Strike-slip Tectonic Regime Research Articles

Controls on the genesis of a giant sand injection complex; insights into the Paleogene evolution of the stress of northern and central California

Giant sand injection complexes and localized swarms of sandstone intrusions are common in Upper Cretaceous to Miocene sedimentary successions of central and northern California within a distance of less than 100 km from the Pacific margin of the North America plate. One of the best preserved and extensively exposed injection complexes is the late Eocene Tumey Giant Injection Complex. The emplacement of sand injectites was driven by overpressure generated by thermal diagenesis of biosiliceous and smectite-rich mudstone host-rocks. The orientation and size distribution of sandstone intrusions was controlled by stress in which σ 1 and σ 3 were horizontal and, respectively, parallel and perpendicular to the present trace of the San Andreas Fault, and σ 2 was vertical. A strike-slip tectonic regime is inferred. Our analysis documents margin-orthogonal extension and provides support for a late Eocene phase of increase of strain, and possibly active slip, along a syn-subduction strike-slip fault zone. Comparison with other injection complexes in the region indicates that the near-field maximum principal stress rotated through time, from normal to parallel with respect to the plate margin, probably in relation to variations of the relative motion vector of the converging plates.

Geomechanical modeling to assess the injection-induced fracture slip-potential and subsurface stability of the Cambro-Ordovician reservoirs of Hassi Terfa field, Algeria

The in-situ stress state and the distribution of the critically stressed fractures have significant implications on optimum wellbore placement, production enhancement, fluid injection, and induced seismicity which largely influence the reservoir management strategies. This study presents a comprehensive geomechanical modeling to infer the likelihood of shear slippage of the optimally oriented weak planes in response to water injection in the deep Paleozoic oil reservoirs from the Hassi Terfa field, central Algerian Sahara. The ‘B-quality’ compressive failures, i.e., breakouts from the acoustic image log indicate the maximum horizontal stress azimuth as N114°E. The inferred in-situ stress magnitudes indicate a strike-slip tectonic regime in the study area. The reservoir is generally tight (porosity <8 %, permeability <0.4 mD) due to extensive silica cementation, however pre-existing closed to partially open natural fractures of variable geometries are identified on cores, thin sections, and image logs. The stress-based slip assessment indicates that none of the fracture geometries is critically stressed and hydraulically conductive at the initial reservoir stress state. The onset of slip on the critically oriented vertical fractures can initiate at 1200 psi of fluid injection at the reservoir level of ∼3500 m. The E-W to EES-WWN oriented fractures, parallel to the maximum horizontal stress azimuth, have a higher likelihood of being critically stressed during injection and therefore can contribute to the permeability enhancement. We restrict the practical injection threshold at 3000 psi, which can create tensile failures on the shale caprocks. We infer that the NE-SW and NNE-SSW striking, steeply dipping fractures and regional faults being perpendicular or at high angles to the regional maximum horizontal stress azimuth, are the most stable ones and therefore, less likely to slip within the practical injection limit.

Volcano tectonic setting of the Salares Norte Au–Ag epithermal belt, central Andes of northern Chile

