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In March 2021, a seismic sequence including three Mw>5.5 events struck northern Thessaly, Greece. Owing to the high temporal resolution of Sentinel-1 images which were sampled every 6 days and recorded the three events separately, we are able to map individually the coseismic deformation fields of the three events. Based on their respective coseismic displacements, we determined the geometry of the fault plane for each earthquake with the method of multipeak particle swarm optimization and inverted the best-fitting slip distribution by linear least squares inversion. Modelling results show that the three events occurred successively on 3, 4 and 12 March 2021 were all dominated by normal-slip motions on previously unknown faults within the top 15km of the Earth’s crust. The 3 March 2021 Mw 6.3 earthquake ruptured a northeast-dipping fault with a strike angle of 301° (clockwise from the North) and a dip angle of 46°, producing the maximum slip of about 2.2m. The slip motion of the 4 March 2021 Mw 5.9 aftershock shows a similar fault geometry (striking 297° and dipping 42°) to the 3 March mainshock, but with a considerably smaller dip-slip component (~0.8m). The 12 March 2021 Mw 5.6 aftershock occurred on a southwest-dipping fault (striking 100° and dipping 40°) with a normal fault slip of up to 0.5m. Static Coulomb stress changes triggered by the earthquake sequence imply a promotion relationship between the first 3 March event and the two subsequent events. Due to the coseismic stress perturbation, more than 70% of aftershocks were distributed in areas with increased Coulomb stress and the northwest segment of the Larissa fault close to the seismic sequence was exposed to a relatively high seismic risk.

Ground deformation on the Earth's surface layer is strongly affected by the nonlinearity of geomaterials. However, the formation process of such deformation has yet to be described in a unified manner based on mechanics. The present study focuses on the normal faults in a submarine ground with highly developed soil skeleton structures and attempts to reproduce the process of normal fault formation associated with the tilting of a horizontally deposited submarine ground using an elastoplastic finite element simulation. The simulation was conducted using the soil–water coupled finite deformation analysis code GEOASIA , which incorporates an elastoplastic constitutive equation of the soil skeleton based on the modified Cam-clay model and the soil skeleton structure concept. The key findings are as follows: 1) Normal faults are formed from the ground surface to depth as shear bands, where shear strain is localized while exhibiting softening behavior with plastic volume compression. 2) Multiple normal faults are almost equally spaced and parallel to each other, with the inter-fault blocks rotating backward. The morphology of normal faults formed by the tilting of the ground shows domino-style characteristics. 3) The degree of the soil skeleton structure influences the formation of normal faults. This study demonstrates that elastoplastic geomechanics can explain the formation process of ground deformation, which has usually been interpreted from the perspectives of geomorphology and geology. [ABSTRACT FROM AUTHOR]

The discovery of a worldclass pre-salt petroleum province in the southeastern Brazilian margin led to an enormous interest in studying tectonic features that may control oil accumulation in rift settings. In the south-central Campos Basin, a dataset of 2D and 3D surveys were integrated with magnetic and gravimetric maps, along with wellbore data, to characterize the evolution of fault systems and their role in the distribution of pre-salt deposits. As a result, a transfer zone, here called Espadarte Transfer Zone (ETZ), was recognized, and its structural architecture, kinematics and evolution through time were interpreted. The ETZ is delimited by overlapping faults, with opposite, divergent dips, strike N20-40E, resulting in a basement high expressed by an N30E elongated horst placed between two half-grabens. In the study area, synthetic normal faults dominate basin geometry in a down-to-basin fashion; however, during the Early Barremian rifting the ETZ high was formed due to the development of antithetic master faults near and along its western border. Those counterregional fault pattern, together with their down-to-basin counterparts, originated a topographic change so controlling the pre-salt stratigraphy on both sides and above the basement high during successive phases of deformation and deposition. Apparently, the deformation migrated eastward as shown by the distribution of the syn-rift sequences preserved in the adjacent half-grabens. In a first approach, the Espadarte Transfer Zone is characterized in mapview by an elongated horst limited by NNE-oriented synthetic and antithetic master faults. Internally, the transfer zone is characterized by an en échelon array of closely-spaced, NE-trending overlapping faults, obliquely-oriented to the basement high, indicative of a left-lateral trantension during rifting. Therefore, negative flower-structures might be interpreted in seismic sections across some of the overlapping faults. Besides the characterization of the ETZ, we compare its geometry and kinematics with many other transfer zones worldwide, and we find many structural similarities. Finally, we propose that the ETZ has a regional relevance in the context of the south Campos Basin, since it composes a segment of a broad tectonic feature - the Araruama Transfer Zone, along which a left-lateral transtension is observed. • The Espadarte Transfer Zone(ETZ) is located in the south portion of the Campos Basin. • The ETZ was formed in the lower Barremian, during the syn-rift phase. • The ETZ shows oblique left-lateral kinematics characterized by en échelon pattern. • The interpretation of negative flower structures is consistent with a transtensional zone. • The ETZ is a segment of the Araruama Transfer Zone. [ABSTRACT FROM AUTHOR]

The Tadaout-Tizi n'Rsas (TTR) polymetallic (Pb, Cu, Zn) vein field, located at the southeastern of the Moroccan eastern Anti-Atlas, is hosted in sedimentary sandstone formations of the Ktaoua Group of the upper Ordovician. These deposits are reported to be late Variscan to Post-variscan in age, and are related to the emplacement of late Permian doleritic magma event outcropping in the Tafilalet region. Structural and paragenetic studies of the TTR mineralization deposit were conducted in order to establish a general model of the mineralization. A two-stage model of the formation of the mineralized veins of the TTR vein field is proposed herein. The first episode is attributed to the late Variscan phase. It is a trantensive regime characterized by the presence of lenticular structures related to the normal dextral movement of the major faults. This episode is coeval with the emplacement and brecciation of the polymetallic mineralization of the TTR vein field (galena, chalcopyrite, sphalerite, and pyrite). The second episode is associated with normal faults, during the extensional phase corresponding to the tectonic relaxation of shortening (Upper Permian) and more probably during the Atlantic rifting. It is characterized by the formation of a banded texture of mineralization. • A model of the formation of the mineralized veins of the TTR vein field, structural interpretations and paragenetic studies. • Mineralogical characterization and textures of the ore bodies of TTR vein field. • Structural controls on mineralization in the Tafilalet metallogenic district (TMD). [ABSTRACT FROM AUTHOR]

In addition to overall uplift of the Qiabuqia region during the Late Cenozoic, three deformation stages can be identified in the northeastern Qinghai–Tibet Plateau. Specifically, these deformation stages were recognized in areas east of the Gonghe Basin that surrounds Waliguan Mountain and include: 1) Late Miocene to Late Pliocene deformation—dominated by thrust napping with dextral strike-slipping; 2) Early Pleistocene to late middle period of Pleistocene deformation—fault structures were dominated by the dextral strike-slipping with thrust napping; and 3) end of Late Pleistocene to Middle Holocene deformation—thrust napping slowed down and finally braked, while the shallow surface began to loosen and extend at Qiabuqia region’s rear-edge. DR4 borehole drilling data indicate that the Xiangshuihe Formation’s buried depth is ∼1,000 m. The Xianshuihe Formation’s top section is characterized by normal fault–type (NF) tectonic stress, while the maximum principal tectonic stress (σ1) is perpendicular and the minimum principal tectonic stress (σ3) is horizontal. In contrast, the deep basement is characterized by thrust fault (TF) and strike-slip (SS) tectonic stress, while the σ1 is in the NE-SW direction, ranging from 20.1° to 75.3° with an average of 40.0°. Based on the aforementioned observations, it can be inferred that there are three sets of hidden faults in the basement of the Qiabuqia region: 1) the NW–NNW trending compressional–torsional faults; 2) the NE trending tensional–torsional faults; and 3) the NWW trending compressional–torsional faults. The findings in this study can potentially offer a robust geological basis for exploring and utilizing hot, dry rock resources within the Gonghe Basin.

