Block Rotation Research Articles

Physical modeling of block rotation and the role of ductile sediments in the structural evolution of Kopeh Dagh and Zagros

دو کمربند کوهزایی زاگرس و کپه داغ از نظر ساختاری شباهتهای بسیاری دارند. در هر دو منطقه تاقدیس‌ها بوسیله گسل‌های عرضی با روند غالب شمال-باختر-جنوب‌خاور بریده شده‌اند. راستای مایل این گسل‌ها نسبت به جهت تنش بیشینه، موجب چرخش پادساعتگرد بلوک‌ها می‌شود که کوتاه‌شدگی در عرض و کشیدگی در راستای کمربند را در خود جای می‌دهد. اما گسل‌های راستالغز این دو منطقه تاثیر متفاوتی را بر روی محور تاقدیس‌ها نشان می‌دهد. به منظور درک بهتر تکامل ساختارهای وابسته به چرخش بلوک‌ها و تاثیر گسل های راستالغز بر روی کمربند چین‌خورده-رانده؛ دو مدل فیزیکی با پنج بلوک مایل، با لایه های متفاوت و متناسب با چینه‌شناسی دو زون ساختاری، مورد بررسی قرار گرفت. نتایج مدلسازی آنالوگ بیانگر تاثیر لایه های شکل پذیر بر چگونگی بروز سطحی گسلها و چرخش محور چین ها است. در منطقه زاگرس به دلیل وجود افق‌های شکل‌پذیر (همانند سازند هرمز) جابجایی در راستای گسل‌های راستالغز پی‌سنگی عمدتا به صورت انحنای محور چین‌خوردگی ها دیده می‌شود. اما در کپه‌داغ به دلیل کمتر بودن لایه‌های شکل‌پذیر این جابجایی در سطح به صورت بریدگی محور چین‌ها نمایان است. رخنمون گسلها در سطح در کپه داغ نسبت به زاگرس پیوسته تر، درازا و جابجایی بیشتری دارد.

Study on the mechanical properties of outwash deposits with random structure method

Abstract Outwash deposit is one of the major threats to the safety and stability of railway transit engineering in the Sichuan–Tibet area. In this paper, different samples of outwash deposits were prepared based on the random structure method, and a series of large-scale direct shear tests were carried out under different normal stresses. The influence of stone content and the spatial distribution of stone blocks on the physical and mechanical properties of outwash deposits were studied. The results show that with the increase of stone content, the shear stress-displacement curve changs from strain softening to strain hardening. The shear zone is larger, and its shape is more tortuous due to the movement and rotation of stone blocks. The internal frictional angle increases linearly while the cohesion diseases with the increase of stone content. The main influence of the spatial distribution of stone blocks on the mechanical properties of outwash deposits is the peak stress. The shear zone is mainly determined by the distribution of the stone blocks near the shear zone.

Thick- and thin-skinned basin inversion in the Danish Central Graben, North Sea – the role of deep evaporites and basement kinematics

