Fault Segments Research Articles

Present-day strain accumulations and fault kinematics at the Hatay Triple Junction using new geodetic constraints

The East Anatolian Fault (EAF), Cyprus Arc and Dead Sea Fault (DSF) intersect at the Hatay Triple Junction (HTJ) in southern Turkey, which is a tectonically controversial zone among researchers. Although it is not as active as the North Anatolian Fault (NAF) or other segments on the EAF in terms of seismicity, the HTJ accumulates strain causing considerable seismic activity in the region. Prior to this study, the strain accumulations and kinematics of the HTJ have not been precisely investigated using such a dense GPS network comprising permanent GPS stations, Turkish National Fundamental GPS Network (TUTGA) and campaign sites. Here, the fault slip rates and locking depths were constrained in the vicinity of HTJ using a new velocity field and improved block modeling. As per the results of block modeling, the EAF and Karatas-Osmaniye Fault (KOF) are fully locked down to depths of 15 km and 7 km, respectively. Furthermore, the Karasu Fault (KF) has a fully locked seismogenic zone to 7 km depth with a similar slip distribution to the EAF. Our kinematic model suggests 9.2 mm/yr left-lateral strike-slip rate and 2.0–2.7 mm/yr thrust faulting slip rate at the southwest end of the EAF. The KF appears to have left-lateral strike-slip at the rates ranging 4.0–5.5 mm/yr, while contrarily it has no significant normal/reverse faulting component. In addition, the KOF accommodates left-lateral strike-slip of 3.3–4.5 mm/yr and extension with the rates of 1.8–2.7 mm/yr. The new constraints on the fault slip rates associated with the HTJ correspond to predictions for a probable large earthquake with possible magnitude ranging from 7.2 to 7.6 for the EAF segment and 6.7–7.2 for the KF and KOF segments.

Architecture of intraplate strike-slip fault zones in the Yanchang Formation, Southern Ordos Basin, China: Characterization and implications for their control on hydrocarbon enrichment

Commercial discoveries in the Ordos, Tarim, and Sichuan Basins of China have aroused widespread interest in strike-slip fault-controlled reservoirs. The productivity of different wells, however, can vary within one strike-slip fault zone, suggesting that variability in fault zone architecture controls hydrocarbon enrichment. To date, very few studies have finely and quantitatively explored fault zone architecture in the southern Ordos Basin, inhibiting hydrocarbon development. With the goal of understanding the architecture variability and scale of strike-slip fault zones in the subsurface, we carried out a refined and quantitative study of faults in the Jinghe Oilfield in the southern Ordos Basin by integrating outcrops, wellbore cores, well logs, and 3D seismic data. We quantitatively constrained the subsurface damage zone boundaries according to the slope changes in the cumulative CFI (comprehensive fracture index log) curves at logging scale and the cumulative FSI (fault shape index seismic attribute) curves at seismic scale. We proposed a model highlighting the effects of fault segmentation, architectural configuration, and damage zone asymmetry on the variability of fault zone architecture. Results showed that strike-slip faults can be divided into transtensional, pure strike-slip, and transpressional segments along the fault strike, with transtensional and pure strike-slip segments dominant in the Jinghe Oilfield. These segments exhibited six types of geometric structures, forming complex architectures with multi-fault cores and multi-damage zones surrounding the main and secondary faults. Each segment was further complicated by three configurations of gouge, breccia, and damage zones along the fault dip. The damage zone asymmetry further increased the architecture variability, with the fracture density and damage zone width of the hanging wall being greater than those of the footwall. Quantitative analysis showed that the fault zone width was the greatest for transtensional segments, intermediate for transpressional segments, and the lowest for pure strike-slip segments. And there was a positive linear correlation between the fault core width and the fault zone width (including the fault core and damage zone). Fault segmentation and damage zone asymmetry affected the hydrocarbon enrichment along the fault strike and dip within one strike-slip fault zone. We conclude that damage zones in transtensional segments, particularly in hanging walls, are primary targets for hydrocarbon development in the southern Ordos Basin.

