Pn-velocity structure beneath Arabia–Eurasia Zagros collision and Makran subduction zones

2014 ◽  
Vol 392 (1) ◽  
pp. 45-60 ◽  
Author(s):  
Ali I. Al-Lazki ◽  
Khaled S. Al-Damegh ◽  
Salah Y. El-Hadidy ◽  
Abdolreza Ghods ◽  
Mohammad Tatar
Keyword(s):  
Subduction Zones ◽  
Velocity Structure ◽  
Pn Velocity

Modeling guided waves to constrain the velocity structure of the oceanic crust in the subduction zone of eastern Alaska

2020 ◽  
Author(s):  
Xiaoyu Guan ◽  
Yuanze Zhou ◽  
Takashi Furumura
Keyword(s):  
Subduction Zone ◽  
Oceanic Crust ◽  
High Frequency ◽  
Subduction Zones ◽  
Guided Waves ◽  
Velocity Structure ◽  
Guided Wave ◽  
S Wave ◽  
Arrival Times ◽  
Velocity Models

<p>Fitting subduction zone guided waves with synthetics is an ideal choice for studying the velocity structure of the oceanic crust. After an earthquake occurs in subduction zones, seismic waves can be trapped in the low-velocity oceanic crust and propagated as guided waves. The arrival time and frequency characteristics of the guided waves can be used to image the velocity structure of the oceanic crust. The analysis and modeling based on guided wave observations provide a rare opportunity to understand the velocity structure of the oceanic crust and the variations in oceanic crustal materials during the subduction process.</p><p>High-frequency guided waves have been observed in the subduction zone of eastern Alaska. On several sections, observed seismograms recorded by seismic stations show low-frequency (<2Hz) onsets ahead of the main high-frequency (>2Hz) guided waves. Differences in the arrival times and dispersion characteristics of seismic phases are related to the velocity structure of the oceanic crust, and the characteristics of coda waves are related to the distribution of elongated scatters in the oceanic crust. Through fitting the observed broadband waveforms and synthetics modeled with the 2-D FDM (Finite Difference Method), we obtain the preferred oceanic crustal velocity models for several sections in the subduction zone of eastern Alaska. The preferred models can explain the seismic phase arrival times, dispersions, and coda characteristics in the observed waveforms. With the obtained P- and S- wave models of velocity structures on several sections, the material compositions they represent are deduced, and the variations of oceanic crustal materials during subducting can be understood. This provides new evidence for studying the details of the subduction process in the subduction zone of eastern Alaska.</p>

New thermal constraints for the Anatolian lithosphere from Curie depth point and Pn tomography

2021 ◽  
Author(s):  
Ali Deger Ozbakir ◽  
Hayrullah Karabulut
Keyword(s):  
Velocity Structure ◽  
Thermal Structure ◽  
Dynamic Topography ◽  
Transform Method ◽  
Radiogenic Heat ◽  
Spectral Leakage ◽  
Support Mechanism ◽  
Pn Velocity ◽  
Curie Depth ◽  
Dynamic Support

<p><span>Continental deformation can be </span><span>described in two end-member approaches: </span><span><em>block</em></span><span> (or microplate) and </span><span><em>continuum </em></span><span>models</span><span>. The first considers a strong lithosphere with deformation localized in fault zones. For </span><span>t</span><span>he latter, however,</span><span> the lithosphere is weak</span><span> and deforms as a thin viscous sheet. The Anatolia – Aegean domain represents both continuum and plate-like deformation. Furthermore, </span><span>r</span>ecent modeling studies suggest a dynamic support mechanism of the Anatolian plateaus, with dynamic topography estimates ranging from 1 to 3 km for various crustal models and geodynamic scenarios, although the gravity and crustal thickness data support predominant Airy isostasy. The solution to both intricacies relies on the thermal structure of the crust and the lithosphere. Available thermal considerations stem from either the uppermost mantle velocity structure or thermal modeling with assumptions on radiogenic heat production and boundary conditions. Yet, homogeneous and independent constraints on the lithospheric structure are scarce. We aim to contribute to this knowledge gap by providing Curie Point Depths (CPDs), which corresponds to the depth at which rock-forming minerals lose their magnetization at the Curie temperature, ~580 <sup>o</sup>C.<br><br>R<span>esolution of deep magnetic sources requires spectral methods with large windows, which reduce the CPD resolution. Moving & overlapping smaller windows have been used in order to increase the resolution, but these introduce spectral leakage and bias. </span>In previous studies, subjective wavenumber ranges of the magnetic anomaly spectra were used, often combined with wrong scaling factors between map units and the equations. This resulted in generally erroneous CPD estimates. Furthermore, CPD uncertainties have often been unquantified for the study area. <span>We use a wavelet transform method, which overcomes the artifacts due to segmentation of magnetic signal to finite windows, results in higher spatial resolution as well as enabling uncertainty estimation. </span>We used as large an area as possible for constraining the edge effects away from the study area. The resultant CPD map spatially correlates well with low Pn velocity areas, locations of volcanoes, and thermal springs.</p>