Syn‐rift deep‐water muds and mudstones preserve a relatively complete stratigraphic record of tectonic and climatic events. This paper investigates mud‐dominated deposits and stratigraphy using core from International Ocean Discovery Program (IODP) Expedition 381 sites M0078 and M0079 in the Gulf of Corinth, Greece. Millimetre‐scale logging defined several bed types: homogeneous and laminated mud beds, bioturbated beds, a variety of graded beds, and rare matrix‐supported conglomerates and slumps. Homogeneous muds and light grey to black laminated muds record deposition from distal, waning low density turbidity currents and terminal mud‐rich quasi‐laminar or laminar plug flows. Graded beds, interpreted as turbidites, range from beds several millimetre to a few centimetres of mud with silt to fine sand bases, to metre‐scale mud beds with coarser sand and pebble bases. Conglomerate and slumped beds record cohesive debris flows, transitional flows and slope failure. Three stratal package types are distinguished: bioturbated, bedded and laminated, recording distinct hydrological conditions. Bioturbated packages record interglacial marine conditions with well oxygenated waters. Bedded packages record hemipelagic processes and low energy density underflows in a mainly dysoxic, stratified, lacustrine setting (glacial phases). In laminated packages, white mm‐scale laminae of calcite or aragonite from varved, hemipelagic sediments demonstrating seasonal variability in a dysoxic non‐marine or transitional setting. Rift stratigraphy is linked to eustatically controlled connections to the global ocean across rift segment boundaries. The ca. 780 to 330 ka succession is dominated by laminated packages with thin bioturbated packages and distinct conglomerates and slumps, suggesting high sills, making ocean connections brief and transitional to lacustrine conditions prolonged. The ca. 330 ka to present succession shows well developed bioturbated and bedded packages, separated by thin laminated packages, suggesting brief transitions and well‐developed marine conditions due to lower sills. Results indicate that structurally controlled rift segment boundaries exert a first‐order control on syn‐rift stratigraphic evolution, with fault segment growth and linkage driving intra‐rift facies and sequence variability. [ABSTRACT FROM AUTHOR]

Buried pipelines inevitably pass through complicated geological areas because of their wide coverage. A three‐dimensional numerical model subjected to normal fault considering the geometrical and mechanical properties of the bell–spigot joint in Prestressed Concrete Cylinder Pipe (PCCP) is proposed to analyze the effects of location, displacement, and dip angle of fault on the rotation angle and axial translation of bell–spigot joints as well as the effects on the deformation of pipe bodies. At a dip angle of 90°, the maximum joint rotation angle and pipe deformation are larger when the relative location of fault and joints is under the odd configuration than under the even configuration. The kinematic characteristics of joints and the mechanical characteristics of pipe bodies on the moving side are opposite to those on the stationary side. The amount of offset has a significant impact on the longitudinal response of the pipeline. The rotation angle and axial translation of the joints on both sides of the fault increase with increasing fault displacement. When the offset reaches 270 mm, the joint rotation angle is 1.05°, which exceeds the specification limit of 1°. On the basis of numerical results, the simplified estimate of the maximum rotation angle is improved, and the error is reduced to 3%. With the increase of fault dip angle, the affected area gradually moves left to the fixed part. When the dip angle is 75°–90°, the pipeline longitudinal response is large, which is unfavorable to the pipeline safety. [ABSTRACT FROM AUTHOR]

Moderate‐to‐large earthquakes in rifts may occur on leading boundary faults or inner antithetic faults. Here we show a rare case of the 2020–2021 seismic sequence in the Corinth rift, that culminated in the shallow rupture of the antithetic fault, neither preceded nor followed by the leading fault rupture. The hypocenter of the largest shock (Mw 5.3 of 17 February 2021) was located at ∼8 km depth. However, seismic waveform data, supported by satellite‐geodetic and tide gauge measurements, pointed to rupture at shallow depth (∼3 km), where no earthquakes were previously observed. We show that the earthquake most probably ruptured two orthogonal, conjugate fault segments: a weak nucleation phase occurred in the microseismically highly active sub‐horizontal detachment layer, followed – a few seconds later – by a larger, shallow moment release on a high‐angle, south‐dipping normal fault. The latter is the Mornos offshore fault, antithetic to the leading, north‐dipping Psathopyrgos fault. Our study presents the first instrumental/observational evidence of a very shallow Mw 5+ event in this rift – and one of the few reported worldwide. The depth limit of the main shallow slip patch coincides with the expected crossing of the Mornos fault with the Psathopyrgos fault, stressing the importance of fault segmentation and rooting inherited from the rift history. This unusual shallow slip in a depth range with little background seismicity and few aftershocks needs to be further investigated by dynamic modeling as a possible prototype of hazardous events in rift environments. Plain Language Summary: The Corinth rift is a key tectonic element in the Eastern Mediterranean, separating mainland Greece from the Peloponnese. The rift is highly seismically active, yet geologically complex and not fully understood. Between December 2020 and February 2021, thousands of small earthquakes and two Mw > 5 events occurred there. Microearthquakes migrated in the rift on a subhorizontal detachment layer, separating the brittle and ductile crust. Similar activity has been well known for decades. However, the Mw 5.3 mainshock of February 17 was peculiar. While it nucleated at a depth of ∼8 km on the detachment, most of the slip occurred at unusually shallow depths of ∼0–5 km. This major rupture segment, well constrained by seismic, geodetic, and tide gauge data, is interpreted here as a rare shallow activation of a south‐dipping offshore western continuation of the Trizonia fault system. This continuation is most likely the Mornos fault, lying opposite (antithetic) to the major north‐dipping Psathopyrgos fault which outcrops on the southern coast. The present complexity of these structures is a result of the tectonic evolution of the rift during the last 0.4 Myr. The gained knowledge, supplemented by new offshore measurement techniques, will improve seismic and tsunami hazard assessment. Key Points: Seismic, geodetic and tide gauge records in Corinth rift reveal a rare shallow rupture (∼0–5 km) on a south‐dipping offshore normal faultThe shallow rupture was preceded, triggered, and followed by microearthquakes mostly occurring deeper, on the detachment layerThe causative fault is along‐dip segmented and rooted beneath detachment as inherited from fault interactions during the rift evolution [ABSTRACT FROM AUTHOR]

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The relationship between normal fault displacement (D) and length (L) varies due to numerous factors, including fault size, maturity, basin tectonic history, and host rock lithology. Understanding how fault D and L relate is useful, given related scaling laws are often used to help refine interpretations of often incomplete, subsurface datasets, which has implications for hydrocarbon and low-carbon energy applications. Here we provide a review of D/L scaling laws for normal faults, discuss factors that could influence these relationships, including both geological factors and errors in measurement, and provide a critique of previously published D/L databases. We then present our newly assembled database of 4059 normal faults from 66 sources that include explicit information on: 1) fault length and displacement, 2) host rock lithology, 3) host basin tectonic history, and 4) maturity, as well as fault D and L through time when these data are available. We find an overall scaling law of D = 0.3L0.92, which is similar to previously published scaling equations and that varies in response to the aforementioned geological factors. Our data show that small faults (

