Browsing by Author "Avadh Ram"

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A correlation integral approach to the study of 26 January 2001 Bhuj earthquake, Gujarat, India
(2006) P.N.S. Roy; Avadh Ram
The 26 January 2001 earthquake (ML = 6.9) of Bhuj, Gujarat, India was one of the major natural calamities in recent time for intraplate regions. The spatial distribution of correlation fractal dimension and generalized fractal dimension obtained with the correlation integral approach using 3 years of events (ML ≥ 4) including fifteen foreshocks, mainshock and 155 aftershocks was divided into six consecutive windows to see its temporal variation. The results have revealed that the spatial distribution of correlation fractal dimension and generalized fractal dimension vary in an approximate oscillating pattern in the range 0.90-2. Thus, it may be concluded that the possibility of presence of asperity/barrier is the controlling factor of the level of stress/seismicity or clustering pattern of aftershocks in the region. The Dq spectrum obtained for all the six time windows show a monofractal nature and not a multifractal pattern of the events, which is in a clustered manner for the region. This finding also supports the predominance of an asperity/ barrier model for such a high energy release along the active fault for intraplate regions without heterogeneity in fractal structure or cluster within cluster. © 2005 Elsevier Ltd. All rights reserved.
A study of the vertical magnetic anomaly caused by magnetite deposits in Sua area of Palamau district, Bihar (India)
(Birkhäuser-Verlag, 1971) C.L. Singh; Avadh Ram
A magnetic survey carried out in Sua area of the Palamau district, Bihar (India) has shown very interesting anomalies. The survey has been conducted specially to obtain the extension of the magnetite deposits which are being quarried at Sua. The interpretation of magnetic anomalies have clearly brought out the following facts: a) the magnetite is extending both sides of the quarry to a considerable distance, b) the nature of the anomaly indicates that the magnetite occurs in the form of veins. It has also been possible to find out the thickness of the veins and the depth at which they occur. © 1971 Birkhäuser Verlag.
Analysis of earthquakes in the distance range 40-70° and inferred lower mantle structure
(1982) Avadh Ram
About fifty earthquakes in the distance range 40-70° and azimuthal range 45-120° from the Celebes, Philippines, Mariana and Kurile Island regions, and recorded at Gauribidanur seismic array in southern India, were used in the present study. Measurements on slowness and apparent azimuths were made on the first 30 s of the short period P-wave trains using an adaptive processing technique. Analysis of this data set has revealed no strong evidence for any triplications in the travel-time curve over the ranges in question. The P-wave velocity increases continuously with an almost uniform gradient below 1000 km depth range and is in very close agreement with the JB model. Almost all the observed slowness values of the events were anomalously low and consistent suggesting that they are caused by some azimuthal dependent structure near the array. © 1982.
Apparent velocity and azimuths of short period P-Waves recorded at indian WWSSN stations network
(1984) Avadh Ram; K.N.S. Yadav
Over 200 earthquakes in the distance range 30°-90° and azimuthal range 0°-360°, recorded at Indian WWSSN stations, have been used in the present study. We have treated the four WWSSN recording stations i.e. New Delhi, Poona, Shillong and Kodai-Kanal, as Super Large Aperture Seismic Array (SLASA) Network with New Delhi being its cross-over point. Short period P-wave data as obtained from these stations have been analysed using a least square technique. Slowness and azimuthal anomalies have been computed for all these events. Relative time residuals have also been calculated. A velocity model has been derived on the basis of the slowness and travel-time data. The results do not indicate presence of any triplication in the travel-time curve. Variations in the relative residuals refer to the tectonic features beneath the recording stations. The P-wave velocity increases continuously in the lower mantle region and there is no indication for the presence of any appreciable velocity gradient. © 1984.
