for these large accumulations. In this work we performed a backstripping analysis, in combination with a stretching-thermal model, which were then compared to different dynamic topography studies. From our backstripping models we found a typical rift basin curve, with the largest subsidence at the synrift stage followed by a decrease in values during the postrift. Assuming the synrift stage was driven by tectonic extension, we correlated the tectonic subsidence curve, obtained from backstripping studies, with a stretching-thermal subsidence model. The best fit among subsidence curves was obtained with a stretching factor beta = 1.285. However, we observed a mismatch along the postrift part of both curves, resulting in a residual subsidence of similar to 323 m. When this anomalous tectonic subsidence was compared to the latest six dynamic topography models, we found a good correlation with one of them. For the models that did not match and using simple isostatic computations, we estimated a lithospheric mantle thickening of 35.4 km to account for the residual subsidence and dynamic topography models. From our analysis it turns out that, in addition to stretching and thermal subsidence, mantle thickening in the lithosphere and in the asthenosphere, controlled the total subsidence in the General Levalle basin. The subduction history of Nazca Plate could have affected the postrift stage in this basin.

The Payunia Volcanic Province is a Quaternary volcanic plateau emplaced in the retroarc area in the northern Neuquen Mesozoic Basin, associated with a hydrocarbon system. At deeper levels, this basin is linked to different intrusive systems that developed in the retroarc region at different times, during the Jurassic, Cretaceous, Eocene, Miocene, and even the Quaternary which influenced the hydrocarbon system maturity. We analyzed the Moho structure through this retroarc region, as well as the crustal structure affected by different stages of regional extension. From continuous seismic noise data, we calculated the autocorrelograms to obtain the reflection response below each seismological station. This allowed imaging the surface of primary crustal reflectors and in a few stations the top of an asthenospheric anomaly (SWAP) found by magnetotelluric survey and in concordance with satellite magnetic data. The crustal reflectors were identified in all stations at a mean twoway travel time of about similar to 8.5 s and similar to 12.5 s using frequency bands of about 1.0-2.4 Hz. Therefore, this is the first geophysical research that estimates the depth of the magmatic system, hosted at the top of the lower crust and the Moho discontinuity. The deepest reflector, only recognized in 4 stations, was observed with a two-way travel time of 17.2 s to 19.6 s. We used a mean one-dimensional Vp model to obtain the corresponding reflector depths which constrain the two-dimensional forward gravity model that fits with the observed regional anomaly for the region. We finally established a relationship between the shallowest sublithospheric electrical conductivity anomalies determined in previous researches and the strong deep reflections observed in some of the seismological stations. This information may help to constrain geochemical and petrological models and reevaluate the hydrocarbon system maturity of the northern Neuquen basin.

Understanding the seismotectonics in the foreland region of orogenic belts is crucial for several reasons. Firstly, it allows us to infer stress conditions and structural controls in distant orogenic areas. Secondly, because these regions are often densely populated, it becomes essential to assess the associated risks, hazards, and vulnerabilities. In this study, we investigate intraplate seismicity in the foreland region of the Neuqu & eacute;n Basin in the southern Central Andes. Our data were obtained from a local broadband seismic network and high- resolution gravimetric enhancement methods. We analysed three distinct sets of earthquakes associated with major subsurface structural features. We found that seismic events near the A & ntilde;elo locality may be linked to anthropogenic causes, underscoring the importance of identifying active structures and understanding regional tectonics. The seismicity is mostly aligned with Mesozoic transfer zones, as well as a large laccolithic magmatic intrusion. Focal mechanisms and enhanced gravimetric methods further elucidate previously unidentified structural features related to seismicity and gravity gradients. Reactivation directions coincide with reported Andean E-W maximum stress orientations. To the south of A & ntilde;elo, seismicity and gravity gradient patterns suggest lineaments within the Huincul System. Notably, NE-SW trending lineaments between 71 degrees W degrees W and 70 degrees W degrees W align with seismicity possibly associated with the Agrio fold and thrust belt, and the projection of the Valdivia Fracture Zone. At 70 degrees W, degrees W, E-W trending lineaments correspond to seismic activity near the Chihuidos anticline and Cortaderas lineament. At 69 degrees W, degrees W, a shorter NE-SW lineament coincides with clustered seismicity, the A & ntilde;elo anticline, and an eastward shift of the deformation front. Lastly, ESE-WNW trending lineaments at 68 degrees W degrees W indicate structural rotations consistent with the complex Mesozoic Huincul System framework. From these results, we propose that the Huincul System exerts strong control over the structural character and seismotectonics of the central foreland region of the Neuqu & eacute;n Basin. This comprehensive analysis underscores the utility of integrating diverse geophysical methods for understanding intraplate seismicity and structural dynamics in foreland basin settings.

