3D Fault Model Research Articles

Multilayer 3D seismic attribute analysis and fault framework modeling of shallow extensional fault systems in the Delaware Basin

Shallow extensional fault systems within the southern Delaware Basin have gained the interest of Permian operators since published works noted them in 2019. These shallow extensional fault systems, referred to as “lineaments” by operators, are seismogenic hazards, pose significant hazards to drilling operations, and are associated with elevated water-oil ratios and H2S concentrations. Previous work using seismic attribute analysis has resulted in the successful mapping of extensional fault systems at the Ochoan/Guadalupian interface, whereas fault geometry, origin, and depth of penetration have remained elusive. First- and second-order ant tracking of the variance cube is rendered on multiple seismic horizons throughout an 856 km2 (approximately 330 mi2) depth-migrated 3D seismic reflection volume to expand the interpretation of the deformation zone at depth and guide a robust 3D fault model that forms the framework for the predictive model. A total of 60 previously undocumented features are identified in southwestern Reeves County — 56 penetrate the Ochoan/Guadalupian interface, 60 penetrate the middle Guadalupian, 29 penetrate the early Guadalupian, and 21 penetrate the early Leonardian. Structural modeling returns an average strike orientation of 318° north-northwest–south-southeast and an average dip of 84°. Spatial and temporal analysis of the model constrains the timing of extension to the Cenozoic. In contrast to previous studies, the improved depth of investigation of the 3D fault model allows for the correlation of documented drilling hazards with offset wastewater disposal wells along shared lineaments. Communication is indicated by H2S risking flags from mass spectrometry data along the vertical and horizontal sections of producing and injecting wells. Drilling data validates the seismic characterization and prediction of the 3D faulted architecture within the largest contiguous study of shallow extensional fault systems within the Delaware Basin and establishes a repeatable workflow for mitigating the negative impacts of shallow lineament geohazards on drilling operations and production profiles.

Three-dimensional fault model and features of chained hazards of the Luding MS 6.8 earthquake, Sichuan Province, China

The MS 6.8 Luding earthquake in 2022 is located on the NNW-trending Moxi segment of the Xianshuihe fault with left-lateral strike-slip behavior. This area is where the Xianshuihe, Anninghe, Daliangshan and Longmenshan faults intersect. China Earthquake Administration has identified that intersection area, among the Moxi segment of the Xianshuihe fault, the Anninghe fault, the Daliangshan fault and the southern part of the Longmenshan fault, as a high-magnitude earthquake hazard area. According to existing data on the Luding earthquake, including the focal parameters, the spatial distribution of re-located aftershocks, dominated azimuth of the earthquake intensities and earthquake-induced ground fissures, we built a 3D earthquake fault model. We found that two discontinuous NNW-trending vertical strike-slip faults with left stepping were the seismogenic faults of the Luding earthquake. Its coseismic left-lateral dislocation triggered transtensional slips and aftershocks on the NW-trending secondary faults at its northernmost tensile area. Meanwhile, local crustal coseismic shortening on the side of Mt. Gongga triggered the aftershocks on the NE- and NW-trending secondary conjugated strike-slip faults, which were confirmed by GNSS observations and InSAR deformation field around the epicenter. This earthquake rupturing pattern also controlled the spatial distribution of the earthquake intensity IX area and earthquake chain hazards. The Coulomb stress calculation shows that the Luding earthquake increases the risk of high-magnitude earthquake occurrence on the southernmost part of the Xianshuihe fault and the Anninghe fault. Finally, we suggested doing good monitoring of the Anninghe fault and the southernmost part of the Xianshuihe fault and avoiding active faults with seismogenic capacity and areas prone to earthquake-chained hazards during the site selection and planning of reconstruction.

