Geodetic evidence for passive control of a major Miocene tectonic boundary on the contemporary deformation field of Athens (Greece)

A GPS-derived velocity field is presented from a dense geodetic network (~5km distance between stations) established in the broader area of Athens. It shows significant local variations of strain rates across a major inactive tectonic boundary separating metamorphic and non-metamorphic geotectonic units. The southeastern part of Athens plain displays negligible deformation rates, whereas towards the northwestern part higher strain rates are observed, indicating the control of the inactive tectonic boundary on the contemporary deformation field of the region. These findings are in agreement with previous geological observations, however, due to the dense local GPS network it was fatherly possible to localize and quantify the effect of such a major inherited tectonic feature on the deformation pattern of the area.

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Velocity field and crustal deformation of broader Athens plain (Greece) from a dense geodetic network

Journal of Applied Geodesy ◽

10.1515/jag-2019-0012 ◽

2019 ◽

Vol 13 (4) ◽

pp. 305-316 ◽

Cited By ~ 1

Author(s):

M. Foumelis

Keyword(s):

Velocity Field ◽

Crustal Deformation ◽

Strain Tensor ◽

Geodetic Network ◽

Motion Field ◽

Strain Accumulation ◽

Tectonic Structures ◽

Single Strain ◽

Geodetic Strain ◽

Tectonic Boundary

Abstract The broader area of Athens, a region exhibiting relatively low crustal deformation, was stroke in 1999 by a catastrophic earthquake posing serious questions regarding strain accumulation in slow deforming regions located within active geodynamic regimes. In the present study, the establishment of a dense geodetic network, primarily designed to monitor local tectonic movements is reported. A comprehensive GNSS velocity field, over the period 2005–2008, as well as calculated geodetic strain rates is presented. It is shown that a single strain tensor is insufficient to express the heterogeneity of the local geodetic field. Local variability of strain is successfully depicted, indicating the western part of Athens as the area of higher strain accumulation. Maximum dilatation rates occur along a NNE-SSW direction between Parnitha Mt. and Thriasio basin. The observed dilatation can be associated to WNW-ESE trending active fault zones, which appear to abruptly terminate towards East along a major NNE-SSW Miocene tectonic boundary. These findings are consistent to the stress field responsible for the Athens 1999 earthquake, also in agreement with geological and tectonic observations. Finally, the implications of the observed motion field on the understanding of the kinematics and dynamics of the region as well as the role of inherited inactive tectonic structures are discussed.

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The mid-Paleozoic deformation in the Hazen fold belt, Ellesmere Island, Arctic Canada

Canadian Journal of Earth Sciences ◽

10.1139/e90-146 ◽

1990 ◽

Vol 27 (10) ◽

pp. 1359-1370 ◽

Cited By ~ 12

Author(s):

Eva M. Klaper

Keyword(s):

Large Scale ◽

Ellesmere Island ◽

Small Scale ◽

Northwestern Part ◽

Fold Belt ◽

Southeastern Part ◽

Lower Paleozoic ◽

Slip Mechanism ◽

Fold Belts ◽

Surface Geology

The mid-Paleozoic deformation of lower Paleozoic subgreenschist-facies sediments of the Hazen fold belt in northern Ellesmere Island is represented predominantly by chevron-style folding. Folded multilayers display cleavage fans suggesting synchronous fold and cleavage formation. Bedding-parallel slip indicates a flexural slip mechanism of folding. The geometry of several large-scale anticlinoria has been interpreted as being due to formation of these structures over detachments and thrust ramps.The constant fold geometry, the parallel orientation of faults and large- and small-scale folds, and the axial-plane foliation are related to a single phase of folding with a migrating deformation front in the Hazen fold belt during the mid-Paleozoic orogeny. The minimum amount of shortening in the Hazen and Central Ellesmere fold belts has been estimated from surface geology to increase from 40–50% of the original bed length in the external southeastern part to 50–60% in the more internal northwestern part of the belts.The convergent, thin-skinned nature of the Hazen and Central Ellesmere fold belts indicates that the postulated transpressive plate motions during the accretion of Pearya did not affect the study area.

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Dynamics of evapotranspiration and variations in different land-cover regions over the Tibetan Plateau during 1961-2014

Journal of Hydrometeorology ◽

10.1175/jhm-d-20-0074.1 ◽

2021 ◽

Author(s):

Shan Lin ◽

Genxu Wang ◽

Zhaoyong Hu ◽

Kewei Huang ◽

Xiangyang Sun ◽

...