Detection of fault zone head waves and the fault interface imaging in the Xianshuihe–Anninghe Fault zone (Eastern Tibetan Plateau)

SUMMARY Fault zone head waves (FZHWs) are an essential diagnostic signal that provides high-resolution imaging of fault interface properties at seismogenic depth. In this study, we validate the existence of a bi-material interface in the Xianshuihe–Anninghe Fault (XAF) zone around their intersection and determine the cross-fault velocity contrast. We employ a semi-automatic workflow to detect and pick FZHWs and direct P waves. In addition, to improve the identification ability of potential FZHWs in the automatic picking process, we adopt a ‘forward-detecting and backward-picking’ strategy combining the short-term average/long-term average (STA/LTA) algorithm with a kurtosis detector. The polarization and characteristic periods of the waveforms are then used to manually refine the picks and evaluate the quality. The results indicate that the average velocity contrast along the southern Xianshuihe Fault is 3–5 per cent, with the northeast side characterizing a faster P-wave velocity, in agreement with tomographic results. A systematic moveout between FZHWs and the direct P waves over a 100 km long fault segment reveals a single continuous interface in the seismogenic zone. The single bi-material fault structure might be conducive to the preparation of large earthquakes and further influences the corresponding dynamic rupture processes.

Kinematic Rupture Process and Its Implication of a Thrust and Strike-Slip Multi-Fault during the 2021 Haiti Earthquake

A devasting Mw7.2 earthquake struck southern Haiti on 14 August 2021, leading to over 2000 casualties and severe structural failures. This earthquake, which ruptured ~70 km west of the 2010 Mw7.0 event, offers a rare opportunity to probe the mechanical properties of southern Haiti. This study investigates the kinematic multi-fault coseismic rupture process by jointly analyzing teleseismic and interferometric synthetic aperture radar (InSAR) datasets. We determined the optimal dip of different segment faults through finite-fault inversion, and the results show that the dips of the first, second and third faults are 62°, 76° and 76°, respectively, coinciding with the relocated aftershock distribution. The results estimated from our joint inversion revealed that the slip was dominated by reverse motion in the first segment and strike-slip motion in the second and third segments. Three slip patches were detected along the strike, with a peak slip of 3.0 m, and the rupture reached the surface at the second segment. The kinematic rupture process shows a unilateral rupture with a high centroid rupture velocity (5.5 km/s), and the rupture broke through the stepover and caused a cascade rupture. The rupture front experiences a directivity pulse of high ground motions with high amplitude and short duration, which may be an additional factor explaining the many landslides concentrated on the western end of the fault. The Coulomb failure stress change result indicates the increases in the probability of future events to the east and west of the 2021 main shock.

Fault-Seg-Net: A method for seismic fault segmentation based on multi-scale feature fusion with imbalanced classification

Fault identification has important geological significance and practical production value. Due to the effects of earth filtering and environmental noise, it is difficult to identify minor faults, and manual fault identification is inefficient. In this study, an end-to-end deep learning semantic segmentation network Fault-Seg-Net is proposed to identify fault on seismic images, which simultaneously learns global semantic features and local detailed features. In Fault-Seg-Net, a multi-scale residual module is designed to expand the receptive field to mine fine-grained fault features from the low-dimensional feature space. Fault-Seg-Attention module is designed to model long-distance dependencies of pixel spatial location to compensate for the spatial continuity loss. In addition, a compound loss is used to guide the model training to handle imbalanced seismic image segmentation tasks. Experimental results on synthetic datasets have verified that Fault-Seg-Net can achieve high Precision (88.6%), Recall (89.2%), Dice (88.8%) and mIoU (81.5%) simultaneously, which is significantly better than traditional image processing methods and deep learning semantic segmentation networks. Experimental results on real large-scale field datasets have verified that Fault-Seg-Net has important practical value and strong robustness. This study provides an effective solution for intelligent seismic fault identification under complex geological environment.