Abstract. Using borehole-constrained 3D reflection seismic data, we analyse the importance of sub-salt, salt, and supra-salt deformation in controlling the geometries and the kinematics of inverted structures in the Danish Central Graben. The Danish Central Graben is part of the failed Late Jurassic North Sea rift. Later tectonic shortening caused mild basin inversion during the Late Cretaceous and Paleogene. Where mobile Zechstein evaporites are present, they have played a significant role in the structural evolution of the Danish Central Graben since the Triassic. Within the study area, Jurassic rifting generated two major W- to SW-dipping basement faults (the Coffee Soil Fault and the Gorm–Tyra Fault) with several kilometres of normal offset and associated block rotation. The Coffee Soil Fault system delineates the eastern boundary of the rift basins, and within its hanging wall a broad zone is characterized by late Mesozoic to early Paleogene shortening and relative uplift. Buttressed growth folds in the immediate hanging wall of the Coffee Soil Fault indicate thick-skinned inversion, i.e. coupled deformation between the basement and cover units. The western boundary of the inverted zone follows the westward pinch-out of the Zechstein salt. Here, thin-skinned folds and faults sole out into Zechstein units dipping into the half-graben. The most pronounced inversion structures occur directly above and in prolongation of salt anticlines and rollers that localized shortening in the cover above. With no physical links to underlying basement faults (if present), we balance thin-skinned shortening to the sub-salt basement via a triangle zone concept. This implies that thin Zechstein units on the dipping half-graben floor formed thrust detachments during inversion while basement shortening was mainly accommodated by reactivation of the major rift faults further east. Disseminated deformation (i.e. “ductile” at seismic scales) accounts for thin-skinned shortening of the cover units where such a detachment did not develop. The observed structural styles are discussed in relation to those found in other inverted basins in the North Sea Basin and to those produced from physical model experiments. Our results indicate that Zechstein units imposed a strong control on structural styles and kinematics not only during rift-related extension but also during basin inversion in large parts of the Danish Central Graben. Reactivated thin-skinned faults soling out into thin Triassic evaporite units within the carapace above Zechstein salt structures illustrate that even thin evaporite units may contribute to defining structures during tectonic extension and shortening. We thus provide an updated and dedicated case study of post-rift basin inversion, which takes into account the mechanical heterogeneity of sub-salt basement, salt, and supra-salt cover, including multiple evaporite units of which the Zechstein is the most important.

Sandbox Modeling of Transrotational Tectonics With Changeable Poles: Implications for the Yinggehai Basin

The main formation of the Yinggehai Basin has been related to the rotation of the Indochina block, resulting in large-scale strike-slip motion along the Red River Fault Zone (RRFZ). Transrotational tectonics played a key role in the evolution of the Yinggehai Basin. In this study, we present analog experiments with a preexisting basal velocity discontinuity boundary, rotation of crustal blocks concerning vertical axes, and syntectonic sedimentations to evaluate how the transrotational tectonics controls the evolutionary process of the Yinggehai Basin. Particle image velocimetry (PIV) was used to monitor the deformation of the model surface. Four successive poles of rotation have been applied to the model. The basin evolution underwent two phases. An early phase of deformation is characterized by the nucleation of the main internal faults above the velocity discontinuity boundary and segmented en echelon border fault systems. In the early phase, the internal and boundary faults mainly accommodated large-scale strike-slip displacement. During progressive extension, the main internal faults deactivated, and tectonic activity is localized along the boundary and secondary internal faults in the late phase. The boundary faults in the rotating block play a dominant role in the widening and deepening of the rift zone at an accelerating rate. The model surface morphology shows similarities to the Yinggehai Basin, which is wide in the middle and converges toward the northwest and southeast. In addition, experimental profiles have been compared with seismic profiles in the Yinggehai Basin. The model results also indicate that the rotation of the Indochina block combines with strong strike-slip motion. The similarities between modeling and nature provide support for ∼250 km sinistral displacement along the RRFZ between ∼32 and ∼21 Ma.

Upper bound analysis of working face passive failure in large-diameter shield tunneling based on a composite mechanism

This paper investigates the passive instability of the working face of large-diameter shield tunneling in frictional soils by developing a new mechanism. The proposed composite mechanism comprises rotational and translational blocks, and failure is involved within the movement of the blocks. The upper bound solution of support pressure for passive instability is derived using a kinematic approach. The stability analysis explores the critical support pressure and associated failure mode by optimizing the mechanism. The proposed mechanism indicates that the failure in the cover layer is fully involved in the translational movement, while in the crossed layer, the failure is partially involved in rotational movement. The mechanism is influenced more significantly by the frictional angle than by cohesion and surcharge on the ground surface. The proportion of rotational blocks to translational blocks decreases with increasing φ′. In the presence of a rotational block, the proposed composite mechanism outperforms the previous translational mechanisms in predicting the critical support pressure and associated failure mode. Finally, the current solution is validated by comparing with previous centrifuge tests, where agreement on the critical support pressure and the associated failure mode is found.