Body-wave wave-form modelling and source parameters for the indochina border earthquakes
(Birkhauser Verlag AG, 1996) Imtiyaz A. Parvez; Avadh Ram
Wave-form modelling of body waves has been done to study the seismic source parameters of three earthquakes which occurred on October 21, 1964 (Mb,-5.9), September 26, 1966 (Mb = 5.8) and March 14, 1967 (Mb = 5.8). These events occurred in the Indochina border region where a low-angle thrust fault accommodates motion between the underthrusting Indian plate and overlying Himalaya. The focal depths of all these earthquakes are between 12-37 km. The total range in dip for the three events is 5°-20°. The T axes are NE-SW directed whereas the strikes of the northward dipping nodal planes are generally parallel to the local structural trend. The total source durations have been found to vary between 5-6 seconds. The average values of seismic moment, fault radius and dislocation are 1.0-11.0 × 1025 dyne-cm, 7.7-8.4 km and 9.4-47.4 cm, respectively whereas stress drop, apparent stress and strain energy are found to be 16-76 bars, 8.2-37.9 bars and 0.1 - 1.7 × 1021 ergs, respectively. These earthquakes possibly resulted due to the tension caused by the bending of the lithospheric plate into a region of former subduction which is now a zone of thrusting and crustal shortening.
Broach (Gujarat) earthquake of March 23, 1970
(Birkhäuser-Verlag, 1972) Avadh Ram
An analysis of the seismicity of Broach region, Gujarat (India) has been made. The activity of the network of faults present in this region, perhaps, has been responsible for the present earthquake. Earthquake energy, magnitude and focal depth are connected by a single equation. An empirical relation for focal depth and magnitude has been derived for the area. © 1972 Birkhäuser Verlag.
Complex seismic signatures and narrow azimuthal study of Hindukush earthquakes
(Springer India, 1981) Avadh Ram
About eighty earthquakes, exclusively from the Hindukush region, which were recorded at Gauribidanur seismic array (GBA) have been used in the present study. Short period P-wave recordings upto 36 seconds were processed using adaptive cross-correlation filtering technique. The main objective of this exercise was to examine the signal complexities and seismic ray direction anomalies of these earthquakes which have identical epicentral distances and a narrow azimuthal range from GBA but different focal depths from 10 to 240 km. Slowness anomalies of the order of 1-4 sec/deg and azimuthal anomalies upto 6° have been found in this case. These deviations have been attributed to the upper mantle region between source and the receiver. Analysis of the data reveals that most of the events occurring at shallower depths had complex signatures as compared to the deeper events. The structure near the source region, complicated source functions and scattering confined to the crust-upper mantle near source are mainly responsible for complexity of the observed signals as the transmission path of the ray tubes from turning point to the recording stations is practically the same. © 1981 Indian Academy of Sciences.
Computation of synthetic seismograms for plane layered earth models including absorption and dispersion phenomena
(Springer India, 1986) K.N.S. Yadav; Avadh Ram
A computer program package has been written in FORTRAN-IV language and tested successfully on an ICL 1904S computer. This program enables one to compute synthetic seismograms for layered earth models. The provision for studying the effect of absorption and dispersion of seismic waves has been made with Subroutines. The present program utilizes eight Subroutines and requires about 35 K core memory. A set of examples are illustrated for absorption and dispersion models. An exponential decay of amplitude has been used for the absorption model. This method is based on the plane wave propagation in a flat-layered earth system. Normal incident P-waves are used to eliminate the effect of other phases. Change in shape of reflected waves is observed in absorption model due to damping of energy of higher frequencies. Lack of resolution is found between closely spaced reflections at higher frequencies. The effect of dispersion on seismic waves decreases the time of primary reflections as well as amplitudes of the seismic waves. © 1986 Indian Academy of Sciences.
Elastic-wave scattering in a random medium characterized by the Von Karman correlation function and small-scale inhomogeneities in the lithosphere
(Oxford University Press, 1997) Jayant N. Tripathi; Avadh Ram
A Gaussian correlation function characterizes smoothly heterogeneous media, while real heterogeneities in the Earth are often non-Gaussian in nature. Using the Born approximation, mean square amplitudes of the scattered waves have been derived for an elastic media characterized by the Von Karman correlation function. Heterogeneities with different power laws can be defined by the Von Karman correlation function. The sensitivity of fore- and backscattering to heterogeneities with different scales and properties (that is velocity and impedance) is discussed in this paper. The analytical expression for total scattered energy for the incident P waves is also derived for a random medium having the Von Karman correlation function. We find that at high frequencies, the scattered power of converted waves is a function of frequency. In the case of codawave excitation by local earthquakes, which must be handled by the full elastic-wave theory, we can define any type of inhomogeneity by the Von Karman correlation function. It also supports the idea that the lithosphere might have multiple-scale inhomogeneities.