Seismotectonics, Geomorphology and Paleoseismology of the Doroud Fault, a Source of Seismic Hazard in Zagros

In this study, the active tectonics, paleoseismicity, and seismic hazards of the Doroud Fault are examined through high-resolution satellite image interpretations, field investigations, outcrop and trench excavations, and the dating of geochronology samples. The Doroud Fault (DF), one of the essential segments of the Main Recent Fault in the northern margin of the Zagros mountain range, has a historical and instrumental background of high seismicity. We present the first constraints from tectonic geomorphology and paleoseismology along the Doroud Fault near the capital city of Dorud. Detailed observations from satellite imagery, field investigations, real-time kinematic (RTK) measurements, paleoseismological trenching, the radiocarbon (C14), and optically stimulated luminescence (OSL) as ages allowed us to map the fault in detail, describe and characterize its kinematics, and document its recent activity and seismic behavior (cumulative displacements, paleoseismicity, and magnitude, as well as recurrence interval) relevant to the recent seismic activity of the Doroud Fault during the late Holocene as one of the most important seismogenic faults in Zagros. Modern alluvial terraces of gullies and loess accumulations are systematically deflected and/or offset with co-seismic rupture, landslides, and scarps, indicating that the Doroud Fault has been active in the late Quaternary and is characterized by dextral strike–slip movements with a normal component. In addition, our findings provide a comprehensive analysis of the fault displacement, the timing of paleoearthquakes, and the right-lateral slip rate of the Doroud Fault. The late Holocene slip rate of the Doroud Fault using the OSL dating the gully is as follows: the minimum and maximum horizontal slip rates are estimated to be 1.82 and 2.71 mm/yr, and vertical slip rates of 1.03 and 1.53 mm/yr are calculated for the past 4600 ± 900 years in the middle segment of the fault. This study focused on a paleoseismological trench within the archeological sites of Darbe-Astaneh. The central portion of the fault has historically hosted more than nine earthquakes in the last 66 ka years, according to the study’s findings. According to paleoseismology studies, the Doroud Fault has the seismic capability to cause earthquakes with a magnitude of more than 7.4 and a total slip rate of about 3.83 ± 0.1 m. The average recurrence interval for the identified paleoearthquakes is approximately 104 ± 7 years.

Fault characterization in a postsalt reservoir interval, Jubarte Field (Campos Basin), using seismic attributes and machine learning

Seismic attributes are routinely applied to interpretation tasks to improve the recognition of geologic features in the subsurface. Subtle changes in the amplitude and phase components of the seismic data can reveal details and provide information about the management of hydrocarbon reservoirs. To this end, we investigate how instantaneous and geometric attributes can help in fault and discontinuity recognition. Seismic data from Jubarte’s 4D/4C Permanent Reservoir Monitoring system, offshore Brazil, were used to test the impact of a variety of algorithms and parameters in improving fault visualization. The presence of seismic noise and geologic units with weak acoustic impedance contrasts motivated the application of additional methods such as data conditioning workflows and unsupervised machine learning methods. We found that spectral balancing and structure-oriented filtering increased the lateral continuity of some stratigraphic reflectors and attenuated the random noise, which improved fault surface visibility. Attributes were calculated on the full-stack data and azimuth-restricted volumes revealing different impacts of the seismic noise and changes in the lateral continuity of the features. In some cases, faults are better delineated when the acquisition direction is oriented perpendicular (or nearly) to the discontinuity. In addition, the most-positive and most-negative curvature components indicate more details of major features. A large number of seismic cubes and attributes motivated the use of principal component analysis and self-organizing maps, which complement the identification of fault segments with clusters composed of specific neurons aligned within structural discontinuities. The improvements obtained in terms of fault visualization demonstrate the importance of having a workflow that combines different fault and fracture identification methods. An integrated study is important as it identifies effects related to seismic noise and stratigraphic features. For the Jubarte Field, a multiattribute approach demonstrates advantages for delimiting the lateral extension of faults and a more precise discontinuity location.