Seismogenic Fault Model for the 2021 Ms 6.4 Yangbi, China, Earthquake, Constraints from Multisource Data

Abstract Deciphering a comprehensive 3D fault model for the regions with moderate-to-strong earthquakes is crucial for understanding earthquake triggering mechanisms and assessing future seismic hazards. On 21 May 2021, a massive Ms 6.4 earthquake occurred in Yangbi, Dali City, China, near the northern Red River fault zone. Despite numerous studies conducted over the past two years, the seismogenic fault of this earthquake remains a topic of controversy. In this article, we refine the workflow for 3D construction of fault surfaces from Riesner et al. (2017) and used it for the Yangbi earthquake. We constructed a seismogenic fault model for the Yangbi earthquake and Caoping fault from the collected multisource data. One utilizes a combination of focal mechanisms and relocated hypocenters, whereas the other combines geological and geophysical data from the study area. Upon analyzing these two fault models and the relocated hypocenter data, we propose that the seismogenic fault in the Yangbi earthquake is an undiscovered blind fault or a secondary blind fault of the Weixi–Qiaohou fault, rather than the surface-emerging Caoping fault.

3D fault model and seismotectonics indicate the potential seismic risk in the Daliang Mountains, southeastern Tibetan Plateau

Areas of active tectonics host many active faults and frequently experience moderate to large earthquakes. The possibility of devastating earthquakes makes the development of major infrastructure projects in these areas risky. World-class large-scale step hydroelectric projects have been built along the Jinsha River, such as the Xiangjiaba, Xiluodu, Baihetan and Wudongde reservoirs in the Daliang Mountains of the southeastern Tibetan Plateau. Using the SKUA-GoCAD modelling platform, we created a thorough 3D model of the active faults. Regional geological information, historical strong earthquake catalogues, small earthquakes with fine displacement and 3D seismic tomography are all integrated in this model. The Mabian–Yanjin fault belt consists of a number of discontinuous faults that are either exposed on the surface or concealed, according to the 3D fault model. Some destructive earthquakes, including two enormous M s 7 and many moderate earthquakes, have occurred along this fault belt. Some pre-existing thrust faults, together with numerous immature faults in specific areas, may have been reactivated and changed into strike-slip faults. The Jinsha River basin's seismic and geological concerns must be carefully considered given the existence of such intricate fault networks and seismic activity. Supplementary material: A video of the 3D fault model is available at https://doi.org/10.6084/m9.figshare.c.6949201

Automatic 3D fault detection and characterization — A comparison between seismic attribute methods and deep learning

Seismic interpretation is crucial for identifying faults, fluid concentrations, and flow migration pathways in the oil and gas industry. Algorithms have been developed to identify faults using seismic data and attributes such as changes in amplitude, phase, polarity, and frequency. Despite technological advancements, challenges remain in seismic interpretation due to noise, quality of data, and fault dimensions. Deep learning has recently been applied to image faults from seismic data, making the process faster and more reliable. This paper evaluates the performance of deep neural networks (DNN) in fault interpretation by comparing the results with traditional seismic attributes in onshore seismic data. Our results indicate that the DNN reveals more structural detail, which is essential in characterizing 3D fault geometry. In addition, DNN results show better continuity, fewer false positives, and are less affected by noise in the onshore seismic data used in this case. The 3D fault model from DNN identifies faults and their fault segments with greater variability of strikes and reveals more minor faults. Based on the DNN fault model, we characterized the 3D geometry of a new fault in the Rio do Peixe Basin without noise influence.

Combining Seismotectonic and Catalog-Based 3D Models for Advanced Smoothed Seismicity Computations

Abstract The new generation seismic hazard maps use 3D seismotectonic fault models, which are more consistent with the actual nature of faults, whereas the classical models based on earthquake catalogs only utilize a 2D representation of the seismicity. Although the former provides more reliable information on seismogenic structures, the latter can deliver trustworthy seismicity rates easily. Therefore, it is necessary to combine both the approaches to create a high-quality seismic hazard assessment model. This study proposes an innovative approach using smoothed seismicity methods that can be advantageous in all contexts with available 3D fault models and high-quality seismic catalogs. We applied our method on the Adriatic Basal Thrust (ABT) in eastern central Italy—a lithospheric-scale active contractional structure with a well-constrained 3D geometric–kinematic reconstruction and a related high-quality catalog. Our new 3D algorithm was applied to smooth the ABT seismicity on the grid, resulting in a 3D earthquake rate model that also provides rupture parameters such as strike, dip, rake, and seismogenic thickness. Our approach is particularly useful for complex seismotectonic settings, such as in cases of lithospheric shear zones, subduction planes, and overlapping multidepth seismogenic volumes.