Keyword(s):

Tibetan Plateau ◽

Land Cover ◽

Northwestern Part ◽

The Tibetan Plateau ◽

Southeastern Part ◽

Available Energy ◽

Forest Region ◽

Energy Factors ◽

Term Change ◽

Increasing Trend

AbstractIn this study, the spatiotemporal changes and driving factors of evapotranspiration (ET) over the Tibetan Plateau (TP) are assessed from 1961-2014, based on a revised generalized nonlinear complementary (nonlinear-CR) model. The average annual ET on the TP was 328 mm/year. The highest ET value (711 mm/year) was found in the forest region in the southeastern part of the TP, and the lowest value (151 mm/year) was found in the desert region in the northwestern part of the TP. In terms of the contribution of different sub-regions to the total amount of ET for the whole plateau, the meadow and steppe regions contributed the most to the total amount of ET of TP, accounting for 30% and 18.5%, respectively. The interannual ET presented a significant increasing trend with a value of 0.26 mm/year from 1961 to 2014, and a significant positive ET trend was found over 35% of the region, mainly in the southeastern part of the plateau. The increasing trend of ET in swamp areas was the largest, while that in the desert areas was the smallest. In terms of the seasonality, the ET over the plateau and different land-cover regions increased the most in summer, followed by spring, while the change in ET in winter was not obvious. The energy factors dominated the long-term change in the annual ET over the plateau. In addition, the available energy is the controlling factor for ET changes in humid areas such as forests and shrublands. Energy and water factors together dominate the ET changes in arid areas.

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Comparison analysis of numerically calculated slip surfaces with measured S-wave velocity field for Just-Tęgoborze landslide in Carpathian flysch

E3S Web of Conferences ◽

10.1051/e3sconf/201913301003 ◽

2019 ◽

Vol 133 ◽

pp. 01003

Author(s):

Krzysztof Krawiec ◽

Paulina Harba

Keyword(s):

Velocity Field ◽

Wave Velocity ◽

Strength Criterion ◽

Deformation Field ◽

Comparison Analysis ◽

S Wave ◽

Velocity Models ◽

Characteristic Features ◽

Analysis Of Dispersion ◽

Comparison Of The Results

The article presents the comparison analysis between deformation field from numerical model and shear wave (S-wave) velocity field obtained from seismic interferometry (SI). Tests were conducted on active Just-Tęgoborze landslide. Geologically, the study area lies in Magura Nappe in the Outer Carpathians. The landslide’s flysch bedrock is covered by Quaternary colluvium built of clays and weathered clayey-rock deposits. During geotechnical investigation, properties of landslide body were established and failure surfaces were distinguished. In order to obtain S-wave velocity models, one-hour of ambient seismic noise was recorded by 12 broadband seismometers. As a result of data processing with SI method, Rayleigh surface wave propagation was reconstructed. The analysis of dispersion curves allowed to estimate a two dimensional S-wave velocity field. The deformation field were calculated assuming an elastic-plastic Coulomb-Mohr strength criterion. Images of shear strain increment, and values of factor of safety of the slope were obtained as a result of calculation. The comparison of the results indicates the similar characteristic features in the S-wave velocity field and the field of deformation calculated numerically.

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Facies, sequence stratigraphy, reservoir and seal potential of the Mafraq Formation, Sultanate of Oman: An integrated outcrop analogue study

GeoArabia ◽

10.2113/geoarabia200317 ◽

2015 ◽

Vol 20 (3) ◽

pp. 17-94

Author(s):

Daniel Bendias ◽

Thomas Aigner

Keyword(s):

