Strike Slip Research Articles

Analysis on the Causative Fault of the 2021 Mw 6.0 Tehoru Earthquake in the South Coast of Seram Island: A Preliminary Result

Seram Island is the northern part of the Banda subduction which is characterized by the existence of a thrust fault structure in the Seram Trough as the main contributor to seismicity in this region. Complex tectonic activity also forms a deformation zone of the Kawa Fault with a sinistral strike slip mechanism and high-angle normal faults in the mainland. On June 16, 2021 a Mw 6.0 earthquake occurred on the south coast of Seram, in Tehoru to be precise, which followed by a small tsunami wave which is thought to have been generated by an underwater landslide. This earthquake has a normal fault mechanism which is quite rare on Seram Island, however, the actual fault plane that caused the earthquake is still unknown. In this study, we investigate potential faults that may have caused the 2021 Tehoru earthquake by performing a seismicity analysis using well relocated hypocenter of the mainshock and the aftershocks sequence. We use the double-difference relocation method with the SVD algorithm performed in the hypoDD program. The results show the distribution of aftershocks that form a northeast-southwest trending lineation. The depth of the hypocenter has also improved from being dominated by fixed depth to being varied with dominance at depths of 8-14 km. An important feature of the relocation results is that the aftershocks distributed downward along a ~35° northwest-dipping plane which indicates a southwest-northeast fault orientation. This result confirmed by using geodetic observations that shows a horizontal displacement of 14 mm toward northwest direction and a land subsidence of 14 mm. This southwest-northeast oriented fault structure is thought to be associated with high-angle normal fault resulting from a north-south extension activity in the central part of Seram Island. The results of this study indicate the existence of other local fault structure in the Seram Island which can be used as a basis for seismic hazard assessment, other than seismic activities from Seram Trough and Kawa Fault.

Variation of Displacement Fields for Great Earthquakes due to Rectangular Fault System

The expressions for the displacement fields produced by a finite rectangular fault associated with great earthquakes are explained by elastic theory of dislocation. The variation of displacement fields has been estimated by considering the elastic half-space in contact with traction free boundary and varying depth, distance from top to bottom of the fault. It is also carried out in an infinite elastic medium. Also, the variation of displacement fields with the distance from fault especially for strike slip fault shows that even if different fault length and approximately equal magnitudes, the variation of displacement fields with the distance from the fault is almost the same in the case of great earthquakes viz. San Francisco (1906) and Bihar-Nepal (1934).

Detachment levels of Colombian caribbean mud volcanoes

Regional analysis of mud volcanoes demonstrates the regional extension of these processes in Northern Colombia. Mud volcanoes are active systems that manifest the characteristics of the underlying sedimentary sequences on the surface, as well as the presence of hydrocarbons. These may which provide information about the oil systems and the characterization of new migration paths. New data acquired during field geology studies, along with the evaluation of acquired aerial images by dron, allowed to observe variations in terms of morphology and neotectonic process, being distinctive between mud volcanoes formed in different structural domains. Mud volcanoes formed in areas of basement without thrust faults (back stop zone) are usually circular, connected to the basement by regional faults. Other mud volcanoes formed in older and younger deformed belts tend to present ellipsoidal shapes, with drainages patterns that suggest local stress fields associated with regional strike slip movements of major faults. The analysis of U/Pb ages in detrital zircons extracted from mud volcanoes and outcropping sedimentary sequences in the Colombian Caribbean, together with the analysis of foraminiferal and palynomorph faunas, suggest different levels of detachment. Clay mineralogy and geochemistry indicate that mud volcanoes formed in the back stop and the Northern part of the San Jacinto deformed belt have sludge material originated in sedimentary sequences with contributions from continental basement rocks, while the mud volcanoes located in the central and Southern parts of the studied area tend to show sediments provided from deepest stratigraphic levels, derived from less evolved magmatic sources (dioritic basements). Gas and water analysis obtained from studied mud volcanoes suggest that the old deformed belt, Paleocene accretionary wedge and back stop areas, have evidences of thermogenic oil systems, while in the domain of the younger deformed belt the tendency is to indicate evidences of microbial process.