Application of Finite Element Technique: A Review Study

The finite element approach is used to solve a variety of difficulties, including well bore stability, fluid flow production and injection wells, mechanical issues and others. Geomechanics is a term that includes a number of important aspects in the petroleum industry, such as studying the changes that can be occur in oil reservoirs and geological structures, and providing a picture of oil well stability during drilling. The current review study concerned about the advancements in the application of the finite element method (FEM) in the geomechanical field over a course of century. Firstly, the study presented the early advancements of this method by development the structural framework of stress, make numerical computer solution for 2D thermal stress then stress analysis of the airplane. The second part focused on the most recent developments of FEM, and this method generates new techniques for solving these problems, such as the 1D, 2D, and 3D finite element models; the dynamic program method (DPM); the finite discrete element method (FDEM); and the finite element extended method (FEXM). The third part of this study presented the reservoir finite element simulation used for injection well testing inside unconsolidated oil sand reservoirs. Also improvement of the FE software program for the analyses, finite element extended approach to convert a 3D fault model were introduced. In addition, the study explored the development of a 3D and 4D model utilizing Visage for FEM analysis for geomechanics investigations, and the software eclipse for pressure drop prediction in carbonate reservoir weak formation and presented the Finite-Element Smoothed Particle Method (FESPM).

Integrated Prospectivity Evaluation of XYZ Field Coastal-Swamp Depobelt Niger-Delta Basin Nigeria

Five studies were conducted on the “XYZ” field to understand its reservoir properties, structural settings, and hydrocarbon-in-place. Petrophysical parameters were calculated using appropriate equations and wireline logs. 3D seismic fault models were created. A stacking pattern of the reservoir sand bodies was interpreted from a gamma-ray motif. The reservoir surface area was deduced using hydrocarbon indicators and seismic amplitude change. A seismic inline section corresponding with the reservoir zone was used for the seismic facie studies. Reservoir R1 has net-thickness of 111.71m and 117.09m, N/G ratio of 76% and 85%, effective porosity of 25% and 28%, hydrocarbon saturation of 44% and 40%, permeability of 14md and 16md, and Formation factor of 156.32 and 13.77 in well “XYZ-03” and “XYZ-05” respectively.Three-ways and two-ways fault-dependent closures with an anticlinal stratigraphic closure were delineated towards the western and middle parts of the field. Reservoir R1 generally shows an aggrading stacking pattern. R1 associated with wells "XYZ-03" and “XYZ-05” has hydrocarbon volume of 272,293.40m3 (1,712,674 bbl) and 193, 502.93m3 (1,217,097 bbl) respectively. Seismic facies showed continuous reservoir sand bodies. The field is endowed with moderate to good multiple reservoirs, and effective fault and stratigraphic closures, which support economically considerable hydrocarbon volume.

New 3D fault model for eastern Flanders (Belgium) providing insights on the major deformation phases in the region since the late Paleozoic