3D Evolution of Detachment Fault Systems in Necking Domains: Insights From the Klakk Fault Complex and the Frøya High, Mid‐Norwegian Rifted Margin

AbstractDetachment fault systems typically record displacements in the order of 10s of kilometers. The principles that control the growth of smaller magnitude normal faults are not fully applicable to the evolution of detachment fault systems. We use interpretation of 2D and 3D seismic reflection data from the mid‐Norwegian rifted margin to investigate how the structural evolution of a detachment fault interacted with the effects of isostatic footwall rollback to produce complex 3D geometries and control the configuration of associated supradetachment basins. We further investigate the effects of lateral interaction and linkage of extensional detachment faults on the necking domain configuration. In our study area, the domain‐bounding Klakk Fault Complex demonstrates how successive incision may induce a complex structural relief in response to faulting and fault plane folding. We interpret the previously proposed metamorphic core complex within its footwall as an extension‐parallel turtleback‐structure. The now eroded turtleback is flanked by a major supradetachment basin, connecting two main basin segments. We attribute footwall‐ and turtleback exhumation to Middle Jurassic‐Early Cretaceous rifting. The study area further demonstrates how detachment fault geometries can change during rifting and lead to the formation of younger, successively incising fault splays. Lateral linkage between the original detachment fault plane and these fault splays enables displacement along a detachment fault system consisting of fault segments generated at different stages in time. Implicitly, detachment faults are complex 3D systems that change configuration during their evolution, perpetually controlling associated basin formation, footwall configuration, subsidence and uplift patterns.

DInSAR and Elastic Dislocation Modelling: A Case Study For The 24 January 2020 Elazig-Sivrice Earthquake

One of Turkey's most important neotectonic structures East Anatolian Fault Zone (EAFZ), has occurred many earthquakes. One of these earthquakes, the 6.8 Mw Sivrice-Elazig earthquake dated January 24, 2020, was felt in various provinces, especially in Elazig and Malatya, and caused the death of 44 people. It is critical to investigate this earthquake, which caused significant economic damage, and to identify possible hazards on the EAFZ. One of the remote sensing methods DInSAR was used in this study. By choosing two Sentinel 1A (Single Look Complex) descending datasets, dated 16/01/2020/01 and 28/01/2020/01 respectively (pre and post earthquake), the surface deformation and time series were determined. In addition, using the data obtained from the DInSAR results, Elastic Dislocation Modelling has been performed by applying linear and nonlinear inverse solutions to determine the slip amount of the fault structure, the fault surface slip distribution, and determine the strain area. According to the DInSAR results, while there is an offset of approximately 26 cm (away from the satellite direction) on the left block of the EAF, 19 cm offset (towards the satellite direction) are observed in the right block, respectively. Elastic Dislocation Modelling shows that the observed deformation pattern can be explained by the slip on a single plane fault of the Elazig earthquake. This fault plane was identified as a southwest strike-slip fault segment, which lies within the upper crustal region and extends to a depth of approximately 10 km. According to the results obtained by elastic modelling; slip amount (slip) was calculated as 1.95 m, Mw 6.75, rupture length 34.78 km, focal depth 10 km, width 7.4 km, strike 240.27°, slope 69.19°, rake 0.19°. Overall, the study reveals the strike-slip of the Sivrice-Elazığ earthquake, shows the deformation after the earthquake, and the elastic half-space fault model.

