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(a) Seismicity map of the Kopili Fault, Shillong Plateau, and Assam Valley (NEIC-USGS, Data set). Stars in the figure symbolize the major earthquakes with their corresponding magnitudes. Inset shows the study region. (b) Map showing major tectonic features of the Kopili Fault region (after Biswas et al 2013a, 2013b).
Source publication
Microearthquakes spectra from Kopili region, one of the seismic prone area of northeast India, are examined to observe the effect of attenuation on these spectra. The spectral ratio method is utilized in order to estimate Q values for both P and S wave in subsurface layer wherein the ratio of spectral amplitudes at lower and higher frequencies are...
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The unknown onshore extent of megathrust earthquake rupture in the Cascadia subduction zone represents a key uncertainty in earthquake hazard for the Pacific Northwest that is governed by the physical state and mechanical properties of the plate interface. The Cascadia plate interface is segmented into an interseismically locked zone located primar...
Citations
... At its eastern syntaxes, NE India is locked by the Mishmi thrust (Nandy, 2001;Kent and Dasgupta, 2004;Mandal and Dasgupta, 2013) (Figs. 1 and 2). The region within these thrust belts encompasses an ENE-WSW trending basin, known as the Assam Basin, which resembles a foreland configuration and has attracted considerable attention from researchers due to its seismicity caused by dextral-slip movement on the Kopili Fault in the Lower Assam Basin (Kayal et al., 2006;Bhattacharya et al., 2008;Kayal, 2008;Kundu and Gahalaut, 2013;Bora et al., 2017) and hydrocarbon potential in the Upper Assam Basin (Sahoo and Gogoi, 2011;Mandal and Dasgupta, 2013;Gogoi and Chatterjee, 2019;Gogoi et al., 2022). ...
Sedimentary basins within fold-and-thrust belts preserve the structural record of complex deformations and are essential to many orogenic systems worldwide. One of the component of such deformations is strike-slip tectonics. This research uses high-quality, three-dimensional seismic reflection data to investigate the geometry and kinematics of strike-slip faults developed within a geologically complex region in the Upper Assam foreland basin, NE India. Faults in the basin have a dominant NE-SW trend, with most faults in the SE and SW parts exhibiting sinistral strike-slip. These lateral movements are evidenced by extensional horsetail splay faults, negative flower structures, and minor transfer faults. The displacement profiles of the strike-slip faults also reveal complex segmentation, linkage, and mechanical interactions at different structural levels, indicating their prolonged histories and development. Tectonic tilts of the basin, along with sediment loading from the bordering fold-and-thrust belts over the geologic time, structurally changed the basin configuration giving rise to strike-slip deformations in the study region. These findings contribute to our knowledge of sedimentary basins within fold-and-thrust belts and their structural records of complex deformations.
... At its eastern syntaxes, NE India is locked by the Mishmi thrust (Nandy, 2001;Kent and Dasgupta, 2004;Mandal and Dasgupta, 2013) (Figs. 1 and 2). The region within these thrust belts encompasses an ENE-WSW trending basin, known as the Assam Basin, which resembles a foreland configuration and has attracted considerable attention from researchers due to its seismicity caused by dextral-slip movement on the Kopili Fault in the Lower Assam Basin (Kayal et al., 2006;Bhattacharya et al., 2008;Kayal, 2008;Kundu and Gahalaut, 2013;Bora et al., 2017) and hydrocarbon potential in the Upper Assam Basin (Sahoo and Gogoi, 2011;Mandal and Dasgupta, 2013;Gogoi and Chatterjee, 2019;Gogoi et al., 2022). ...
The Upper Assam Basin is a historic oil producing province of NE India, although Assam is seismically the most active region for recurring earthquakes. The basin is a SE dipping shelf bounded by the Himalayan orogenic belt in the North, the Mishmi thrust in the east, and the Assam Arakan ranges on the south. Tectonic deformation and underthrusting of the Indian plate below the Eurasian and Burmese plates have resulted in the development of several geologic structures for hydrocarbon accumulation within the basin. In this work, we use new, high-quality, three-dimensional (3D) seismic reflection data to investigate the occurrence of strike-slip faults within the Oligocene to Miocene lithological units of the basin. The dominant trend of the fault system (~n=44) is NE-SW direction, with faults in the SE and SW parts exhibiting sinistral strike-slip movement. These faults are characteristically evidenced by extensional horsetail splay faults, negative flower structures, and minor transfer faults. Importantly, the displacement profiles of these faults reveal complex segmentation, linkage, and mechanical interactions at different structural levels. Our research innovatively shows that during the Oligocene to Miocene period the basin experienced transtensional tectonics resulting in widening of the basin and development of large depocenters in the southern part of the study area. Subsequent sediment inflow from the Himalayan river system filled these depressions thereby making the Cenozoic units prolific for sediment accumulation.
... It is pertinent to mention here that Indian tectonic plate is continuously wedging into the Eurasian plates at a speed of 44 mm/year which is a large contributor of strain build-up. [2][3][4][5][6][7][8][9][10] Discussions Several researchers opined that Kopili Zone has been witness to high seismic activities in the recent past. Attenuation studies as well as micro earthquake studies also evinces this assertion. ...
... Attenuation studies as well as micro earthquake studies also evinces this assertion. [2][3][4][5][6] Additionally, major part of Assam is characterized by alluvium soils which make cities as well as locations more vulnerable to seismic waves. In the context of epicentral zone of this major event, Tezpur, India comes under direct impact of it. ...