A new 3D fault model was created for the Upper Paleozoic to Cenozoic subsurface in eastern Flanders (Belgium). The model was based on the integration of 2D seismic interpretations, borehole and gravimetric data, as well as coal mining and topographic maps. Four major tectonic phases, taking place during the latest Paleozoic, Jurassic, Late Cretaceous and Cenozoic, shaped the fault network. The latest Paleozoic phase was transpressional and expressed by local folding of the Carboniferous strata underneath the base Permian unconformity. The largest anticlines were asymmetric, with amplitudes of up to 500 m and SSW-NNE oriented axal planes. The subsequent Jurassic phase caused normal faulting across the area, resulting in the development of the northeast-dipping, western border fault systems of the Campine Basin and Roer Valley Graben. Fault strikes were predominantly WNW-ESE to NNW-SSE. Both fault directions were most likely inherited from early Carboniferous and older tectonic phases. Jurassic fault reactivation explains the activity along fault populations with different orientations as well as the linkage of these faults into long (>10 km) systems, despite displaying generally relatively small vertical throws (<500 m). Soft-linked boundaries (accommodation zones) between Jurassic fault domains are located on top of the largest latest Paleozoic transpressional anticlines.The Late Cretaceous major tectonic phase was compressional and involved inversion of the Roer Valley Graben with subsequent subsidence and carbonate deposition in the flanking Campine Block.During the Cenozoic extensional phase, most normal faults that developed were rooted in Jurassic faults and therefore displayed similar WNW-ESE to NNW-SSE strikes. Cenozoic extension was, however, weaker than Jurassic extension; Cenozoic fault numbers, lengths and vertical throws were smaller than during the Jurassic phase. Also during the Cenozoic phase, faulting was more localized onto the pre-existing Roer Valley Graben border fault system compared to the more diffuse Jurassic faulting. The Cenozoic faults were generally planar, whereas some of its Jurassic roots near and in the border fault system of the Roer Valley Graben were listric.

Three-Dimensional Fault-Fold Growth Deciphered from Combined Seismic and Geological Data: A Case Study from the Xiongpo Anticline, Longmen Shan Piedmont

The Xiongpo fault-fold belt shows prominent NE, ENE- and ~N–S-trending relief, which resulted from multi-stage upper crustal shortening in the Longmen Shan piedmont during the eastward growth of the eastern Tibetan Plateau. Previous studies have determined its 2D structural configurations from seismic profiles and field-based geological cross-sections. Here, we extend this analysis into the entire belt to explore the 3D structural evolution of this complex fault-fold belt and have built a 3D regional fault model. The results reveal along-strike variation of subsurface structural architecture of the Xiongpo fault-fold belt, which is characterized by transformation from a complex superimposition of a deep fault-bend fold beneath a shallow structural wedge in the center segment to a simple shallow fault-bend fold on both ends of the structure, and then to a trishear fault propagation fold on the plunging edges. This structural transformation determines the contrast between the NE-striking relief of the central segment, and the ENE- and ~N-S-striking relief in the two plunging zones. We combine our results with published low-temperature thermochronology and growth strata results to propose a three-stage evolution for the Xiongpo fault-fold belt that closely relates with regional stress field changes, including a NE-striking fault under the NW–SE compression between 40–25 Ma and 15–10 Ma, lateral propagation of the NE-striking fault and initiation of ENE-striking fault by WNW–ESE compression from ~5–2 Ma, ~N–S fault under ~E–W compression until the present. This work enhances our understanding of the stress field changes of eastern Tibet since the Late Eocene. It also can serve as a typical case study deciphering 3D fault-fold growth using seismic and geological imaging, which is helpful to understand 3D structural and landscape evolutions of other complex fault-fold belts worldwide.

Structural complexities and tectonic barriers controlling recent seismic activity in the Pollino area (Calabria–Lucania, southern Italy) – constraints from stress inversion and 3D fault model building

Abstract. We reconstruct the 3D fault model of the structures causative of the 2010–2014 Pollino seismic activity by integrating structural–geological and high-resolution seismological data. We constrained the model at the surface with fault-slip data, and at depth, by using the distributions of selected high-quality relocated hypocenters. Relocations were performed through the non-linear Bayloc algorithm, followed by the double-difference relative location method HypoDD applied to a 3D P-wave velocity model. Geological and seismological data highlight an asymmetric active extensional fault system characterized by an E- to NNE-dipping low-angle detachment, with high-angle synthetic splays, and SW- to WSW-dipping, high-angle antithetic faults. Hypocenter clustering and the time–space evolution of the seismicity suggest that two sub-parallel WSW-dipping seismogenic sources, the Rotonda–Campotenese and Morano–Piano di Ruggio faults, are responsible for the 2010–2014 seismicity. The area of the seismogenic patches obtained projecting the hypocenters of the early aftershocks on the 3D fault planes, are consistent with the observed magnitude of the strongest events (Mw=5.2, and Mw=4.3). Since earthquake-scaling relationships provide maximum expected magnitudes of Mw=6.4 for the Rotonda–Campotenese and Mw=6.2 for the Morano–Piano di Ruggio faults, we may suppose that, during the sequence, the two structures did not entirely release their seismic potential. The reconstructed 3D fault model also points out the relationships between the activated fault system and the western segment of the Pollino Fault. The latter was not involved in the recent seismic activity but could have acted as a barrier to the southern propagation of the seismogenic faults, limiting their dimensions and the magnitude of the generated earthquakes.

