Narrow Fault Zone Research Articles

Tectonic evolution of high grade metamorphic tectonites of the Meelpaeg structure near Port aux Basques, southwestern Newfoundland during the Silurian Salinic and Early to Middle Devonian Acadian orogenies

The Meelpaeg structure in southwestern Newfoundland comprises allochthonous tectonites formed during the Salinic (D1-2) and Acadian (D3) orogenies. D1-2 occurred between 451 and 417 Ma and culminated in Barrovian metamorphism during terminal collision of the Gander margin with composite Laurentia. Collision was followed by tectonic escape of the deeply buried rocks between 417 and 412 Ma. Rocks of the Victoria arc and Exploits backarc preserved in the Port aux Basques and Grand Bay complexes were emplaced during D1 by the Grandys River shear zone, which is outlined by a narrow band of the ca. 451 Ma Port aux Basques granite, towards the southeast above the Harbour le Cou Group. The contrasting histories displayed across the Grandys River shear zone are typical of the Dog Bay Line further northeast. Salinic structures were overprinted by faults and folds formed during Acadian D3 transpression (≤ 412 Ma), which produced the bi-vergent Meelpaeg structure and emplacement of amphibolite facies tectonites above greenschist facies rocks along its bounding shear zones. F3 folding progressively steepened the faults, which in turn led to progressive localisation of dextral strike-slip in narrow fault zones. The High grade of metamorphism in the Meelpaeg structure is attributed to protracted underthrusting of the Cabot promontory of the Gander margin beneath composite Laurentia. Salinic convergence was sinistral but became dextral during the Early Devonian, diachronous Acadian orogeny. The kinematic switch is proposed as a tool to separate Salinic from Acadian structures in the central part of the northern Appalachians.

Thrust force requirements in fault zones with squeezing ground

Shield jamming constitutes a critical hazard in mechanized tunnelling under squeezing conditions. These are often encountered within narrow fault zones interspersed between competent rock layers, where the competent rock exhibits much smaller deformations, thus mobilising shear stresses at the interfaces. This so-called “wall-effect” results in substantially reduced deformations and rock pressures in the fault zone and is thus favourable with respect to shield jamming. Building on existing design nomograms for evaluating the required thrust force in homogeneous ground, this paper proposes two novel, simple and practical thrust force estimation methods that additionally consider the favourable influence of the wall-effect in narrow fault zones. The first method performs an a priori modification of the nomogram input via an equivalent improved ground stiffness that depends on the fault zone length. The second method performs an a posteriori correction of the nomogram output via an analytically determined coefficient, established via multiparametric regression that considers the results of 3450 numerical analyses. Both methods allow for a fast evaluation of the required thrust force in fault zones with reasonable accuracy, thereby providing a valuable tool for design.

Comparing intrarift and border fault structure in the Malawi Rift: Implications for normal fault growth

Early stages of normal fault growth are seldom described using field observations of active normal faults. Here we first estimate the displacements of active border and intrarift faults in the Zomba Graben in the low extension (< 10 %) Malawi Rift, and then quantify micro-to macroscale fault damage and mineralisation associated with their surface exposures. The 22 km long Mlunguzi and 39 km long Chingale Step intrarift faults have fault zones 4–52 m wide. In contrast, we estimate the fault zone of the 51 km long Zomba border fault is 32–118 m wide. Calcite and clay alteration is limited to the fault damage zones and fault cores, and the extent and intensity of fault damage and mineral alteration is greater on the Zomba border fault compared to the intrarift faults. Relative to global compilations, normal faults in the Zomba Graben have lengthened quickly while developing narrow fault zones, given their displacement. The minor damage on these long, low-displacement normal faults may reflect the influence of lithology, negligible fault healing, and/or activation of pre-existing weaknesses.

Large-scale, crustal-block vertical extrusion between the Hines Creek and Denali faults coeval with slip localization on the Denali fault since ca. 45 Ma, Hayes Range, Alaska, USA