Sequence Stratigraphy ◽

Northwestern Part ◽

Southeastern Part ◽

Terrestrial Environment ◽

Oman Mountains ◽

Facies Associations ◽

Potential Reservoir ◽

Lateral Extent ◽

Member Sequence ◽

Mixed Carbonate

ABSTRACT The mixed carbonate-siliciclastic Lower to Middle Jurassic Mafraq Formation unconformably overlies the Triassic Mahil Formation in outcrops of the Oman Mountains (pre-Mafraq Unconformity, known as pre-Marrat unconformity in other regions of Arabia). Together with the overlying Dhruma Formation, it is part of the Sahtan Group. This study provides: (1) a detailed facies analysis based on sedimentological logging of 12 outcrops. Twenty-four facies types were established and grouped into five facies associations, which can also be recognized in subsurface core intervals; (2) a detailed sequence-stratigraphic framework of the Mafraq Formation. Facies stacking and log patterns reveal cycle hierarchies on four scales from m-scale cycles, to several m-thick cycle sets, to tens of m-thick, high-frequency sequences, to 100 m-thick composite sequences; and (3) a documentation of potential reservoir and seal units. The study follows an approach from 1-D (outcrop sections) to 2-D (correlations and potential reservoir dimensions). The Mafraq outcrop type section, located in Wadi Sahtan is documented in an integrated way (facies, litho-, bio-, chemo- and sequence stratigraphy), together with additional outcrops of the Mafraq Formation throughout North Oman. 2-D correlation of the Mafraq Formation throughout North Oman is essentially based on cycle sets and provides key information about the lateral paleogeographic development of the formation. A general proximal-distal trend, from south to north, has been proposed by Ziegler (2001); outcrop data from the Oman Mountains confirms this trend and adds an EW-deepening component. The mixed carbonate-clastic Lower Mafraq Member (Sequence) with a coastal/estuarine to shallow-marine environment forms onlaps onto the pre-Mafraq Unconformity below, and thins out completely after some 10s of kilometers towards the southeast. The Upper Mafraq Member (Sequence) seems to be continuous over 10s of kilometers with less thickness decrease. Instead, a transition from a more distal carbonate shoal - backshoal environment in the northwest to a proximal clastic coastal/estuarine/terrestrial environment in the southeast can be observed. On a 100s km-scale significant thinning and a change towards terrestrial clastic facies can be observed southeast of the Oman Mountains area. Combined results from lateral/vertical logging, paleoenvironmental interpretations and correlation provided 3-D information about the dimensions of potential reservoir and seal units. Several potential reservoir/seal intervals and their dimensions in dip direction could be identified: (1) Lower Mafraq Sequence: various types of sandbodies, most of them with a lateral extent ca. 5 km, sealed by shales. (2) Upper Mafraq Sequence, northwestern part: oolitic grainstones, laterally correlative over 10–20 km, sealed by shales. (3) Upper Mafraq Sequence, southeastern part: channelized sandstones units, lateral extent up to km, sealed by shales.

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Spatial variation in seismic anisotropy beneath the eastern and northeastern Iranian plateau and its geodynamic implications

10.5194/egusphere-egu21-8590 ◽

2021 ◽

Author(s):

Yifan Gao ◽

Ling Chen ◽

Morteza Talebian ◽

Zimu Wu ◽

Xu Wang ◽

...

Keyword(s):

Large Scale ◽

Seismic Anisotropy ◽

Strike Slip ◽

Surface Strain ◽

Deformation Pattern ◽

Strain Rates ◽

Lithospheric Deformation ◽

Iranian Plateau ◽

Lut Block ◽

Imaging Results

The Iranian plateau is a natural laboratory for studying the early stage of continental collision and plateau development. The collisional front and northern plateau are the major areas accommodating the Arabia-Eurasia convergence. GPS observations suggest that the blocks of central Iran with minor shortening may be relatively rigid. However, recent seismic imaging results suggest that the lithosphere in this region might not be rigid for it is thin and not seismically fast. Widespread mantle-derived magmatism since Middle Miocene also lends support to a relatively hot and weak lithosphere. It may raise a question of why these blocks could behave rigidly when transmitting stresses to the north.Deformation patterns of the lithosphere and asthenosphere in the northeastern and eastern Iranian plateau, which can be constrained by seismic anisotropy, may help to understand the nature of the lithosphere within the continental interior and its responses to the Arabia-Eurasia collision. We studied the seismic anisotropy of the region via teleseismic shear-wave splitting analysis on dense array data and compared the new results with multidisciplinary observations, particularly the surface strain rates and the structure of the lithosphere-asthenosphere system. In northeastern Iran around the Paleo-Tehtys suture, the dominant fast polarization direction (FPD) is NW-SE, subparallel to the strikes of thrust faults and orogenic belts. This combined with the relatively higher strain rates and thicker crust and lithosphere suggests that northeastern Iran with pre-existing weakness may have experienced considerable lithospheric shortening. The Lut block, which is a major block of eastern Iran bounded by large-scale strike-slip faults and previously assumed rigid, shows a complex anisotropic structure. In its northern part where the strain rates are low, the average NE-SW FPD has no obvious link to active faults but is roughly parallel to the collision-induced asthenospheric flow. The area to the south around the Dasht-e-Bayaz fault shows high strain rates and a complex structure of Moho. The generally NW-SE FPDs are subparallel to the direction of the surface right-lateral shear, possibly reflecting a fault-controlled lithospheric deformation pattern. Further south is the central Lut area with moderate strain rates. It is characterized by a two-layer structure of anisotropy, with the FPDs in the upper and lower layers being similar to those of the area around the Dasht-e-Bayaz fault and the northern Lut block, respectively. This feature indicates that the anisotropy and deformation of the central Lut area could be affected by both large-scale strike-slip faults and collision-induced mantle flow.Collectively, our observations suggest that both the collisional processes at the plate boundary and the nature and structural heterogeneities of the continental lithosphere may control the intracontinental deformation of the Iranian plateau. The observed minor deformation of the Lut block and also other blocks within this young plateau does not necessarily mean that these blocks are rigid, but is probably because of significant deformation preferentially taking place at not only the collision front but also mechanically weak zones in the hinterland, which may have accommodated most of the Arabia-Eurasia convergence.