Spatial variations of coda wave attenuation in Andaman-Nicobar subduction zone

2020 ◽  
Author(s):  
Chandrani Singh ◽  
Rahul Biswas ◽  
Namrata Jaiswal ◽  
M. Ravi Kumar
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Velocity Structure ◽  
Wave Attenuation ◽  
Broad Band ◽  
Spatial Variations ◽  
Indian Plate ◽  
Coda Wave ◽  
Volcanic Island ◽  
Attenuation Characteristics

<p>We investigate the spatial variations of coda attenuation (Qc) structure in the tectonically complex Andaman–Nicobar subduction zone (ANSZ), which is one of the most seismically active subduction zones on the Earth. The region constitutes the northernmost part of the Sunda subduction zone, where the Indian plate disappears beneath the Burmese plate along the Burma and Andaman arcs to the east. This is probably the first attempt to map the Qc variations across the whole ANSZ. In a seismically active area, the spatial distribution of Qc is important to evaluate the seismic hazard in relation to tectonics and seismicity.</p><p>A total of 289 high-quality events recorded at a network of broad-band stations operational since 2009 are considered for the analysis. The variations in attenuation characteristics at different frequencies reveal a marked contrast from the northern to the southern Andaman region, consistent with the geotectonic diversity of the region. At low frequencies, low Qc values are observed in the northern part of ANSZ in the vicinity of the Narcondum volcanic island, which does not appear in the high-frequency image. The low values are in agreement with the 3-D tomogram, which suggests a distinct low-velocity structure below this volcanic island. The Andaman trench also exhibits a relatively low Qc, which is well correlated with the low-Vp zone. The spatial distributions of Q0 (Qc at 1 Hz) structure of the region are further projected onto three east–west profiles to capture the detailed attenuation characteristics from north to south. Results show that the northernmost part of ANSZ is more attenuative than the southern part, which may be indicative of the changes in physical properties of the crust. The frequency relation parameter (n) shows an inverse correlation with the observed Q0 values. Furthermore, we have observed a good correlation between the Q0 variation and the seismicity pattern of the area that enables us to enhance our understanding about the role of crustal heterogeneity in the earthquake occurrence in this area.</p><p><br><br></p>

Deep Probe: imaging the roots of western North America

2002 ◽  
Vol 39 (3) ◽  
pp. 375-398 ◽  
Author(s):  
Andrew R Gorman ◽  
Ron M Clowes ◽  
Robert M Ellis ◽  
Timothy J Henstock ◽  
George D Spence ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Structural Model ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Spherical Geometry ◽  
Data Sets ◽  
Western Canada Sedimentary Basin ◽  
Southern Rocky Mountains ◽  
Continental Scale ◽  
Wyoming Province