Physics‐Based Earthquake Simulations in Slow‐Moving Faults: A Case Study From the Eastern Betic Shear Zone (SE Iberian Peninsula)

AbstractIn regions with slow‐moving faults, the incompleteness of earthquake and fault data complicates the study of seismic hazard. The instrumental and historical seismic catalogs cover a short period compared with the long‐time interval between major events. Paleoseismic evidence allows us to increase the time frame of actual observations, but data is still scarce and imprecise. Physics‐based earthquake simulations overcome the limitations of actual earthquake catalogs and generate long‐term synthetic seismicity. The RSQSim earthquake simulator used in our study reproduces the earthquake physical processes based on a 3D fault model that contains the kinematics, the long‐term slip rates and the rate‐and‐state friction properties of the main seismogenic sources of a region. The application of earthquake simulations to the Eastern Betic Shear Zone, a slow fault system at southeastern Spain, allows the compilation of 100 kyr‐synthetic catalogs ofMW &gt; 4.0 events. Multisection earthquakes and complete ruptures of some faults in this region, preferentially on strike‐slip dominant ruptures, are possible according to our simulations. The largestMW &gt; 6.5 events are likely as a result of jumping ruptures between the Carboneras and the Palomares faults, with recurrence times of &lt; 20,000 years; and less frequently between the Alhama de Murcia and the Los Tollos faults. A great variability of interevent times is observed between successive synthetic seismic cycles, in addition to the occurrence of complex co‐ruptures between faults. Consequently, the occurrence of larger earthquakes, evenMW ≥ 7.0, cannot be ruled out, contrasting with the low to moderate magnitudes recorded in the instrumental and historical earthquake catalog.

Identification of local sesars of tejakula buleleng bali with anomaly gravity data using second vertical derivative method

Research has been carried out related to subsurface structures in the Tejakula Buleleng Bali area and its surroundings using the gravity method. This study aims to identify the local Tejakula fault. The data used in this study is gravity anomaly data obtained from observations of Geodetic Satellite (GEOSAT). The method used in interpreting the type of disturbance uses the Second Vertical Derivative method, which then produces two-dimensional (2D) and three-dimensional (3D) fault model interpretations. Based on the results obtained in the study, the condition of the bouguer gravity anomaly value in the Tejakula area and its surroundings at the research location is in the range of 65 mGal to 185 mGal. Meanwhile, based on the Second Vertical Derivative method in determining the type of fault, the Tejakula Fault can be categorized as a mandatory fault with an upward trend.

An integrated workflow for multiscale fracture analysis in reservoir analog

The study of the naturally fractured reservoirs is very challenging with the main difficulty being how to model and predict the fracture networks at different scales extending from outcrops and shallow depth to the reservoir and basin depths. Advanced 3D seismic and well data are needed to characterize and model fractures, a process which is time consuming and requires great effort in terms of data collection and analysis. The study of the reservoir analog maybe an easier approach with more readily accessible data. The results can be used to characterize and model fractures at different scales using several available workflows. 3D model is used to understand the fracture distribution, connectivity, fractures kinematics, and emulate the fluid flow simulation. In this paper, an integrated workflow is presented to characterize and model the natural fractures using as case study in the Cambro-Ordovician reservoirs analog located at the Southern edge of the Mouydir basin, Saharan platform in Algeria. The workflow uses the temporal and spatial fracture distribution at the outcrops to predict their extension later at the subsurface. The analysis composed of two main steps. Firstly, the global fault map corresponding to the area of study, generated from the combination of curvature and illumination attributes, geological maps, satellite images, and digital elevation models, is built. The outcomes are the determination of fault sets, length distributions, correlation coefficients, power law coefficients, and fractal dimensions. Secondly, using the same input data and parameters, the fracture impact on the basement formations, in this case, different Cambro-Ordovician units, is analyzed. The proposed methodologies help to determine the major and minor fault sets at different scales to understand the fractography and typology of fractures affecting the Cambro-Ordovician units. The 3D deterministic fault model for each formation is built to illustrate the fractures distribution in space and time. The models superposition helps to determine the fracture origin, their relationship, kinematics, and illustrate the impact of the basement’s faults on the sedimentary cover and the basin’s structure.