The Chongón/Colonche orocline transrotational bending and the coeval opening of the Progreso basin in southwestern Ecuador

Integration of geological and geophysical studies of Progreso Basin in SW Ecuador provided a unique opportunity to propose an unorthodox model for the Progreso Basin opening within a strike slip regime. Shearing couple transrotation of the Chongón/Colonche (C/C) orocline bending accounted for the atypical, isosceles triangle shape, Progreso Basin opening during the Oligocene oblique convergence amid the Farallon and South America plates. Transrotation commenced with the sinistral strike slip reactivation of the Paleocene Chongón-Jipijapa-Jama (CJJ) Suture. This suture is inferred based on field kinematics of Cretaceous outcrops in the Santa Elena Peninsula and published high resolution potential field maps. The reactivated suture worked as the sinistral La Cruz (LCF) Fault and their “en echelon” synthetic Riedels C/CF, Consuelo (COF), and Carrizal (CAF) faults accommodated most of the basin heterogeneous transtension and transrotation. While the synthetic Riedels migrated northward along the La Cruz Fault, a narrow segment of the Paleogene foredeep and the intra-oceanic arc sequence of the C/C High attached to the Estancia Hills was scrapped off and rotated. The shearing couple between the “en echelon” Riedels enhanced the transrotation and transtension and triggered the counterclockwise crustal rotation of the C/C High. The subvertical block rotation involved significant lithospheric decoupling of this high that set off the C/C Orocline development and coeval opening of the Progreso Basin.Early Zapotal Formation deposition characterized by alluvial fan aggradation rapidly filled the graben between the Consuelo and Carrizal faults as the Consuelo Fault underwent strain hardening and confining. In doing so, the sediment input by the active alluvial fan complex spilled over the Carrizal Fault displaying down lapping and progradation along the hanging wall. Its listric behavior on other hand, set off the tilting of the pre-extensional Paleogene sequences, which in turn caused the onlapping and diachronous deposition of the Zapotal Formation toward the La Cruz Fault. Protracted marine incursion and deposition of a fine grained siliciclastic sequence that encompassed the whole Oligocene took place around the already opened basin toward the south.Early Miocene breakup of the Farallon Plate not only increased the convergence rate but also gradually changed the convergence from oblique to orthogonal. Multiple intraformational unconformities and high sedimentation and subsidence rates in the Dos Bocas Formation documented this change. Recurrent deposition of the diatomaceous Villingota Formation suggested episodic upwelling in the basin enriched by the high siliceous tuffs supply from the coeval Saraguro Arc volcanism in the Western Cordillera. Basin transtension terminated during Late Miocene inception of the Rodeo and Playas synthetic Riedels to the reactivated Pallatanga Suture known as the dextral Chingual-Cosanga-Pallatanga-Puna (CCPP) fault system. However, as this fault continued into the Gulf of Guayaquil, the transtension was transferred to this area. Hitherto, the Progreso Basin underwent a sagging phase characterized by the onlapping of the Subibaja and Progreso formations against the La Cruz Fault High as well as a localized, subtle tectonic inversion due to space problems linked to the synthetic Riedels inception.

Significance of Northern Andes Terrane Extrusion and Genesis of the Interandean Valley: Paleomagnetic Evidence From the “Ecuadorian Orocline”