Analysis of the Lithoprobe Deep Probe and Southern Alberta Refraction Experiment data sets, focusing on the region between Deep Probe shots 43 and 55, has resulted in a continental-scale velocity structural model of the lithosphere of platformal western Laurentia reaching depths of ~150 km. Three major lithospheric blocks were investigated: (i) the Hearne Province, a typical continental Archean cratonic province lying beneath the Western Canada Sedimentary Basin; (ii) the Wyoming Province, an even older block of Phanerozoic-modified Archean crust with an enigmatic lower lithosphere; and (iii) the Yavapai–Mazatzal Province, Proterozoic terranes underlying the Colorado Plateau and Southern Rocky Mountains. In this study, the northern two of these regions are investigated with a modified ray-theoretical traveltime inversion routine that respects the spherical geometry of the Earth. The resulting crustal velocity structure, combined with supporting geological and geophysical data, reveals that the Medicine Hat block (MHB), lying between the Hearne and Wyoming provinces, is a third independent Archean crustal block. The subcrustal lithosphere along the profile is homogeneous in velocity structure, but two significant northward-dipping reflectors are apparent and interpreted as relic subduction zones associated with sutures between the three Archean blocks. The Hearne crust is typical of an Archean shield or platform both in its thickness of 34–50 km and its seismic velocity structure. The crust of the Archean MHB and Wyoming Province, which ranges in thickness from 49 to 60 km, includes a 10–30 km thick high-velocity layer, interpreted to be Proterozoic in age. Such a feature is unexpected beneath Archean crustal provinces, but if the region is considered to be the remanent marginal portion of a larger Archean continent, then the interpreted Proterozoic underplating and lack of an Archean lithospheric root can be explained. The variable topography along the reflective upper and lower boundaries of this layer, especially within the MHB, suggests considerable variability in its emplacement and subsequent tectonic history.

scholarly journals Seismicity and Pn Velocity Structure of Central West Antarctica

2021 ◽  
Vol 22 (2) ◽  
Author(s):  
Erica M. Lucas ◽  
Andrew A. Nyblade ◽  
Andrew J. Lloyd ◽  
Richard C. Aster ◽  
Douglas A. Wiens ◽  
...  
Keyword(s):  
Velocity Structure ◽  
West Antarctica ◽  
Pn Velocity

Petrologic and geochemical role of serpentinite in subduction zones and plate interface domains

2015 ◽  
Vol 37 ◽  
pp. 61-64
Author(s):  
Marco Scambelluri ◽  
Enrico Cannaò ◽  
Mattia Gilio ◽  
Marguerite Godard
Keyword(s):  
Subduction Zones ◽  
Plate Interface

Evolution of Orogenic Plateaus at Subduction Zones - Sinking and raising the southern margin of the Central Anatolian Plateau

2018 ◽  
Author(s):  
David Fernández-Blanco
Keyword(s):  
Tectonic Evolution ◽  
Subduction Zones ◽  
Inversion Tectonics ◽  
High Discharge ◽  
Anatolian Plateau ◽  
Surface Uplift ◽  
Southern Margin ◽  
Wide Range ◽  
Forearc Basins ◽  
Orogenic Plateaus

Orogenic plateaus have raised abundant attention amongst geoscientists during the last decades, offering unique opportunities to better understand the relationships between tectonics and climate, and their expression on the Earth’s surface.Orogenic plateau margins are key areas for understanding the mechanisms behind plateau (de)formation. Plateau margins are transitional areas between domains with contrasting relief and characteristics; the roughly flat elevated plateau interior, often with internally drained endorheic basins, and the external steep areas, deeply incised by high-discharge rivers. This thesis uses a wide range of structural and tectonic approaches to investigate the evolution of the southern margin of the Central Anatolian Plateau (CAP), studying an area between the plateau interior and the Cyprus arc. Several findings are presented here that constrain the evolution, timing and possible causes behind the development of this area, and thus that of the CAP. After peneplanation of the regional orogeny, abroad regional subsidence took place in Miocene times in the absence of major extensional faults, which led to the formation of a large basin in the northeast Mediterranean. Late Tortonian and younger contractional structures developed in the interior of the plateau, in its margin and offshore, and forced the inversion tectonics that fragmented the early Miocene basin into the different present-day domains. The tectonic evolution of the southern margin of the CAP can be explained based on the initiation of subduction in south Cyprus and subsequent thermo-mechanical behavior of this subduction zone and the evolving rheology of the Anatolian plate. The Cyprus slab retreat and posterior pull drove subsidence first by relatively minor stretching of the crust and then by its flexure. The growth by accretion and thickening of the upper plate, and that of the associated forearc basins system, caused by accreting sediments, led to rheological changes at the base of the crust that allowed thermal weakening, viscous deformation, driving subsequent surface uplift and raising the modern Taurus Mountains. This mechanism could be responsible for the uplifted plateau-like areas seen in other accretionary margins. ISBN: 978-90-9028673-0

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