Bayesian regional moment tensor from ocean bottom seismograms recorded in the Lesser Antilles: implications for regional stress field

SUMMARY Seismic activity in the Lesser Antilles (LA) is characterized by strong regional variability along the arc reflecting the complex subduction setting and history. Although routine seismicity monitoring can rely on an increasing number of island stations, the island-arc setting means that high-resolution monitoring and detailed studies of fault structures require a network of ocean bottom seismometers (OBS). As part of the 2016–2017 Volatile recycling at the Lesser Antilles arc (VoiLA) project, we deployed 34 OBS stations in the forearc and backarc. During the deployment time, 381 events were recorded within the subduction zone. In this paper, we perform full-waveform regional moment tensor (RMT) inversions, to gain insight into the stress distribution along the arc and at depth. We developed a novel inversion approach, AmΦB—‘Amphibious Bayesian’, taking into account uncertainties associated with OBS deployments. Particularly, the orientation of horizontal components (alignment uncertainty) and the high noise level on them due to ocean microseisms are accounted for using AmΦB. The inversion is conducted using a direct, uniform importance sampling of the fault parameters within a multidimensional tree structure: the uniXtree-sampling algorithm. We show that the alignment of the horizontal OBS components, particularly in high noise level marine environments, influences the obtained source mechanism when using standard least-squares (L2) RMT inversion schemes, resulting in systematic errors in the recovered focal mechanisms including high artificial compensated linear vector dipole (CLVD) contributions. Our Bayesian formulation in AmΦB reduces these CLVD components by nearly 60 per cent and the aberration of the focal geometry as measured by the Kagan angle by around 40 per cent relative to a standard L2 inversion. Subsequently, we use AmΦB-RMT to obtain 45 (Mw > 3.8) regional MT solutions, out of which 39 are new to any existing database. Combining our new results with existing solutions, we subsequently analyse a total of 151 solutions in a focal mechanism classification (FMC) diagram and map them to the regional tectonic setting. We also use our newly compiled RMT database to perform stress tensor inversions along the LA subduction zone. On the plate interface, we observe the typical compressional stress regime of a subduction zone and find evidence for upper-plate strike slip and normal fault behaviour in the north that becomes a near arc-perpendicular extensional stress regime towards the south. A dominant slab perpendicular extensional stress regime is found in the slab at 100–200 km beneath the central part of the arc. We interpret this stress condition to be a result of slab pull varying along the arc due to partial slab detachment along previously hypothesized lateral slab tear near Grenada, at the southern end of the LA arc, leading to reactivation of pre-existing structures around the subducted Proto-Caribbean ridge.

Opposite microplate rotations on the East African Rift: Similarity to double saloon door tectonics

Documented opposite rotations of the Victoria and Rovuma Microplates in the East African Rift (EAR) are compared to opposite microplate rotations in backarc basins related to subduction rollback. Counter-clockwise rotation of the Victoria Microplate implies northward propagation should occur on the Lakes Rukwa/Tanganyika portion of the Western Branch of the EAR despite the orthodox view that southerly propagation occurs there. A compilation of evidence for propagation including volcanic isotopic ages, border fault throws, subsidence and sediment thickness and age shows northwestern younging of volcanics from 25.9 to 0 Ma at Rungwe southeast of Lake Rukwa to 5.8–2.6 Ma ages at Mwenga-Kamituga, northern end of Lake Tanganyika, and north propagation in Rusizi to Kivu, and Virunga to Toro Ankole segments. Predicted southerly propagation on the Lake Malawi Rift is supported by southerly decreasing border fault throws and sediment isopachs. Where the southern Victoria Microplate meets the northern Rovuma Microplate, rather than a simple strike slip interface as previously modelled, a triangular rift basin develops widening to the ENE and narrowing to the WSW. Seismicity, digital elevation models and a new geological map indicate this is represented by the combined Ruhuhu/Kilombero/Kilosa/Ruvu/Rufiji Rift complex.