AbstractGPS data suggest that the NW South America corner forms a semi‐rigid block drifting NE‐ward along the regional dextral strike‐slip faults that bound an oceanic terrane accreted in Late Cretaceous times to W Ecuador and Colombia. However, the relevance of both strike‐slip versus thrust tectonics during Cenozoic times and their relation with oceanic terrane accretion are unclear. Here we report on the paleomagnetism of 31 mid‐upper Eocene to upper Miocene mainly volcanic sites from the Cordilleras Occidental and Real of southern Ecuador. Eleven sites show that the western Cordillera Occidental underwent a 24° ± 10° clockwise (CW) rotation with respect to South America after late Miocene times, while no rotation occurred further east. We relate the regional CW rotation to the emplacement of the Cordillera Occidental nappe onto the continental sediments of the Interandean Valley, blanketing the Cordillera's eastern margin. As rotation and continental sedimentation onset ages are similar, we interpret such tectonic depression as a narrow flexural basin formed ahead of the advancing nappe front. The 20°–30° CW Neogene rotation of the Cordillera Occidental is indistinguishable from the post‐Cretaceous rotation of the Coastal forearc oceanic blocks, implying that the whole W Ecuador Andean chain was detached and rotated over a mid‐crustal detachment during the last 10 Ma. Eocene‐Miocene paleomagnetic inclination values are systematically consistent with those expected for South America, thus excluding latitudinal terrane drift. We suggest that the Andes of Ecuador and Peru form the “Ecuadorian Orocline”, formed by opposing orogenic rotations around the Amazonian craton indenter.

Сейсмологические исследования на территории Алтае-Саянской горной области

The paper provides a brief overview of seismological studies in the Altai-Sayan mountain region. The de-velopment of a network of seismological stations and experiments with temporary stations in the epicen-tral zones of large earthquakes is described. It is shown that the background seismicity of the region is or-dered over time into structures with a hierarchy in the rate of occurrence. Large earthquakes in some cases occur in places that do not match with the areas of increased background seismicity. Major earthquakes in Eastern Tuva (Busingol, Belin-Biy-Khem, etc.) occur as shifts and rotations of blocks near rift depressions. Large earthquakes of the Western Sayan Ridge and the Academician Obruchev Ridge (Tuvan First and Second earthquakes, Sayan earthquake) are associated with faults transverse to these structures and are the result of the uneven extension of blocks of the Tuva hollow and the Tuva highlands to the north. Stud-ies in the Altai Mountains found that after a long period (about 10 years) of the aftershock process of the Chui earthquake dominating the seismicity, a period of seismic activation of adjacent (60-80 km) and dis-tant (within a radius of approximately 260-280 km) structures occurred. The center of seismic activity shifted from the epicenter of the 2003 Chui earthquake to the epicenter of the 2019 Aigulak earthquake. Experimental work with powerful vibrators has determined the capabilities of a network of seismological stations in vibroseismic monitoring of the Earth's crust.

Dexterous manual movement facilitates information processing in the primary somatosensory cortex: A magnetoencephalographic study.

The interaction between the somatosensory and motor systems is important for control of movement in humans. Cortical activity related to somatosensory response and sensory perception is modulated by the influence of movement executing mechanisms. This phenomenon has been observed as inhibition in the short‐latency components of somatosensory evoked potentials and magnetic fields (SEPs/SEFs). Although finger is the most dexterous among all the body parts, the sensorimotor integration underlying this dexterity has not yet been elucidated. The purpose of this study was to examine the sensorimotor integration mechanisms in the primary somatosensory cortex (SI) during simple and complicated finger movement. The participant performed tasks that involved picking up a wooden block (PM task) and picking up and turning the wooden block 180° (PTM task) using the right‐hand fingers. During these tasks, the SEFs following right median nerve stimulation were recorded using magnetoencephalography. The amplitude of the M20 and M30 components showed a significant reduction during both manual tasks compared to the stationary task, whereas the M38 component showed a significant enhancement in amplitude. Furthermore, the SEFs recorded during continuous rotation of the block (rotation task) revealed a characteristic pattern of SI activity that was first suppressed and then facilitated. Since this facilitation is noticeable during complicated movement of the fingers, this phenomenon is thought to underlie a neural mechanism related to finger dexterity.

