54,213 research outputs found
Constraints on the active tectonics of the Friuli/NW Slovenia area from CGPS measurements and three-dimensional kinematic modeling
We use site velocities from continuous GPS (CGPS) observations and kinematic
modeling to investigate the active tectonics of the Friuli/NW Slovenia area. Data from 42
CGPS stations around the Adriatic indicate an oblique collision, with southern Friuli
moving NNW toward northern Friuli at the relative speed of 1.6 to 2.2 mm/a. We
investigate the active tectonics using 3DMove, a three-dimensional kinematic model tool.
The model consists of one indenter-shaped fault plane that approximates the Adriatic
plate boundary. Using the ‘‘fault-parallel flow’’ deformation algorithm, we move the
hanging wall along the fault plane in the direction indicated by the GPS velocities. The
resulting strain field is used for structural interpretation. We identify a pattern of
coincident strain maxima and high vorticity that correlates well with groups of
hypocenters of major earthquakes (including their aftershocks) and indicates the
orientation of secondary, active faults. The pattern reveals structures both parallel and
perpendicular to the strike of the primary fault. In the eastern sector, which shows more
complex tectonics, these two sets of faults probably form an interacting strike-slip
system
Coastal Terraces, Sea Level, and Active Tectonics
In this exercise, students investigate the use of coastal landforms from ancient shorelines in studying tectonic movements. Introductory materials explain how coastal landforms are classified on the basis of sediment supply and positions of the land relative to sea level, and describe the features of erosional coastal terraces. Using data on the coastal terraces of San Clemente Island, off the coast of Southern California, students will construct a topographic profile, measure shoreline angles, and calculate rates of uplift of the island relative to the sea. The exercise includes a map and stereo pair, data on sea level fluctuations and ages of coastal terraces, and a problem set with study questions. A bibliography is also provided. Educational levels: High school, Undergraduate lower division
Neotectonic Activity in Quetta-Ziarat Region, Northwest Quetta City, Pakistan
Geomorphic parameters are very helpful as they can quickly explain the concerned area, which is going through a tectonic adjustment. For this purpose, four indices were applied to examine the active tectonics in the QuettaZiarat region. These indices include: sub-basins asymmetry (Af), transverse topography (T-Factor), hypsometric integral (HI) and stream-length gradient (SL). The calculation of the three indices as denoted by Af, HI and SL show low active tectonics, whereas T-Factor suggests moderate to high level of tectonic activity. While index of active tectonics (IAT) indicated a low to moderate level of active tectonics. In addition, these indices are compared with lithological and climatic consequences to detect the final neotectonics judgement
The Ability of Significant Tidal Stress to Initiate Plate Tectonics
Plate tectonics is a geophysical process currently unique to Earth, has an
important role in regulating the Earth's climate, and may be better understood
by identifying rocky planets outside our solar system with tectonic activity.
The key criterion for whether or not plate tectonics may occur on a terrestrial
planet is if the stress on a planet's lithosphere from mantle convection may
overcome the lithosphere's yield stress. Although many rocky exoplanets closely
orbiting their host stars have been detected, all studies to date of plate
tectonics on exoplanets have neglected tidal stresses in the planet's
lithosphere. Modeling a rocky exoplanet as a constant density, homogeneous,
incompressible sphere, we show the tidal stress from the host star acting on
close-in planets may become comparable to the stress on the lithosphere from
mantle convection. We also show that tidal stresses from planet-planet
interactions are unlikely to be significant for plate tectonics, but may be
strong enough to trigger Earthquakes. Our work may imply planets orbiting close
to their host stars are more likely to experience plate tectonics, with
implications for exoplanetary geophysics and habitability. We produce a list of
detected rocky exoplanets under the most intense stresses. Atmospheric and
topographic observations may confirm our predictions in the near future.