The Zhuozishan West Piedmont Fault (ZWPF) is an active normal fault in the northwestern corner of the Ordos Block. Studying the recurrence characteristics of paleoearthquakes is useful for understanding the regional seismic hazard potential. In this study, paleoseismic trench and optically stimulated luminescence (OSL) dating methods are used to determine the temporal sequence of paleoearthquakes. Severn earthquakes were constrained to be E7 (73.4 ± 12.9 ka to 75.3 ± 10.6 ka), E6, (63.7 ± 7.4 ka to 64.4 ± 8.2 ka), E5 (53.2 ± 7.0 ka to 58.7 ± 6.5 ka), E4 (42.6 ± 6.3 ka to 47.7 ± 5.8 ka), E3 (31.0–3.4 ka to 31.3 ± 3.4 ka), E2 (26.1 ± 2.7 ka to 28.1 ± 3.8 ka) and E1 (15.8 ± 1.9 ka to 20.2 ± 2.6 ka). The recurrence interval of strong earthquakes in the ZWPF is roughly constrained to be 8.1–14 ka, with magnitudes of Mw 7.0–7.4 that ruptured the entire fault. Based on the timing of the latest earthquake event, the elapsed time approached or exceeded the recurrence interval revealed from paleoearthquakes. Hence, we suggest that the northwestern corner of the Ordos Block has a significantly high seismic hazard potential and that the occurrence of a strong earthquake should not be underestimated.

Copyright of Journal of Geomechanics is the property of Journal of Geomechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• We produce an updated fault map of the Okavango (ORB) and Makgadikgadi (MRB) rifts. • MRB shows diffuse faulting with exponential length distribution and no border fault. • The relatively more evolved, border-faulted ORB shows power-law length distribution. • Rifts initiate via exponential fault length distribution that later evolve to power-law. Continental rifts are thought to transition from a power-law fault length distribution during the juvenile stages of extension, to an exponential distribution during break-up and oceanic spreading. However, fault scaling relationships have rarely been quantified in natural incipient rifts, particularly in the absence of magmatic influence. We address this knowledge-gap in the incipient Okavango-Makgadikgadi Rift Zone, Northern Botswana, consisting of the amagmatic Okavango Rift Basin (ORB) and Makgadikgadi Rift Basin (MRB). We utilize high-resolution satellite topography data (12.5 m TanDEM-X and 30 m SRTM) and aeromagnetic data to image and map faults across the rift zones and generate a new robust fault map for the region. Further, we analyze the length-frequency distribution of faults using a two-sample Kolmogorov-Smirnov test. The results show that the Makgadikgadi Rift Basin exhibits an exponential distribution associated with a nucleating rift as it exhibits diffuse faulting and lacks a border-fault, whereas the Okavango Rift Basin exhibits a power-law distribution that is consistent with its relatively more evolved rift structure with established border faults. Thus, we propose that continental divergent plate boundaries commonly nucleate with an initial exponential distribution of fault lengths which subsequently transition into a power-law distribution as the rift evolves into its stretching phase, and may again transition into an exponential distribution as break-up initializes. [Display omitted] [ABSTRACT FROM AUTHOR]

The slip rates of normal faults on the northern margin of the Ordos Block are critical for understanding the deformation of the Ordos Block and adjacent areas. In this study, we obtain the late Pleistocene slip rate of an active normal fault, the Zhuozishan West Piedmont Fault (ZWPF), in the northwestern corner of the Ordos Block. Satellite imagery interpretation and field investigations suggest that the fault displaces late Pleistocene alluvial fans and forms west-facing fault scarps. To quantify the vertical slip rate of the ZWPF, we measured the displacements along the fault scarps using differential GPS and an unmanned aerial vehicle system and dated the displaced geomorphic surfaces using optically stimulated luminescence (OSL) dating methods. The vertical slip rate of the fault is constrained to 0.1 ± 0.02 mm/a, which suggests a horizontal extension rate of 0.05 mm/a for a dip of 65°. This rate is consistent with those on similar structures in the northwestern Ordos Block. Combining this result with published slip rates along other active faults, we infer that the NW-directed extension rate across the northwestern corner of the Ordos Block is ∼0.6–1.3 mm/a. This rate is comparable with the geodetic strain rate. Given the extension rate, we believe that extensional deformation is mainly concentrated on the western side of the basin.

Multiple fault planes often coexist within a fault zone during fault dislocation. However, all the previous analytical models assume that there is only one fault plane during a fault dislocation, which is inconsistent with the actual engineering conditions. In this paper, theoretical analysis and numerical simulations are used to investigate the mechanical response and damage characteristics of tunnels subjected to multiple normal faulting. A nonlinear theoretical model is established for analyzing the mechanical response of tunnels subjected to multiple normal faulting. The number of fault planes, the shear effect of the soil and the tunnel, the fault zone width, and the nonlinear soil−tunnel interaction are applied inside the theoretical model, significantly improving the analysis accuracy and applied range. The corresponding numerical simulation based on the Concrete Damaged Plasticity (CDP) Model is carried out to study the damage characteristics of the tunnel. The proposed theoretical model is verified by model tests and numerical simulations, which exhibit consistency in both qualitative and quantitative aspects. A parametric analysis is presented, wherein the impacts of varying numbers of fault planes, fault plane distances (d), fault displacement ratios (ξ), and buried depths (C) on the tunnel response are investigated. The results show that an increasing number of fault planes leads to a reduced peak bending moment (M max) and shear force (V max). As the number of fault planes increased from one to four, M max and V max decreased by 1.57 times and 3.31 times, respectively. Expanding d corresponds to a reduction in both M max and V max. The minimum V max within the tunnel materializes at ξ 4 (Δf d1 = Δf d2 = Δf d3), and the tunnel's V max appears at the fault plane of maximum fault displacement. Moreover, with the augmentation of C , an increase in both M max and V max was observed. Additionally, upon attaining a normal fault displacement of 0.2 m, the tunnel lining undergoes both tensile and compressive failure at the fault plane. As the normal fault displacement surpasses 0.4 m, the failure range of the tunnel at the fault plane undergoes a precipitous escalation, marked by a maximum increase of 68.8 % in tensile failure and a 29.6 % increase in compressive failure. [ABSTRACT FROM AUTHOR]

During earthquakes on low (<1–2 km) displacement faults in isotropic crust, more earthquake energy is consumed by fracturing and gouge formation than in ruptures along more mature faults. To investigate how pre‐existing weaknesses affect earthquake energy dissipation along low displacement faults, we studied fault rocks from the 110 km long, 0.4–1.2 km displacement, Bilila‐Mtakataka Fault (BMF), Malawi. Where the BMF is parallel to surface metamorphic fabrics, macroscale fractures define a narrow (5–20 m wide) damage zone relative to where the BMF is foliation‐oblique (20–80 m), and to faults with comparable displacement in isotropic crust (∼40–120 m). Enhanced microfracturing and widespread gouge formation, typically reported from comparable‐displacement faults, are not observed. Therefore, minimal evidence for earthquake energy dissipation into the BMF's surrounding wall rock exists, despite geomorphic evidence for MW 7.5–8 earthquakes. We attribute this finding to differences in earthquake energy partitioning along incipient faults in isotropic and anisotropic crust. Plain Language Summary: Earthquakes release elastic energy stored in the Earth's crust. Some of this energy radiates to the Earth's surface, where it causes the ground to shake and poses a risk to human life and infrastructure. However, some of this energy is also absorbed by breaking and fragmenting the rocks around the fault. This process is important in faults with small total displacements (<1–2 km), because these faults are still growing by breaking surrounding intact rock. The Bilila‐Mtakataka Fault (BMF) in southern Malawi is 110 km long but has a low displacement (0.4–1.2 km). We show that limited fracturing of the surrounding rock has occurred, despite an inferred history of MW 7.5–8 earthquakes. We propose that this is because earthquakes along the BMF exploited older planes of weakness in the Earth's crust, such as cracks and aligned mineral grains. Our results suggests that these pre‐existing weaknesses can influence how earthquake energy is released. Key Points: The 110 km long, 0.4–1.2 km maximum displacement, Bilila‐Mtakataka Fault (BMF) locally follows shallow crustal weaknessesThe BMF has limited fault gouge and a narrow damage zone compared to a similar displacement fault in intact crustLimited fracturing implies less seismic energy is consumed by fracture and frictional energy when ruptures follow pre‐existing weaknesses [ABSTRACT FROM AUTHOR]