Geodetic Extension Across the Southern Basin and Range and Colorado Plateau

AbstractRates of crustal deformation in the southern Basin and Range (SBR) and Colorado Plateau (CP) provinces are relatively low in the context of the Pacific‐North America plate boundary (PA–NA); however, the accumulation of small amounts of strain over long periods of time can lead to large earthquakes such as the Mw 7.5 1887 Sonoran earthquake in northern Mexico. SBR and CP rates of deformation are difficult to quantify due to a dearth of young faulting and seismicity. Moreover, strain accumulation and release related to the adjacent, more active San Andreas and Gulf of California fault systems to the west and southwest can mask the background strain rates associated with SBR and CP tectonics. With data from an enhanced continuous GPS network, we estimate crustal surface velocities of the SBR and CP, after removing coseismic and postseismic displacements, and elastic loading effects arising from major fault zones to the (south)west. We use cluster analysis and geologic data to separate the GPS velocity field into regions and calculate distinct block rotation and uniform strain rates for each region. We find the highest strain rate region includes southwestern Arizona; an area with sparse Quaternary faults, relatively low seismicity, and a relatively large discrepancy between geodetic and geologic rates of deformation. This anomalous strain rate may reflect residual, unmodeled PA‐NA strain seeping into the Arizona study area from the west. Alternatively, it may represent the potential for one or more rare, future, large‐magnitude earthquakes or indicate strain is being released through other process(es).

Dextral Strike‐Slip and Normal Faulting During Middle Miocene Back‐Arc Extension and Westward Anatolia Extrusion in Central Greece

AbstractThe present‐day Aegean tectonic configuration is marked by the interplay between Hellenic slab rollback and Anatolian extrusion, explaining the formation of extensional basins and dextral strike‐slip faults. We aim to constrain middle Miocene activity of dextral strike‐slip and normal faults in Central Greece with structural analysis and low‐temperature data. We show that onshore middle Miocene basins are controlled by both NW‐striking normal faults and NE‐striking dextral strike‐slip faults. E‐striking normal faults developed during the Plio‐Quaternary inside pre‐existing NW‐striking fault zones. Stress tensor calculations show that in the middle Miocene, NW‐striking normal faults and NE‐striking dextral faults are compatible, confirming their coeval activity. In contrast, the Plio‐Quaternary stress tensor suggests an almost N‐S radial extension, which is not compatible with NE‐striking dextral faults in Central Greece. Apatite fission‐track data additionally constrain middle Miocene local cooling near NW‐striking normal faults. They also support a difference in the amount of exhumation between Central Greece and the Cyclades, likely accommodated by the Pelagonian dextral strike‐slip fault. We propose that in the middle Miocene, the co‐existence of dextral strike‐slip and normal faults is associated with an almost N‐S extension related to trench retreat and an E‐W compression related to westward extrusion of Anatolia. The progressive trench curvature during rollback implies block rotation, accommodated by the Pelagonian fault, and subsequent normal fault and extensional stress rotation. During the Plio‐Quaternary, a change in extensional direction from NE‐SW to N‐S implies the formation of E‐striking normal faults inside NW‐striking fault zones, defining oblique rift systems.

Stress field and tectonic regime of Central Iran from inversion of the earthquake focal mechanisms

This paper provides a latest compilation of data on the present-day stress pattern in Central Iran and its tectonic regime. We compiled 103 focal mechanism data collected from the Global Centroid Moment Tensor Project (GCMT) including data from Harvard University (HRVD) and the International Seismological Center (ISC). Stress inversion of all shallow focal depths provides a first order stress field with a N029°E maximum horizontal compressive stress (SHmax) direction corresponding to a general compressive tectonic regime. In order to reconstruct the second and third order stress fields, we subdivided the study area into eight zones on the basis of their structures, relatively similar focal mechanisms and relatively homogeneous deformation. For each zone and for the same data set, reduced stress tensors have been obtained by formal stress inversion using the Win-Tensor program and modified SLICK method. Both inversion methods show similar results for horizontal stress axes orientations and for the tectonic regimes.The obtained NE-SW direction of the first order stress field is related to Arabia-Eurasia convergence as confirmed by the geodetic measurements. This stress field is responsible for accommodation of shortening within Central Iran and right-lateral movement along the N-S faults as well as left-lateral movement along the E-W faults. Solid block rotation between strike-slip and thrust faults, vertical rotation of the fault bounded blocks, escape tectonics, block extrusion and strain partitioning occurred due to second and third order stress fields with variable SHmax directions from N006° to N081° and in different tectonic regimes.