Satellite based detection of pre-earthquake thermal anomaly, co-seismic deformation and source parameter modelling of past earthquakes

The presented work brings satellite-based detection of pre-earthquake transient thermal anomaly and coseismic deformation mechanism using InSAR (SAR Interferometry) observations of the two major earthquakes that occurred recently (the Iran-Iraq border earthquake of Nov. 12, 2017 (Mw 7.3) and the New Mirpur, Pakistan earthquake of 24th Sept. 2019 (Mw 5.4)). Near Iran-Iraq border earthquake, a rise of 4–6 ​°C from the normal temperature in both day and night Land Surface Temperature (LST) maps along the SW part of the fault is observed. In case of the New Mirpur, Pakistan earthquake, a rise of 3–5 ​°C from normal temperature in both day and night LST maps around the SSW and NW side of the epicenter is observed. Further, Sentinel-1A microwave satellite data employing InSAR technique have been used to estimate co-seismic ground deformations and fault geometry and slip distribution of both earthquakes. The results show that both events occurred due to blind reverse fault mechanism dipping NE with shallow dip. The weightage of strike slip component and dip slip component is more or less equal to each other in total slip distribution for Iran-Iraq border earthquake. Similarly, New Mirpur, Pakistan earthquake have more strike slip components than dip slip components in the weightage in total slip distribution. Considerable number of aftershocks have also occurred in the regions as estimated by coulomb static stress along the SW side of the fault geometry of Iran-Iraq border earthquake and for New Mirpur, Pakistan earthquake, along the SSW, NW, and east side of the fault geometry. The correlation between high stress regions before and after the occurrence of earthquakes using thermal anomaly map and Coulomb static stress map has been also observed.

Characteristics of stress field and crustal kinematics of the southern region of Sichuan-Yunnan block, southern Tibet Plateau

The Red River fault is a massive tectonic shear zone of the Sichuan-Yunnan block, southern Tibet Plateau. The target area of this study is the Red River fault's middle-northern section and adjacent areas. Considering the spatial difference of tectonic structures and the inhomogeneity of focal mechanism solutions, we divided the target area into three structural units: the northern extension area, the middle strike-slip movement area, and the west complex rupture area. The study is carried out on the basis of zoning. Using the CAP method to invert the focal mechanism of moderate earthquakes and the principal compressive and tensile stress. Restoring the seismic source spectrum of small and medium earthquakes, then inversion the stress drops in three sub-units based on Brune model using digital waveform records. Our study suggests that: (1) Many high-stress drop earthquakes occurred in the transitional areas from the Weixi-Qiaohou fault to the Red River fault and from the Chuxiong fault to the Qujiang fault, also occurred in the Changning-Baoshan-Yongping area, revealing a large accumulation of local tectonic stress. (2) Some events with Δσ ≥ 20 MPa have occurred in the prominent low-speed anomaly area, indicating that a passive deformation crossed the Red River fault and extended to the west. Yangbi MS 6.4 earthquake (2021) occurred in a strongly locked area with high potential earthquake risk. (3) In the north of the study region, the movement of the Sichuan-Yunnan block to SE-SSE orientation was governed by the dextral strike-slip movement of the NW strike fault; in the middle region, the SE-orientated movement of the block relative to the South China block was governed by the sinistral slip movement of the SN-strike faults; and in the west region, the tectonic stress was governed by clockwise rotation of the block and the sinistral slip movement of the NE strike faults. We suggest that strike slip and rotation of the Red River fault's middle section may drive and aggravate passive movement in the north section, resulting in locally geophysical field responses. Therefore, the potential risk of a large earthquake in the middle-northern section of the Red River fault should be monitored.