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Crustal Deformation Prior to the 2017 Jiuzhaigou, Northeastern Tibetan Plateau (China), Ms 7.0 Earthquake Derived from GPS Observations

Remote Sensing ◽

10.3390/rs10122028 ◽

2018 ◽

Vol 10 (12) ◽

pp. 2028 ◽

Cited By ~ 2

Author(s):

Weiwei Wu ◽

Xiaoning Su ◽

Guojie Meng ◽

Chentao Li

Keyword(s):

Tibetan Plateau ◽

Strain Rate ◽

Crustal Deformation ◽

Multiscale Approach ◽

Deformation Pattern ◽

Strain Rate Tensor ◽

Strain Rates ◽

Shear Strain Rate ◽

Jiuzhaigou Earthquake ◽

Epicentral Area

The 2017 Jiuzhaigou Ms 7.0 earthquake occurred on the northeastern margin of the Tibetan Plateau, with no noticeable rupture surface recognized. We characterized the pre-seismic deformation of the earthquake from GPS (Global Positioning System) data at eight continuous and 73 campaign sites acquired over the 2009–2017 period. With respect to the Eurasian plate, the velocity field showed a noticeable decrease, from west of the epicenter of the Jiuzhaigou earthquake to the western edge of the Longmenshan fault, in the southeast direction. The total northwest west–southeast east shortening rate in the vicinity of the epicentral area was in the range of 1.5 mm/y to 3.1 mm/y. With a GPS velocity transect across the Huya fault (HYF), where the epicenter was located, we estimated the activity of the HYF, showing a dominant left-lateral slip rate of 3.3 ± 0.2 mm/y. We calculated strain rates using a spherical wavelet-based multiscale approach that solved for the surface GPS velocity according to multiscale wavelet basis functions while accounting for spatially variable spacing of observations. Multiscale components of the two-dimensional strain rate tensor showed a complex crustal deformation pattern. Our estimates of strain rate components at the scale of seven and eight revealed extensional strain rate on the northern extension of the HYF. The Jiuzhaigou earthquake occurred at the buffer zone between extensional and compressional deformation, and with significant maximum shear rates being 100–140 nanostrain/y. In addition, a maximum shear strain rate of 60–120 nanostrain/y appeared around the epicenter of the 2013 Ms 6.6 Minxian–Zhangxian earthquake. These findings imply that inherent multiscale strain rates could be separated to identify strain accumulation related to medium- and large-sized earthquakes.

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Development of a stream function-upper bound analysis applicable to the process of plate rolling

Multidiscipline Modeling in Materials and Structures ◽

10.1108/mmms-06-2015-0029 ◽

2016 ◽

Vol 12 (2) ◽

pp. 254-274 ◽

Cited By ~ 2

Author(s):

Amir Asgharzadeh ◽

Siamak Serajzadeh

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Velocity Field ◽

Stream Function ◽

Upper Bound ◽

Deformation Zone ◽

Deformation Pattern ◽

Element Analysis ◽

Content Type ◽

Plate Rolling

Purpose – The purpose of this paper is to develop a mathematical solution to estimate the deformation pattern and required power in cold plate rolling using coupled stream function method and upper bound theorem. Design/methodology/approach – In the first place, an admissible velocity field and the geometry of deformation zone are derived from a new stream function. Then, the optimum velocity field is obtained by minimizing the corresponding power function. Also, to calculate the adiabatic heating during high speed rolling operations, a two-dimensional conduction-convection problem is sequentially coupled with the mechanical model. To verify the predictions, rolling experiments on aluminum plates are conducted and also, a finite element analysis is performed by Abaqus/Explicit. The predicted deformation zone is then compared with the experimentally measured region as well as with the results of the finite element analysis. Findings – The results show that the predicted deformation zone and the temperature distribution fit reasonably with the experimental data while much lower computational cost needs comparing to the fully finite element analysis. Originality/value – A new stream function is proposed to properly describe the velocity field and deformation pattern during plate rolling considering the neutral point. Furthermore, the employed algorithm can be simply coupled with the thermal finite element analysis.

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