Transform Fault Research Articles

Position Tracking Control of Fully-Actuated Underwater Vehicles With Constrained Attitude and Velocities

This article presents a redundant control strategy of fully-actuated underwater vehicles. The proposed strategy offers vehicles more control flexibility for addressing the position tracking problem under the attitudes and velocities constraints. In kinematics, position tracking is formulated as a convex optimization problem, where the velocity constraints are considered as a feasible region and the attitudes are bounded via a barrier function. Then, a conservative boundary is determined in the context of stability analysis of the dynamic controller with a disturbance observer and an auxiliary system so that kinematic variables lie in the constraints even with the velocity tracking error. Also, it is proven that the position tracking error can converge to a neighborhood about zero, which can be made arbitrarily small. The simulations and experimental results through multiple scenarios have illustrated the efficiency of the proposed strategy.

Pismanta geothermal play in the iglesia basin related to transverse fault systems in the andean orogen

The intermontane Iglesia Basin constitutes the northern Uspallata-Calingasta-Iglesia tectonic depression that holds the Pismanta geothermal field, genetically connected with the basin evolution and structure. Understanding the local structure associated with this geothermal field and linking this system to the regional tectonics is essential to characterize thermal water rising in this area. To address this issue, we carried out a field-based structural analysis and an examination of sedimentary outcrops at the Pismanta area. Also, we linked surface structural data to the subsurface basin structure by means of a previously interpreted seismic reflection line. Our integrated analysis reveals that the Pismanta geothermal field is located in an area of favorable lithology at the intersection of WNW- and NNE-trending thrust faults. These jointly developed a permeability anomaly zone at the Pismanta locality that allows hot underground water rising from deep sedimentary sequences. This observation explains why the thermal springs are only locally concentrated in the study area; a key aspect that was not taken into account in previous models for the Pismanta geothermal field. These results and the overall basin tectonic evolution allowed us to define a new and more complex structural geothermal play model at the Pismanta field.

The formation of the 8˚20’ N seamount chain, east pacific rise

Near-axis seamounts provide a unique setting to investigate three-dimensional mantle processes associated with the formation of new oceanic crust and lithosphere. Here, we investigate the characteristics and evolution of the 8˚20’N Seamount Chain, a lineament of seamounts that extends ~ 175 km west of the East Pacific Rise (EPR) axis, just north of the fracture zone of the Siqueiros Transform Fault. Shipboard gravity, magnetic, and bathymetric data acquired in 2016 are utilized to constrain models of seamount emplacement and evolution. Geophysical observations indicate that these seamounts formed during four distinct episodes of volcanism coinciding with changes in regional plate motion that are also reflected in the development of intra-transform spreading centers (ITSCs) along the Siqueiros transform fault (Fornari et al. 1989; Pockalny et al. 1997). Although volcanism is divided into distinct segments, the magnetic data indicate continuous volcanic construction over long portions of the chain. Crustal thickness variations along the chain up to 0.75 km increase eastward, inferred from gravity measurements, suggest that plate reorganization has considerably impacted melt distribution in the area surrounding the Siqueiros-EPR ridge transform intersection. This appears to have resulted in increased volcanism and the formation of the 8˚20’N Seamounts. These findings indicate that melting processes in the mantle and subsequently the formation of new oceanic crust and lithosphere are highly sensitive to tectonic stress changes in the vicinity of fast-spreading transform fault offsets.

Robust design for 3-DoF anti-windup framework based on QFT

On the basis of the fact that all signals in the practical system are always bounded, this paper proposes a practical QFT-based approach for the synthesis of anti-windup compensation for uncertain LTI systems. Meanwhile, a modified version of the circle criterion is developed for saturated systems with parametric uncertainty to reduce the conservativeness of the anti-windup compensator design within the non-interfering anti-windup framework. In the context of QFT, it means enlarging the allowed zone of the compensator remarkably in the Nichols chart compare to the traditional version of the circle criterion. As a result, the less conservative stability boundary provides more room for the compensator synthesis, making the performance improvement possible. Numerical examples demonstrate the effectiveness and the performance improvement as expected of the proposed technique based on QFT for the anti-windup compensator design.