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The extensional structure as a normal fault could be found in many places at the southern part of Java compressive tectonic regime. The research area is in the eastern part of the South Serayu Mountains. This normal fault structure is the boundary of the South Serayu Mountains at the eastern part with Kulon Progo Tertiary volcanic Mountains. In the field, these normal fault lineament zones create the Bogowonto river as a boundary of two different geological styles. The influence of this structure on the geological dynamic of the South Serayu Mountains and the Kulon Progo Mountains is important to be explained. The study was conducted by measuring and analyzing fault data and lithology that developed in the area around the two basins boundary. The distribution of the Kulon Progo volcanic rocks indicates the presence of the extensional fault structure. The volcanic facies distribution of the volcano is cut and becomes narrow in the west, while the northward is very wide. Normal fault striations analysis on the fault plane along the fault line shows the least stress trending west-northwest that has worked to create North-South normal faults. The fault-controlled by stress with the vertical main compression area. They have worked to create North Northeast-South Southwest (NNE-SSW) normal faults with westward dipping.

Copyright of Geologické Práce Správy is the property of State Geological Institute of Dionyz Stur and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The geometry and kinematics of active faults have a significant impact on their seismic potential. In this work, a structural characterization of the active Baza Fault (central Betic Cordillera, southern Spain) combining surface and subsurface data is presented. Two sectors are defined based on their surface geometry: a northern sector striking N–S to NNW–SSE with a narrow damage zone and a southern sector striking NW–SE with a wide damage zone. A kinematic analysis shows pure normal fault kinematics along most of the fault. Geometric differences between the northern and southern sectors are caused by i) a heterogeneous basement controlling the fault geometry at depth and in the cover; ii) different orientations of the Baza Fault in the basement with respect to the regional extension direction and iii) interaction with other active faults. We use this structural characterization to analyse the segmentation of the Baza Fault. According to segmentation criteria, the entire Baza Fault should be considered a single fault seismogenic segment. Consequently, the seismic potential of the fault is defined for a complete rupture. Magnitude for the Mmax event is calculated using several scale relationships, obtaining values ranging between Mw 6.6 and Mw 7.1. Recurrence times range between approximately 2,000 and 2,200 years for Mmax events and between 5,300 and 5,400 years for palaeo-events. A geodetic scenario modelled for an Mmax event of Mw 6.7 shows permanent vertical displacements of more than 0.40m and an overall WSW–ENE extension during entire ruptures of the Baza Fault.

Upper-plate normal faults along forearcs often accumulate slip during >Mw 6 earthquakes. Such normal faults traverse the forearc of the Hellenic Subduction System (HSS) in Greece and are the focus of this study. Here, we use detailed field-mapping and analysis of high-resolution Digital Elevation Models (DEMs) to study 42 active normal faults on the islands of Kythira and Antikythira in the Aegean Sea. Onshore fault kinematic data are complemented by seabed bathymetry mapping of ten offshore faults that extend along the Kythira-Antikythira Strait (KAS). We find that normal faults in the KAS have lengths of ∼1–58 km and scarps ranging in height from 1.5 m to 2.8 km, accommodating, during the Quaternary, trench-orthogonal (NE-SW) extension of ∼2.46 ± 1.53 mm/a. Twenty-eight of these faults have ruptured since the Last Glacial Maximum, with their postglacial (16 ± 2 ka) displacement rates (0.19–1.25 mm/a) exceeding their Quaternary (≤0.7–3 Ma) rates (0.03–0.37 mm/a) by more than one order of magnitude. Rate variability, which is more pronounced on short (

A 6.6 (Mw) earthquake struck the western part of Gökova Gulf in the eastern Aegean Sea on July 20, 2017. The fault plane solution for the mainshock shows an E-W striking normal fault with approximately N-S (N4°E) tensional axis (T-axis). Fault plane solutions for 33 aftershocks offer two groups of normal faulting with E-W and NE-SW to ENEWSW orientations. The inversion of the focal mechanisms of the aftershocks yields two different extensional stress regimes. The stress regime obtained from 12 focal mechanisms of aftershocks and the mainshock is characterized by an approximately N-S (N5°E) s3 axis, while the other regime calculated from 21 focal mechanisms of aftershocks exhibits s3 axis in an NW-SE (N330°E) direction. The latter extension significantly affects the basin's growth in the area where the earthquake occurred. Twenty-four focal mechanisms of earthquakes in and around Gökova Basin before the 2017 earthquake (1933-2017) were included in the inversion to determine the stress state effective in a larger area. The inversion yielded an extensional stress regime characterized by approximately N-S (N356°E) s3 axis. E-W trending faults inferred in the central part of Gökova Fault Zone, bordering Gökova Gulf in the north, also indicate N-S extension. The NW-SE extension obtained from NE-SW aftershocks appears to be locally effective in the northwest of Gökova Gulf. N-S extension, which appears to act on a regional scale, may be attributed to geodynamic effects related to the roll-back of the African subduction beneath the Aegean. [ABSTRACT FROM AUTHOR]

This paper documents the various factors contributing to the evolution of landforms in the Kosi River valley, Ukhaldhunga area of the Kumaun Himalaya, Uttarakhand. The area falls in the major tectonic boundary between the Lesser Himalaya and the sub-Himalaya. Passing through the Parewa-Ukhaldhunga-Dabara area, this tectonic contact is known as the Main Boundary Thrust (MBT), which is characterized by presence of varied landforms. Study of the development of geomorphology, particularly those evolved in the MBT zone, suggests that the morphological features are intimately associated with the tectonic activities related to the movement of rocks along the MBT and the surface processes such as fluvial and mass movement. The various landforms observed in the MBT zone include strath terraces, fill terraces, paleochannels and V-shaped valley that pertain to fluvial genesis; gravity induced landforms such as landslide debris and colluvial fans; and tectonic landforms such as linear fault traces, swerving/swing of river course and linear depressions. Signature of recent tectonic activity along the MBT is observed between Dabara and Khakrakot. The activity is evident in the form of 8-km-long active fault trace trending NW-SE. Normal fault related landforms are observed in the hanging wall block of the MBT. Neotectonic strath terraces and fill terraces are well developed in the MBT zone. Multiple events of recurrence of landslides are evident from exposed section of landslide debris fans. The bedrocks are highly sheared, suggesting successive tectonic movements along the MBT. As a consequence, tectonic wedges have developed in the bedrocks. These wedges have facilitated for the recurrence of a number of landslides. The anthropogenic activities have also aggravated the slope stability. Truncation of older debris fan surfaces by an erosional/fault scarp is observed and the scarp separates the older fans from the youngest debris fan deposit. The scarp runs parallel to the MBT and Kosi River. Swerving of the Kosi River is as a result of the tectonic forcing along active lineaments/faults. The trend of lineaments of the maximum and high density is NE-SW, which is transverse to the trend of the NW-SE trending Himalayan fold-thrust belt. [ABSTRACT FROM AUTHOR]

