Structural information derived from ambient noise tomography over a hydrocarbon‐producing region in the Cachar fold belt, lower Assam, northeast India

Shekar, Bharath; Gurusamy, Mohan; Singh, Sunil Kumar

doi:10.1111/1365-2478.13289

Cited by 5 publications

(5 citation statements)

References 71 publications

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“…4b) reveals variation in the subsurface topography that correlates well with the gentle surface topography of the Cachar fold belt. Ambient noise tomography (Shekar et al, 2023) using the current seismic network also revealed near surface (≤ 2km) structures beneath the Cachar fold belt that correlate with the observed subsurface deformation pattern. The geometry of the Balakandi and Silchar synclines and the Ramphan anticline are well delineated beneath the pro le A-A'.…”

Section: Vertical Sectionsmentioning

confidence: 56%

Local earthquake tomography of the Cachar fold and thrust belt in lower Assam, Northeast India

Singh

Gurusamy

Shekar

et al. 2023

Preprint

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Local earthquake tomography was performed to image the subsurface structure beneath the seismically active Cachar fold and thrust belt in lower Assam, northeast India. A total of 3341 P phases and 1833 S phases corresponding to 180 local microearthquakes recorded over 11 months by a temporary, dense network of 76 stations were used to simultaneously locate the hypocenters and estimate the velocity structure in three dimensions. The entire crust till a depth of ≈ 40km is seismically active with about 70% of the microearthquakes occurring in the upper crust. The velocity tomograms were well resolved up to a depth of 10km and reveal strong lateral heterogeneity in the shallow upper crust in terms of alternating patterns of high and low velocity anomalies that correlate with the NE-SW trending en-echelon pattern of the Cachar fold belt. The velocity perturbations upto ± 10% are observed in the shallow subsurface (< 5km) beyond which they are within ± 5% and reduce to within ± 2% at a depth of 10 km. The vertical sections of P wave velocity reveal deformation of the sediments leading to shallow subsurface structural highs and lows that correlate with the surface topography. About 50% of the observed seismicity occurs within the sediments at shallow depths(≤ 5km) revealing faulting due to the compressional tectonics in northeast India. The present study provides seismological evidence of deformation of the shallow sediments accompanied by faulting leading to the observed seismicity consistent with thin skinned tectonics for the evolution of the Cachar fold belt.

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Section: Vertical Sectionsmentioning

confidence: 56%

Local earthquake tomography of the Cachar fold and thrust belt in lower Assam, Northeast India

Singh

Gurusamy

Shekar

et al. 2023

Preprint

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“…Surface wave group velocity maps produced by ray-based methods (e.g. Shekar et al 2022) can be used to characterize Earth structure in our source inversion scheme. More generally, such maps can be used as starting structure models in a future joint source-structure acoustic inversion scheme, which may serve to refine traditional ambient noise tomographic models.…”

Section: Discussionmentioning

confidence: 99%

Acoustic full waveform inversion for 2-D ambient noise source imaging

Datta¹,

Shekar²,

Kumar³

2023

Preprint

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We present a method for estimating seismic ambient noise sources, by acoustic full waveform inversion of interstation cross-correlations. The method is valid at local scales for laterally heterogeneous media, and ambient noise sources confined to the Earth's surface. Synthetic tests performed using an actual field array geometry, are used to illustrate three unique aspects of our work. First: the method is able to recover noise sources of arbitrary spatial distribution, both within and outside the receiver array, with high fidelity. This holds true for complex velocity models and does not require a good initial guess for inversion, thereby bridging a clear gap in the existing research literature. Second: we analyse the extent of biases in source inversion, that arise due to inaccurate velocity models. Our findings indicate that source inversion using simplified (e.g. homogeneous) velocity models may work reliably when lateral variations in velocity structure are limited to 5 or 10\% in magnitude, but is vitiated by strong variations of 20\% or higher. Finally, our technique is implemented without the adjoint method, which is usually inextricably linked to full waveform inversion. Inversions are performed using source kernels computed for each receiver pair, and this approach is computationally tractable for real-world problems with small aperture seismic arrays.

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“…Surface wave group velocity maps produced by ray-based methods (e.g. Shekar et al 2023) can be used to characterize Earth structure in our source inversion scheme. More generally, such maps can be used as starting structure models in a future joint source-structure acoustic inversion scheme, which may serve to refine traditional ambient noise tomographic models.…”

Section: Discussionmentioning

confidence: 99%

Acoustic full waveform inversion for 2-D ambient noise source imaging

Datta

Shekar

Kumar

2023

Geophysical Journal International

Self Cite

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Summary We present a method for estimating seismic ambient noise sources by acoustic full waveform inversion of interstation cross-correlations. The method is valid at local scales for laterally heterogeneous media, and ambient noise sources confined to the Earth’s surface. Synthetic tests performed using an actual field array geometry, are used to illustrate three unique aspects of our work. First: the method is able to recover noise sources of arbitrary spatial distribution, both within and outside the receiver array, with high fidelity. This holds true for complex velocity models and does not require a good initial guess for inversion, thereby addressing an outstanding issue in the existing research literature. Second: we analyse the extent of biases in source inversion that arise due to inaccurate velocity models. Our findings indicate that source inversion using simplified (e.g. homogeneous) velocity models may work reliably when lateral variations in velocity structure are limited to 5 or 10% in magnitude, but is vitiated by strong variations of 20% or higher, wherein the effect of strong scattering and/or phase distortions become significant. Finally, our technique is implemented without the adjoint method, which is usually inextricably linked to full waveform inversion. Inversions are performed using source kernels computed for each receiver pair, and this approach is computationally tractable for real-world problems with small aperture seismic arrays.

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Structural information derived from ambient noise tomography over a hydrocarbon‐producing region in the Cachar fold belt, lower Assam, northeast India

Cited by 5 publications

References 71 publications

Local earthquake tomography of the Cachar fold and thrust belt in lower Assam, Northeast India

Local earthquake tomography of the Cachar fold and thrust belt in lower Assam, Northeast India

Acoustic full waveform inversion for 2-D ambient noise source imaging

Acoustic full waveform inversion for 2-D ambient noise source imaging

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