AbstractOblique convergence along strike-slip faults can lead to both distributed and localized deformation. How focused transpressive deformation is both localized and maintained along sub-vertical wrench structures to create high topography and deep exhumation warrants further investigation. The high peak region of the Hayes Range, central Alaska, USA, is bound by two lithospheric scale vertical faults: the Denali fault to the south and Hines Creek fault to the north. The high topography area has peaks over 4000 m and locally has experienced more than 14 km of Neogene exhumation, yet the mountain range is located on the convex side of the Denali fault Mount Hayes restraining bend, where slip partitioning alone cannot account for this zone of extreme exhumation. Through the application of U-Pb zircon, 40Ar/39Ar (hornblende, muscovite, biotite, and K-feldspar), apatite fission-track, and (U-Th)/He geo-thermochronology, we test whether these two parallel, reactivated suture zone structures are working in tandem to vertically extrude the Between the Hines Creek and Denali faults block on the convex side of the Mount Hayes restraining bend. We document that since at least 45 Ma, the Denali fault has been bent and localized in a narrow fault zone (&amp;lt;160 m) with a significant dip-slip component, the Mount Hayes restraining bend has been fixed to the north side of the Denali fault, and that the Between the Hines Creek and Denali faults block has been undergoing vertical extrusion as a relatively coherent block along the displacement “free faces” of two lithospheric scale suture zone faults. A bent Denali fault by ca. 45 Ma supports the long-standing Alaska orocline hypothesis that has Alaska bent by ca. 44 Ma. Southern Alaska is currently converging at ~4 mm/yr to the north against the Denali fault and driving vertical extrusion of the Between the Hines Creek and Denali faults block and deformation north of the Hines Creek fault. We apply insights ascertained from the Between the Hines Creek and Denali faults block to another region in southern Alaska, the Fairweather Range, where extreme topography and persistent exhumation is also located between two sub-parallel faults, and propose that this region has likely undergone vertical extrusion along the free faces of those faults.

Synrift basin inversion: Significant role of synchronous strike-slip motion in a rift basin

Abstract In rift basins with superposed strike-slip deformation, the structural style of wrench elements and the roles they play in synrift architecture and evolution are important, poorly understood issues for basin analysis and hydrocarbon exploration. The NE-SW–striking Tan-Lu fault zone, located in eastern China, runs through the Liaodong Bay subbasin within the Cenozoic Bohai Bay Basin and experienced dextral strike-slip motion during the later synrift stage of the basin (ca. 40 Ma to 23 Ma). Investigations of the Liaodong Bay subbasin indicate that rift-fault reactivation and wrench-fault development during strike-slip reactivation were strongly controlled by the distribution and geometry of preexisting rift faults, and local synrift basin inversion, induced by strike-slip reactivation of a preexisting graben during a later synrift stage, was a significant manifestation of synchronous strike-slip motion modifying synrift architecture and evolution. Moreover, synrift basin inversion within the Liaodong Bay subbasin manifested in two ways. First, stronger inversion occurred along the restraining bends of preexisting extensional faults. This induced uplift of the footwalls of graben-controlling faults, leading to deformation characterized by abundant shortcut thrusts and folds. The Liaodong uplift formed via this mechanism, triggered by strike-slip movement along the Tan-Lu fault zone at ca. 40 Ma. Second, weaker inversion induced by newly formed, subvertical, strike-slip faults occurred near the central part of the graben, with the characteristics of positive flower structures. Although inversion was limited to a very local area along a narrow fault zone, it substantially modified the basin’s physiography. In this rift system, coincident with local inversion-induced uplift, large-scale, rift-related subsidence occurred beyond the inversion belt within the flanking graben, leading to complexity and variety in intrabasinal structural deformation and filling, and exerting a complex influence on hydrocarbon prospects. This model of synrift basin inversion has profound implications for the interpretation of inversion structures and basin dynamics in any rift basin with superposed strike-slip deformation.

A szeizmikus reflexiós módszerek szerepe a nem szénhidrogénipari kutatásokban Magyarországon – Példák a Magyar Bányászati és Földtani Szolgálat és elődei tevékenységéből