The understanding of each geological-structural aspect in the field is fundamental to be able to reconstruct the geological history of a region and to give a geological meaning to the data acquired in the outcrop. The description of a brittle extensional environment, which is dominated by normal fault systems, is based on: (I) image interpretation, which aims to find evidence suggestive of an extensional geological environment, such as the presence of scarp lines and fault scarps, horst, graben and/or half-graben, among others, that allow the identification of the footwall and hanging wall blocks; ii) definition of the sites of interest for testing; and iii) analysis of the outcrops, following a systematic procedure that consists of the observation and identification of the deformation markers, their three-dimensional schematic representation, and their subsequent interpretation, including the stereographic representation in the outcrop. This procedure implies the unification of the parameters of structural data acquisition in the field, mentioning the minimum fields necessary for the registration of the data in tables. Additionally, the integration of geological and structural observations of the outcrop allows to understand the nature of the geological units, the deformation related to the extensional environment and the regional tectonic context of the study area.

Multi-channel seismic reflection and sub-bottom profiling data reveal landward-dipping normal faults as potential conduits for mantle-derived fluids in the coseismic slip area of the 2011 Tohoku earthquake (Mw9.0). Normal faults below the helium isotope anomaly sites appear to develop through the forearc crust (i.e., the seafloor sedimentary section and Cretaceous basement) and to evolve to lower dip angles as extension progresses deeper, potentially extending down to the mantle wedge, despite their intermittently continuous reflections. The faults are characterized by high-amplitude, reverse-polarity reflections within the Cretaceous basement. Moreover, deep extension of the faults connecting to a low-velocity region spreading from the Cretaceous basement into the mantle wedge across the forearc Moho suggests that the faults are overpressured by local filling with mantle-derived fluids. The locations of the normal faults are roughly consistent with aftershocks of the 2011 Tohoku earthquake, which show normal-faulting focal mechanisms. The 2011 Tohoku mainshock and subsequent aftershocks can lead the pre-existing normal faults to be reactive and more permeable so that locally trapped mantle fluids can migrate up to the seafloor through fault fracture zones. The reactivated normal faults may be an indicator of shallow coseismic slip to the trench. Locally elevated fluid pressures can decrease the effective normal stress for the fault plane, facilitating easier slip along the fault and local tsunami. The landward-dipping normal faults developing from the seafloor down into the Cretaceous basement are predominant in the middle slope region of the forearc. A possible shear zone with high-amplitude, reverse-polarity reflections above the plate interface, which is almost localized to the middle slope region, suggests more intense basal erosion of the overlying plate in that region.

South Western Anatolia is dominated by E-W and NW-SE trending active faults. The dip-slip Yatağan Fault is one of these active structures that trends in a NW direction for ~30 km. To assess the relative tectonic activity of the Yatağan Fault, two geomorphic segments were defined along the fault: the FS-1 (northern segment) and the FS-2 (southern segment). The vertical slip rate pattern of the fault was analyzed using steepness indexes, chi (X) plots, and log-log slope area graphs. Results of the analyses indicate that the steepness of the streams draining the footwall reveal increasingly higher values downstream along the fault. All of the main basins contain at least one slope-break knickpoint associated with tectonic uplift. Facet morphology-based investigations using empirical methods along faceted spurs of the Yatağan Fault indicate vertical slip rates of 0.16 ± 0.05 mm/year and 0.3 ± 0.05 mm/year for the FS-1 and the FS-2, according to relationship of facet slope angle (Rsa). Additionally, using the facet basal height relationship (Rbh) we calculated slip rates of 0.24 mm/year and 0.36 mm/year for the FS-1 and the FS-2 segments, respectively. Mountain front sinuosity analysis yields values of 1.34 and 1.2, while the ratio of valley-floor width to valley height gives values of 0.64 and 0.24 for the FS-1 and the FS-2 respectively, indicating typical active mountain front where the uplift rates are = 0.5 mm/year. Hypsometric analysis suggest a transition from mature to older stage for catchments along the Yatağan Fault. Comprehensive interpretation of the results from morphometric analysis, vertical slip rate calculations, and data based on field observations suggest preponderance of tectonic activity over erosional process along the Yatağan Fault. Our analyses reveal that the rate of the tectonic activity gradually increases from the FS-1 to the FS-2 along the fault. [ABSTRACT FROM AUTHOR]

The Taupō Volcanic Zone (TVZ) is characterised by a negative residual gravity anomaly that correlates with a zone of normal faulting, subsidence and voluminous silicic volcanism from c. 2 Ma. A steep gravity gradient is associated with downfaulting of the Mesozoic metasedimentary basement at its eastern and western margins, and all known calderas are associated with prominent local gravity lows. New Bouguer and residual gravity anomaly maps are presented that show improved detail over previous maps. The western margin of the TVZ shows as a series of parallel northeast-trending boundaries and northwest-trending step-over zones. The new map also reveals the complex boundaries of the Okataina caldera, and greater detail north of Taupō where gravity lows at Reporoa and Mihi form part of a larger and more extensive, elliptical low-gravity feature, suggesting that they may be separate collapse areas within a larger caldera complex. Around the margins of the TVZ, the Hauraki graben/rift and sedimentary basins at Hamilton, Waimiha, Galatea and Waiohau are also characterised by low residual gravity. [ABSTRACT FROM AUTHOR]

Earthquakes can rupture multiple fault segments as well as faults with complex geometry, or heterogeneous pre-stress and frictional properties. These observations have been documented mainly for moderate-to-large earthquakes by inverting geodetic and seismic data and by studying the influence of fault orientation and rheology within the regional stress field. In this work we have studied the Gorzano fault, GF, a large normal fault within the active fault system of Central Italy that during the last two largest Italian seismic sequences, L'Aquila (2009) and Amatrice-Visso-Norcia (2016–2017), was reactivated via a series of 5.0 < Mw < 6.0 events. We calculated moment tensor solutions for 134 M > 3 events and evaluated their normalized slip-tendency. Merging these results with high resolution earthquake catalogs, available M > 5 earthquake slip distributions, and frictional properties characterizing the activated fault, we develop a mechanical model and discuss potential earthquake rupture scenarios. The GF is an optimally oriented fault within the regional stress field and from, the reactivation via aftershock or mainshock slip of complementary fault portions from 2009 to 2017 indicates that the fault behaves as a single fault structure. The geometrical and mechanical heterogeneities suggest that the most likely slip behavior of GF is the reactivation of different fault portions with M > 5.0. However, due to favorable initial stress conditions, we suggest that a seismic rupture can produce the complete reactivation of the fault, resulting in a M 6.5–6.6 earthquake as documented in paleoseismological data. • Seismic complexity influenced by geometry and pre-stress heterogeneity. • 5.0 < M < 6.0 events reactivate the fault during major Central Italy sequences. • Moment tensor, slip, and frictional properties unveil rupture scenarios. • Geometry of Gorzano fault varies, influencing seismic behavior at different depth. • Gorzano fault may result in a M 6.6 earthquake, under favorable stress conditions. [ABSTRACT FROM AUTHOR]