The Salares Norte (SN) Au–Ag belt is here defined as an Upper Miocene-Pliocene metallogenic area, extending for nearly 200 km, located NE of the northern end of the Upper Oligocene-Lower Miocene Maricunga Belt in the central Andes of northern Chile. The belt is located just east of the main reverse NS fault systems which are part of the Sierra Castillo, Potrerillos Mine and Claudio Gay Cordillera faults, limited to the north and south by the NW-striking oblique to the arc Imilac and Wheelwright-Incahuasi regional faults systems.The epithermal deposits within the SN belt are intimately associated with the occurrence of Middle Miocene volcaniclastic basins and Middle to Upper Miocene phreatomagmatic vents and their related high-sulfidation hydrothermal systems. The volcanostratigraphy of the SN epithermal belt comprises volcaniclastic sequences, subvolcanic and volcanic rocks ranging between the Lower Miocene and the Pliocene. High-angle NS reverse faults involving Paleozoic and lower Cenozoic units form the western-southwestern limit of the belt. Folded and faulted Middle Miocene volcaniclastic and volcanic sequences form the main host rock of at least 4 phreatomagmatic events that generated maar-diatreme fields and discrete maar vents, with their related subvolcanic facies, within the widespread Upper Cenozoic volcanic arc, ranging in age between ca. 15 and ca. 4 Ma. These four phreatomagmatic events are spatially and temporarily associated to 4 main high-sulfidation hydrothermal events which have altered both the phreatomagmatic rocks and the Cenozoic country rock of the explosive activity. These hydrothermal systems have formed dozens of discrete hydrothermally altered areas where argillic, advance argillic, silicification and steam-heated alteration are common. Most of the maar fields and the hydrothermal alteration systems are emplaced within a strike-slip tectonic regime with NE-trending shortening which is accommodated in the NW-striking sinistral-normal faults and NE-striking extension structures. These fault systems crosscutting interaction favor the hydrothermal fluid circulation and migration, as well as mineral precipitation on structural and/or primary lithological traps and on NE-striking tension cracks.In summary, the SN epithermal belt is an almost 200 km long and 60 km wide area, mainly NNE-oriented, where epithermal deposits have formed during the Upper Miocene and Pliocene (ca. 13-4 Ma), emplaced within Middle to Upper Miocene volcanic and volcaniclastic sequences associated to small volcanotectonic basins oriented in NS, NE-SW and NW-SE directions, in which most of the high-sulfidation systems are associated to discrete or repetitive structurally-controlled Upper Miocene-Pliocene phreatomagmatic vents and maar fields.

Stress field and tectonic regime of the Eastern Mediterranean from inversion of earthquake focal mechanisms

The formal stress inversions of 1258 earthquake focal mechanism solutions reveal the presence of six distinct stress regimes. However, the predominant tectonic regimes comprise normal faulting (39%), strike-slip faulting (29%), thrust faulting (25%), and unspecified oblique faulting (7%). The division of the study area into zones based on structural and deformation patterns has provided valuable insights into the variations in the stress field and tectonic processes within this seismically active region. For each designated zone, reduced stress tensors were derived using the improved right dihedron method and the rotation optimization technique implemented by the Win-Tensor software.The stress field derived from the entire dataset is characterized by R′ = 1.0 and an NW-SE SHmax orientation, strongly influenced by the tectonic stress regime of the Hellenic Arc. In specific regions such as CYS, CEM, and WEM, the prevailing tectonic regimes is characterized by a predominant compressive setting with a stress index (R' = 2.0 to 2.5). This pattern aligns with neotectonic deformation associated with the subduction of the African Plate beneath the Eurasian Plate. The EMZ Zone exhibits a strike-slip tectonic regime with an R' of 1.50, primarily influenced by the Dead Sea Transform Fault. This fault accommodates differential motion between the African and Arabian plates in the NNE direction, resulting in left-lateral strike-slip motion along the plate boundary. The mean slip tendency values, varying between 0.62 and 0.66, suggests that the faults in the study area are appropriately oriented for slip or shear displacement, indicating an elevated probability of reactivation.

Tectonic stress of northeastern Indian region derived from seismic focal mechanisms and the effect of focal mechanism on stress drop: a comparative analysis with Kachchh intraplate region of India

SUMMARY In this study, the focal mechanism solutions and source parameters of recent earthquakes that occurred in the northeastern region of India have been determined. The region has very complex tectonics as it is subjected to the compressional forces from all sides, due to the collision of the Indian Plate with the Eurasian, Burma and Tibetan plates. Waveform data from deployed broad-band seismographs (BBS) and strong motion accelerographs (SMA) in the northeastern India are used to determine the focal mechanism solutions and source parameters of moderate earthquakes, respectively. The estimated focal mechanisms are used to understand the existing stress field in the region. It is found that the Shillong-Plateau as well as the Indo-Burma subduction zone is dominated by the compressional tectonic regime, Mikir Hills and Bengal basin are dominated by the trans-tension tectonic regime, and the easternmost Himalayan region is dominated by the strike-slip tectonic regime. The maximum horizontal stress direction Shmax is also determined for above subregions. The direction of Shmax is southeast in the Bengal basin, northeast in Mikir Hills and Indo-Burma subduction zone whereas it is NNE in Shillong Plateau and SSW in the eastern Himalayas. The estimated stress drop value of the earthquakes in the region ranges from 2.11 to 23.89 MPa. The relationship between the source parameters and focal mechanisms is also explored. It is found that the earthquakes with a strike-slip mechanism have the highest average stress drop (7.05 MPa) followed by reverse (6.82 MPa) and normal (5.12 MPa) in the northeastern region of India. According to the examined data set, the stress drop is found to be dependent on the type of focal mechanism, seismic moment and hypocentral depths. The comparison of the results with the Kachchh intraplate region in western India shows earthquakes in Kachchh have larger mean stress drop for all types of mechanisms. In both intraplate and interplate regions of India, the stress drop of earthquakes depends on the type of focal mechanism solution.