Az Eötvös Loránd Geofizikai Intézet kutatási hagyományait megőrizve a Magyar Bányászati és Földtani Szolgálat keretein belül jelenleg is folynak alkalmazott szeizmikus kutatások a mai igényekhez alkalmazkodva. Az archív földtani adatok és az új szeizmikus mérési eredmények együttes értelmezésével hatékonyan csökkenthető a kutatási fázis (rövidtávú) földtani kockázata, így az ezek segítségével kialakított földtani modell jelentős mértékben hozzájárulhat egy a földtani közeget érintő beruházás sikerességéhez. A földtani képződményeket is érintő beruházásoknál, legyenek azok nyersanyagtermeléssel, hulladék elhelyezéssel, vagy akár építésföldtannal kapcsolatosak, a legnagyobb bizonytalanságot az egyes földtani képződmények lehatárolása, kőzetfizikai állapotának, inhomogenitásának meghatározása jelenti. Ezek térképezése pontszerű fúrási adatok alapján csak nagyfokú bizonytalanság mellett tehető meg. &#x0D; Jelen munkában három magyarországi esettanulmányt ismertetünk, melyeknél kézzelfogható, hogy a projektek teljes költségvetéséhez képest kis kutatási költségeket jelentő szeizmikus mérések milyen pozitív hatása van a földtani bizonytalanság csökkentésében.&#x0D; A Nyugat-Mecsek területén tervezett nagyaktivitású atomhulladék tároló létesítésnek feltétele, hogy a megcélzott földtani közeg, a Bodai Agyagkő Formáció (BAF) kiterjedése, vastagsága, térbeli pozíciója a tervezett paramétereknek megfeleljen. Az új szeizmikus eredmények alapján a BAF elterjedésének nyugati határa módosult, a területet tagoló szerkezeti elemek lefutása pontosítható volt, illetve megerősítést nyert az intenzív miocén szerkezeti mozgások jelentősége.&#x0D; A Győri Geotermikus Projekt Pér–Bőny környéki geotermikus kútpárjai egy többlépcsős szeizmikus kutatás eredményeként kerültek lemélyítésre. A projekt gazdaságosságának kulcsa a repedezett, karsztosodott karbonátos víztartóban a megfelelő vízadó képességű, jelentős mélységű, de laterálisan korlátozott méretű vetőzónák kitérképezése volt, melyhez a fokozatosan közelítő 2D és 3D szeizmikus mérések szolgáltattak lokális, részletező szerkezeti ismereteket.&#x0D; A nyugat-borsodi Sajómercse szénterület földtanában a legkevésbé ismert, így gazdasági szempontból a legnagyobb kockázatot jelentő képződmények a vetők. A 2019-es kismélységű szeizmikus kutatás keretében a nagyfelbontású karotázskorreláció alapján feltételezett vetők bizonyítást nyertek, kinematikájuk tisztázódott: a szeizmikus szelvények alapvetően transzpressziós tektonika jelenlétére utalnak. Továbbá számos olyan kisebb, de a széntelepek vastagságával összemérhető vetőt sikerült kimutatni, melynek létezése eddig ismeretlen volt.

An analysis of the factors that control fault zone architecture and the importance of fault orientation relative to regional stress

AbstractThe moment magnitude 7.2 El Mayor–Cucapah (EMC) earthquake of 2010 in northern Baja California, Mexico produced a cascading rupture that propagated through a geometrically diverse network of intersecting faults. These faults have been exhumed from depths of 6–10 km since the late Miocene based on low-temperature thermochronology, synkinematic alteration, and deformational fabrics. Coseismic slip of 1–6 m of the EMC event was accommodated by fault zones that displayed the full spectrum of architectural styles, from simple narrow fault zones (&amp;lt; 100 m in width) that have a single high-strain core, to complex wide fault zones (&amp;gt; 100 m in width) that have multiple anastomosing high-strain cores. As fault zone complexity and width increase the full spectrum of observed widths (20–200 m), coseismic slip becomes more broadly distributed on a greater number of scarps that form wider arrays. Thus, the infinitesimal slip of the surface rupture of a single earthquake strongly replicates many of the fabric elements that were developed during the long-term history of slip on the faults at deeper levels of the seismogenic crust. We find that factors such as protolith, normal stress, and displacement, which control gouge production in laboratory experiments, also affect the architectural complexity of natural faults. Fault zones developed in phyllosilicate-rich metasedimentary gneiss are generally wider and more complex than those developed in quartzo-feldspathic granitoid rocks. We hypothesize that the overall weakness and low strength contrast of faults developed in phyllosilicate rich host rocks leads to strain hardening and formation of broad, multi-stranded fault zones. Fault orientation also strongly affects fault zone complexity, which we find to increase with decreasing fault dip. We attribute this to the higher resolved normal stresses on gently dipping faults assuming a uniform stress field compatible with this extensional tectonic setting. The conditions that permit slip on misoriented surfaces with high normal stress should also produce failure of more optimally oriented slip systems in the fault zone, promoting complex branching and development of multiple high-strain cores. Overall, we find that fault zone architecture need not be strongly affected by differences in the amount of cumulative slip and instead is more strongly controlled by protolith and relative normal stress.