• Core of fault fracture zone and boundaries are the main sites for the severe structural deformation of tunnels. • In comparison to straight bolts, oblique bolts significantly alter the stress distributions of segment rings and joints • Circumferential joint in the form of oblique bolt is more suitable than that of straight bolt for anti-fault design Due to evidence that active-fault tunnels can result in structural damage, a three-dimensional numerical model of a shield tunnel spanning a normal fault was developed by employing the Qingdao Jiaozhou Bay Second Subsea Tunnel in order to examine the structural response and failure characteristics of the shield tunnel while taking into account the segment width and the bolt form of the circumferential joint (straight bolts, oblique bolts), which are the two main influencing factors. The findings demonstrated that the core of the fault fracture zone and the boundaries between the fault and the competent rock were the main sites for the severe structural deformation of tunnels. It is readily available to ascertain how effectively segment width alters the internal force and deformation by looking at the circumferential joint's mechanical characteristics and deformation. In comparison to straight bolts, oblique bolts significantly altered the stress distributions of segment rings and joint bolts. They additionally possessed a greater tensile strength. The procedures of gray clustering and analytical hierarchy were applied to make a model suggestion for evaluating tunnel deterioration. The oblique bolt is more suitable for anti-fault design, according to the case study. Although the motivation for the research came from the demands of a specific project, the analysis strategy, the design concepts, and many of the findings need further investigation. [ABSTRACT FROM AUTHOR]

The island of Malta (central Mediterranean) is dissected by several WSW-trending fault-line valleys related to Miocene-Pliocene extensional tectonics. Some valleys host remnants of alluvial deposits that could provide information on possible Quaternary faulting, but the thickness of these deposits and their subsurface extent is poorly constrained. Our study aimed to investigate the structural configuration of the southern sector of the Mellieha valley, which is located in the north-west part of the island and is limited by the ENE-WSW general trending Mellieha and Ghadira faults, and their relation with a thin layer of infill sediments. We employed different near-surface geophysical techniques (electrical resistivity tomography, active and passive seismic methods, ground-penetrating radar), as well as remote sensing techniques (unmanned aerial vehicle digital photogrammetry and ground-based Light Detection and Ranging) to complement classic structural surveys. The valley structure has an asymmetric graben configuration, being bounded by a normal fault to the southeast (Mellieha Fault) and other to the north-west (Ghadira Fault). Our study provides insights of possible Quaternary fault displacements and revealed the presence of an additional fault splay, the previously unmapped NNW-dipping Mellieha Fault 2 at the south-eastern edge of the valley. Additionally, by integrating results from geophysical surveys, we estimated the thickness of the valley's recent deposits, being thicker towards the Mellieha Bay sector, with maximum values of 8–10 m. Our study aligns with the general model of horst and graben structuring with associated regional tilting since the late Miocene, and supports the hypothesis that some segments of NW-trending normal faults within the North Malta Graben exhibit Quaternary activity, although with minimal throw rates (<< 0.1 mm/yr). • Geophysical methods unveil recent sediment thickness in horst-and-graben domain. • Integration of geophysics and digital outcrops reveals valley structure. • Bathymetric data is used to map offshore fault extensions. [ABSTRACT FROM AUTHOR]

Abstract The 2011 Tohoku-Oki offshore subduction earthquake (M w 9.0) triggered many normal-type earthquakes inland in northeastern Japan. Among these were two very similar normal-faulting earthquakes in 2011 (M w 5.8) and 2016 (M w 5.9), which created surface ruptures along the newly named Mochiyama fault within the southern Abukuma Mountains, northeastern Japan, where no active faults had been previously mapped by interpretation of aerial photographs. We conducted field surveys in this area immediately after both earthquakes, and we performed trench excavations and observations of fault fracture zones after the 2016 event. These activities were complemented by an interferometric synthetic aperture radar analysis that mapped the areas of deformation and locations of surface discontinuities for both events. The combined results document the coseismic behavior of the Mochiyama fault during both events. Subtle tectonic geomorphic features associated with the fault were evident in a lidar digital elevation model of the area, and layered structures of gouge were documented in the field. These lines of evidence indicate repeated activity at shallow crustal levels and the possibility of Quaternary activity. In addition, our trench excavations revealed at least one faulting event before 2011. Our comparison of paleoseismic records on this and two other normal faults in the Abukuma Mountains suggests that great earthquakes in the Japan Trench supercycle of 500–700 years do not consistently trigger ruptures on these faults, and the case of 2011, in which the Tohoku-Oki megathrust earthquake triggered all three faults, is a rare occurrence.

The lateral sealing ability of a normal fault is a major factor in creating hydrocarbon traps. Therefore, a methodology for assessing the sealing ability of faults in the siliciclastic sequences of subsidence basins has been established; moreover, by using this methodology, the uncertainty inherent in hydrocarbon exploration can be decreased. Moreover, the petrophysical properties of fault rocks and reservoirs are emphasized by the methodology. In addition, the petrophysical properties of fault rocks and reservoirs are mainly determined based on clay contents and compaction pressure according to experiments on manmade rock samples which are representative of the researching area. Furthermore, by using this methodology, the petrophysical properties of fault rocks and reservoirs, which are mainly determined based on clay content and compaction pressure according to experiments on manmade rock samples representative of the researching area are emphasized. Thus, the lateral sealing ability of the fault can be assessed as follows: First, a best-fit equation describing the displacement pressures, clay contents, and compaction pressures of the rock samples is established by us. Then, the positive pressure on the fault plane from the decomposition of effective overburden pressure is calculated; afterwards, the clay content of the fault rock (Shale Gouge Ratio) is calculated by us. Finally, the displacement pressures of the fault rock and the juxtaposed reservoir rock are predicted. Ultimately, based on this study which has been carried out, the results for the case study of the Tangjiahe fault in Well Gang 64, in the western part of the Qikou Sag, China coincide with the exploration results, which this coincidence confirms that this methodology is capable of evaluating the lateral sealing ability of faults in certain geologic settings.

Abstract We conducted a broadband magnetotelluric (MT) survey along a north–south transect across Unzen graben, Japan. The MT survey line is located ~ 2 km west of the most recent lava dome and consisted of 27 stations along a 9-km profile. We estimated the 3-D resistivity structure and correlated it with the seismic reflection structure obtained by the same survey line as in the present study. The best-fit resistivity structure shows an upper resistive layer underlain by a moderately conductive layer. The resistive layer, which is interpreted as a cold groundwater zone, is cut by four faults marked by their relatively high conductivity. The underlying layer, which is interpreted as a hydrothermal-water-rich layer, also shows relatively conductive values near the faults. By assuming that the faults are imaged as relatively conductive zones, we infer the dip and depth extent of fracture zones around the faults. Beneath the Chijiwa Fault, which is the longest and most active fault of Unzen graben, the dominant conductor (C1) has a width of 2 km and extends down to below 4 km depth. C1 corresponds to a zone of strong seismic reflection and is located close to one of the pressure sources causing surface deformation. In this study, we interpret C1 as a network of fractures generated by the Chijiwa Fault to which magmatic volatiles are supplied from a deeper pressure source. Given that C1 extends to a greater depth and its resistivity is lower than other conductive zones, it is possible that earthquakes have occurred repeatedly on the Chijiwa Fault. In the center of the study area, we identify a vertically oriented body of high resistivity (R1) that corresponds to a zone of low seismic reflectivity. We interpret R1 as a cooled dyke complex that may have acted as a volcanic conduit.

