Browsing by Author "J.P. Narayan"

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Analysis of local seismic events and inferred P* velocity near Koyna Dam, Maharashtra, India
(1995) A. Ram; R. Juneja; J.P. Narayan
Koyna region in Maharashtra, India got its place in the seismicity map of the world when a major shock occurred in this area on December 10, 1967. The seismic tremors were being monitored in this region with the seismological network operated by Central Water Power research Station (CWPRS), Poona since 1963. Four local seismological stations i.e. Koyna (KN), Satara (STA), Mahabaleshwar (MAH) and Poona (POO) were used as an array keeping KNI as crossover point. About 200 local events, which have occurred in this region and were recorded during the period 1967-1973, have been processed and analyzed using a least squares technique.
Application of acoustic wave solution for the analysis of reverberation
(1994) J.P. Narayan; A. Ram
Finite difference method offers a versatile approach to numerical computation of synthetic seismograms for a given subsurface complex geological model. Numerical solution for the acoustic wave has been derived using the Lax-Wendroff scheme for an inhomogeneous medium and implemented for the modelling of localized areas in the offshore region. The analysis of numerical seismograms indicates that the energy radiating from a point source and remaining completely within a water layer may not cause singing, whereas the energy reflected from the deeper horizons is responsible for the singing effect on the reflections. -from Authors
Optimum inverse filtering of seismic signatures
(1995) A. Ram; J.P. Narayan
Inverse filters have been employed in the past to obtain the desired results from overlapping and contaminated input seismic data. The filter described in this paper acts in an error distribution sense and is known as an 'error-free' filter. It has been reported by various scientists that the deconvolution of wavelets whose poles lie on the unit circle arouses stability problem. Transformation of wavelet (1, 2, 1) into a spike whose poles lie on the unit circle has been done in the presence and absence of white noise. The result demonstrates that the filter is stable for such a type of wavelets. It has been found that filtering in the presence of noise causes rapid decrease of error spikes, the amplitude of the filter weights and finally the length of the filter.
Simulation of geological structure using the SH-wave solution
(1998) J.P. Narayan; Avadh Ram
Spatial derivative of elastic parameters causes error in the reflection and transmission coefficients in the heterogeneous finite difference formulation due to smoothing over one grid spacing at the interfaces. The first order hyperbolic equation, free from spatial derivative of elastic parameters and divergence, has been solved for SH-wave using the Lax-Wendroff scheme for an inhomogeneous medium. The scheme allows course sampling and fast fluctuations in medium parameters and also behaves well at the discontinuities of elastic parameters. The present work has concentrated on the numerical solution and computational procedure for the SH-wave simulation. A relevant computer program package has been developed and implemented for the modelling of cross-well geometry and hard rock terrain overlain by a weathered layer.
Simulation of the hydrocarbon structures using the P-SV wave solution
(Birkhäuser-Verlag, 1995) Avadh Ram; J.P. Narayan
Numerical solution of the scalar and elastic wave equations has greatly aided geophysicists in modeling seismic wave fields in the complicated geologic structures containing hydrocarbons and hence increases the geologic interpretation. Finite-difference method offers a versatile approach to compute synthetic seismograms numerically for given subsurface complex geological structures. To avoid the spatial derivative of the elastic parameters and density, elastodynamic equation (first-order hyperbolic equation) has been solved using the Lax-Wendroff scheme. A numerical finite-difference modeling program has been developed for the P-SV wave using the above solution. A line source with a time delay of 0.015s and dominant frequency of 120 Hz has been utilized in the simulation. In order to avoid the large values of the displacement vector in the source region, Alterman and Karal's method (1968) has been utilized. Horizontal and vertical component synthetic seismograms have been computed for two different geological models with and without oil and gas bearing zones. It has been concluded from the response that a finite-difference technique not only yields the relative arrival times but also accounts for the variation in amplitude and phase according to the elastic impedance contrast across the interfaces. It should come as no surprise to learn that in spite of the limitation of this numerical method, the scheme has provided a valid response for the thin layer, high acoustic impedance contrast and the pinch out. © 1995 Birkhäuser Verlag.
Synthetic seismograms for a layered earth geological model using the absorption and dispersion phenomena
(Birkhauser Verlag AG, 1997) Avadh Ram; J.P. Narayan
An algorithm has been developed to compute the dispersive and dissipative seismic response using FUTTERMAN'S (1962) third attenuation-dispersion relationship. In the computation, frequency-dependent velocity and quality factor Q have been used but in the case of the nondispersive synthetic seismogram, frequency-independent velocity has been used. The model's parameters are density, phase velocity, quality factors and thicknesses of the layers. Dispersive and nondispersive synthetic seismograms have been computed with and without absorption for a layered earth geological model. Fast Fourier transform (FFT) technique has been adopted for converting the frequency domain response into the time domain. The frequency spacing, Δf= 0.976 Hz, has been considered to avoid the aliasing effect. The results have revealed changes in the reflected waveforms in the frequency domain as well as in the time domain for absorption and dispersion cases. It is also concluded that dispersion reduces the arrival time and this effect is increasing with the travel time. The effect of constant Q on the seismic response has also been studied.