The ratio of tectonic structure and modern movements of the crust in area of geodynamic proving ground in Bishkek

According to the various scale GPS measurements, the process of collision between India and Eurasia is still ongoing and is reflected on Central Asia territory. The maximum velocity of shortening on northern component between India and Asia is ∼35 mm/year; the longitudinal (east-west) extension of the Tien Shan is ∼20 mm/year. The maximum deformations of shortening ∼15 mm/year along the north coordinate operate in a narrow fault zone between the Pamir and Tien Shan. Not on all Cenozoic (neotectonic) faults occur modern movements of the earth’s crust, these faults may have separate segments of active at different times. The general kinematic tendencies of modern movements correlate well enough with the general kinematic structure of neotectonic faults. In the fault zones at distances from the first hundreds meters to the first kilometers, intense elastic changes in the baseline lengths up to 4 cm (strains of 10–4) can occur within a week and up to 3-5 months. Such high-frequency elastic events have a different character of manifestations and are 2-4 orders of magnitude greater level than stable many years’ residual deformations.

New interpretation of the reduction phenomenon in the electrical resistivity of rock masses before local earthquakes

Based on long-term observational data from the area of Peter the Great Ridge (Pamir), a decrease in the electrical resistivity of the rock massif before local earthquakes has been observed. To explain the observed phenomenon, a hypothesis has been proposed: the structure of the pore space of a rock in the focal zone of an earthquake changes during the compression/tension associated with earthquake preparation. However, the models proposed have only qualitatively interpreted the experimental data. This article attempts to quantify this hypothesis based on 3D modeling of the observed electromagnetic effects. It is shown that variations in the apparent resistivity are due to changes in the electrical resistivity in a narrow fault zone located at the focus of the dipole-dipole sounding system. The changes occur at depths of <2–2.5 km and are due to low-resistivity fluid saturation of the highly porous fracture crushing zone. Small, smooth changes in the resistivity of the containing medium on both sides of the fault are associated with regional stresses in blocks of rocks and are not associated with the local earthquakes. An analysis of electromagnetic monitoring data at the Bishkek test site (Tien Shan) showed that the observed variations in apparent resistivity during pulse soundings are related to stresses and deformations of rocks in a wide region and cannot be used as a tool for predicting earthquakes. It is shown that, for studies of variations in the resistivity of rock massifs, measuring the response of the medium by grounded electrodes is ineffective due to the “static shift effect” generated by 3D inhomogeneities of the upper layer of the medium. To eliminate this effect, it was proposed that pulse technologies with magnetic field measurements made by ungrounded antennas be used.

Strain variations in a seismogenic normal fault (Baza Sub-basin, Betic Chain): Insights from magnetic fabrics (AMS)

AMS and structural analysis are here applied to study the deformed zone associated with a large-scale, active normal fault in the central Betic Cordillera (Spain), namely the Baza fault system, to determine: i) the kinematics of structures and their relation with fault zone architecture and segmentation degree, ii) the correlation between deformational structures and the different types of magnetic fabrics and iii) the evolution of magnetic fabrics patterns, from sedimentary to shear-related, associated with normal faults. Five outcrops (969 samples) were analysed along the fault trace, which shows different degrees of segmentation along strike and strong localization of deformation along narrow fault zones. A first, main set of magnetic fabric data corroborates the normal kinematics of the Baza fault, showing magnetic lineations parallel to the dip-slip, transport direction. A second, secondary set of magnetic lineations, is parallel to the intersection lineation, and can be related to less intense deformation in the fault rocks. Furthermore, a detailed study (523 samples) of a trench excavated across the fault zone, where two fault splays tend to coalesce in a linkage relay zone indicates that i) lithology and distance to fault planes are two factors that control the development of extension-related magnetic fabrics in weakly deformed sediments, ii) the development of shear-related fabrics in fault zones entails the mechanical rotation of minerals, iii) different orientation of magnetic lineations are related to different intensity of bulk deformation and iv) magnetic lineation is useful to define local deviations of deformation axes produced by changes in the local extension direction (from fault-perpendicular to fault-parallel extension) in the linkage zone between adjacent fault splays.