The heterogeneity of petrophysical and elastic properties in carbonate rocks controlled by strike-slip fault: A case study from yangjikan outcrop in the tarim basin

The petrophysical and elastic properties of the carbonate rocks controlled by strike-slip fault are still poor understood due to their significant complexities and strong heterogeneities, causing challenges for the exploitation and development of these carbonate reservoirs. To better comprehend the heterogeneity of petrophysical and elastic properties of the fault-controlled carbonate rocks, a small carbonate strike slip fault zone is selected, which is located in Yangjikan section in the Tarim basin. We combine the geostatistical, microscopic observation, petrophysical and ultrasonic analyses to characterize and understand the complexities and heterogeneity of petrophysical and elastic properties with different distance to the main fault core. The results show significant complexities and heterogeneities of petrophysical and elastic properties, and the variations of rocks drilled from the fault core are relatively drastic compared to those from the damage zone. The equivalent pore aspect ratios of the rocks are calculated from the differential effective medium theory, the values in the fault core are much higher compared to those from the damage zone, which can discriminate the pore network architectures and can represent reference for determination of the boundary of fractured damage zone. The controlling factors on the heterogeneity of the petrophysical and elastic properties for the selected fault zone are discussed, which mainly include the influence of fault structure position on fracture development, fluid selective filling on effective fracture and pore development, and the sequence on pore development. The results can contribute to the recognition and prediction of the petrophysical and elastic properties and hydrocarbon exploration in carbonate strike-slip fault zone in the Tarim Basin, and can provide reference for the construction of integrate multiscale heterogeneities models.

A New Model for the Evolution of Oceanic Transform Faults Based on 3D Broadband Seismic Observations From São Tomé and Príncipe in the Eastern Gulf of Guinea

AbstractOceanic Transform Faults are one of manifestations of the three major plate boundaries and a key tectonic feature of oceanic crust. They are broadly considered to accommodate strike‐slip displacement along simple vertical faults and to be largely without magmatic addition. We present the first observations from broadband 3D seismic of buried, Cretaceous‐aged transform faults in the Gulf of Guinea with complex internal architectures including crustal scale detachments and rotated packages of volcanics within oceanic crust. In the study area, several Oceanic Fracture Zones (OFZ) are described from Top Crust to Moho. OFZ scarps are observed to connect at depth with zones of low angle reflectivity which dip into the OFZ and perpendicular to the spreading orientation. At depth they detach onto the Moho, necking the adjacent crust in the manner of extensional shear zones. Thickly stacked and tilted reflectors, interpreted as extrusive lava flows, are common above the shear zones and infill up to 75% of the crustal thickness. The entire OFZ stratigraphy is overlain and sealed by late‐stage lavas that are continuous from the abyssal hills of the trailing spreading ridge. These insights demonstrate complexity previously only predicted in numerical simulations. We propose a model with extension at a high angle to the spreading orientation along a low angle shear zone that acts as a conduit for decompression related melt and volcanism. We conclude that oceanic transforms are non‐conservative and not simple strike slip fault zones, contradicting the conventional view.

RESEARCH ON THE CHARACTERISTICS OF PRESENT CRUSTAL DEFORMATION IN BEIJING AREA BASED ON GNSS

Abstract. We use the GAMIT/GLOBK software to process more than 100 GNSS sites observation covering the Beijing area from 1999–2021 to obtain the three-dimensional velocity field of present-day crustal movement, and the deformation and strain characteristics of Beijing were calculated and comprehensively analyzed by combining with historical earthquakes. The results show that: 1) The present-day horizontal crustal motion of Beijing is dominated by the SEE direction with a rate of 5-10 mm/a with relative to the stable Eurasian reference frame, and the northern and southern areas show uplift as a whole with a rate of 1–3 mm/a, while the central plain area shows overall subsidence, with a maximum subsidence rate of about 130 mm/a. 2) The horizontal deformation is mainly N-E/N-W extension, accompanied by weak shear activity. 3) The N-W trending faults show sinistral strike slip movement as a whole, with about 1.1–2.0 mm/a, and N-E trending faults show dextral strike slip with a rate of less than 1 mm/a. 4) The historical large earthquakes are distributed within the positive and negative gradient zones of the first shear strain rate, transition zones of the rotation rate, and are mostly distributed at the edges of the high and low value zones of the second shear strain rate, and the edges of the high value zones of the east-west strain rate also have a background of large earthquakes.