Neotectonics and Geothermal potential of the East Anatolian Tectonic Block: A case study in Diyadin (Ağrı) geothermal field, NE Turkiye

The study area is Diyadin, which is situated 71 km ESE of Ağrı very close to the Turkish-Iranian State border. It is one of several type localities of promising geothermal fields in the Eastern Anatolia. The neotectonic regime and related structures are dominated by a strike-slip tectonic regime governed by a stress field in the Eastern Anatolia where the greatest principal stress (σ1) is operating in NNW direction (N22°W) while the least principal stress (σ3) is N68°E. This stress field state was proved once more by the tensor solution of the 12 June 2022 Akçift (Muradiye-Van) earthquake of Mw = 5.1. The strike-slip neotectonic regime started at the time of latest Pliocene-early Quaternary and then triggered the first occurrence of the fissure eruption along the NNW trending Kaletepe open fracture. This event was followed by the development of both the two-peaked Tendürek strato-shild volcano and the Diyadin geothermal field (DGF). The geothermal potential of the DGF is high and its most common manifestations are the active tectonic regime and related faults (extensional horse tail strucure), active volcanoes (Tendürek and Ağrı volcanoes), fumeroles, numerous hot water springs to artesian wells, widespread iron-rich alteration zones, actively &#x0D; growing fissure-ridge travertines and the probable presence of the unroofed hypabyssal felsic to intermediate intrusions of Quaternary age at the roots and their near environs of the isolated Quaternary volcanoes in the Eastern Anatolia. In addition, some significant similarities and contrasts are seen between the DGF and the IGF when they are compared.

Tectonic Regime as a Control Factor for Crustal Fault Zone (CFZ) Geothermal Reservoir in an Amagmatic System: A 3D Dynamic Numerical Modeling Approach

Crustal fault zones provide interesting geological targets for high-temperature geothermal energy source in naturally deep-fractured basement areas. Field and laboratory studies have shown the ability of these systems to let fluid flow down to the brittle–ductile transition. However, several key questions about exploration still exist, in particular the fundamental effect of tectonic regimes on fluid flow in fractured basement domains. Based on poro-elasticity assumption, we considered an idealized 3D geometry and realistic physical properties. We examined a model with no tectonic regime (benchmark experiment) and a model with different tectonic regimes, namely a compressional, an extensional and a strike-slip tectonic regime. Compared to the benchmark experiment, the results demonstrate that different tectonic regimes cause pressure changes in the fault/basement system. The tectonic-induced pressure changes affect convective patterns, onset of convection as well as the spatial extent of thermal plumes and the intensity of temperature anomalies. Driven by poro-elastic forces, temperature anomalies around vertical faults in a strike-slip tectonic regime have a spatial extent that should be considered in preliminary exploratory phases.

Estimation of horizontal stresses from wellbore failures in strike-slip tectonic regime: A case study from the Ordovician reservoir of the Tinzaouatine field, Illizi Basin, Algeria

We present a geomechanical analysis of the Ordovician reservoir from the Tinzaouatine field situated in the prolific Illizi Basin, eastern Algeria. The sandstone reservoir has a hydrostatic pore pressure gradient (9.95 MPa/km). We analyzed a cumulative of 300 m of acoustic image log data and identified the coexistence of B-quality extensive drilling-induced tensile failures (DITFs) and compressive failures, i.e., breakouts (BOs), indicating a mean maximum horizontal stress ([Formula: see text]) orientation of N140°E. We used a combined BO and DITF-based solution to estimate horizontal stress magnitudes when the two failure types coexist. Based on the C-quality minifrac measurements, we interpreted the minimum horizontal stress ([Formula: see text]) gradient as 17.4–17.47 MPa/km, whereas the new approach indicates an [Formula: see text] range of 17.31–18.67 MPa/km. Using the BO width and DITF-based approaches, we inferred an [Formula: see text] gradient range of 28.37–38.59 MPa/km within the studied reservoir. Based on the relative stress magnitudes, we infer a strike-slip tectonic stress regime in the studied field.