Andean broken foreland zones, located to the east of the highest Andes, are associated with populated areas and sedimentary basins with relative economic importance. Understanding their seismogenic potential is crucial for urban development and infrastructure planning. In particular, the San Rafael Block is part of the broken foreland developed to the south of the Chilean-Pampean flat subduction zone. A local seismic network allows analyzing the seismogenic potential of the San Rafael Block. Earthquake distribution suggests a northeast-dipping ramp rooting at the lower crust, cropping out at the western topographic front of the basement uplift. Gravity data confirm the asymmetry of the San Rafael block with a western topographic front associated with the main structure that exhumes the basement. Seismological and gravity data allow proposing a west-verging structure, contrary to previous interpretations based on surficial structural data. The results presented here identify the highest shallow seismogenic potential on the western side of the block, near the El Nihuil dam, and only deep events at the eastern neotectonic front which allegedly hosted historical earthquake occurrences such as the Villa Atuel-Las Malvinas earthquake in 1929.

The Salinas Grandes and Salina de Ambargasta salt pans are located in the Eastern Sierras Pampeanas in the Pampean broken foreland zone, a product of the Chilean-Pampean flat subduction zone, constituting an anomalously flat morphology of 350 x 150 km and occupying an extensive area in a northeast-southwest direction. These flat depressions abruptly interrupt the eastern Sierras Pampeanas morphology, burying the structure beneath Late Cenozoic-Quaternary deposits of the Andean orogenic front. We obtained from a previous model in spherical harmonics, the geometry of the Moho observing a lower crustal attenuation below the salt pan areas, which is maximum towards the north of the Salina de Ambargasta. From the Bouguer anomaly, calculated by unifying data from different sources, and its residual anomaly, we calculated the analytical signal in order adjust the wavelength of the gravimetric anomaly, that shows that this flat morphology follows NE to NNE gravity minima. Werner deconvolution and localized Euler deconvolution calculated from the residual Bouguer anomaly (figure 4), indicate that the anomalous masses are located above 15 km depth, in accordance with the wavelengths of the anomalies, presumably indicating the differential uplift of high-density rocks placed in the lower and mid crust, in accordance with the measured crustal attenuations. Additionally, these solutions show that this NE depression is segmented by NNW structures perpendicular to the main trough. Crustal thickness attenuation is interpreted as related to the track of the Juan Fernandez Ridge beneath the eastern Pampean broken foreland sector, based on plate kinematic reconstructions. Its tearing and related asthenospheric upwelling, as depicted in recently released tomographic data, could have promoted lithospheric localized extension, explaining the Salinas Grandes-Ambargasta depressions that are segmenting the eastern Sierras Pampeanas at the Andean orogenic front.