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

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

Seismicity, Fault Architecture, and Slip Mode of the Westernmost Gofar Transform Fault

AbstractOceanic transform faults accommodate plate motions through both seismic and aseismic slips. However, deformation partition and slip mode interaction at these faults remain elusive mainly limited by rare observations. We use 1‐year ocean bottom seismometer data collected in 2008 to detect and locate earthquakes at the westernmost Gofar transform fault. The ultra‐fast slipping rate of Gofar results in ∼30,000 earthquakes during the observational period, providing an excellent opportunity to investigate interrelations between the slip mode, seismicity, and fault architecture at an unprecedented resolution. Earthquake distribution indicates that the ∼100‐km‐long Gofar transform fault is distinctly segmented into five zones, including one zone contouring a M6 earthquake that was captured by the experiment. Further, a barrier zone east of the M6 earthquake hosted abundant foreshocks preceding the M6 event and halted its active seismicity afterward. The barrier zone has two layers of earthquakes at depth, and they responded to the M6 earthquake differently. Additionally, a zone connecting to the East Pacific Rise had quasi‐periodic earthquake swarms. The seismicity segmentation suggests that the Gofar fault has multiple slip modes occurring in adjacent fault patches. Spatiotemporal characteristics of the earthquakes suggest that complex fault architecture and fluid–rock interaction play primary roles in modulating the slip modes at Gofar, possibly involving multiple concurrent physical processes.

CAGE21-3 Cruise Report: Ocean bottom seismics and acoustic surveys on the West-Svalbard margin – a study of local seismicity and its effect on methane seepage

Cruise CAGE21-3 with UiT’s research vessel R/V Helmer Hanssen was carried out to address the following objectives within the SEAMSTRESS project (Tectonic stress effects on Arctic methane seepage):1- Recovery of 10 Ocean Bottom Seismometers (OBS) deployed last year north of the Knipovich Ridge-Molloy Transform Fault corner (see report CAGE20-5).2- Conduction of an active source OBS experiment for the study of shear waves propagation in relation to local stress field and focused fluid flow.3- Acquisition of seismic lines for completing a side survey for the FRAME-IODP proposal.In 2020, 10 ocean-bottom seismometers (OBS) were deployed at the northern termination of the Knipovich Ridge to monitor seismic activity. The aim is to detect regional and local earthquakes. If localearthquakes are captured we will investigate the stress field in the region and how faults and fluids react to such stress (Figure 1). From the 10 instruments 8 are from Awi and 2 from UiT. IODP proposal 985 Eastern Fram Strait Palaeo-archive (FRAME) proposed to drill five sites on the western Svalbard margin in order to study chronostratigraphy, palaeoceanography, the palaeoclimatic evolution, and the forcing mechanisms responsible for main climatic transitions and the dynamics of the Svalbard Barents Sea Ice Sheet complex. This cruise acquired additional site survey seismic data for proposed primary and alternate drill sites. The cruise may be known as: CAGE21_3

Interpretation of 2D Seismic Data of Shurau and Sheikh Alas Formations in Ismail Area, Northern Iraq

The 2D seismic reflection data were used to study the structure of Shurau and Sheikh Alas formations (Oligocene) in the Ismail area, northern Iraq. The horizons of Shurau and Sheikh Alas reflectors were identified based on seismic data and well logs through a synthetic seismogram construction. The Two-Way Time, velocity and depth maps of two coinciding formations were obtained. A Great coincidence was noticed between two identical maps of the two formations. The Main closure (syncline) trending NE-SE was detected at the southwestern part of the study area, the syncline is associated with many anticlines in the same trend. The northern part of Bai Hassan structure was appeared at the southeast part of the study area, while some northeastern part of Qara chauq structure was detected in the southwestern part of the study area. The structure features of the two formations mostly trending NW-SE with some local variations may be due to transversal faults.

