Seismic attenuation tomography of the North-Western Himalaya using Coda waves

2020 ◽  
Author(s):  
Amit Bera ◽  
Himanshu Agrawal ◽  
Supriyo Mitra ◽  
Shubham Sharma
Keyword(s):  
Quality Factor ◽  
Western Himalaya ◽  
Coda Waves ◽  
Projection Algorithm ◽  
Lapse Time ◽  
Scattering Model ◽  
The North ◽  
Temporal Decay ◽  
Back Scattering ◽  
Least Squares Approach

<p>We use 4695 local waveforms from 1206 earthquakes (epicentral distance < 350 km and 2.0 ≤ Mw ≤ 5.5) recorded by IISER Kolkata network (IK) at 22 stations (32°N to 35°N latitude and 74°E to 77°E longitude), located within the North-Western Himalaya (28°N to 39°N latitude and 68°E to 81°E longitude). We study the coda waves which are generally the tail of a seismogram and arrive after the main seismic waves. We use the temporal decay of coda amplitude to calculate the coda quality factor (Q<sub>c</sub>) from which we estimate the attenuation (Q<sub>c</sub><sup>-1</sup>). We consider the single back-scattering model (Aki & Chouet, 1975) where both the scattering (Q<sub>sc</sub><sup>-1</sup>) and intrinsic (Q<sub>i</sub><sup>-1</sup>) component of the attenuation are included in the measurement. We use a lapse time of 2t<sub>s</sub> (t<sub>s</sub> is the S-wave arrival time) as the starting point of the coda window. Then, we consider multiple forward-scattering model, where the attenuation (Q<sub>c</sub><sup>-1</sup>) is dominantly dependent on the intrinsic (Q<sub>i</sub><sup>-1</sup>) component. In this model we use lapse time greater than 2t<sub>s</sub> so that the coda waves encounter multiple scatterers and enter the diffusive regime. We calculate the frequency dependent quality factor for each earthquake-receiver path at frequencies 1 to 14 Hz using the linear least squares approach on temporal decay of coda amplitude. We calculate Q<sub>0</sub> (quality factor at a reference frequency f<sub>0</sub> which is chosen to be 1 Hz for the analysis) and its frequency dependence (η) using weighted least squares approach on the power law dependence of Q<sub>c </sub>on frequency. To see the lateral variation of Q in our study area, we have produced 2-D maps by combining the Q<sub>c </sub>measurements together in a tomography. For single back-scattering model we use the back-projection algorithm which is based on the calculation of area overlap of ellipses with the gridded region. For multiple forward-scattering model, the same back-projection algorithm is modified to calculate the length overlap of traces with the gridded region. To understand the spatial resolution of the 2-D Q<sub>c </sub>maps, we use the point spreading function test which quantifies the recovery of Q<sub>c </sub>perturbation. In addition to this, we also perform a standard checkerboard resolution test to ensure simultaneous recovery of Q<sub>c </sub>perturbation. We observe low Q in the Kashmir basin and Lesser Himalaya and high Q in surrounding northeastern Higher Himalaya which clearly correspond to the coda wave attenuation signatures in the older Tethyan sedimentary rocks and crystalline igneous rocks in these regions respectively.</p>

Understanding pre- and syn-orogenic tectonic evolution in western Himalaya through age and petrogenesis of Palaeozoic and Cenozoic granites from upper structural levels of Bhagirathi Valley, NW India

2021 ◽  
pp. 1-27
Author(s):  
Aranya Sen ◽  
Koushik Sen ◽  
Amitava Chatterjee ◽  
Shubham Choudhary ◽  
Alosree Dey
Keyword(s):  
Inductively Coupled Plasma ◽  
Age Distribution ◽  
Normal Fault ◽  
Western Himalaya ◽  
Indian Plate ◽  
Low Grade ◽  
Inductively Coupled ◽  
The North ◽  
Plasma Mass Spectrometry ◽  
Structural Levels