Variable magnetic fabrics under heterogeneous deformation across a shallow fault zone in the Iberian Chain (Monroyo thrust, N Spain)

A Cenozoic, N100E-striking thrust fault located in the Iberian Chain, provides an opportunity for testing the applicability of anisotropy of magnetic susceptibility (AMS) to the study of fault rocks deformation in shallow fault zones. The Monroyo thrust, which is probably a splay of the Castellote–Herbers fault, involves Cretaceous and Paleogene rocks in its hanging wall and footwall, respectively, shows a history of frontal thrusting without a strike-slip component. Fault kinematics are inferred from macro- (mapped trace of the thrust surface and folds in the Cretaceous series of the hanging wall) and meso-structures (pressure-solution foliation in Paleocene conglomerates of its footwall). The studied segment of the Monroyo thrust shows a 20 m thick fault zone consisting of brecciated limestones, marls and clays, showing pressure-solution foliation and oriented phyllosilicates (muscovite and chlorite), that can be identified in X-ray diffraction analysis. Analysis of AMS in fault rocks indicates that magnetic fabrics are dependent on the deformation degree, which is interpreted to vary across this relatively narrow fault zone. With increasing deformation, the magnetic lineation changes from parallel to the intersection lineation between foliation and shear planes in the area closest to the hanging wall, to a scattered pattern within the foliation plane in intermediate areas, and finally it gets parallel to the projection of the transport direction onto the magnetic foliation plane near the contact with the footwall (pitch of 90o within the foliation plane). The results obtained also give clues on the tectonic history of the Iberian Chain, in which frontal, NNE-directed thrusting seems to be the main mechanism for E–W trending basement-involved thrusts, in the linking zone between the Iberian Chain and the Catalonian Range.

Coseismic extension recorded within the damage zone of the Vado di Ferruccio Thrust Fault, Central Apennines, Italy

Recent high resolution hypocentral localisation along active fault systems in the Central Apennines illuminates the activation of seismogenic volumes dipping at low angle (<30°) in extensional settings overprinting contractional deformations affecting the continental crust of the Adria microplate. Individuation of the geological structures and of the fault processes associated with these seismic patterns will contribute to the interpretation of seismic sequence evolution, and seismic hazard studies.Here we report field and microstructural evidence of seismogenic extensional faults localized within pre-existing thrust fault zones. The Vado di Ferruccio Thrust Fault (VFTF) is a narrow fault zone (<2.5 m thick fault core) in the Central Apennines of Italy, accommodating ∼1 km of shortening during Miocene-Pliocene and exhumed from <3.5 km depth. In the thrust zone, exposures throughout the Fornaca Tectonic Window show Late Triassic bituminous dolostones thrust over Middle Jurassic interlayered carbonates upon a SSW-dipping fault. Isoclinal folds are dragged and sheared by thrust-parallel reverse faults in the footwall block whereas NW-striking faults occur within the hanging wall. Fault core observations are consistent with stable pressure solution-mediated aseismic sliding towards N024° during thrusting, with cyclic veining and faulting. Later extension has been accommodated at the regional scale by major normal faults cutting through the VFTF, while veins and pressure-solution seams crosscut the microstructures associated with thrusting and record the extensional stress regime within the thrust fault core. Lenses of shattered rocks (up to 10 s m thick), cut by a dense network of small displacement (<1.2 m) mirror-like normal faults, are reported in the hangingwall of the VFTF. These minor faults, related to a sharp principal slipping surface on the upper margin of the VFTF fault core, are interpreted as fossil evidence of microseismicity compartmentalized within the hanging wall of the VFTF. Synthetic and antithetic normal faults within the VFTF hangingwall damage zone are geometrically and kinematically similar to small earthquake ruptures (Mw < 2) in the hangingwall of low angle structures such as the thrust flats illuminated during the 2009 Mw 6.1 L'Aquila seismic sequence.

The transtensional offshore portion of the northern San Andreas fault: Fault zone geometry, late Pleistocene to Holocene sediment deposition, shallow deformation patterns, and asymmetric basin growth