Raman thermometry and (U-Th)/He thermochronometry reveal Neogene transpressional exhumation in the Nacimiento block of central California, USA

Abstract We present a novel approach for mapping vertical uplifts in exhumed metasedimentary rocks by coupling Raman spectroscopy of carbonaceous material with (U-Th)/He thermochronometry on apatite and zircon. We apply this approach to carbonaceous metasedimentary rocks of the Franciscan subduction complex, exposed in the Nacimiento block of central California, USA, an area that records high-pressure–low-temperature metamorphism prior to entrainment within the present-day transform plate boundary. We reveal the extent and magnitude of previously unrecognized exhumation gradients, which, combined with regional structural observations, can be used to quantify vertical crustal motion associated with localized transpression. We propose that the Nacimiento block was affected by a kilometer-scale, post-subduction thermal anomaly linked to a localized transpressive regime since ca. 25 Ma, with an uplift rate of ∼0.3 mm/yr.

Nonlinear Damping Property and Limit Cycle of VSC

The synchronization stability of the system that one single VSC is connected to an infinite source via the line is studied in this letter. Based on Bendixson criterion, closed orbit (limit cycle) does not exist in the derived stable region, while may exist in the region between the conservative stable boundary and the unstable equilibrium point (UEP). Nonlinear damping effect on the system stability is analytically defined, and an unstable limit cycle appears when the positive and negative damping effect of the system over one period is mutually balanced. Numerical results verify the existence of limit cycle and nonlinear damping property of VSC.

Seismicity Induced at the Northern Dead Sea Transform Fault, Kinneret (Sea of Galilee) Basin, by Shallow Creep Involving a Salt Body

AbstractIn October 2013 and July–August 2018, two extensive earthquake swarms shook the northern reaches of Lake Kinneret (Sea of Galilee). Former studies explored the swarms, resulting in discrepant depths and mechanisms. Here, we attempt to settle the discrepant interpretations using alternative seismological methods and some unpublished data from borehole seismometers. We propose a hypothesis for the faulting phenomenon focusing on the interaction of the two plate boundary segments that step‐over the northern Kinneret depocenter: a creeping segment in the south and a locked segment in the north. The energy accumulated from the interaction induces earthquake swarms from time to time. A shallow fault patch (from the surface down to 1.5 ± 1.0 km) south of the swarms is thought to creep in association with a salt formation underlying some of the basin fill. We use regional seismograms, including two near‐source borehole stations, to refine the characteristics of the swarms. We test hypocentral and centroid depths using several methods and different velocity models and corroborate shallow ruptures: the majority are shallower than 6 km (all shallower than ≤10 km). The hypocentral locations and focal mechanisms suggest shallow NW‐SE normal faults splaying from the tip of the creeping segment in a horsetail pattern. We test the hypothesis by Coulomb stress calculations that show stress concentration at the step‐over interaction zone, consistent with focal locations and mechanisms of the earthquake swarms.

Geological and Geophysical Studies of the Double Transform Fault Charlie Gibbs (North Atlantic) during Cruise 50 of R/V Akademik Nikolaj Strakhov

Geological and Geophysical Studies of the Double Transform Fault Charlie Gibbs (North Atlantic) during Cruise 50 of R/V Akademik Nikolaj Strakhov

Pliocene transverse shortening in the southern central Andes recorded in the Iglesia basin

The Iglesia basin is a ∼3.5 km thick depocenter that holds an outstanding record of the late Cenozoic tectosedimentary evolution of the southern Central Andes. Previous studies have indicated an initial tectonic stage associated with NNE-striking basin-bounding faults, formed by extension in the Late Oligocene (?)-early Miocene, and a subsequent basin inversion stage in the middle-Late Miocene. We conducted a multi-disciplinary study that allowed us to unravel a conspicuous structural system orthogonal to the previous basin-bounding faults. The analysis of seismic reflection lines, satellite and local gravimetry, and field data allowed the recognition of WNW-striking thrust fault zones involving the basement and Cenozoic sedimentary cover of the Iglesia basin. Also, we document Pliocene growth strata in seismic reflection lines and intra-Pliocene thrust faults at the surface that inform the timing of transverse fault activity. Therefore, we propose new tectonic stage during the Pliocene associated with the onset of a transitory NNE-trending contractional stress field, which triggered the reactivation of inherited basement structures transverse to the main Andean strike. This indicates a transient shifting in the stress field at ∼5 Ma that we associate with a major upper-plate reconfiguration caused by the full development of the Pampean flat-slab and major plate coupling.