Tectonic geomorphology of Bozdoğan and Karacasu grabens, western Anatolia

Western Anatolia is one of the most rapidly extending and seismically active regions in the world. The circa N-S extension since the Early Miocene caused the formation of E-W trending major grabens and intervening horsts, having earthquake potentials with magnitude ≥5. The E-W oriented Büyük Menderes graben cross-cuts the broadly N-S oriented Bozdoğan and Karacasu grabens, of which the boundary faults of the latter are the source of seismic activity. Geomorphic indices, including drainage basin asymmetry, mountain front sinuosity, valley-floor width to valley height ratio, stream length-gradient index and normalized channel steepness index, were used to evaluate the boundary fault segments of the Bozdoğan and Karacasu grabens. The results indicate that both grabens are tectonically active and therefore regions of earthquake potential, consistent with the epicenters of earthquakes. Thus, it can be inferred that fault segments of second-order grabens, which are crosscut by the boundary faults of seismically active main depressions, are apparently reactivated by ongoing tectonism and may represent seismic activity. This suggestion applies also for similar basins located in the western Anatolia.

Structural evolution characteristics and genesis of buried hill faults in the Chengdao–Zhuanghai area

The buried hills in the Chengdao–Zhuanghai area are rich in oil and gas resources, and their structures exhibit complex styles with unique evolutionary characteristics. Based on the most recent exploration progress in this region, the structural characteristics and active parameters of the buried hill faults in this region were quantitatively analyzed using the balanced section technique. In addition, the structural evolution process of the study area was reproduced by combining the structural-physical simulation experiment. Its spatio-temporal evolution characteristics and genesis mechanisms were also systematically investigated. As observed, the study area developed three basic sets of fault systems: the NW-trending extensional strike-slip fault, the NNE-trending left-handed compression–torsion fault, and the near-EW-trending extensional fault. The study area was further segmented into six buried hills: West Row Hill, Middle Row Hill, East Row Hill, Zhuanghai Buried Hill, Zhuangxi Buried Hill, and Changdi Buried Hill. The inner fault of the NW-trending Buried Hill is a strike-slip extensional fault that formed under the influence of the right-lateral strike-slip activity of the NW-trending Chengbei Fault from the Late Jurassic to the Early Cretaceous. In particular, the NNE-trending fault was a left-handed compression–torsion fault that formed under the left-handed strike-slip activity and regional compression stress field of the Tanlu fault zone. The near-EW fault was closely related to the near-SN extension stress field in the Late Cretaceous. Since the late Triassic, the study area has experienced six evolution stages, namely, overall uplift erosion (T3), overall coating deposition (J1+2), fault segmentation (J3-K1), extrusion uplift differentiation (K2), middle buried hill differentiation E), and overall stable subsidence (N-Q). Its tectonic evolution was primarily controlled by the significant variations in the tectonic stress field in the study area as well as its adjacent areas since the late Triassic, which were controlled by the tectonic stress field.

Tectonic geomorphology and Quaternary fault slip rates in the Tsambagarav Massif, Mongolian Altai

AbstractThe NNW‐striking Mongolian Altai is a Late Cenozoic dextral strike–slip deformation belt affected by the far‐field stress caused by the collision between India and Eurasia. The Tsambagarav Massif is bounded by faults, has a triangular plan shape, and attains the highest elevation of the belt. This massif is adjacent to the central segment of the Hovd fault, which is the largest fault in the Mongolian Altai. Here, we use 10Be surface exposure dating, radiocarbon dating, and paleoseismic trenching to reveal deformation patterns and Quaternary slip rates for two range‐bounding faults: the Tsambagarav dextral reverse fault and the Lower thrust fault. The Lower thrust exhibits thrusting motion along the low‐angle structural fabric of the basement rock and cuts Quaternary alluvial fan deposits, vertically offsetting their surfaces by 3.9–5.1 m, with fault scarps extending several kilometres along‐strike. The Tsambagarav dextral reverse fault is characterized by strike–slip motion along the high‐angle structural fabric of basement rock. Various surface deformation features indicate recent dextral strike–slip, including displacements of Late Quaternary moraine by ~50 m. Dividing the measured displacements by 10Be surface exposure ages of alluvial fan surfaces (for the Lower thrust) and moraine (for the Tsambagarav dextral reverse fault) gives a reverse slip rate of 0.3–1.7 mm/yr for the Lower thrust and a horizontal slip rate of 1.7–2.6 mm/yr for the dextral reverse fault. Radiocarbon ages of animal bones in a pond deposit accumulated along an associated tensional crack indicate that the last earthquake that caused a surface rupture occurred between 1924 and 1708 cal yr BP. Our study suggests that strain partitioning has occurred on the faults of the Tsambagarav Massif.