The Domuyo volcanic complex (DVC) and its geothermal field in the retroarc zone of the southern Central Andes of Argentina present reduced seismicity according to different catalogs (USGS and INPRES). However, in 2015/ 2016, a local project was carried out in the area to describe its seismo-volcanic activity, registering a large number of volcano-tectonic (VT) events (538 VT). Considering there is scarce information on these events, this study focuses on analyzing the Domuyo Volcanic Complex (DVC) to assess its seismicity. Therefore, we installed a local seismological network in the study area and compared results with data registered by other authors. Four seismological networks were used, to obtain a more precise location of the seismic events and calculate the focal mechanisms of earthquakes with magnitudes greater than 2. For the first record of crustal seismicity detected by INPRES the September 10th, 2016 with a Ml 3.3, we calculated the focal mechanism with two possible solutions: a thrust solution with a strike component and a favored normal solution with a strike component. Additionally, we relocated the largest event in the Domuyo region on March 27th, 2019, with a magnitude of 4.4 (NEIC - USGS) and focal mechanism with a normal solution and a small strike component, obtaining a shallower depth of 3.9 km instead of 10 km. The new seismological data used in this paper, correspond to September 10th 2016, and two different time periods, the first comprising continuous data from March to April 2019, when the largest registered earthquake occurred in the Domuyo region, and the second from December 2019 to January 2021. At these periods, registered seismicity had magnitudes Ml between 1.9 and 2.8, and focal depths between 1.8 and 5.2 km. Four of these events count with focal mechanisms with extensional and limited strike-slip components that are tentatively linked to the known neotectonic structures affecting the western slope of the DVC. This seismic sequence agrees with previous proposals in which degasification from a magmatic body at shallow depths constitutes the trigger factor.

The combined analysis of aeromagnetic and gamma-ray spectrometry data, allowed us to determine and differentiate the responses of hydrothermal rocks units and low sulfidation epithermal gold systems, in the south area of the San Rafael Block, in the Mendoza province. The data processing approach was focused on mapping geological limits and structures, and their response over the gold mineralization area, linked to hydrothermal zones. To do this, filtering algorithms, such as vertical derivative, tilt derivative, logistic function, and analytic signal were applied to the aeromagnetic data. For the analysis of gamma-ray spectrometry data, images of K, eU, and eTh concentrations, K/eTh ratios, and an F-parameter were used. The analytic signal filtering of the data reveals relatively low magnetic intensity zones associated with hydrothermally altered rock areas. The radiometric data delineate local anomalies that reflect enrichment with high potassium values in the deteriorated zones. A broad K/eTh anomaly correlates with the extension of the magnetic low intensity zones, indicating a generalized potassium enrichment in the Don Sixto area. These results indicate that the main structural directions are arranged in NW-SE strikes and the secondary ones in N–S strikes. These lineaments are spatially correlated with the most significant structures in the study area, evidencing that the mineral deposits located in the study area respond to the main lineaments. In addition, the main geophysical characteristics allowed us to identify the zone of hydrothermal alteration related to the low sulfidation epithermal gold and silver deposit Don Sixto, which would be related to high levels of K/eTh ratios and low intensity magnetic zones.

Over the past decade, the three largest and most destructive earthquakes in recent history with associated tsunamis occurred: the Mw = 9.2 Sumatra-Andamam in 2004, then the Mw = 8.8 Maule in 2010, and finally the Mw = 9.1 Tohoku- Oki in 2011. Due to the technological and scientific developments achieved in recent decades, it has been possible to study and model these phenomena with unprecedented resolution and precision. In addition to the coseismic slip models, for which joint inversions of data from various sources are carried out (e.g., teleseismic data, GNSS, INSAR, and Tsunami, among others), depicting the space-time evolution of the rupture, we have high-resolution models of the degree of interseismic coupling (based on GNSS) and also maps of seismic b-value changes. Among these advances, new Earth gravity field models allow mapping densities distribution homogeneously and with a resolution (in wavelengths) of approximately the large rupture areas of great megathrust earthquakes. In this regard, the maximum resolution of GOCE-derived static models is in the order of λ/2≈66 km, while GRACE monthly solutions are in the order of λ/2≈300 km. From the study of the static and dynamic gravitational field, it has been possible to infer mass displacements associated with these events, which have been modeled and compared to the deformation inferred using other methods, yielding very good results. In this work we study the kinematic behavior of the rupture process for one of these largest events, the Mw = 9.1 Tohoku-Oki 2011 earthquake, employing the vertical gradient of gravity derived from the GOCE satellite, finding that the maximum slip occurred close to a lobe of minimum Tzz, as was observed for other case-studies in other subduction-related settings studied in previous works (e.g., the Maule earthquake and the Sumatra-Andaman earthquake, among others). In addition, from the rupture propagation using kinematic models, it can be observed that the rupture is arrested when it approaches high-density structures and, it is enhanced when connecting with lobes of low vertical gravity gradient. We also mapped a block expressed as a low Tzz lobe, developed along the marine forearc, which is controlled by a parallel-to-the-trench normal fault that accommodates subsidence during the interseismic period, as it is coupled with the subducted slab. Then, after rupturing the plate interface, this block is decoupled promoting tectonic inversion and uplift. In this way, the hypothesis that the density structure along the forearc is the ultimate first-order factor that governs the rupture process is reinforced.