Deep hydration and lithospheric thinning at oceanic transform plate boundaries.

Transform faults accommodate the lateral motions between lithospheric plates, producing large earthquakes. Away from active transform boundaries, former oceanic transform faults also form the fracture zones that cover the ocean floor. However, the deep structure of these faults remains enigmatic. Here we present ultra-long offset seismic data from the Romanche transform fault in the equatorial Atlantic Ocean that indicates the presence of a low-velocity anomaly extending down to ~60 km depth below sea level. We performed 3D thermal modelling that suggests the anomaly is likely to be due to extensive serpentinization down to ~16 km depth, overlying a hydrated, shear mylonite zone down to 32 km depth. The water is considered to be sourced from seawater-derived fluids that infiltrate deep into the fault. Below 32 km is interpreted to be a low-temperature, water-induced melting zone that elevates the lithosphere-asthenosphere boundary, causing significant thinning of the lithosphere at the transform fault. The presence of a thinned lithosphere at transform faults could explain observations of volcanism, thickened crust and intra-transform spreading centres at transform faults. It also suggests that migration and mixing of water-induced melt with the high temperature melt may occur beneath the ridge axis.

Low-volume magmatism linked to flank deformation on Isla Santa Cruz, Galápagos Archipelago, using cosmogenic 3He exposure and 40Ar/39Ar dating of fault scarps and lavas

Isla Santa Cruz is a volcanic island located in the central Galápagos Archipelago. The island’s northern and southern flanks are deformed by E–W-trending normal faults not observed on the younger Galápagos shields, and Santa Cruz lacks the large summit calderas that characterize those structures. To construct a chronology of volcanism and deformation on Santa Cruz, we employ 40Ar/39Ar geochronology of lavas and 3He exposure dating of fault scarps from across the island. The combination of Ar–Ar dating with in situ-produced cosmogenic exposure age data provides a powerful tool to evaluate fault chronologies. The 40Ar/39Ar ages indicate that the island has been volcanically active since at least 1.62 ± 0.030 Ma (2SD). Volcanism deposited lavas over the entire island until ~ 200 ka, when it became focused along an E–W-trending summit vent system; all dated lavas < 200 ka were emplaced on the southern flank. Structural observations suggest that the island has experienced two major faulting episodes. Crosscutting relationships of lavas indicate that north flank faults formed after 1.16 ± 0.070 Ma, but likely before 416 ± 36 ka, whereas the faults on the southern flank of the island initiated between 201 ± 37 and 32.6 ± 4.6 ka, based on 3He exposure dating of fault surfaces. The data are consistent with a model wherein the northeastern faults are associated with regional extension owing to the young volcano’s location closer to the Galápagos Spreading Center at the time. The second phase of volcanism is contemporaneous with the formation of the southern faults. The expression of this younger, low-volume volcanic phase was likely related to the elongate island morphology established during earlier deformation. The complex feedback between tectonic and volcanic processes responsible for southward spreading along the southern flank likely generated persistent E-W-oriented magmatic intrusions. The formation of the Galápagos Transform Fault and sea-level fluctuations may be the primary causes of eruptive and deformational episodes on Santa Cruz.