Coseismic Rupture Behaviors of the January and March 2022 MW > 5.5 Hala Lake Earthquakes, NE Tibet, Constrained by InSAR Observations

On 23 January and 25 March 2022, two MW > 5.5 Hala Lake earthquakes characterized by right-lateral strike-slip faulting occurred around the Elashan Fault in Northeastern Tibet, marking the two largest events since the 1927 MW 6.2 Hala Lake earthquake. Since no surface rupture related to the two earthquakes has been reported, the seismogenic faults and coseismic rupture behaviors of the two events are still unknown. The occurrence of the two events provides a rare opportunity to gain insight into the seismogenic structure and rupture behavior of the less studied region, further helping us accurately evaluate the regional seismic hazard. Here, we first exploit Interferometric synthetic aperture radar (InSAR) data to obtain the coseismic deformation associated with the two earthquakes and then invert for the fault geometry and detailed coseismic slip of the two events. Coseismic modeling reveals that the January and March 2022 earthquakes ruptured two buried west-dipping moderate-angle and high-angle right-lateral strike-slip faults, respectively. Most of the slip of the January event occurred at depths from 1.7–7.6 km, while the majority of the slip associated with the March event occurred at depths from 2.5–10 km, which may have been restricted by the intersections between the January and March Hala Lake seismogenic faults. By a comprehensive analysis of the coseismic inversions, stress changes, and early postseismic signal, we suggest that the significant fault dip difference (~30°), highlighting a fault segmentation, stops the rupture propagation from one fault segment to another and that fluid migration may encourage the restart of the rupture of the later event, which requires further investigation. Moreover, Coulomb stress modeling shows stress loading on the eastern segment of the Daxueshan–Shule Fault and the northern segment of the Elashan fault, which we should pay more attention to.

Tectonic landform and paleoseismic events of the easternmost Matano fault in Sulawesi, Indonesia

The 190-km-long Matano fault is a major left-lateral strike-slip fault in Sulawesi, Indonesia that accommodates the rapid westward motion of the Pacific plate relative to the Australian plate. The Matano fault has remained unruptured at least in the past two centuries. The lack of geologic information, such as precise active fault traces, paleoseismic history, and slip rates has been a significant barrier to assessing the seismic hazards of the Matano fault. This paper presents the results of tectonic geomorphic and paleoseismic investigations on the 30 km long easternmost portion of the Matano fault. We identified four geometrical fault segments, documented five surface faulting events, and calculated a surface-rupturing earthquake recurrence interval of 200–470 years and a slip rate of 21 ± 9 mm/yr. The timing of the most recent surface-rupturing earthquake was constrained between 1432 and 1819 CE with an estimated Mw ∼ 7.4 and a probable rupture length of ∼110 km. At least 200 years have passed since the latest faulting event, exceeding the shortest recurrence interval. Thus, the next surface-rupturing earthquake is already due. Integrating our interpretations with results from several published studies clarifies that the Matano fault slips slower than the Palu-Koro fault and connects to the South Sula fault in addition to the Tolo thrust.