We mapped an ~120 km offshore portion of the northern San Andreas fault (SAF) between Point Arena and Point Delgada using closely spaced seismic reflection profiles (1605 km), high-resolution multibeam bathymetry (~1600 km 2 ), and marine magnetic data. This new data set documents SAF location and continuity, associated tectonic geomorphology, shallow stratigraphy, and deformation. Variable deformation patterns in the generally narrow (∼1 km wide) fault zone are largely associated with fault trend and with transtensional and transpressional fault bends. We divide this unique transtensional portion of the offshore SAF into six sections along and adjacent to the SAF based on fault trend, deformation styles, seismic stratigraphy, and seafloor bathymetry. In the southern region of the study area, the SAF includes a 10-km-long zone characterized by two active parallel fault strands. Slip transfer and long-term straightening of the fault trace in this zone are likely leading to transfer of a slice of the Pacific plate to the North American plate. The SAF in the northern region of the survey area passes through two sharp fault bends (∼9°, right stepping, and ∼8°, left stepping), resulting in both an asymmetric lazy Z–shape sedimentary basin (Noyo basin) and an uplifted rocky shoal (Tolo Bank). Seismic stratigraphic sequences and unconformities within the Noyo basin correlate with the previous 4 major Quaternary sea-level lowstands and record basin tilting of ∼0.6°/100 k.y. Migration of the basin depocenter indicates a lateral slip rate on the SAF of 10–19 mm/yr for the past 350 k.y. Data collected west of the SAF on the south flank of Cape Mendocino are inconsistent with the presence of an offshore fault strand that connects the SAF with the Mendocino Triple Junction. Instead, we suggest that the SAF previously mapped onshore at Point Delgada continues onshore northward and transitions to the King Range thrust.

Investigation of the Huge Tsunami from the 2011 Tōhoku-Oki, Japan, Earthquake Using Ocean Floor Boreholes to the Fault Zone

Integrated Ocean Drilling Program (IODP) Expedition 343, named the Japan Trench Fast Drilling Project (JFAST), drilled ocean floor boreholes through the fault zone of the 2011 Tōhoku-Oki earthquake (M9.0) to enhance understanding of the rupture process and tsunami generation. This project investigated the very large fault slip that caused the devastating tsunami by making borehole stress measurements, sampling the plate boundary fault zone, and taking temperature measurements across the fault zone. The results show that the earthquake rupture occurred in a narrow fault zone (< 5 m). Based on both laboratory experiments on fault zone material and temperature monitoring of the fault zone, we show that the fault had very low friction during the earthquake. The low friction properties of the fault zone might be attributed to high smectite clay content of the sediment. These physical and frictional characteristics contributed to the unusually large fault slip that occurred during the earthquake and generated the tsunami. © 2014 by The Oceanography Society. All rights reserved.

Coseismic thrusting and folding in the 1999 Mw 7.6 Chi‐Chi earthquake: A high‐resolution approach by aerial photos taken from Tsaotun, central Taiwan

AbstractWe used aerial photos taken before and after the 21 September 1999, Mw 7.6, Chi‐Chi earthquake in central Taiwan to measure the near‐field ground deformation. A total of 12 pairs of images were processed with Co‐registration of Optically Sensed Images and Correlation to produce a horizontal displacement map of a 10 km × 10 km area near Tsaotun. Using pairs of images with different viewing angles, both the horizontal and vertical slip across the fault zone can be measured. Our measurements when resampled into lower resolution are consistent with lower resolution measurements of horizontal displacements obtained from SPOT images, as well as with vertical displacements obtained from repeated leveling measurements and field observations. Horizontal strain is strongly localized along the Chelungpu fault (CLPF) and along a secondary scarp that runs parallel to the CLPF about 2 km to the east, the Ailiao fold scarp (ALF). This pattern closely matches the surface ruptures mapped in the field. Horizontal strain across CLPF correlates remarkably well with the topographic features produced by long‐term deformation. The cumulative horizontal shortening across the CLPF and ALF amounts to 4.9 ± 0.4 and 6.1 ± 0.6 m, respectively, and fault‐parallel displacement is 3.4 ± 0.4 m. The pattern of surface strain is consistent with the interpretation of the ALF as a fold scarp formed over an active axial hinge zone. This study shows that, even in this compressional setting, most surface deformation is localized within narrow fault zones or active axial hinges.