Plio-Quaternary strike-slip tectonics in the Central Mallorca Depression, Balearic Promontory: Land–sea correlation

The Balearic Promontory (Spain) is of key importance to understand the tectonic kinematics of the westernmost Mediterranean, because its continued marine sedimentation has recorded the contrasting effects expected from competing geodynamic models proposed for the region. Near the center of this promontory, between the islands of Mallorca and Ibiza, the Miocene to Pleistocene stratigraphy of the Central Mallorca Depression presents an ideal record of the tectonic deformation that has received only limited attention. We use a widespread dataset of 2D seismic reflection profiles to identify, interpret and map the main prominent reflectors and extrapolate the thickness of the pre-Messinian and Pliocene-Quaternary sedimentary units. We then quantify the timing and style of deformation related to the various fault systems. Our results reveal for the first time a series of aligned small depressions bounded by extensional and strike-slip faults and filled with Plio-Quaternary sediment, perfectly aligned with the sub-basins of the onshore Mallorca Graben. A subsidence analysis confirms this correlation. We identify non-cylindrical deformation within the Plio-Quaternary unit that is remarkably similar to that observed onshore, suggesting continuous fault zones from the Central Mallorca Depression to Mallorca Island. We interpret an intra-PQ unconformity as the marker of a transition from extensional to strike-slip tectonic regime. The strike-slip stage is represented by both transpressional and transtensional structures, interpreted as restraining/releasing bends respectively and step overs along the faults. We show that these offshore faults in the Central Mallorca Depression overlap well with seismic epicenters and suggest major active strike-slip corridors that have an onshore continuity both until eastern Mallorca and in the southwestern Ibiza margin. The role of previous tectonic inherited structures (rifting, Betic thrusts, post-orogenic collapse) on the deformation reported here is discussed and we propose a tentative sketch that integrates our results in a Miocene to Present-day evolution at regional scale.

Active tectonics of Gülpınar-Tuzla area (Biga Peninsula, NW Turkey): The source of 6 February-24 March 2017 earthquake cluster

The variation in the motion sense of Anatolian platelet in Aegean Sea resulted in a strike-slip tectonic regime and related neotectonic domain, the central to northern Aegean neotectonic province, which also includes both western Marmara Sea and Biga Peninsula. Our study focuses mostly on the Gülpınar-Tuzla earthquake area located at the southwestern tip of Biga Peninsula, which is controlled by the southern major strand of the North Anatolian Fault System (NAFS). The strand consists of two sections, the onshore Biga and offshore Babakale-Skyros sections. Both sections are seismically very active. The Gülpınar-Tuzla earthquake area is composed of the Paleozoic metamorphic rocks, the Oligo-Miocene granitoid pluton, Lower-Middle Miocene calc-alkalic volcanic rocks and the Upper Miocene-Pliocene sedimentary sequence. All of these rocks, which formed and deformed (folded to tilted) in palaeotectonic period, are overlain with an angular unconformity by the Quaternary neotectonic basin fill, that is nearly flat-lying except for the faulted basin margins. Both the onshore and offshore sections of the southern strand are linked to each other in terms of the structures characterizing the Babakale pull-apart basin and the Gülpınar-Tuzla earthquake area. The latter is shaped by the NE-trending Gülpınar (GFZ) and Yenice-Gönen Fault Zone (YGFZ), the ENE-trending Edremit fault zone (EFZ), the WNW-trending Tuzla Fault Zone (TFZ) and three strike-slip basins (Ayvacık, Behramkale and Tuzla basins) developed along them. Some segments of both the TFZ and GFZ were reactivated by the occurrences of seven moderate-to small-sized independent earthquakes and related aftershocks over 2760. Five of the independent earthquakes have an origin of oblique-slip normal faulting, while the rest two seismic events are strike-slip faulting in origin. Focal mechanism solution diagrams of these two groups of earthquakes reveal that the Gülpınar-Tuzla area is under the control of a strike-slip neotectonic regime, which commenced in Early Quaternary time owing to the major inversion in extensional palaeotectonic regime. This is also supported by the palaeostress analysis of slip-plane data measured on fault slickensides. The uniform slip rates on both the YGFZ and EFZ are 10.8 mm/yr and 7.3 mm/yr, respectively.