Fault orientation modeling of Sonda- Jherruck coalfield, Pakistan

Faults are the most critical tectonic factors in geological structures, which have major economic impacts on mining economics. Thus it is necessary to understand faults in order to identify the actual risks and complications associated with mining. In the preliminary investigation of the Sonda-Jherruck coalfield, 3D geological modeling was not performed. The purpose of this work was to perform fault orientation modeling in order to document pre-mine planning information and discuss the obstacles that may cause problems in mine planning and development stages. Using the drill hole data, 3D fault models based on the calculation of dip angle and dip direction were established. In the first step, surface models of coal seams were established by applying the triangulation method to the coal seam roof elevations. Then an appropriately oriented grid was overlain to regularize the data and to find the unknown points. The calculation of dip and dip direction was done using an algorithm. The models showing the variation in the dip and dip direction were generated using the inverse distance squared weighted (ID2W) interpolation technique. The generated 3D models were compared with the pre-existing fault lines (based on the aerial map). An attempt was made to create comprehensive models that demonstrate a better understanding of the faults in the studied area.

A case study of forward calculations of the gravity anomaly by spectral method for a three-dimensional parameterised fault model

Spectral methods provide many advantages for calculating gravity anomalies. In this paper, we derive a kernel function for a three-dimensional (3D) fault model in the wave number domain, and present the full Fortran source code developed for the forward computation of the gravity anomalies and related derivatives obtained from the model. The numerical error and computing speed obtained using the proposed spectral method are compared with those obtained using a 3D rectangular prism model solved in the space domain. The error obtained using the spectral method is shown to be dependent on the sequence length employed in the fast Fourier transform. The spectral method is applied to some examples of 3D fault models, and is demonstrated to be a straightforward and alternative computational approach to enhance computational speed and simplify the procedures for solving many gravitational potential forward problems involving complicated geological models. The proposed method can generate a great number of feasible geophysical interpretations based on a 3D model with only a few variables, and can thereby improve the efficiency of inversion.

Fault Modeling and Testing for Analog Circuits in Complex Space Based on Supply Current and Output Voltage

This paper deals with the modeling of fault for analog circuits. A two-dimensional (2D) fault model is first proposed based on collaborative analysis of supply current and output voltage. This model is a family of circle loci on the complex plane, and it simplifies greatly the algorithms for test point selection and potential fault simulations, which are primary difficulties in fault diagnosis of analog circuits. Furthermore, in order to reduce the difficulty of fault location, an improved fault model in three-dimensional (3D) complex space is proposed, which achieves a far better fault detection ratio (FDR) against measurement error and parametric tolerance. To address the problem of fault masking in both 2D and 3D fault models, this paper proposes an effective design for testability (DFT) method. By adding redundant bypassing-components in the circuit under test (CUT), this method achieves excellent fault isolation ratio (FIR) in ambiguity group isolation. The efficacy of the proposed model and testing method is validated through experimental results provided in this paper.