Abstract The Himalaya is characterized by the presence of both pre-Himalayan Palaeozoic and syn-Himalayan Cenozoic granitic bodies, which can help unravel the pre- to syn-collisional geodynamics of this orogen. In the Bhagirathi Valley of Western Himalaya, such granites and the Tethyan Himalayan Sequence (THS) hosting them are bound to the south by the top-to-the-N extensional Jhala Normal Fault (JNF) and low-grade metapelite of the THS to its north. The THS is intruded by a set of leucocratic dykes concordant to the JNF. Zircon U–Pb laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) geochronology of the THS and one leucocratic dyke reveals that the two rocks have a strikingly similar age distribution, with a common and most prominent age peak at ~1000 Ma. To the north of the THS lies Bhaironghati Granite, a Palaeozoic two-mica granite, which shows a crystallization age of 512.28 ± 1.58 Ma. Our geochemical analysis indicates that it is a product of pre-Himalayan Palaeozoic magmatism owing to extensional tectonics in a back-arc or rift setting following the assembly of Gondwana (500–530 Ma). The Cenozoic Gangotri Leucogranite lies to the north of Bhaironghati Granite, and U–Pb dating of zircon from this leucogranite gives a crystallization age of 21.73 ± 0.11 Ma. Our geochemical studies suggest that the Gangotri Leucogranite is a product of muscovite-dehydration melting of the lower crust owing to flexural bending in relation to steepening of the subducted Indian plate. The leucocratic dykes are highly refracted parts of the Gangotri Leucogranite that migrated and emplaced along extensional fault zones related to the JNF and scavenged zircon from the host THS during crystallization.

Intrinsic and Scattering Attenuations in the Crust of the Racha Region, Georgia

2019 ◽  
Vol 14 (02) ◽  
pp. 2050006
Author(s):  
Ia Shengelia ◽  
Nato Jorjiashvili ◽  
Tea Godoladze ◽  
Zurab Javakhishvili ◽  
Nino Tumanova
Keyword(s):  
Time Window ◽  
Frequency Range ◽  
Quality Factors ◽  
Lapse Time ◽  
Intrinsic Attenuation ◽  
Total Attenuation ◽  
Relative Contribution ◽  
Normalization Methods ◽  
Coda Normalization ◽  
Back Scattering

Three hundred and thirty-five local earthquakes were processed and the attenuation properties of the crust in the Racha region were investigated using the records of seven seismic stations. We have estimated the quality factors of coda waves ([Formula: see text]) and the direct [Formula: see text] waves ([Formula: see text]) by the single back scattering model and the coda normalization methods, respectively. The Wennerberg’s method has been used to estimate relative contribution of intrinsic ([Formula: see text]) and scattering ([Formula: see text]) attenuations in the total attenuation. We have found that [Formula: see text] and [Formula: see text] parameters are frequency-dependent in the frequency range of 1.5–24[Formula: see text]Hz. [Formula: see text] values increase both with respect to lapse time window from 20[Formula: see text]s to 60[Formula: see text]s and frequency. [Formula: see text] and [Formula: see text] parameters are nearly similar for all frequency bands, but are smaller than [Formula: see text]. The obtained results show that the intrinsic attenuation has more significant effect than scattering attenuation in the total attenuation. The increase of [Formula: see text] with lapse time shows that the lithosphere becomes more homogeneous with depth.

Paleomagnetic results from the western Himalaya indicate multi-stage India-Eurasia collision

2021 ◽  
Author(s):  
Craig R Martin ◽  
Oliver Jagoutz ◽  
Rajeev Upadhyay ◽  
Leigh H Royden ◽  
Michael P Eddy ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Classical Model ◽  
Western Himalaya ◽  
Paleomagnetic Data ◽  
Northwestern Part ◽  
Himalayan Orogeny ◽  
The North ◽  
Multi Stage ◽  
Early Paleocene ◽  
Stage Process

<p>The classical model for the collision between India and Eurasia, which resulted in the formation of the Himalayan orogeny, is a single-stage continent-continent collision event at around 55 – 50 Ma. However, it has also been proposed that the India-Eurasia collision was a multi-stage process involving an intra-oceanic Trans-Tethyan subduction zone south of the Eurasian margin. We present paleomagnetic data constraining the location the Kohistan-Ladakh arc, a remnant of this intra-oceanic subduction zone, to a paleolatitude of 8.1 ± 5.6 °N between 66 – 62 Ma. Comparing this result with new paleomagnetic data from the Eurasian Karakoram terrane, and previous paleomagnetic reconstructions of the Lhasa terrane reveals that the Trans-Tethyan Subduction zone was situated 600 – 2,300 km south of the contemporaneous Eurasian margin at the same time as the first ophiolite obduction event onto the northern Indian margin. Our results confirm that the collision was a multistage process involving at least two subduction systems. Collision began with docking between India and the Trans-Tethyan subduction zone in the Late Cretaceous and Early Paleocene, followed by the India-Eurasia collision in the mid-Eocene. The final stage of India-Eurasia collision occurred along the Shyok-Tsangpo suture zone, rather than the Indus-Tsangpo. The addition of the Kshiroda oceanic plate, north of India after the Paleocene reconciles the amount of convergence between India and Eurasia with the observed shortening across the India–Eurasia collision system. Our results constrain the total post-collisional convergence accommodated by crustal deformation in the Himalaya to 1,350 – 2,150 km, and the north-south extent of the northwestern part of Greater India to < 900 km.</p>