Spatial distribution and tectonic significance of the landslides triggered by the 2021 Ms6.4 Yangbi earthquake, Yunnan, China

An Ms6.4 earthquake occurred on 21 May 2021 in Yangbi County, Yunnan Province, located in the strong earthquake hazard zone, the border of the Sichuan-Yunnan rhomb block, southeast Tibetan Plateau, causing severe loss of life and property. Adequate research on the distribution characteristics and seismotectonic mechanisms of seismic chain-generated hazards in the region is meaningful for mitigating seismic hazard risks. In this paper, based on the interpretation of remote sensing satellite images and the analysis on GeoScene platform, we compile a detailed inventory of landslides induced by the Yangbi earthquake and analyze the correlation of their spatial distribution with the influence factors. The results show that 95 landslides were interpreted, and their spatial distribution is correlated to the topographic, seismic and geological factors. Statistically, the landslide number and mobility increase with the slope angle; the south- and southeast-facing slopes and weaker metamorphic rocks are more prone to landslides; the higher the seismic intensity, the larger the density and scale of landslides. Furthermore, the development of the landslides is not only influenced by the Ms6.4 mainshock, but also by the Ms5.6 foreshock, which is significantly correlated with the size of landslides. Notably, the long axis of the landslide distribution area is in NW-SE direction, which is nearly parallel to the strike of the Weixi-Qiaohou-Weishan fault zone (WQWF). The landslides are mainly distributed in the southwest wall and southeast section of the fault. The landslide number and density unstably decrease with the vertical distance from the fault with many fluctuations. Combined with the previous studies, two possible seismogenic structure models are inferred. One model is a parallel secondary fault of the WQWF, Another one is a flower structure in the southwest wall of the WQWF. Both models are mainly characterized by right-lateral strike slip with a small normal-fault component. Additionally, the seismic rupture propagated mainly to the southeast along the seismogenic fault in the subsurface without surface rupture.

Contribution of advanced edge-detection methods of potential field data in the tectono-structural study of the southwestern part of Cameroon

The southwest part of Cameroon is composed of a range of geological structures and sedimentary basins, whose geological history dates from the Cretaceous, and their establishment would have originated from the opening of the South Atlantic. Among these structures, the most important is the Cameroon Volcanic Line, generally denoted CVL, followed by the southern part of the Central African Shear Zone (CASZ) called the Foumban Shear Zone (FSZ), the Ntem Complex, the Benue Trough, the northern margin of the Congo Craton, and many others. The major structures identified in this part are formed as a result of geodynamic activity between the Oligocene and the recent period, to which we can add the volcanism that exists along with the continental limit. The XGM201e_2159 model is used to highlight the geological structures of Southwestern Cameroon. First, we separated the regional and residual anomalies from Bouguer gravity data. Then, we used a combination of filters to enhance the signature of the residual anomalies in Southwest Cameroon. These filters identified various geological structures in the area. Finally, we applied the enhanced horizontal gradient amplitude (EHGA) and multi-scale horizontal derivative of the vertical derivative (MSHDVD) methods to reveal the geological contacts, allowing us to establish the corresponding structural map of the region. In addition, the results obtained in this study are the first to precisely define the circumferential demarcation of the continental and oceanic expansions of Mount Cameroon, while clearly illustrating the Bao, Bomana, Tiko, and Ekona faults that extend to the Bakassi Peninsula and the Douala outlet. Furthermore, they highlight the strike–slip faults in the summit vicinity. The structural map shows that most of the geological boundaries identified in the area are trending in the NE–SW, NNE–SSW, ENE–WSW, N–S, and NW–SE directions.

Seismogenic environments of earthquakes on the southeastern margin of the Tibetan Plateau revealed by double-difference tomography