Denizli and its surroundings is one of the most seismically active regions in Turkey. The region is located at the eastern end of the two most important graben (Gediz and Buytik Menderes) in Western Anatolia. Particularly, in recent years, earthquakes occurring in the region in general are the result of a complex tectonic deformation, dominated by the N-S directed extensional tectonic regime in Western Anatolia. However, the penetration of the African Tectonic Plate under the Anatolian Plate, which is particularly effective on the southwest coasts, makes the defined uniform deformation in the region very complex and as a result of this, intense seismic activity occurs. Denizli Graben, Denizli basin, Denizli Graben- horst system or Great Denizli Fault Zone (GDFZ) are aligned in Northwest-Southeast direction situated in the region. Great Denizli Fault Zone consists of many active and young segments. GDFZ is an active young basin about 90 km long, with a width of 25-40 km in places and containing many secondary fault segments. In this region, three earthquake series (Mw> 5.4-5.8) occurred between the years of 2003-2019. In addition, within the scope of the study, detailed information on earthquakes, occurred in Denizli region in the historical and instrumental period, were compiled. In this study, we analyzed the activity of earthquake clusters that occurred in the region, especially in recent years. With the analysis of the data obtained in the research, intense seismic activi-ty was observed where the central and southern parts of GDFZ were active, and especially around Bozkurt, Acipayam, Honaz, Saraykoy, Buldan. The fault plane solutions of earthquakes (47 in total) that occurred in the region during the instrumental period were compiled within the scope of the study. Additionally, fault plane solutions of 42 recent earthquakes in the region have been determined. Fault plane solutions revealed that earthquakes generally occur on normal faults, containing oblique components. The depths of the earthquakes were in the range of 8-10 km. The stress analysis results show that the exten-sion is in NNE-SSW direction which is dominant in the region. This reveals that in the regional sense. Western Anatolia continues its tectonic evolution under the extensional regime. [ABSTRACT FROM AUTHOR]

The identification and characterisation of faults in urban environments is important to inform seismic and landslide hazard, yet urban development often obscures geological and geomorphological evidence of fault traces. On the other hand, urban development also generates a wealth of borehole data, which, when combined with geophysical surveys, can enable a view into the subsurface. Here we combine geomorphological and geological mapping, gravity surveying, and 3D geological modelling to identify, map and characterise several faults in Beachlands, Auckland, some of which have large offsets. Our work has identified one new fault, the Motukaraka Fault, and confirmed the presence of two proposed faults, the Waikopua North and Te Puru faults. The Motukaraka and Waikopua North faults are both steeply dipping normal faults, which strike NNW and downthrow Mesozoic basement to the west. The Motukaraka Fault has an offset of 250 m (±100 m) and the Waikopua North Fault a combined offset of 240 m (±50 m) across two parallel fault segments. The Te Puru fault strikes northeast near the northern extent of the Waikopua Fault, and downthrows Mesozoic basement to the northwest by 60–100 m. Further investigations are required to determine whether these buried faults are active. [ABSTRACT FROM AUTHOR]

Abstract Active normal faults on the Mediterranean island of Crete form prominent limestone scarps together with basin and range topography. These faults mainly strike E‐ESE and N‐NNE in southern and northern Crete, respectively, with fault sets commonly intersecting and northerly trending faults being a factor of 3 more abundant. Lengths, displacements, and displacement rates have been analyzed for 84 active faults sampled over 2 ± 0.5 Ma (long‐term) and 16.5 ± 2 ka (short‐term) time‐intervals, with half showing no resolvable short‐term activity. Active faults record earthquake processes on timescales of thousands to million years and constrain sampling biases, which can lead to under and over estimates of fault parameters. The available data provide no evidence for fault propagation and support a model in which fault lengths were established early in the development of the fault system. Short‐term displacement rates (0.09–1.2 mm/year) are generally higher than long‐term rates (0.002–0.7 mm/year), with a factor of 4 disparity in the average recurrence intervals for the two time periods (∼2.5 Kyr vs. ∼11 Kyr). We attribute these differences to “clustering” of surface‐rupturing (e.g., >Mw6) earthquakes on individual faults over millennial timescales, and to preferential sampling of the most seismically active faults during the short‐term. Displacement rates are comparable when averaged for each time interval on the longest faults (>10 km), indicating that for these faults earthquake “clustering” spans time‐intervals of Mw6 on Crete are at least three times more frequent than historical earthquakes since ∼1920, possibly because multi‐fault surface‐rupturing earthquakes are double counted in the paleo‐record.

Dynamic disasters often occur in coal mining process, while mining disasters near faults are more serious and complex. Faults are distorted by mining, which releases a lot of energy and easily induces dynamic disasters such as rockburst and roadway instability. This study takes the 10,416 working face of Yang Liu Coal Mine (YLCM) as the engineering background, and uses numerical simulation to study the dynamic response characteristics of the working face advancing towards the hanging wall of the normal fault. In addition, the influence law of normal fault dip on fault stability is discussed in this study. The results show that when the working face of the hanging wall is mined and the working face is 30 m away from the fault, the abutment pressure in the middle of the face reaches the maximum. When the width of the fault coal pillar is 20–30 m, the possibility of rock burst on the working face is the greatest. The static load type impact ground pressure is more likely to occur when the hanging wall face advances. The greater the dip angle of fault, the higher the possibility of fault activation. High dip faults are more likely to induce dynamic disasters such as rock burst, mine earthquake, bracket pressure and so on. The research results of this study provide a scientific basis for the division, prediction and prevention of rock burst dangerous zone in mining face under similar geological conditions. [ABSTRACT FROM AUTHOR]

Active normal faults on the Mediterranean island of Crete form prominent limestone scarps together with basin and range topography. These faults mainly strike E‐ESE and N‐NNE in southern and northern Crete, respectively, with fault sets commonly intersecting and northerly trending faults being a factor of 3 more abundant. Lengths, displacements, and displacement rates have been analyzed for 84 active faults sampled over 2 ± 0.5 Ma (long‐term) and 16.5 ± 2 ka (short‐term) time‐intervals, with half showing no resolvable short‐term activity. Active faults record earthquake processes on timescales of thousands to million years and constrain sampling biases, which can lead to under and over estimates of fault parameters. The available data provide no evidence for fault propagation and support a model in which fault lengths were established early in the development of the fault system. Short‐term displacement rates (0.09–1.2 mm/year) are generally higher than long‐term rates (0.002–0.7 mm/year), with a factor of 4 disparity in the average recurrence intervals for the two time periods (∼2.5 Kyr vs. ∼11 Kyr). We attribute these differences to "clustering" of surface‐rupturing (e.g., >Mw6) earthquakes on individual faults over millennial timescales, and to preferential sampling of the most seismically active faults during the short‐term. Displacement rates are comparable when averaged for each time interval on the longest faults (>10 km), indicating that for these faults earthquake "clustering" spans time‐intervals of <∼16.5 Kyr. Paleoerthquakes > Mw6 on Crete are at least three times more frequent than historical earthquakes since ∼1920, possibly because multi‐fault surface‐rupturing earthquakes are double counted in the paleo‐record. Key Points: Displacement and fault length constrain earthquake and fault growth processes on orthogonal fault setsMillenial displacement rates are a factor of 4 higher than million‐year rates, with the greatest disparity for short (<10 km) faultsPaleoearthquakes on Crete three times more frequent than historical earthquakes for the last 100 years, possibly due to multi‐fault ruptures. [ABSTRACT FROM AUTHOR]