Geosciences of the Himalaya–Karakoram–Tibet orogen

The Himalaya–Karakoram–Tibet orogen, a product of India–Eurasia collision *55 Ma back, continues to attract global attention for its many geoscientific uniqueness. This orogen is the most exciting ‘natural laboratory’ to study continental dynamics and its evolution. During past few decades, phenomenal progresses have been made in uplift and extrusion models, dynamic metamorphism, magmatism, climate–tectonics interaction, etc. This thematic volume on the geosciences of the Himalaya–Karakoram– Tibet consists of eighteen papers and two Geosites. In the first paper, Kirby and Harkins correlated variation in slip rate along the Kunlun fault with topography of the Anyemaqen Shan Mountain at the eastern Tibetan plateau. Their work indicates that fault terminations might be associated with crustal thickening of the plateau and demonstrate that the upper crustal deformation of the Tibetan plateau to be pervasive and dispersed throughout the crustal blocks rather than localized along narrow fault zones. Robinson and Pearson compiled an orogen-wide correlation of footwall and hanging wall units of the Ramgarh and Munsiari thrust sheets. They considered the Ramgarh–Munsiari thrust sheet as a single ‘major orogenscale fault’ system. They hypothesized that the extensional shear within the South Tibetan Detachment was triggered possibly by ‘slip transfer’ from the Main Central Thrust into the Ramgarh–Munsiari Thrust during the Miocene. Thakur reviewed the tectonics of the Siwalik range of the Himalaya. He concluded in-sequence deformation and critical taper mechanism acted in this terrain. Presuming the crustal channel flow model to be correct, Mukherjee estimated a viscosity of 10–10 Pa s, and a Prandtl number of 10–10 for the Greater Himalayan Crystallines. Moharana et al., described the Munsiari Thrust from Kumaun Himalaya to consist of a core and a damage zone and described their structural geology in detail. Mukherjee described a ‘basal detachment’ of extensional ductile shear from the base of the Greater Himalayan Crystallines at Bhagirathi section of the Indian Himalaya and explained it in terms of a shifting crustal channel flow. Ubiquitous backthrusts within this terrain were another new finding and were explained by southward subduction of Eurasian plate below the Indian plate. Based on balanced crosssection studies, Khanal and Robinson estimated slip along major Himalayan faults from the Budhi-Gandhaki river section of central Nepal. Sen and Collins inferred dextral transpression and changing angle of convergence of the formation of the Ladakh magmatic arc. They also reported Late Eocene S-type granite magmatism in its central part. Mathew et al. discuss the tectonothermal evolution of the Arunachal Himalaya. They obtained isothermal decompression for the Greater Himalayan Sequence and isobaric cooling from the Main Central Thrust region. Jayangondaperumal et al. reevaluated co-seismic slip of the Himalayan Frontal Thrust. The estimated shortening around the Himalayan Frontal Thrust would lead a bigger earthquake in the western part of Indian Himalaya. Shah presented a geomorphologic study from Kashmir Basin in India, identified faults from remote sensing studies, and predicted a future earthquake of Mw 7.6. Srivastava et al. S. Mukherjee (&) Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai, India e-mail: soumyajitm@gmail.com

Scientific Drilling

Abstract. Integrated Ocean Drilling Program (IODP) Expedition 340T returned to the 1.4-km-deep Hole U1309D at Atlantis Massif to carry out borehole logging including vertical seismic profiling (VSP). Seismic, resistivity, and temperature logs were obtained throughout the geologic section in the footwall of this oceanic core complex. Reliable downhole temperature measurements throughout and the first seismic coverage of the 800–1400 meters below seafloor (mbsf) portion of the section were obtained. Distinct changes in velocity, resistivity, and magnetic susceptibility characterize the boundaries of altered, olivine-rich troctolite intervals within the otherwise dominantly gabbroic se-quence. Some narrow fault zones also are associated with downhole resistivity or velocity excursions. Small deviations in temperature were measured in borehole fluid adjacent to known faults at 750 mbsf and 1100 mbsf. This suggests that flow of seawater remains active along these zones of faulting and rock alteration. Vertical seismic profile station coverage at zero offset now extends the full length of the hole, including the uppermost 150 mbsf, where detachment processes are expected to have left their strongest imprint. Analysis of wallrock properties, together with alteration and structural characteristics of the cores from Site U1309, highlights the likely interplay between lithology, structure, lithospheric hydration, and core complex evolution. doi: 10.2204/iodp.sd.15.04.2013

IODP Expedition 340T: Borehole Logging at Atlantis Massif Oceanic Core Complex

Integrated Ocean Drilling Program (IODP) Expedition 340T returned to the 1.4-km-deep Hole U1309D at Atlantis Massif to carry out borehole logging including vertical seismic profiling (VSP). Seismic, resistivity, and temperature logs were obtained throughout the geologic section in the footwall of this oceanic core complex. Reliable downhole temperature measurements throughout and the first seismic coverage of the 800–1400 meters below seafloor (mbsf) portion of the section were obtained. Distinct changes in velocity, resistivity, and magnetic susceptibility characterize the boundaries of altered, olivine-rich troctolite intervals within the otherwise dominantly gabbroic se-quence. Some narrow fault zones also are associated with downhole resistivity or velocity excursions. Small deviations in temperature were measured in borehole fluid adjacent to known faults at 750 mbsf and 1100 mbsf. This suggests that flow of seawater remains active along these zones of faulting and rock alteration. Vertical seismic profile station coverage at zero offset now extends the full length of the hole, including the uppermost 150 mbsf, where detachment processes are expected to have left their strongest imprint. Analysis of wallrock properties, together with alteration and structural characteristics of the cores from Site U1309, highlights the likely interplay between lithology, structure, lithospheric hydration, and core complex evolution. &lt;br&gt;&lt;br&gt; doi:&lt;a href="http://dx.doi.org/10.2204/iodp.sd.15.04.2013" target="_blank"&gt;10.2204/iodp.sd.15.04.2013&lt;/a&gt;