The uplift and expansion of Tibetan Plateau has dramatically changed the tectonics, climate and environment of Asia, and has caused high seismic hazards at its southeastern margin as well. To better understand the generating mechanisms of regional damaging earthquakes and the plateau crustal material expansion, a high resolution crustal P-wave velocity (VP) model is obtained by double-difference tomography using the updated dataset of dense seismic array deployed in the southeastern margin of the Tibetan Plateau (SETP). The results show significant lateral heterogeneities in the upper crust and two prominent low-VP belts are revealed at mid-lower crust (20–35 km), which has a good correspondence with the major faults and has potential for the mid-lower crustal flow. Although almost all the large earthquakes are located at the boundary between high- and low-VP anomalies related to the two low-VP belts, the seismogenic mechanisms are somewhat different. Ludian and Yiliang earthquakes may be associated with the eastern low-VP anomalies in mid-lower crust, which decouples the upper and lower crust and drags the upper brittle crust leading to sinistral strike slip and thrust accompanied with dextral strike slip earthquakes, respectively. Yangbi earthquake is mainly caused by the upper crustal movement and also probably related to the compressive tectonic loading from western material migration of low-VP anomalies in mid-lower crust. As for Changning earthquake, the seismotectonics are mostly affected by water injection at slat mines. Whether the fluids or low-VP anomalies in mid-lower crust, they may weaken the seismogenic layer and make the stress concentration easier. Our results provide a new perspective to study the seismogenesis that the inhomogeneity of upper crust and the mechanically weak materials in mid-lower crust play an important role in triggering and generating crustal damaging earthquakes in SETP, which also helps illuminate the uplift and deformational mode of the plateau.

The boundary between the North China Craton and the Central Asian Orogenic Belt in NE China: Seismic evidence from receiver function imaging

• 38 broadband seismic stations (profile NCISP-10, 400-km-long) were deployed across the North China Craton (NCC) and the Central Asian Orogenic Belt (CAOB) in Northeast China. • Receiver function CCP images reveal a southward thrust nappe structure at the boundary of the NCC and the CAOB. • Yilan-Yitong fault (YYF) cuts through the Moho and has a vertical offset of 2–3 km indicating that it represents an ultra-crust normal fault. This study imaged the crustal structure and tectonic state of the interacting North China Craton (NCC) and Central Asian Orogenic Belt (CAOB) using receiver function imaging. The seismic profile derived from the NCISP-10 broadband seismic array spanning a northeasterly area of the NCC and a southeasterly area of the CAOB. The profile shows a flat Moho with localized anomalies but generally resting at an average depth of 32 km. The average Vp/Vs ratio was about 1.75 but the crust around the Songliao Basin exhibits a relatively high Vp/Vs ratio and a shallow Moho. An obvious velocity discontinuity appears within the crust beneath the Songliao Basin as evidenced by theoretical model tests which managed effects from multiple waves generated by sedimentary layers in the basin. This discontinuity inclines gently and is interpreted to represent the deep extension of the Chifeng-Kaiyuan fault (CKF), which itself serves as the surface boundary between the NCC and CAOB. The NCC feature appears to the south of this boundary, while a nappe structure formed during subduction-collision and composed primarily of a subduction-accretionary complex lies to the north. The Tanlu Fault consists of two branches in the study area, the Yilan-Yitong fault (YYF) and the Dunhua-Mishan fault (DMF). The YYF cuts through the Moho and has a vertical offset of 2–3 km indicating that it represents a crustal-scale normal fault. The DMF gives no obvious indication of vertical offset in the images but may be mainly characterized by sinistral strike slip movement.

Mechanical Models of Fault-Slip Rates in the Transverse and Peninsular Ranges, California

AbstractThe Transverse and Peninsular Ranges of Southern California host a geometrically complex network of seismically active faults with a range of slip senses. Here, we present 3D mechanical models of this region that are driven by the total Pacific-North American plate motion and slip on the San Andreas, San Jacinto, and Garlock faults. Based on these boundary conditions, we solve for the full 3D distribution of slip rates on 83 faults and compare model slip-rate predictions to long-term slip-rate data from Uniform California Earthquake Rupture Forecast version 3 (UCERF3) as well as individual geologic point-based estimates of long-term slip. About 46/68 (68%) model-predicted average fault-slip rates are within the UCERF3 slip-rate ranges with a root mean squared error (RMSE) of 1.03 mm/yr to the nearest (upper or lower) UCERF3 limit. The largest slip-rate discrepancies occur on the San Gabriel, Pine Mountain, and Big Pine faults, which may be presently inactive. We find that removing these three faults (i.e., assuming they are inactive) results in an improvement in all goodness-of-fit metrics with 47/63 (75%) UCERF3 slip rates fit with an RMSE of 0.40 mm/yr. We also compare this same model to existing point-based long-term slip-rate estimates and fit 39/69 (60%) with an RMSE of 0.79 mm/yr. The ability for the model to fit independent slip-rate data implies that strike slip along the “Big Bend” of the San Andreas fault (in conjunction with slip on the Garlock and San Jacinto faults) along with total plate motion is sufficient to reproduce both reverse-slip rates throughout the Transverse ranges and strike-slip rates in the Peninsular Ranges regions without additional driving forces needed. Overall, the models provide slip rates and distributions for 83 faults, including faults that currently do not have geologic slip-rate estimates and/or may not produce interseismic deformation.