From surface geology to aftershock analysis: Constraints on the geometry of the L’Aquila 2009 seismogenic fault system

The aim of this study is the definition of the geometry and structural style of the extensional fault system involved during the L'Aquila 2009 seismic sequence. The surface tectonic setting of the late Quaternary faults in the epicentral areas (i.e., the Paganica, Mt. Gorzano and Montereale faults in northwestern Abruzzo) was defined by integrating data from the literature with original field work. The geometry of the faults at depth was interpreted using high-resolution aftershock distributions (based on a dataset covering 6 April to 27 December 2009, Ml ≥?1.9). The 3D fault model was reconstructed through 39 sections variously oriented across the epicentral area and represented in a map view as depth contour lines.Consistent geometric and kinematic correlations between the geological and seismological data were observed. The seismic sequence reactivated four well-distinguished fault sources differing in geometry, size and the degree of involvement. In order of importance, these sources may be ranked as follows: 1) the SW-dipping Paganica fault system activated during the 6 April mainshock (Mw 6.1/6.3) from the surface to a depth of ~10.5 km (along-strike length, L, 21 km; surface rupture length 13 km); 2) the NE-dipping hidden Ocre source activated during the strongest aftershock (9 April, Mw 5.4/5.5) at depths between 11 km and 16 km; 3) the WSW-dipping Mt. Gorzano fault activated by four relevant aftershocks (6 to 13 April, Mw ~5.0 to 5.5) at depths between 6 km and 12 km; 4) the WSW-dipping Montereale fault system and its continuation into the S-dipping Mt. San Franco fault activated at depths between 6 km and 10 km in a large number of minor events with Mw up to 3.6.The hypocentre of the 6 April main event is sited at a depth of ~9.5 km close to the intersection line between the SW-dipping Paganica fault and the S-dipping Mt. Stabiata fault, suggesting that the fault plane complexities (in this case, the sharp bend of the fault strike) may represent a favoured site for earthquake nucleation. The L'Aquila 2009 seismic sequence did not reactivate the entire surface of the involved faults. Nevertheless, on the basis of other geological and seismological constraints, the overall fault extent is schematically reconstructed and parameterised. Some considerations related to the structural style of the intra-Apennine Quaternary extensional structures and their patterns at depth are advanced.

3D geological modeling of the Trujillo block: Insights for crustal escape models of the Venezuelan Andes

Abstract The Venezuelan Andes form a N50°E-trending mountain belt extending from the Colombian border in the SW to the Caribbean Sea in the NE. The belt began to rise since the Middle Miocene in response to the E–W collision between the Maracaibo block to the NW and the Guyana shield belonging to South America to the SE. This oblique collision led to strain partitioning with (1) shortening along opposite-vergent thrust fronts, (2) right-lateral slip along the Bocono fault crossing the belt more or less along-strike and (3) crustal escape of the Trujillo block moving towards the NE in between the Bocono fault and the N–S-striking left-lateral Valera fault. The geology of the Venezuelan Andes is well described at the surface, but its structure at depth remains hypothetic. We investigated the deep geometry of the Merida Andes by a 3D model newly developed from geological and geophysical data. The 3D fault model is restricted to the crust and is mainly based on the surface data of outcropping fault traces. The final model reveals the orogenic float concept where the mountain belt is decoupled from its underlying lithosphere over a horizontal decollement located either at the upper/lower crust boundary. The reconstruction of the Bocono and Valera faults results in a 3D shape of the Trujillo block, which floats over a mid-crustal decollement horizon emerging at the Bocono–Valera triple junction. Motion of the Trujillo block is accompanied by a widespread extension towards the NE accommodated by normal faults with listric geometries such as for the Motatan, Momboy and Tuname faults. Extension is explained by the gravitational spreading of the upper crust during the escape process.

A new 3D fault model of the Bouillante geothermal province combining onshore and offshore structural knowledge (French West Indies)

The Bouillante area hosts geothermal resources located in a complex structural area (Guadeloupe Island, French West Indies). On one hand, faults observed on the field mainly elongate along the E–W direction. On the other hand, offshore structures interpreted from marine seismic lines shows a larger range of directions. A coherent 3D interpretation is proposed through a fault model combining onshore and offshore structural knowledge in a zone crossing the island coastline. The fault network constructed reveals a hierarchy in the family of structures and highlights the prevalence of the NNW–SSE direction, associated with secondary NE–SW-trending structures, and the E–W direction. On a geographical point of view, the modelled faults are gathered in 3 clusters. Data available to build the 3D fault model are sometimes sparse, especially inland because of intense vegetation cover. Consequently, not only the results and impacts of the 3D fault model are discussed but also its limitations as well as its possible evolution.