Tectonic Influence on Speleogenesis of Sea Caves on Biševo Island (UNESCO Global Geopark Vis Archipelago, Adriatic Sea, Croatia)

A geological and speleological investigation was conducted in the famous Blue Cave (Modra špilja) and the Monk Seal Cave (Medvidina špilja) on Biševo Island (Croatia) to promote the island’s geoheritage through the new Visitor Centre. The island is mainly composed of Cretaceous to Paleogene neritic carbonates, which form the bedrock, whereas parts of the island are covered with thin Quaternary sediments. The caves are of small dimensions and a simple layout, composed of the main channel and few shorter side channels, all positioned in the tidal zone. Thus, the caves are semi-submerged sea caves located along the coastline. The Blue Cave and the Monk Seal Cave developed within the bedrock limestones and dolostones, respectively, within a zone of left-lateral NNE–SSW striking strike-slip faults that belong to the Biševo fault system. Conjugated discontinuities within the carbonate bedrock indicate a specific strike-slip tectonic regime. Additionally, the host rocks were probably also deformed and fractured during the rise of salt diapirs that characterise this part of the Adriatic foreland. Tectonic and bedding discontinuities form the fragments of the host rock, that combined with the impacts of the strong southern waves, significantly influenced the genesis of the caves.

Miocene to present-day tectonic control on the relief of the Duero and Ebro basins confluence (North Iberia)

ABSTRACT This article presents a morpho-structural map at 1:50,000 scale of the confluence area between three regional units: (1) the Burgalesa Platform (Mesozoic; Cantabrian Mountains), (2) the Duero Basin and (3) the Ebro Basin (Cenozoic foreland basins). The map covers an area of 527 km2 in north Iberia. Additionally, structural lineaments such as joints are well preserved and documented in the Upper Cretaceous sediments of the Burgalesa Platform, represented by four main sets regarding their orientation. The foreland basins are incised in Miocene materials by rivers that have developed a complex drainage system controlling the deposition of the most recent alluvial sediments, following the four structural orientations. The map, together with the analysis of orthophotos and a Digital Terrain Model, and outcrop-scale observations, have led us to document the influence of the Miocene to present-day compression and strike-slip tectonic regime on the configuration of the drainage system and the geomorphological features.

The March 2017 earthquake sequence along the E-W-trending Mcid Aïcha-Debbagh Fault, northeast Algeria

In Northeast Algeria, a sequence of 143 small earthquakes (Md ≤ 4.7) occurred near the Mcid Aicha-Debbagh (MAD) Fault between 4 and 16 March, 2017. During this sequence, 74% of the seismic activity occurred in the first two days. Although the earthquakes were not large, they yielded important new information and have improved our understanding of seismic activity in three distinct regions along the fault. In the Sidi Dris region (western MAD Fault), 106 events (1 ≤ Md ≤ 3.2) were located in an aftershock cluster trending NNE-SSW, highlighting a transverse fault with ∼6 km of strike-slip displacement that locally cuts the MAD Fault. In the El Kantour region (central MAD Fault), 31 events were recorded along a 3 km long fault segment, including the Mw 4.7 mainshock. The mainshock had a focal mechanism consistent with predominantly strike-slip motion on a N110°E-striking fault plane, in agreement with the WNW-ESE orientation of the central MAD Fault segment. Finally, six diffuse events occurred in the Hammam Debbagh region (eastern MAD Fault). A significant event (Md 3.0) in this region had a focal mechanism consistent with strike-slip movement and a normal component trending NW-SE. This is consistent with the fault plane orientations of key events in the time period 2003–2014, likely related to the NW-SE-striking Hammam Debbagh Fault. The present-day stress tensor is characterized by a strike-slip tectonic regime and a σ1 orientation (N342°E) that closely matches the maximum regional compressive stress orientation (NNW-SSE).