Our study was focused on the parageneses of heterogeneous fractures in the large fault zones of West Transbaikalia,Russia. We reconstructed the latest deformation in the fault zones of Transbaikalia, within which paleoseismic dislocations are known and M 4.7 earthquakes take place. To obtain statistically justified solutions on the kinematic types of the largest faults ofWest Transbaikalia, we collected the required data and conducted the structural and paragenetic analysis of the fractures in the study area. In the Chikoi-Ingoda, Khilok, North Tugnui andNorth Zaganfault zones, we created a network of 54 observation points and measured more than 5500 details of local fractures and faults. Recorded were the observed slickensides, the displacements of markers, and other details of rock fracturing. Based on the analysis results, we calculated a ratio of heterochronous dynamic settings for formation of the observed fault group. It shows that NW-SE-trending extension and compression are dominant in the study region. The parageneses of E-NE-striking faults, i.e. regional faults longitudinal to the depressions ofWest Transbaikalia, are abundant in the studied fault zones and generally observed in heterochronous formations, including the Cenozoic sediments. This fact, along with the focal mechanisms of the recently recorded earthquakes, suggests that these faults are young. Besides, in the Tugnui basin and the area southeast of the Chikoy depression, the right-lateral strike-slip setting was reconstructed for E-NE-trending faults. Our study pioneers in the quantitative analysis of the fault parageneses ofWest Transbaikalia. Considering the development of the network of large faults in the study area, we reconstructed the main stages and the kinematic types of the second-order fractures that constitute the internal structure of the studied fault zones at each stage of their tectonic development.

Abstract In this study, which was conducted to investigate present-day geological deformations occurring off the central Ryukyu Arc along the Ryukyu Trench (Okinawa-jima) in the vicinity of Japan, we obtained and examined dense, high-resolution, 2D grid (high-density) multichannel seismic reflection data. The forearc slope of the central Ryukyu Arc lacks a large forearc basin but has a steep narrow slope that dips to the southeast in the direction opposite to the plate convergence. However, while the seismic profiles obtained in our investigation do not reveal any active structures indicative of compressional stress in this convergent subduction zone, recent tectonic deformations are characterized by normal faults that strike perpendicular to the Ryukyu Trench axis. Examinations of high-density geological data show that the recent relative motion of the overriding plate has resulted in an active, arc-parallel extensional field. Furthermore, the results of our observations indicate two stages of extensional stress beneath the forearc slope of the central Ryukyu Arc that resulted from back-arc rifting in the Okinawa Trough.

Low‐angle normal faults (LANFs; dip <30°) accommodate kilometers of crustal extension, yet it remains unclear whether these faults can host large earthquakes or if they predominantly creep aseismically. Most active LANFs typically slip at rates of <3 mm/year. Here, we report U‐Th ages from a series of distinct levels of formerly shallow‐living corals killed by uplift‐induced emergence of the footwall of one of the world's fastest‐slipping LANFs, the Mai'iu fault in Papua New Guinea, which slips at rates of 8–12 mm/year. Coral ages and coastal morphology indicate punctuated episodic uplift events consistent with seismic slip on the Mai'iu fault. Maximum episodic uplift increments of 0.5–1.8 m imply earthquakes of Mw > 7. We present the first coral paleoseismological record of normal fault earthquakes, which constrain the timing and surface uplift patterns of multiple LANF seismic cycles and confirm that LANFs can slip in large (Mw > 7) earthquakes. Plain Language Summary: The Earth's crust breaks along fractures and faults, including "normal faults," where tectonic plates pull apart. Subsequent slip on these faults enables plates to move away from each other and can occur via slow fault creep or infrequent fast earthquakes. Although normal faults typically intersect the surface of the Earth at a steep angle, some low‐angle normal faults intersect the Earth's surface at a shallower angle. It remains unclear whether these faults typically creep gradually or slip in large earthquakes because active low‐angle normal faults are uncommon and slip at low long‐term slip rates. This study uses uplifted fossilized coral reefs to reconstruct the timing and style of fault slip near one of the world's fastest‐slipping low‐angle normal faults, the Mai'iu fault in Papua New Guinea. Isotopic and geomorphological evidence from corals killed by fault‐related coastal uplift show that the Mai'iu fault slips infrequently and episodically, revealing a history of large earthquakes in this region. Key Points: U‐Th dating of emerged coral reefs confirm active tectonic uplift at rates of 1.6–2.9 mm/year along the southern Goodenough Bay coastlineSequences of preserved reef platforms and eroded sea level notches indicate that coastal uplift is episodicEpisodic uplift increments >1 m imply Mw > 7.0 earthquakes with slip on a shallowly dipping segment of the Mai'iu‐Goodenough normal fault [ABSTRACT FROM AUTHOR]

Offshore northern Ishigaki‐Jima Island, in the southern Okinawa Trough, offers outstanding opportunities to explore the rifting stage of a backarc system. We report the results of integrated marine geological and geophysical surveys with high‐density survey lines in this area. We identify a graben bounded by normal faults and extending approximately 59 km in an ENE‐WSW direction off‐axis of the southern Okinawa Trough. Submarine volcanoes with active hydrothermalism and associated intrusive structures lie in the graben. Magnetic anomaly and seismicity data in and around the graben suggest the presence of relatively shallow magma acting as a heat source. All features identified in and around the graben suggest active rifting in the southern Okinawa Trough. Plain Language Summary: The Okinawa Trough, adjacent to the southwesternmost Japanese islands, has experienced rifting of its continental crust since 2 Ma. The southern part of the Trough includes a rift valley, the Yaeyama Rift, where rifting is active. Herein, using marine geological and geophysical data, we report the discovery of a graben bounded by normal faults on the southern margin of the southern Okinawa Trough. The graben hosts several submarine volcanoes, under which magnetic anomalies suggest relatively shallow magma. Because these geologic features resemble graben in the axial trough, we propose that the newly identified graben represents a rifting episode previously undocumented in the geological evolution of the Okinawa Trough. Key Points: A graben controlled by a normal fault was discovered in the southern Okinawa Trough offshore northern Ishigaki‐Jima IslandMagnetic anomaly and seismicity data indicate relatively shallow magma acting as a heat sourceThe graben likely manifests embryonic rifting on the southern margin of the southern Okinawa Trough [ABSTRACT FROM AUTHOR]

We used the audio magnetotelluric (AMT) method to delineate subsurface resistivity structures associated with the western Ilan Plain, which is emerged from the orogenic belt in northeastern Taiwan and is thought to be influenced by the opening Okinawa Trough. The most recent extension phase of the Okinawa Trough starting from approximately 0.1 Ma involved ENE- and WSW-trending normal faults off the Ilan Plain. Nevertheless, the region was originally a thrust-and-fold belt related to the subduction of the Philippine Sea Plate under the Eurasia Plate. Our study focuses on how the later opening of the Okinawa Trough has affected this previously compressional region. From the results of the AMT surveys, we found that the area features a series of N-S trending fracture zones in addition to the E-W normal fault systems. Comparing the AMT data with the data from seismic reflection profiles, we found that the normal fault systems are truncated by young strike-slip faults and modified the relief of the rock basement in a recent stage of formation. The western part of the study area is dominated by left-lateral strike-slip faults while the eastern part is dominated by right-lateral strike-slip faults. The findings drawn from our AMT resistivity images as well as from the reinterpreted seismic profiles constitute new evidence that the extrusion regime may have gradually taken over the regional stress state and reset the regional stress-strain conditions that was one dominated by the Okinawa extension in the western and southern part of the Ilan plain. [ABSTRACT FROM AUTHOR]