Fold formation in Kurdish Zagros (N Iraq)

Analysis of seismic sections and wells near the frontal folds of Iraqi Kurdistan (Low- and Highly folded zone) document the interplay of folds, faults and possible mechanisms of their generation.Serial sections from 3D seismic volume in the Low folded zone are interpreted based on calibration wells. Sections display fold evolution from low amplitude kinked monocline to high amplitude ramp folding. The fold continues towards the exposed Safeen anticline with a subvertical limb. These lowland sections can also be considered as the lateral growth segment of Safeen anticline.Three geoseismic sections through frontal folds were constructed with variable quality seismic and dips, formation tops from surface and from mountains wells. These sections show tight anticlines with thrust faults cutting to near surface on both limbs; remnant normal faults; a subvertical southern limb crossed by flat thrusts; and a Triassic ductile core.Sections suggest that this part of Zagros is built of two ‘rigid’ units: an upper, Mesozoic-Neogene and a lower, Paleozoic one, separated by a ductile detachment along the lower Triassic. The upper unit is prone to folding and faulting, the lower one to faulting. The detachment in-between comprises the Kurrachine C, lower Triassic Beduh and Mirga Mir formations, and potentially the top members of Permian Chia Zairi formation. Detachment is possibly dominated by evaporites. Our detachment is thicker than only Beduh-Mirga Mir detachment proposed by recent reconstructions of others.Folds are initiated as detachment folds above thickened parts of the Lower Triassic, then evolve into ramp folds. Ramp is formed by the merger of flat thrusts with pre-existing steep earlier normal faults that affect the Mesozoic section. Shear and drag beneath these ramps lead to steepening of the southern limb and to fault propagation. A basal flat thrust is the final element of this fault propagation stage. Underlying rigid Paleozoic can form imbricates that push the Triassic detachment upwards, creating passive folds. These Paleozoic imbricates dip to the south and not to the north, as suggested by reconstructions of others. Finally, strike slip shear documented at outcrops also contributes to the final fold form.Own and others' surface geological observations, indications from seismic and radiometric data suggest that fold generation started in Late Cretaceous, continued in the Paleogene in internal Highly folded zone. In our study area only Late Neogene fold growth can be documented, which is in harmony with 5–8 Ma uplift dates of others. Others’ geomorphologic work suggests fold lateral growth is a quick process. We propose that regional folds, such as Safeen anticline grow in distinct short periods separated by longer quiet intervals.

Finite Element Modelling of a Nonplanar Strike Slip Fault in Vertically Inhomogeneous Viscoelastic Medium

Finite Element Modelling of a Nonplanar Strike Slip Fault in Vertically Inhomogeneous Viscoelastic Medium

Late Pleistocene Boulaaba travertine and calcareous tufa, Kasserine, Central Tunisia: Implications for North African spring-fed Ca-carbonates