Strike-slip reactivation of a high-angle normal fault induced by increase of reservoir pore pressure: insight from 3D coupled reservoir-geomechanical modeling

How would high-angle normal faults be reactivated under a present-day strike-slip tectonic regime if reservoir pore pressure (Pp) increased during injection operations? What parameters would control shear slip localization? To answer these questions, 3D one-way coupled reservoir geomechanical modeling of potential fault reactivation in the St. Lawrence Platform, Quebec is performed. We evaluate the risk of shear failure along the pre-existing subsurface Yamaska high-angle normal fault under the present-day strike-slip tectonic regime. Slip may be generated by pressure perturbations in deep saline aquifers of the Early Paleozoic sedimentary basin; this has implications for the assessment of risks associated with CO2 storage and deep geothermal energy potential. The Yamaska Fault is oriented NE-SW with a strike varying from subparallel to ∼35° to the orientation of maximum horizontal stress (NE63°) and dips to the SE at ∼60° with ∼800 m of vertical throw. Multiple runs of the 3D model simulate steps of increasing Pp by 4, 6, 8 and 15 MPa in the footwall sandstone reservoir at a depth of 1.25-1.5 km. Our modeling results show plastic shear deformation along the Yamaska Fault is initiated by pressure increase of 4-6 MPa. More model fault cells fail when pore pressure is increased by 8 MPa, when the reservoir pressure reaches ∼21-24 MPa, and a larger area slips during the next injection stage. The non-linear geometry of the fault results in localization of plastic shear strain on the fault segments optimally oriented, while other segments remain inactive. The dextral plastic shear deformation occurs mostly at the depth of the injection interval, propagating upward to the caprock in highly stressed fault segments. Our study helps to quantify the risk of fault reactivation induced by injection operations.

Modelling tectonic deformation along the North-Anatolian Fault in the Sea of Marmara

Using analogue techniques, we attempted to model the complex tectonic deformation pattern observed along the North-Anatolian Fault in the Sea of Marmara from morpho-bathymetry and seismic reflection images. In particular this paper focuses on the so-called Cinarcik segment of the fault connecting the eastern Izmit segment, which entirely ruptured during the Mw 7.4, 1999 earthquake, to the western segment of the Central High. The Çınarcık segment, potentially loaded after the Izmit earthquake, is expected to rupture during an earthquake occurring in the near future, possibly the next decades, with a high potential to affect the Istanbul metropolitan area. Our analysis suggests that the development of the observed structures accommodating strike-slip, transtensional and transpressional deformations, could be explained by changes in the geometry of fault segments within a right-lateral strike-slip tectonic regime. Tectonic deformations were reproduced in the analogue model by imposing a small (about 10°) and sharp difference in the relative orientations of the strike-slip segments at the edges of a major releasing bend. In the model slower strain accumulation occurs along the analogue of the Çınarcık segment than along the analogue of the Izmit segment of the fault. This would predict a delay for earthquakes triggered by stress transfer between the Izmit and Çınarcık segments. The model further predicts that most of the deformation in the Çınarcık basin is controlled by the sharp changes in the geometry of the fault itself.

Deep submarine landslide contribution to the 2010 Haiti earthquake tsunami

Abstract. The devastating Mw 7.1 Haiti earthquake in 2010 was accompanied by local tsunamis that caused fatalities and damage to coastal infrastructure. Some were triggered by slope failures of river deltas in the close vicinity of the epicenter, while others, 30 to 50 km to the north across the Bay of Gonâve, are well explained by the reverse component of coseismic ground motion that accompanied this mostly strike-slip event. However, observations of run-up heights up to 2 m along the southern coast of the island at distances up to 100 km from the epicenter, as well as tide gauge and DART buoy records at distances up to 600 km from the epicenter, have not yet received an explanation. Here we demonstrate that these observations require a secondary source, most likely a submarine landslide. We identify a landslide scar 30 km from the epicenter off the southern coast of Haiti at a depth of 3500 m, where ground acceleration would have been sufficient to trigger slope failure in soft sediments. This candidate source, 2 km3 in volume, matches observations remarkably well assuming that the sediment collapse obeys a viscous flow with an initial apparent viscosity of 2×105 Pa s. Although that particular source cannot be proven to have been activated in 2010, our results add to a line of evidence that earthquake-triggered submarine landslides can cause significant tsunamis in areas of strike-slip tectonic regime.