Experimental substantiation of the optimal technique for choosing the rotation of the femoral component of the knee endoprosthesis

There was experimental justification of the optimal technique for choosing the rotation of the femoral component of the knee joint endoprosthesis carried out in this research. The individual morphometric characteristics of the femoral condyles and the condition of the collateral ligaments were taken into account in the experiment. The research was conducted on polymer-embalmed preparations of the knee joint, which were divided into three groups, according to the forms of the femoral condyles. We used the standard technique of positioning the resection block and the technique of individual selection of the rotation of the resection block (rotation of the femoral component of the endoprosthesis), based on the assessment of individual morphometric characteristics of the femoral condyles and the state of the auxiliary elements of the knee joint. To implement this surgical approach, typical resections of the proximal condyles of the tibia and distal condyles of the femur were performed, which technically did not differ from the sawdust used in the standard procedure. Then the knee joint was flexed to an angle of 90, Homan retractors were removed and two laminar dilators (Laminar Spreader) were installed in the gap between the proximal tibial sawdust and the posterior parts of the lateral and medial condyles of the femur. This technique provided isometric tension of the fibular and tibial collateral ligaments of the knee joint. Then carried out the positioning of the femoral resection block "four in one". In this case, only the line of the proximal tibial sawdust was used as a reference point, for which the posterior flange of the resection block was positioned parallel to the sawed upper articular surface of the tibia. It is established that the use of the considered technique of positioning the femoral resection block ensures the formation of a uniform flexor gap, regardless of the variant anatomy of the femoral condyles. Thus, there was research a uniform flexion gap in the experiment, which ensured isometric movements in the knee joint and its stability at the control points of the amplitude after implantation of the trial or final components of the endoprosthesis.

Tectonic Implications of the Deformation Front in Southwest Taiwan: Revealed by 3D Seismic b Values

We conduct a study on 3D seismic b values in southwest Taiwan and provide new insight into the characteristics of seismogenic structures through the heterogeneity of stress distribution and the variations in stress states in a seismic cycle. Our results indicate that, prior to the 2010 Jiasian earthquake and the 2016 Meinong earthquake, significantly low seismic b values occurred in the upper crust. For depths greater than 14 km, stress heterogeneity was more significant. We also propose a new scenario with a block rotation model derived from GPS data to explain how the rupture directions of the 2010 Jiasian and 2016 Meinong earthquakes are associated with the development of new fault systems in the mid-crust region.

The Qutn granite, a hotspot-related A-type granite from the northeastern Arabian Shield?

The Qutn granite is a 579 Ma alkaline ring complex consisting of an incomplete biotite granite outer rim and a porphyritic core. It belongs to the late Ediacaran Abanat suite which encompasses the youngest posttectonic granitic intrusives in the NE Arabian Shield. The Qutn rocks are geochemically classified as A-type granites and belong to A2-subtype of anorogenic granites. The Qutn granite is clearly postcollisional and probably represents the exhumed root of a collapsed caldera. Magma genesis is thought to have been induced by mantle delamination through the detachment of a part of the subcrustal lithospheric mantle following continental collision. The Qutn complex displays an exceptionally well-developed arcuate trail of satellite plutons diminishing in size away from the main Qutn mass. This type of distribution would indicate a migration of the center of magmatic activity in response to counterclockwise rotation around a pole situated about 10 km northeast of Jabal Qutn. In the past, some authors have commented on the possibility of such migrating complexes being the manifestation of plate movement above a mantle hot spot. Invoking a rising mantle plume to explain the situation at Qutn and similar small intrusions is untenable; a more realistic approach involving magma generation in the lower crust following mantle delamination combined with block rotation in the upper crust in response to sinistral strike-slip movement along the regional Najd transcurrent system is more plausible.