... This poses as a major threat for seismic amplification. [3][4][5][6][7][8] Apart from this, resonance frequency estimates come in the range of 0.5 to 2.8 Hz which is further accompanied by larger amplification values in certain pockets. 10 All these increase vulnerabilities of major chunk of Tezpur and its surrounding region towards seismic risk. ...
The recent Assam Earthquake has been previewed in the context of the recent seismicity
pertaining to Kopili Fault of northeast India. Kopili fault of northeast India is known for its
active seismicity. The ground motion parameters in the context of peak ground acceleration,
peak ground velocity and peak spectral acceleration stand out for their implications.
Considering the strong magnitude of the event, there is imminent need for earthquake
resilient buildings as well as hazard mitigation strategies in order to tackle post-earthquake
scenarios.
... Several researchers opined that Kopili Zone has been witness to high seismic activities in the recent past. Attenuation studies as well as microearthquake studies also evinces this assertion [2][3][4][5][6]. Additionally, major part of Assam is characterized by alluvium soils which make cities as well as locations more vulnerable to seismic waves. ...
... Recent studies indicate that Tezpur and its neighbouring region are characterized by low velocity zones at certain points. This poses as a major threat for seismic amplification [3][4][5][6][7][8]. Apart from this, resonance frequency estimates come in the range of 0.5 to 2.8 Hz which is further accompanied by larger amplification values in certain pockets [10]. ...
... Kopili fault has been experiencing higher seismic and tectonic activity ([1], [2]) during the recent years. These kinds of active tectonics can be inspected by examining coda-wave attenuation and its dependence with frequency. ...
... This is also linked with the underlying geology. In order to further investigate this, we have found a noticeable evidence from [2], as they reported that as DMK is located on an alluvial plain, which generally traps seismic waves. As a result, the waves are attenuated. ...
Kopili fault has been experiencing higher seismic and tectonic activity ([1], [2]) during the recent years. These kinds of active tectonics can be inspected by examining coda-wave attenuation and its dependence with frequency. Here, we report spatial variation of coda attenuation of this region. The obtained results reveal that there is velocity anomaly at depth 210-220 km as there arises sharp changes in attenuation coefficient ({\gamma}) and frequency parameter (n) which are supported by available data reported by other researchers for this region.
We report new findings for producing broad-band ground motion time histories (1–19 Hz) of a future earthquake in a sedimentary basin based on the application of extended rupture modelling together with the use of empirical Green’s functions (EGFs). This technique is used to model a MW6.0 earthquake in Kopili fault zone (KFZ), north-eastern India (NER). We ran simulations for a sediment site (VS30 = 360–760 m/s) and a rock site (VS30 = 760–1500 m/s) to obtain the ground motions, which were then compared with a number of ground motion prediction equations (GMPEs). These GMPEs agree with the simulated ground motion amplitude, confirming that once we have precise source terms along with representative EGFs, the artificial ground motions generated from earthquake scenarios of a specific site may be employed for seismic design safety in that given site. This work may open the door to additional in-depth, site-specific research in this area.
The Upper Assam Basin is an intermontane foreland basin surrounded by gigantic mountain belts in NE India. The structural geometry of the basin is controlled by the tectonic interactions of the Himalayan orogenic belt in the north, Mishmi thrusts in the east, and the Assam-Arakan fold-and-thrust belts in the south. The basin has received significant attention not only because of its complex geological set-up but also due to its petroliferous nature for hosting significant hydrocarbon resources. The present study attempts to explore the tectonic subsidence history of the Cenozoic succession using subsurface stratigraphic details of ten (10) boreholes drilled within the upper shelf of the basin. Subsidence analysis is carried out using the backstripping technique. It is observed that the tectonic subsidence in the basin developed through four different stages. During the Paleocene-Eocene epoch, the basin witnessed slow subsidence. It increased gradually through Oligocene and attained rapid speed in the Miocene. Further, during the deposition of post-Miocene sediments (Plio-Pleistocene epoch), the tectonic subsidence in the basin remained accelerated. Subsidence curves obtained from the studied borehole depict a convex-upward profile, indicating that the basin attained a foreland configuration over time and is presently a SE dipping shelf bounded by opposite verging fold-and-thrust belts. Overall, the basin experienced tectonic subsidence of ∼2 km throughout its lifespan with an average subsidence rate of ∼30 m/Ma. This case study prominently elucidates the tectonic history of the basin, which underwent during the Cenozoic time. Our findings stress the importance of subsidence analysis through the backstripping technique as a potential approach for untangling the geohistory of sedimentary basins worldwide.
Attenuation study of a province is considered as a basic quantity for seismic hazard assessment. It has already been established that the study of two physical processes, namely the seismic sources and propagation of the waves, is essential for seismic-hazard mapping. Additionally, attenuation plays an important role towards scaling seismic hazard. Accordingly, a computational tool entitled CodaQback is presented. Based on back scattering model, this versatile software is equipped with user-friendly graphical user interface. It also allows quick picking of phases for computing coda attenuation parameter. All outputs after each execution step in CodaQback are efficiently exported step-wise into a separate folder in Excel and text formats. To validate the computing tool, it is tested in real data analysis and there is found to be good matching of computed values with already established ones. It is envisioned that this package will enable user to derive quick and reliable estimation of coda attenuation parameter irrespective of geological and geo-morphological units.