Tectonic evolution of the Indio Hills segment of the San Andreas fault in southern California, southwestern USA

Abstract. Transpressional uplift domains of inverted Pliocene–Pleistocene basin fill along the San Andreas fault zone in Coachella Valley, southern California (USA), are characterized by fault linkage and segmentation and deformation partitioning. The Indio Hills wedge-shaped uplift block is located in between two boundary fault strands, the Indio Hills fault to the northeast and the main San Andreas fault to the southwest, which merge to the southeast. Uplift commenced about or later than 0.76 million years ago and involved progressive fold and faulting stages caused by a change from distributed strain to partly partitioned right-slip and reverse/thrust displacement on the bounding faults when approaching the fault junction. Major fold structures in the study area include oblique, right-stepping, partly overturned en echelon macro-folds that tighten and bend into parallelism with the Indio Hills fault to the east and become more open towards the main San Andreas fault to the west, indicating an early and close relationship of the macro-folds with the Indio Hills fault and a late initiation of the main San Andreas fault. Sets of strike-slip to reverse step-over and right- and left-lateral cross faults and conjugate kink bands affect the entire uplifted area, and locally offset the en echelon macro-folds. Comparison with the Mecca Hills and Durmid Hills uplifts farther southeast along strike in Coachella Valley reveals notable similarities, but also differences in fault architectures, spatial and temporal evolution, and deformation mechanisms. The present work contributes to better understand the structure and tectonic history of a major fault system along a transform plate boundary.

Contribution of Viscoelastic Stress to the Synchronization of Earthquake Cycles on Oceanic Transform Faults

AbstractEarthquake clustering can be promoted by local, regional, and remote triggering. The interaction between faults by static and dynamic stress transfer has received much attention. However, the role of quasi‐static stress interaction mediated by viscoelastic flow is still poorly understood. Here, we investigate whether the tight synchronization of moment‐magnitude 6 earthquakes every about 6 years on distant asperities in the Gofar‐Discovery fault system of the East Pacific Rise may be caused by mechanical coupling within the lithosphere‐asthenosphere system. We build a three‐dimensional numerical model of seismic cycles in the framework of rate‐ and state‐dependent friction with a brittle layer overlaying a viscoelastic mantle with nonlinear rheology to simulate earthquake cycles on separate asperities. The brittle section of the West Gofar fault consists of two frictionally unstable 20 km‐long by 5 km‐wide asperities separated by a velocity‐strengthening barrier, consistent with seismic observations, allowing stress transfer by afterslip and viscoelastic relaxation. We find that viscoelastic stress transfer can promote the synchronization of earthquakes. Even if the asperities are separated by as far as 30 km, synchronization is still possible for a viscosity of the underlying mantle of 1017 Pa s, which can be attained by dislocation creep or transient creep during the postseismic period. Considering the similarities in tectonic and structural settings, viscoelastic stress transfer and earthquake synchronization may also occur at 15’20 (Mid‐Atlantic Ridge), George V (Southeast Indian Ridge), Menard and Heezen transform fault (Pacific‐Antarctic Ridge).

Strain localization and migration during the pulsed lateral propagation of the Shire Rift Zone, East Africa

We investigate the spatiotemporal patterns of strain accommodation during multiphase rift evolution in the Shire Rift Zone (SRZ), East Africa. The NW-trending SRZ records a transition from magma-rich rifting phases (Permian-Early Jurassic: Rift-Phase 1 (RP1), and Late Jurassic-Cretaceous: Rift-Phase 2 (RP2)) to a magma-poor phase in the Cenozoic (ongoing: Rift-Phase 3 (RP3)). Our observations show that although the rift border faults largely mimic the pre-rift basement metamorphic fabrics, the rift termination zones occur near crustal-scale rift-orthogonal basement shear zones (Sanangoe (SSZ) and the Lurio shear zones) during RP1-RP2 period. In RP3, the RP1-RP2 sub-basins were largely abandoned, and the rift axes migrated northeastward (rift-orthogonally) into the RP1-RP2 basin margin, and northwestward (strike-parallel) ahead of the RP2 rift-tip. The northwestern RP3 rift-axis side-steps across the SSZ with a rotation of border faults across the shear zone, and terminates farther northwest at another regional-scale shear zone. We suggest that over the multiple pulses of tectonic extension and strain migration in the SRZ, pre-rift basement fabrics acted as: 1) favorably-oriented zones of mechanical strength contrast that localized the large rift faults, and 2) mechanical ‘barriers’ that refracted and possibly, temporarily halted the lateral propagation of the rift zone. Further, the cooled RP1-RP2 mafic dikes localized later-phase deformation in the form of border fault hard-linking transverse faults that exploited strength contrasts within the dike clusters and served as mechanically-strong zones that arrested some of the RP3 fault-tips. Overall, we argue that during pulsed rift propagation, inherited crustal strength anisotropies may serve as both strain-localizing, refracting, and ‘strain barrier’ tectonic structures.