Paleolatitude and tectonic rotations of the Early Carboniferous Fountain Lake Group, Cobequid Highlands, Nova Scotia, Canada

The ca. 355 Ma Fountain Lake Group in the Cobequid Highlands of Nova Scotia, is part of the transtensional basin fill that formed during dextral strike-slip motion between Avalonia and the Meguma terranes following the Acadian Orogeny. Paleomagnetic analysis of the Fountain Lake Group offers a paleolatitude estimate for the Laurentian accretionary margin in the Early Carboniferous as well as locality-specific paleomagnetic directions, which indicate clockwise-sense block rotations during dextral strike-slip motion along the Cobequid Fault zone. Stepwise demagnetization of 142 specimens from 20 sites in three Fountain Lake Group localities across the Cobequid Highlands (Squally Point, West Moose River, and Wentworth exposures) reveals remanence consisting of an easily removed component of probable recent origin, and more persistent components carried by magnetite and hematite, which in petrographic and electron beam analysis appear to be of primary igneous and volcanic oxidation origins, respectively. Sites from all three localities carry stable characteristic remanent magnetization (ChRM) directions that assume similar moderate downward inclinations when tilt-corrected. A Block Rotation Fisher analysis inclination-only fold test demonstrated best agreement at 90% unfolding, showing that remanence acquisition pre-dates Alleghenian deformation in the Late Carboniferous and is most likely of primary 355 Ma age. Paleomagnetic results for the Squally Point, West Moose River, and Wentworth localities show relative rotations between the blocks that are variously clockwise-rotated compared with a Laurentia cratonic reference frame. Inclinations at all three localities imply a subtropics paleolatitude for the margin (at Squally Point, 27.2° ± 9.4°; N = 7 sites), directly supporting the depicted location of Laurentia and its Appalachian accretionary margin in most Devonian to Early Carboniferous reconstructions.

Sensitivity analysis of control parameters errors and current parameters to motion accuracy of underwater glider using Sobol’ method

Control parameters errors and current can weaken the motion accuracy of underwater gliders, which will obstruct the achievement of high accuracy exploration missions. To improve the glider motion accuracy more pertinently, it is necessary to identify the key factors that affect the glider motion accuracy. To resolve the above problem, we employ Sobol’ method to analyze the sensitivity of control parameters errors and current parameters to the glider motion accuracy. The control parameters errors include the net buoyancy adjustment amount error, the movable mass block translation amount error and the movable mass block rotation amount error. The current parameters include the current intensity, action depth and direction. First, the dynamic model of an underwater glider is established, and this model considers the effects of hull deformation, water density variation and current simultaneously. Then the dynamic model is validated by experimental data. After the evaluation parameter of motion accuracy is given, the glide motion accuracy is preliminarily analyzed, and then the sensitivity analysis is carried out. In this paper, we calculate the sensitivity coefficients by Monte Carlo method. To reconcile calculation efficiency with calculation accuracy, a convergence rule is proposed to reduce the number of sample points that are used for calculating sensitivity coefficients as much as possible. Besides, based on simulation results of dynamic model, the surrogate models are established to participate in the calculation of sensitivity coefficients, which can improve analysis efficiency further. For two typical motion modes, analysis results identify the key factors affecting the glider motion accuracy and illustrate the form of their effect on the glider motion accuracy. This research may be valuable for the achievement of the glider precision operation.