An active tectonic field for CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; storage management: the Hontomín onshore case study (Spain)

Abstract. One of the concerns of underground CO2 onshore storage is the triggering of induced seismicity and fault reactivation by the pore pressure increasing. Hence, a comprehensive analysis of the tectonic parameters involved in the storage rock formation is mandatory for safety management operations. Unquestionably, active faults and seal faults depicting the storage bulk are relevant parameters to be considered. However, there is a lack of analysis of the active tectonic strain field affecting these faults during the CO2 storage monitoring. The advantage of reconstructing the tectonic field is the possibility to determine the strain trajectories and describing the fault patterns affecting the reservoir rock. In this work, we adapt a methodology of systematic geostructural analysis to underground CO2 storage, based on the calculation of the strain field from kinematics indicators on the fault planes (ey and ex for the maximum and minimum horizontal shortening, respectively). This methodology is based on a statistical analysis of individual strain tensor solutions obtained from fresh outcrops from the Triassic to the Miocene. Consequently, we have collected 447 fault data in 32 field stations located within a 20 km radius. The understanding of the fault sets' role for underground fluid circulation can also be established, helping further analysis of CO2 leakage and seepage. We have applied this methodology to Hontomín onshore CO2 storage facilities (central Spain). The geology of the area and the number of high-quality outcrops made this site a good candidate for studying the strain field from kinematics fault analysis. The results indicate a strike-slip tectonic regime with maximum horizontal shortening with a 160 and 50∘ E trend for the local regime, which activates NE–SW strike-slip faults. A regional extensional tectonic field was also recognized with a N–S trend, which activates N–S extensional faults, and NNE–SSW and NNW–SSE strike-slip faults, measured in the Cretaceous limestone on top of the Hontomín facilities. Monitoring these faults within the reservoir is suggested in addition to the possibility of obtaining a focal mechanism solutions for micro-earthquakes (M&lt;3).

ANÁLISE ESTRUTURAL RÚPTIL NA ZONA DE INFLUÊNCIA DO ARCO DE PONTA GROSSA: ESTUDO DE CASO NA ÁREA DA UHE-MAUÁ-PR

A pesquisa foi realizada no entorno da Usina Hidrelétrica de Mauá (UHE-Mauá), localizada no rio Tibagi, a noroeste do município de Telêmaco Borba divisa com Ortigueira, região central do Estado do Paraná. O local em que a usina está implantada é formado por soleira de diabásio aflorante, pertencente à Formação Serra Geral, intrudida em rochas sedimentares paleozoicas da Bacia do Paraná. No local o controle estrutural se dá em função da intersecção de estruturas regionais como o Arco de Ponta Grossa, localizado entre as Zonas de Falha São Jerônimo-Curiúva e a Zona de Falha Jacutinga. A análise estrutural possibilitou o reconhecimento de falhas, com predomínio de azimute N50-60E em mesoescala. Em fotointerpretação, no entanto, os lineamentos mais marcantes possuem azimute N40-50W. As descontinuidades mapeadas são caracterizadas, principalmente por juntas, falhas e zonas de falhas cataclásticas associadas a regime tectônico transcorrente, por vezes transtensivo com formação de estrutura em flor negativa e falhas oblíquas, identificadas nos sedimentos paleozoicos e nas rochas básicas. Este trabalho aponta a existência de pelo menos dois pulsos de deformação pós-cretácicos, que deformaram a soleira de diabásio e o conjunto de rochas sedimentares encaixantes, alterando o comportamento reológico da rocha e a disposição geométrica final dos grandes planos de fraquezas. O primeiro está ligado a um campo de paleotensão variável entre NNE-SSW e NNW-SSE e o segundo a um campo de paleotensão variável entre WNW-ESSE e ENE-WSW