Mapping the near‐surface trace of the seismically active Kachchh Mainland Fault and its lateral extension in the blind zone, Western India

ABSTRACTThe W–WNW‐striking Kachchh Mainland Fault (KMF) is the largest intra‐basinal fault in the Kachchh Rift Basin (KRB) located at the western continental margin of the Indian plate, and is responsible for several historic earthquakes, including the 2001 Bhuj earthquake and the 1956 Anjar earthquake. The objective of the study is to constrain the precise location and near‐surface characteristics of the KMF using field and ground penetrating radar (GPR) studies. Efforts were also made to ascertain and map the eastward continuity of the KMF. The fault has a prominent geomorphic expression up to the east of Devisar, where the KMF scarp finally dies out. The KMF marks the lithotectonic contact between Mesozoic rocks in the south and Tertiary rocks in the north. The segmented nature of the KMF has been previously attributed to transverse faults, complex deformation zones and heterogeneous assemblages of unconformable Quaternary deposits. Eight survey sites between Nirona and Sikra were chosen for near‐surface investigation of KMF using GPR. Comparatively, high‐amplitude radar reflections were received from well‐compacted sand‐ and shale‐rich Mesozoic rocks, whereas low‐amplitude weak reflections were observed from softer and clay‐rich Tertiary rocks. In the upper section of the GPR profiles, Quaternary deposits display low‐ to moderate‐amplitude semi‐continuous to wavy reflections. The traceable length of the KMF has been extended eastward by ∼20 km through the current study, which is considered a blind zone as feeble surficial evidence is present, but the fault trace is confirmed near the surface using GPR. The eastern part of the KMF is inferred to be a near‐vertical north‐dipping normal fault based on GPR data analysis. The tendency of the KMF to transform into a reverse fault in the vicinity of the intersection with transverse faults implies zones of relatively higher stress accumulation that might activate and trigger devastating earthquakes in the future.

Locked crustal faults associated with the subducting Indian Lithosphere and its implications in seismotectonic activity in the Central Indo-Burmese Ranges, Northeast India

Northeast India is a geodynamic hotspot for tectonic activities where three different plates viz., Indian, Eurasian and Burma Plates collide and deform with respect to each other. Northeast moving Indian Plate subducting transversely beneath Burma Plate results in the formation of the Indo-Burmese Ranges (IBR). In central IBR, the north-south trending Churachandpur-Mao Fault (CMF) is situated in the east of the Mizoram-Tripura Fold belt. The northwest-southeast trending Mat River Fault or Mat Fault (MF), which is another major crustal-scale strike-slip transverse fault, upholds the movement of the CMF. In this work, seismotectonic analysis of these two active intra-plate faults which are related to the June-September 2020 earthquake series, have been discussed. It is observed from satellite imageries, earthquake data and confirmed by the field investigation that these faults are not directly involved in the generation of the earthquakes; rather epicenters are distributed in the junction between the MF and CMF. It is evident from the seismotectonic analysis that this stress is distributed through some northwest-southeast synthetic faults, located north of MF and parallel to it, close to the junction with the CMF. The focal solution of the strongest of the 2020 earthquakes, the 5.5 Mw Champhai earthquake (on 22nd June 2020 at 04:10 IST) in Mizoram shows that the principal nodal plane was aligning along MF. Therefore, it is these synthetic faults that are responsible for the earthquakes rather than the locked zone between intra-plate MF and CMF crustal faults. This juxtaposition has caused a major shift in the geodynamic regime in the central IBR. Champhai earthquake might not be the only large devastating earthquake in the region and could be followed by more major earthquakes in the future.