Study on the Influence of Soil Engineering Geological Characteristics at Key Tectonic Sites on High-Speed Railway Foundation—A Case of the Beijing–Zhangjiakou High-Speed Railway (Huailai Section)

The soil engineering geological characteristics and hidden fault creep activity are the main geological factors affecting the stability of the Beijing–Zhangjiakou high-speed railway foundation. In order to reveal the deep formation structure and physical and mechanical properties of the soil under the Beijing–Zhangjiakou high-speed railway foundation and explore the influence of soil settlement under the static load and dynamic load of high-speed railways, according to the deep-hole engineering geological drilling and soil test, this paper reveals the soil structure and physical and mechanical properties within a 500 m buried depth of the Huailai section of the Beijing–Zhangjiakou high-speed railway. Based on the drilling data, we constructed a 3D geological structure model across fault segments to study the influence mechanism of the dynamic load of trains on differential ground settlement. The results show that the basic physical and mechanical parameters of all kinds of soil have little change with the increase of buried depth, and the ratio of secondary consolidation index Cs to compression index Cc is 0.0036–0.0516. Under the dynamic load of a high-speed train, the vertical displacement of soil gradually decreases with the increase of depth, which mainly affects the soil within a 50 m depth. Within the influence range, the vertical displacement at a certain point is negatively correlated with the speed of a high-speed railway and the horizontal distance from the railway line and the fault. The research results are expected to provide scientific support for the safe operation of the Beijing–Zhangjiakou high-speed railway.

Tectonic stress changes related to plate spreading prior to the 2021 Fagradalsfjall eruption in SW Iceland

The Reykjanes Peninsula in SW Iceland is a part of the Mid-Atlantic plate boundary. It forms its transtensional segment with several volcanic and faulting systems. We focus on the 2017 seismicity that occurred in the central part of Reykjanes at the place of the Fagradalsfjall volcano prior to its eruption on March 19, 2021. We invert well-determined focal mechanisms of the 2017 seismicity and provide mapping of tectonic stress in space and time. Our results disclose heterogeneous stress field manifested by mix of shear, tensile and compressive fracturing. The prominent stress direction was in the azimuth of 120° ± 8°, which represents the overall extension related to rifting in the Reykjanes Peninsula. The activity initiated on the transform fault segment with predominantly shear strike-slip events. The non-shear fractures occurred later being associated with normal dip-slips and corresponding to the opening of volcanic fissures trending in the azimuth of 30–35°, perpendicular to the extension. The dip-slips were mainly located above an aseismic dike detected in the centre of the 2017 swarm. This dike represents a zone of crustal weakening during a preparatory phase of the future 2021 Fagradalsfjall volcanic eruption located at the same place. Moreover, we detected local variation of stress when the stress axes abruptly interchanged their directions in the individual stress domains. These stress changes are interpreted in a consequence of plate spreading and upcoming fluid flow during a preparatory phase of a rifting episode.

A time-dependent seismic hazard model following the Kaikōura M7.8 earthquake

ABSTRACT Following the 2016 M7.8 Kaikōura earthquake, a time-varying seismic hazard model (KSHM) was developed to inform decision-making for the reinstatement of road and rail networks in the northern South Island. The source model is the sum of a gridded 100-year earthquake clustering model and an updated fault source model. The gridded model comprises long-term, medium-term and short-term components. The 100-year gridded model is constructed as the sum of 100 annual forecasts. A discounting method trades off expected earthquake occurrences of the distant future against those of the near future. The fault source model includes updates to account for newly revealed faults that ruptured in the Kaikōura earthquake and other recently obtained new information, and new time-varying probabilities of rupture for four fault segments. Two different characterisations of the Hikurangi subduction interface are incorporated via a logic tree, with weights determined by an expert panel. A suite of ground motion prediction equations contribute to a logic tree in order to account for epistemic uncertainties in source modelling for each of four tectonic region types. Here, we compare the resulting hazard estimates with the 2010 National Seismic hazard Model and recorded motions in past New Zealand and global earthquakes.