Spatial variations of seismic attenuation in the North West of Iranian plateau from analysis of coda waves

2017 ◽  
Vol 708 ◽  
pp. 70-80 ◽  
Author(s):  
M. Naghavi ◽  
H. Rahimi ◽  
A. Moradi ◽  
S. Mukhopadhyay
Keyword(s):  
Seismic Attenuation ◽  
Spatial Variations ◽  
Coda Waves ◽  
Iranian Plateau ◽  
North West ◽  
The North

scholarly journals Siwalik basin of Arunachal Himalaya, India: a case study

1998 ◽  
Vol 18 ◽  
Author(s):  
P. K. Das ◽  
H. Baruah
Keyword(s):  
Sedimentary Facies ◽  
Western Himalaya ◽  
Large River ◽  
Ocean Basin ◽  
North West ◽  
The North ◽  
Late Neogene ◽  
Main Boundary Fault ◽  
Uplift And Erosion ◽  
Arunachal Himalaya

The Siwalik basin of Arunachal Himalaya is a part of the Himalayan foreland. Due to continental collision between Indian and Eurasian plates, the Himalayan mountain system experienced intense uplift and erosion and as a result, a large amount of siliciclastic sediments accumulated within the foreland and a remnant ocean basin (which was commonly known as foredeep) was developed during Eocene. Moreover, the sediments were deposited by a large river draining the uplifted Himalayan belt during late Neogene. From the pattern of lithofacies, the river may be envisaged as braided type and was a bit shallow relative to its width, floored by bars and channels of low sinuosity and with a bed load of sand and pebbly sediments. These sediments present in the Arunachal foothills are bounded by the Brahmaputra Alluviums in the south and the Gondwana belt in the north and, by a system of frontal faults and the Main Boundary Fault, respectively. The sediments are mostly of molasse type (Upper Tertiary sediments), of different sedimentary facies present in the form of thick accumulation of multilateral and multistoried bodies. Moreover, the depositional basin suffered from some tectonic disturbances for which open folds and many reverse faults were formed. With the formation of foredeep infront of the Himalaya, a reversal of slope towards north-west took place in post-Barail times and during the later part of the Tertiary, the Himalayan and the Upper Assam basin were continuous below the Brahmaputra Alluviums as evidenced by field and laboratory observations. From these observations, it is seen that the Siwalik basin of Arunachal Himalaya has close resemblance with the Tertiary basin (Neogene basin) of Upper Assam rather than the Siwalik basin of western Himalaya and thus, this basin may be treated as a separate basin which may be renamed as "Tertiary basin of Arunachsl".

scholarly journals A range extension of Gentiana capitata Buch.-Ham. ex D.Don subsp. harwanensis (G.Singh) Halda (Gentianaceae) to Ladakh Trans-Himalaya, India

Check List ◽  
2019 ◽  
Vol 15 (1) ◽  
pp. 105-108
Author(s):  
Mohd Shabir ◽  
Anzar A. Khuroo ◽  
Priyanka Agnihotri ◽  
Jay Krishan Tiwari ◽  
Tariq Hussain
Keyword(s):  
Geographic Distribution ◽  
Western Himalaya ◽  
Range Extension ◽  
North West ◽  
The North ◽  
Biogeographic Region ◽  
First Time

We collected Gentiana capitata subsp. harwanensis for the first time from Suru valley in Kargil district of Ladakh region, India, and thus extend this subspecies’ geographic distribution to the Trans-Himalayan biogeographic region. This subspecies is endemic to India and so far recorded from the North-west and Western Himalaya of India. 

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