A 3000-Year Record of Ground-Rupturing Earthquakes along the Central North Anatolian Fault near Lake Ladik, Turkey

The North Anatolian fault (NAF) is a similar to 1500 km long, arcuate, dextral strike-slip fault zone in northern Turkey that extends from the Karliova triple junction to the Aegean Sea. East of Bolu, the fault zone exhibits evidence of a sequence of large (M(w) > 7) earthquakes that occurred during the twentieth century that displayed a migrating earthquake sequence from east to west. Prolonged human occupation in this region provides an extensive, but not exhaustive, historical record of large earthquakes prior to the twentieth century that covers much of the last 2000 yr. In this study, we extend our knowledge of rupture events in the region by evaluating the stratigraphy and chronology of sediments exposed in a paleoseismic trench across a splay of the NAF at Destek, similar to 6: 5 km east of Lake Ladik (40.868 degrees N, 36.121 degrees E). The trenched fault strand forms an uphill-facing scarp and associated sediment trap below a small catchment area. The trench exposed a narrow fault zone that has juxtaposed a sequence of weakly defined paleosols interbedded with colluvium against highly fractured bedrock. We mapped magnetic susceptibility variations on the trench walls and found evidence for multiple visually unrecognized colluvial wedges. This technique was also used to constrain a predominantly dip-slip style of displacement on this fault splay. Sediments exposed in the trench were dated using both charcoal and terrestrial gastropod shells to constrain the timing of the earthquake events. While the gastropod shells consistently yielded (14)C ages that were too old (by similar to 900 yr), we obtained highly reliable (14)C ages from the charcoal by dating multiple components of the sample material. Our radiocarbon chronology constrains the timing of seven large earthquakes over the past 3000 yr prior to the 1943 Tosya earthquake, including event ages of (2 sigma error): A. D. 1437-1788, A. D. 1034-1321, A. D. 549-719, A. D. 17-585 (1-3 events), 35 B. C.-A. D. 28, 700-392 B. C., 912-596 B. C. Our results indicate an average interevent time of 385 +/- 166 degrees yr (1 sigma).

Morphotectonic development of the Marmara Region

The Marmara Region of northwest Turkey covers the Marmara Sea Basin and the surrounding lands. In the region, morphologically different areas may be distinguished. The Marmara Sea Basin is a structural depression. The land to the north is known as the Thrace-Kocaeli Peneplain, a flatland elevated above a horst. This may be referred to as the Istanbul Horst, bounded by two strike-slip fault zones which define the structural boundaries of two sea basins; the Black Sea in the north and the Marmara Sea in the south. The southern boundary fault is part of the North Anatolian Transform Fault Zone (NAFZ) which cuts through the region in the E–W direction and extends to the Aegean Sea Region. The land to the south of the Marmara Sea is a plateau about 300 to 800 m high known as the Bursa-Balıkesir Plateau. It has a rather rugged topography represented by NW and NE trending ridges separated by depressions. The ridges and the depressions correspond to horsts and grabens respectively. The data reveal that the Marmara Region has passed through the following morphotectonic evolution. Together with the surrounding region it suffered a long period of denudation between the Oligocene and the end of the late Miocene, which formed a regionwide peneplain. The N–S extensional regime followed this phase and began to produce a horst-graben system, and thus, fragmented the peneplain. The flat-lying erosional surfaces have been elevated above the horsts. Later, the NAFZ reached the Marmara Region. In the initial stage, it affected NW Anatolia extensively as a wide right-lateral shear regime. This has evolved, and through time the present narrow fault zone has developed. The major morphological difference between the regions to the north and the south of the Marmara Sea Basin is mainly related to the NAFZ. As a plate boundary, it formed a barrier to the N–S extension, saving the northern sector from the effect of the extension. The southern region has gradually elevated to much higher altitudes.