Structural styles, deformation, and uplift of the Olympic Mountains, Washington: Implications for accretionary wedge deformation

Abstract The Olympic subduction complex is the exposed subaerial Cascadia accretionary wedge in the Olympic Mountains of Washington State. Uplift of the mountains has been attributed to two competing models: margin-normal deformation from frontal accretion and underplating, and margin-parallel deformation from the clockwise rotation and northward movement of the Oregon Coast Range block compressing the Olympic Mountains block against the Canadian Coast Range. East-northeast–oriented folds and Quaternary thrust faults and paleostress analysis of faults in the Coastal Olympic subduction complex, west of the subduction complex massif, provide new evidence for north-south shortening in the Coastal Olympic subduction complex that fills a large spatial gap in the north-south shortening documented in prior studies, substantially strengthening the block rotation model. These new data, together with previous studies that document north-south shortening in the subduction complex and at numerous locations in the Coast Range terrane peripheral to the complex, indicate that margin-parallel deformation of the Cascadia forearc has contributed significantly to uplift of the Olympic Mountains. Coastal Olympic subduction complex shallow-level fold structural style and deformation mechanisms provide a template for analyzing folding processes in other accretionary wedges. Similar-shaped folds in shallow-level Miocene turbidite sediments of the Coastal Olympic subduction complex formed in two shortening phases not previously recognized in accretionary wedges. Folds began forming by bed-parallel flow of sediment into developing hinges. When the strata could no longer accommodate shortening by flexural flow, further shortening was taken up by flexural slip. Similar-shaped folds in the deeper accretionary wedge rocks of the subduction complex massif have a well-developed axial-surface cleavage that facilitated shear folding with sediment moving parallel to the axial surface into the hinges, a structural style that is common to accretionary wedges. The pressure-temperature conditions and depth at which the formation of similar folds transitions from bed-parallel to axial-surface–parallel deformation are bracketed.

Effect of the seepage flow on the face stability of a shield tunnel

To assess the face stability of a shield tunnel excavated in saturated soils under steady seepage flow condition, both numerical simulation and theoretical analysis are carried out. Based on the characteristics of the hydraulic head distribution, an analytical solution for the hydraulic head distribution ahead of tunnel face in the homogeneous and isotropic ground is proposed. And based on the upper bound theorem of the limit analysis, the analytical head equation is introduced into the 3D rotational rigid block collapse mechanism to take into account of the effect of the seepage flow. The comparisons show that the presented method agrees well with the numerical analysis and other existing studies. Finally, an analytical solution for the hydraulic head distribution ahead of tunnel face considering the permeability anisotropy is also presented and discussed. It is suggested that the neglect on the permeability anisotropy of soils may lead to an overestimate on the required face pressure.

Basement Structure and Styles of Active Tectonic Deformation in Central Interior Alaska

Central Interior Alaska is one of the most seismically active regions in North America, exhibiting a high concentration of intraplate earthquakes approximately 700 km away from the southern Alaska subduction zone. Seismological evidence suggests that intraplate seismicity in the region is not uniformly distributed, but concentrated in several discrete seismic zones, including the Nenana basin and the adjacent Tanana basin. Although the location and magnitude of the seismic activity in both basins are well defined by a network of seismic stations in the region, the tectonic controls on these intraplate earthquakes and the heterogeneous nature of Alaska’s continental interior remain poorly understood. We investigated the crustal structure of the Nenana and Tanana basins using available seismic reflection, aeromagnetic and gravity anomaly data, supplemented by geophysical well logs and outcrop data. We developed nine new two-dimensional forward models to delineate internal geometries and the crustal structure of Alaska’s interior. The results of our study demonstrates a strong crustal heterogeneity beneath both basins. The Tanana basin is a relatively shallow (up to 2 km) asymmetrical foreland basin with its southern, deeper side controlled by the northern foothills of the Central Alaska Range. Northeast-trending left lateral strike-slip faults within the Tanana basin are interpreted as a zone of clockwise crustal block rotation. The Nenana basin has a fundamentally different geometry. It is a deep (up to 8 km), narrow transtensional pull-apart basin that is deforming along the left-lateral Minto Fault. This study identifies two distinct modes of current tectonic deformation in Central Interior Alaska and provides a basis for modeling the interplay between intraplate stress fields and major structural features that potentially influence the generation of intraplate earthquakes in the region.