Investigations of planets with significant tidal stress can not only lead to
observable parameters linked to the presence of active plate tectonics, but may
also be used as a tool to test theories on the main driving force behind
tectonic activity.Comment: 34 pages, 3 figures, 3 Tables, accepted to Icaru
Active tectonics of the Hellenic subduction zone
This thesis is remarkable for the wide range of the techniques and observations used and for its insights, which cross several disciplines. It begins by solving a famous puzzle of the ancient world, which is what was responsible for the tsunami that destroyed settlements in the eastern Mediterranean in 365 AD. By radiocarbon dating of preserved marine organisms, Shaw demonstrates that the whole of western Crete was lifted out of the sea by up to 10 metres in a massive earthquake at that time, which occured on a previously unknown fault. The author shows that the resulting tsunami would have the characteristics described by ancient writers, and uses modern GPS measurements and coastiline geomorphology to show that the strain build-up near Crete requires such a tsunami-earthquake about every 6.000 years - a major insight into Mediterranean tsunami hazard. A detailed seismological study of earthquakes in the Cretan arc over the last 50 years reveals other important features of its behaviour that were previously unknown. Finally, she provides fundamental insights into the limitations of radiocarbon dating marine organisms, relating to how they secrete carbon into their skeletons. The thesis resulted in three major papers in top journals
Geomorphic signal of active faulting at the northern edge of Lut Block. Insights on the kinematic scenario of Central Iran
Recent works documented Neogene to Quaternary dextral strike-slip tectonics along the Kuh-e-Sarhangi and Kuh-e-Faghan intraplate strike-slip faults at the northern edge of the Lut Block of Central Iran, previously thought to be dominated by sinistral strike-slip deformation. This work focuses on the evidence of Quaternary activity of one of these fault systems, in order to provide new spatio-temporal constraints on their role in the active regional kinematic scenario. Through geomorphological and structural investigation, integrated with Optically Stimulated Luminescence (OSL) dating of three generations of alluvial fans and fluvial terraces (at ~53, ~25 and ~6 ka), this study documents (i) the topographic inheritance of the long-term (Myr) punctuated history of fault nucleation, propagation, and exhumation along the northern edge of Lut Block; (ii) the tectonic control on drainage network evolution, pediment formation, fluvial terraces, and alluvial-fan architecture; (iii) the minimum Holocene age of Quaternary dextral strike-slip faulting; and (iv) the evidence of Late Quaternary fault-related uplift localized along the different fault strands. The documented spatial and temporal constraints on the active dextral strike-slip tectonics at the northern edge of Lut Block provided new insights on the kinematic model for active faulting in Central Iran, which has been reinterpreted in an escape tectonic scenario
Active Tectonics in Southern Xinjiang, China: Analysis of Terrace Riser and Normal Fault Scarp Degradation Along the Hotan-Qira Fault System
The northern piedmont of the western Kunlun mountains (Xinjiang, China) is marked at its easternmost extremity, south of the Hotan-Qira oases, by a set of normal faults trending N50E for nearly 70 km. Conspicuous on Landsat and SPOT images, these faults follow the southeastern border of a deep flexural basin and may be related to the subsidence of the Tarim platform loaded by the western Kunlun northward overthrust. The Hotan-Qira normal fault system vertically offsets the piedmont slope by 70 m. Highest fault scarps reach 20 m and often display evidence for recent reactivations about 2 m high. Successive stream entrenchments in uplifted footwalls have formed inset terraces. We have leveled topographic profiles across fault scarps and transverse abandoned terrace risers. The state of degradation of each terrace edge has been characterized by a degradation coefficient τ, derived by comparison with analytical erosion models. Edges of highest abandoned terraces yield a degradation coefficient of 33 ± 4 m^2. Profiles of cumulative fault scarps have been analyzed in a similar way using synthetic profiles generated with a simple incremental fault scarp model. The analysis shows that (1) rate of fault slip remained essentially constant since the aggradation of the piedmont surface and (2) the occurrence of inset terraces was synchronous at all studied sites, suggesting a climate-driven terrace formation. Observation of glacial and periglacial geomorphic features along the northern front of the western Kunlun range indicates that the Qira glaciofluvial fan emplaced after the last glacial maximum, during the retreat of the Kunlun glaciers (12–22 ka). The age of the most developed inset terrace in uplifted valleys is inferred to be 10 ± 3 ka, coeval with humid climate pulses of the last deglaciation. The mass diffusivity constant (k=τ/T, being time B.P.) in the Hotan region is determined to be 3.3 ± 1.4 m^2/10^3 years, consistent with other estimates in similar climatic and geologic environments of western China. These results imply a minimum rate for the Tarim subsidence of 3.5 ± 2 mm/yr. If Western Kunlun overthrusts the Tarim platform on a crustal ramp dipping 40°–45° to the south, it would absorb at least 4.5 ± 3 mm/yr of convergence between western Tibet and Tarim
Tectonics, volcanism, landscape structure and human evolution in the African Rift