Internal architecture and structural evolution of a horst relay zone from the northern Gulf of Suez rift, Egypt: Implications for syn-rift sedimentation

A remarkable outcrop of an extensional NW-oriented horst block takes place between conjugate normal fault segments at the Akheider-El Ramliya fault block (ARFB), along the northwestern termination of the Gulf of Suez rift. Detailed field geological mapping is accomplished to identify the architecture, linkage style as well as evolution of the encountered normal fault system at the ARFB. The resultant structural model revealed several geometries of normal faults interaction that form soft- and hard-linkage relay zones affecting pre- and syn-rift rock units. Such relay zones are well developed between the boundary faults of the ARFB. Additionally, three E-W oriented fault belts are mapped at the northern, central and southern parts of the ARFB enclosing left-stepping en echelon normal faults, where several relay zones are formed between the overlapped fault segments. Structural analysis and evolution of the mapped area revealed that the overall architecture of the ARFB representing a broad horst relay zone between the conjugate divergent boundary normal faults. Also, two sub-basins have been recognized at the downthrows of the border faults comprising syn-rift Oligocene and Miocene sediments. The results show that these faults are rejuvenated by a continued NE-SW extension through Late Eocene, Oligocene and Miocene times. Additionally, the formed relay zones via growth and propagation of such faults have main controls on syn-sedimentation at the northern Gulf of Suez rift. The results of the present study offer constraints on horst relay zones including, internal structural architecture, geometries and interaction of boundary faults as well as role of inherited structures. Also, it provides an outcrop model for architecture and evolution of similar structural styles (e.g., the Gulf of Suez rift) as well as for subsurface mapping and exploration in extensional relay zones.

Transient Behavior and Interplay Between Seismic and Aseismic Deformation Near the Tip of a Creeping Segment: Insights From the Northern Jordan Valley Segment of the Dead Sea Fault

AbstractTransient aseismic deformation is observed using dense geodetic measurements across the northern Jordan Valley Fault (JVF) segment of the Dead Sea Fault (DSF). The fault was creeping until 2013 at a rate of 2.6 ± 0.3 mm/yr. It stopped creeping between 2013 and 2018 and then started creeping again at a similar rate. These transitions between the creep and locked modes of deformation correlate well with the 2013 and 2018 seismic sequences that occurred near the tip of the northern JVF creeping segment. The creep caused the accumulation of Coulomb stresses near the fault tip, which promoted earthquake nucleation in this region. The 2013 seismic sequence, with a maximum moment magnitude of 3.7, was probably too small to release these stresses, and they were released during the 2018 seismic sequence, with a maximum moment magnitude of 4.5, which allowed the fault to creep again. We suggest that seismic activity will continue to occur near the tip of the northern JVF creeping segment.

The characteristics of strike-slip faults and their control on hydrocarbon distribution in deep carbonate reservoirs of the central Sichuan Basin

The past decade has witnessed a breakthrough in the gas exploration of deep marine carbonates of the central Sichuan Basin. Deep faults research has also attracted increasing attention, as faulting plays an important role in reservoir control. Previous studies have suggested a developed series of high-angle strike-slip fault systems in the central Sichuan Basin, but correlated exploration activities are limited, as distribution rules and dynamic mechanisms remain unclear. In this study, the spectral decomposition coherence method was used to describe the geometric and kinematic characteristics of these strike-slip faults. Using a comprehensive analysis technique to assess the strike-slip fault tectonic activity history, the formation and evolution processes of strike-slip faults and their control on hydrocarbon distribution were examined. The results showed that the deep strike-slip fault system, mostly distributed in the Dengying Formation, can be divided into four stages, three levels, and three groups of orientation, which controlled the structural framework and shape of the central Sichuan area, as well as the zoning from north to south, and blocking from west to east. The faults showed features of layered deformation and staged evolution in the vertical direction. The segmentation of strike-slip faults strongly controls the quality of fractured vuggy reservoirs. Reservoirs of the hard-linked zone of the strike-slip fault are the most developed, followed by those of soft-linked segments, with translational sections of the strike-slip fault being relatively undeveloped. Strike-slip faults are important hydrocarbon migration paths, and their multistage activities have different controlling effects on hydrocarbon accumulation.