Late Pleistocene (≈21000 BP) travertine and calcareous tufa deposits have been recognized in the region of Boulaaba, Kasserine in Central Tunisia with a variety of morphological aspects and depositional facies. Morphological aspects of these deposits consist of two elongated continental Ca-carbonate masses defined as fissure-ridges built-up around old fissure networks. Distinction between travertine and tufa lithofacies, based on textural, compositional and topographic settings regarding the entire carbonate masses, have led for travertine to 5 lithofacies: (1) banded travertine fissure infill, (2) bacterial shrubs, (3) stromatolitic laminae, (4) pisoids and (5) speleothem-like travertine growth habits. Tufa is composed of autochtonous tufa lithofacies with (1) phytoherme framestone tufa, (2) calcified insect larval constructions, and clastic alllochtonous tufa lithofacies with (1) matrix-supported microdetrital tufa and (2) grain-supported macrodetrital phytoclast tufa. Both lithofacies show variable diagenetic evolutions with an overall lithification. These deposits are concentrated along the Foussana trough-related normal faults and fractures that belong to the extensional regime of the major strike slip fault of Kasserine that enhanced and facilitated fluid upwelling along with movements of faults which damage and fracture the rocks and increase the overall permeability. During this phase (Late Pleistocene), the deposition of Boulaaba travertine and tufa has implied some paleo-hydroclimatic conditions marked in most North African travertine and tufa depositing sites by (1) a higher water table with abundant effective rainfall on the recharge areas, (2) dense plant cover and soils giving acidic water infiltrations, (3) karstic dissolution of Cretaceous limestones (especially the limestone aquifers of Bireno and Abiod), and (4) a strong water mineralization of the groundwater.

Airborne geophysics and remote sensing of an Nimas-Khadra area, southern Arabian shield: New insights into structural framework and mineral occurrences

The Shwas-Tayyah and Khadra belts belonging to the Asir terrane include potential mineralization zones, hosted in intensely deformed Precambrian basement rocks. Analysis of geophysical aeromagnetic data and satellite images, constrained by field data, highlights the deep hierarchy and structuring of the An Nimas-Khadra area in its regional litho-structural setting and geodynamic evolution. The N-S and NNE-SSW major trends, with other E-W, NE-SW and NW-SE minor directions, were identified. The Tarj, Ibran, and Junaynah close to N-S oriented master shear zones, delimit and cross the Al Lith-Bidah, Shwas-Tayyah and Khadra belts; they characterize the Asir composite terrane. Structural and kinematic models were highlighted, showing the control of intense deformations on the basement structures. The deep-seated faults are linked to wide tectonic movements induced by regional E-W to ENE-WSW contractional orogenic episodes. The tectonics induced genesis of the accreted terrane rocks with differentiated belts and shear zones. The resulted structures seem to be in accordance with the Riedel model that includes conjugate movements of right-lateral strike slip faults and right-oblique reverse faults.Correlation of geophysical and geochemical analyses is a crucial technique used for better assessment and valorization of mineral resources. The spatial association between the interpreted lineament patterns and mineralization rates testifies the tectonic deformations-mineral deposits relationship. The AHP-based MCDM statistical support model highlights the mining interest areas. The MCDM allows further spatial statistical evaluation and reveals new prospective metal occurrences in the Shwas-Tayyah and Khadra belts. N-S and NNE-SSW lineament networks show the highest mineralization rates, suggesting their priority for more detailed prospections. The metallic mineral deposits have to be related to prominent steeply dipping and brittle-ductile shear zones.

Imbricated structure and hydraulic path induced by strike slip reactivation of a normal fault

In carbonates, fault zones strongly influence local reservoir properties and act as drains or barriers to flows. In the case of reactivated faults, newly developed fracture and fault systems rework and cross-cut pre-existing fault structures. The modifications of initial damage zone and fault core properties alter the fault zone properties and potentially created new fluid pathways. This study of the polyphase Castellas fault zone, developed as normal and later reactivated as strike slip, characterizes the structural pattern related to tectonic reactivation, and estimates the hydraulic behaviour of the fault zone through time. This fault affects carbonates located on La Fare anticlinal (SE France). High resolution mapping, 848 measurements and cross-sections allowed to discriminate the fault structures and the lateral heterogeneity of its architecture. Along the 850m-long studied damage zone we identify 8 principal fault planes, 2 relay zones, 19 secondary fault planes, and fault lenses. The study shows that the fault zone developed as isolated fault segments during the normal activity and acted as a drain to fluid flows during its nucleation. Later strike-slip reactivation led to the main structures visible presently as a well-connected fracture network and un-cemented breccia allowing the fault to be a drain to fluid flows.