Tectonic movements and volcanism in the African Rift have usually been considered of relevance to human evolution only at very large geographical and chronological scales, principally in relation to longterm topographic and climatic variation at the continental scale. At the more loca1 scale of catchment basins and individual sites, tectonic features are generally considered to be at worst disruptive and at best incidental features enhancing the preservation and exposure of early sites. We demonstrate that recent lava flows and fault scarps in a tectonically active region create a distinctive landscape structure with a complex and highly differentiated topography of enclosures, barriers and fertile basins. This landscape structure has an important potential impact on the co-evolution of prey-predator interactions and on interspecific relationships more generally. In particular, we suggest that it would have offered unique opportunities for the development of a hominid niche characterised by bipedalism, meat-eating and stone tool use. These landscape features are best appreciated by looking at areas which today have rapid rates of tectonic movement and frequent volcanic activity, as in eastern Afar and Djibouti. These provide a better analogy for the Plio-Pleistocene environments occupied by early hominids than the present-day landscapes where their fossil remains and artefacts have been discovered. The latter areas are now less active than was the case when the sites were formed. They have also been radically transfomed by ongoing geomorphological processes in the intervening millennia. Thus, previous attempts to reconstruct the local landscape setting adjacent to these early hominid sites necessarily rely on limited geological windows into the ancient land surface and thus tend to filter out small-scale topographic detail because it cannot be reliably identified. It is precisely this local detail that we consider to be of importance in understanding the environmental contribution to co-evolutionary developments
Evidence for late Quaternary surface rupture along the Leech River fault near Victoria, British Columbia
New surficial and bedrock mapping and paleoseismic trenching of the Leech River fault provide the first evidence for Quaternary surface-rupturing earthquakes in southwestern British Columbia, Canada. The Leech River fault extends ~60 km across southern Vancouver Island, from Victoria, British Columbia to the Pacific shoreline and is a terrane-bounding structure separating the Pacific Rim Terrane from basalts of the Eocene Crescent Terrane. The fault is not currently listed in the active fault catalogue for Canada, and post-Eocene-Oligocene slip had not been documented prior to this study. However, based on new field mapping aided by lidar topography, we identify >60 individual, sub-parallel, linear scarps, sags and swales occurring in semi-continuous, en echelon arrays that offset bedrock and late Pleistocene-Holocene deposits. Field observations of these scarps confirm that they are not the result of anthropogenic, glacial or landslide processes, and in several places the scarps are located above exposures of faulted bedrock with brittle fracture networks and gouge. At a site ~5 km west of Leechtown, British Columbia, we estimate ~6 m of dip-slip reverse displacement of a post-Last Glacial Maximum (<~15 ka) colluvial surface and ~4 m of displacement of intervening channels. Two paleoseismic trenches at this site reveal (1) Jurassic Leech River Schist in fault contact with latest Pleistocene loess and colluvium, and (2) latest Pleistocene till thrust over post-glacial colluvium. These trenches preserve a record of at least three, and possibly four, earthquakes since the Last Glacial Maximum, each with ~1 m vertical displacement. We interpret the active Leech River fault as a 500–1000 m-wide, steeply dipping fault zone that accommodates transpression across the northern Cascadia forearc. The onshore trace of the Leech River fault may continue offshore to the east, south of Victoria, and may be kinematically linked to active faults in western Washington (e.g., Devils Mountain and Southern Whidbey Island faults). The Leech River fault is likely one of several active crustal faults that should be considered in seismic hazard assessments for southern British Columbia and northwestern Washington
Spatio-temporal evolution of intraplate strike-slip faulting: the Neogene-Quaternary Kuh-e-Faghan Fault, Central Iran
Central Iran provides an ideal region to study the long-term morphotectonic response to the nucleation and propagation of intraplate faulting. In this study, a multidisciplinary approach that integrates structural and stratigraphic field investigations with apatite (U+Th)/He (AHe) thermochronometry is used to reconstruct the spatio-temporal evolution of the Kuh-e-Faghan Fault (KFF) in northeastern Central Iran. The KFF is a narrow, ca. 80 km long, deformation zone that consists of three main broadly left stepping, E-W trending, dextral fault strands that cut through the Mesozoic-Paleozoic substratum and the Neogene-Quaternary sedimentary cover. The AHe thermochronometry results indicate that the intra-fault blocks along the KFF experienced two major episodes of fault-related exhumation at ~18 Ma and ~4 Ma. The ~18 Ma faulting/exhumation episode is chiefly recorded by the structure and depositional architecture of the Neogene deposits along the KFF. A source-to-sink scenario can be reconstructed for this time frame, where topographic growth caused the synchronous erosion/exhumation of the pre-Neogene units and deposition of the eroded material in the surrounding fault-bounded continental depocenters. Successively, the KFF gradually entered a period of relative tectonic quiescence and, probably, of regional subsidence during which a thick pile of fine-grained onlapping sediments were deposited. This may have caused resetting of the He ages of apatite in the pre-Neogene and the basal Neogene successions. The ~4 Ma faulting episode caused the final exhumation of the fault system, resulting in the current fault zone and topography. The two fault-related exhumation episodes fit with the regional early Miocene collision-enhanced uplift/exhumation, and the late Miocene–early Pliocene widespread tectonic reorganization of the Iranian plateau. The reconstructed long term, spatially and temporally punctuated fault system evolution in intraplate Central Iran during Neogene-Quaternary times may reflect states of far-field stress changes at the collisional boundaries
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