This chapter focuses on the structural styles of the Villa Unión-San Isidro basement-involved fold and thrust belt in the northern Ischigualasto-Villa Unión Basin of the western Sierras Pampeanas, La Rioja Province, Argentina. The region is situated within the Pampean flat-slab subduction segment (28°–32°30′S) of the Central Andes, and it records the Neogene phase of the Andean orogeny through many basement-involved structures, such as analyzed in this chapter. Detailed seismic interpretation of two poststack time migrated seismic reflection profiles indicates the presence of three WSW–ENE to SW–NE-trending and SE-vergent reverse and thrust blind faults that generate fault-bend folds and fault-propagation folds. In addition to these structures, roughly S–N trending imbricate fault-bend folds contribute to the overall structural grain of the region, which are closely related to thin-skinned faults. The geometry and kinematic of the structures is unraveled based on field work, time-depth conversion of the seismic profiles, implementation of fault-related fold models, and the analysis of Mio-Pliocene growth-strata sediments. We hypothesize that the diverse structural styles and kinematics of folds and faults, as well as their mutual spatial and angular relationships, are strongly suggestive of the influence of preexisting discontinuities in the Proterozoic metamorphic-igneous basement. In addition, this suggests that one or more other episodes of deformation probably developed jointly within a complex but generally synchronous strain field, which, in turn, influenced the Andean tectonic evolution in the region during the Neogene.

During the last two decades, space geodesy allowed mapping accurately rupture areas, slip distribution, and seismic coupling by obtaining refined inversion models and greatly improving the study of great megathrust earthquakes. A better understanding of these phenomena involving large areas of hundreds of square kilometers came from the last gravity satellite mission that allowed detecting mass transfer through the Earth interior. In this work, we performed direct modeling of satellite GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) derived gravity gradients up to degree/order N = 200 of the harmonic expansion and then corrected this by the effect of topography. Cutting off the model up to this degree/order allows inferring mass heterogeneities located at an approximate depth of 31 km, just along the plate interface where most (but not all) significant slip occurs. Then, we compared the vertical gravity gradient to well-constrained coseismic slip models for three of the last major earthquakes along the Sunda interface. We analyzed seismic rupture behavior for recent and for historical earthquakes along this subduction margin and the relationship of the degree of interseismic coupling using the gravity signal. From this, we found that strong slip patches occurred along minima gravity gradient lobes and that the maximum vertical displacements were related quantitatively to the gravity-derived signal. The degree of interseismic coupling also presents a good correspondence to the vertical gravity gradient, showing an inverse relationship, with low degrees of coupling over regions of relatively higher density. This along-strike segmentation of the gravity signal agrees with the along-strike seismic segmentation observed from recent and historical earthquakes. The thermally controlled down-dip ending of the locked fault zone along central Sumatra also presented an inverse relationship with the density structure along the forearc inferred using our modeling. From this work, we inferred different mass heterogeneities related to persistent tectonic features along the megathrust and along the marine forearc, which may control strain accumulation and release along the megathrust. Combining these data with geodetical and seismological data could possibly delimit and monitor areas with a higher potential seismic hazard around the world.