Strike-slip related folding within the Malvinas/Falkland Trough (south-western Atlantic ocean)

The Malvinas/Falkland Trough (M/FT) is an E-W trending bathymetric depression along which runs the present-day South American-Scotia plate boundary. To the north of the M/FT lies the southern sector of the South Malvinas/Falkland Basin, and to the south lies the Burdwood Bank, an elongated morphological high constituting part of the South Scotia Ridge. Analysis of bathymetric and slope maps, integrated with seismic reflection profiles, have allowed describing in detail the M/FT in the sector comprised between 60° and 57° W. Data show the presence of an array of folds forming a thin-skinned fold-and-thrust Belt (FTB), previously interpreted as an active compressional field. The thin-skinned FTB is developed in a triangular-shaped area, which extends ca. 100 km in the E-W direction and 16 km in the N-S direction. Four parallel, asymmetric folds that develop to progressively greater water depths (between 1600 and 2600 m depth) towards the north, with orientations ESE-WNW and lengths that vary between 22 and 98 km, have been recognized. These folds are constituted by Late Cenozoic sediments that are undeformed in the Malvinas/Falkland Trough. The development of folds, which began in the late Miocene (ca. 7 Ma), was associated with the left-lateral strike-slip tectonic regime of the Magallanes-Fagnano-Malvinas lineament, the western segment of the South American-Scotia plate boundary.

Cenozoic paleostress evolution in south central Vietnam: Implication for changing dynamics of faulting along the eastern Indochina continental margin

The tectonics of the Indochina continental margin before and after the Neogene-Quaternary basalt eruption is poorly understood. The analysis of 1500 striated faults observed in different rocks, mostly from volcano-plutonic rocks with ages ranging from Cretaceous to Quaternary, at more than 140 locations in south central Vietnam by direct inversion method allowed us to determine four paleostress regimes that affected eastern Indochina from Oligocene up to present day. The first tectonic paleostress regime with Oligocene age was responsible for the sinistral and dextral motions along the NW-SE and NE-SW striking faults respectively. This stress state is typical for a strike-slip tectonic regime with maximum principal stress (σ1) and minimum principal stress (σ3) axes oriented nearly in E-W and N-S direction and both plunging at average angle of 80 and 100, respectively. The paleostress ellipsoid shape ratio Φ (Φ = (σ2 − σ3)/(σ1 − σ3)) ranges from 0.23 to 0.77 with an average of 0.50 ± 0.15. The subsequent strike-slip tectonic stress state prevailing from the Late Oligocene to very Early Miocene, was characterized by σ1 and σ3 axes trending in NNW-SSE and ENE-WSW and plunging at 120 ± 90, and 120 ± 130, respectively. The paleostress ellipsoid shape ratio Φ ranges from 0.12 to 0.88 with a 0.52 ± 0.23 average. Under this paleostress regime, the N1100 to N1400 and N1600 to N200 striking faults moved with dextral and sinistral movements, respectively. The third paleostress state with assigned Early Miocene to Late Miocene age was responsible for dextral and sinistral motions along N1400 to N1600 and N200 to N400 striking faults, coeval with emplacement of N-S striking basaltic dykes. This pattern shows consistency and homogeneity of the σ1 and σ3 axes in N-S trend, plunging at 120 ± 90 and σ3 in E-W trend, plunging at 130 ± 110, respectively. The paleostress ellipsoid shape ratio Φ varies from 0.41 to 0.89 with an average of 0.53 ± 0.16. The fourth tectonic stress regime occurring since the Late Miocene to the present day is characterized by a consistency of sub-horizontal NNE striking σ1, plunging 110 ± 100 and ESE striking σ3, plunging at 130 ± 11, and an average of ellipsoid shape ratio Φ = 0.45 ± 0.24. Under the latest tectonic stress state, the N-S and N450 to N600 striking faults continue to move as dextral and sinistral faults, respectively. The first three paleostress regimes have evolved clockwise, and were induced by the force exerted from the eastern Himalayan syntaxis during the northward Indian plate motion, while the fourth tectonic stress regime is most likely linked to the force originated from the Sunda subduction.