Estimation of hard rock aquifers hydraulic conductivity from geoelectrical measurements: A theoretical development with field application
(2008) Subash Chandra; Shakeel Ahmed; Avadh Ram; Benoit Dewandel
Based on the analogy between Darcy's law for groundwater flow and Ohm's law for electric current flow, a methodology has been developed to estimate the hydraulic conductivity and transmissivity of hard rock granite aquifer from geoelectrical parameters. The common parameter, aquifer thickness (t), has been used to combine the two relations and form an analytical equation. Mathematical relation shows a negative correlation between hydraulic conductivity and aquifer resistivity, and a positive correlation between transmissivity and longitudinal conductance. The methodology has been calibrated and validated in hard rock granite aquifers in India. The good agreement between aquifer hydraulic conductivity (K) and transmissivity (T) obtained from the resistivity sounding parameters and those obtained from pumping test analysis proves the potentiality of the methodology. It has been applied to estimate the K and T from the surface electrical resistivity parameters and results were utilized to prepare the K and T maps of Maheshwaram watershed in hard rock terrain in India. © 2008 Elsevier B.V. All rights reserved.
Estimation of velocity perturbations using amplitude and phase fluctuations for earthquakes recorded at Gauribidanur Seismic Array in southern India
(1996) Jayant N. Tripathi; Avadh Ram
The Chernov medium approach has been applied for analysie of 24 earthquakes recorded at Gauribidanur Seismic Array (GBA) in southern India. Correlation coefficients of log-amplitude and phase fluctuations between every possible pair of seismometers are used to determine the correlation length of the medium. The Chernov theory can be well applied for the observed P-wave velocity perturbations at 0.5 Hz. Thus, the average correlation length for the Gaussian correlation function is determined to be about 18 km. The estimated velocity perturbations for GBA are around 1.4 % - 2.3 %, which is slightly greater than the corresponding estimates by previous workers for the array while the extension of the medium is around 660 km. The scattering coefficient under GBA at 0.5 Hz is 9.0 - 22.7 × 10-4 km-1. The Born approximation condition is violated for frequencies higher than 0.5 Hz due to the strong scattering coefficient for the region under GBA.
Evidence for upper mantle heterogeneity around 650 km depth beneath the Indian subcontinent
(1980) Avadh Ram; Lalaji Yadav
Results of seismic ray direction anomalies as obtained from eighty earthquakes, occurring exclusively in the Hindukush focal region are reported. These earthquakes, which were recorded at Gauribidanur seismic array (GBA) in southern India, have identical epicentral distances and a narrow azimuthal range but varying focal depths from 10 to 240 km. Short-period P-wave recordings (up to 30 sec) of these events were processed using an adaptive cross-correlation filtering technique. Slowness anomalies of the order of 1.4 sec/ degr. and azimuthal anomalies of up to 6° have been found in this case. These deviations have been attributed to the upper mantle region. The results confirm the presence of lateral heterogeneities in the 400–750 km depth range beneath the Indian subcontinent where the seismic rays have bottommed. © 1980, All rights reserved.
Focal-mechanism solutions of earthquakes and tectonics of the hindukush region
(1984) Avadh Ram; Lalaji Yadav
Seventeen focal-mechanism solutions have been obtained for earthquakes occurring in the Hindukush region using P-wave first motion directions observed from short as well as long period records. These solutions have indicated a thrust type of faulting. Some of the solutions show small components of strike slip motions. The trend of nodal planes in these solutions was found to vary between northeast and southeast directions. The dip of the compressional axes rarely exceeds 25°. Orientation of tensional axes was found to be almost vertical in all cases. These findings together with the spatial distribution of earthquakes in the Hindukush region suggested that earthquakes were caused by down-dip extension within a sinking slab. © 1984.
Fractal dimensions of blocks using a box-counting technique for the 2001 Bhuj earthquake, Gujarat, India
(2005) Avadh Ram; P.N.S. Roy
Several destructive earthquakes have occurred in the Kachchh region of Gujarat during the past two centuries, among them Allah Bund earthquake (M7.8) in 1819, Anjar earthquake (M6) in 1956 and the recent Bhuj earthquake (M7.6) in 2001. The Anjar earthquake was on KMF (Kachchh Mainland Fault) and the recent Bhuj events were caused by a hidden fault north of KMF. The present study discusses the fractal analysis of tectonics governing seismic activity in the region. The region has been divided into five blocks and the fractal dimension of each block has been calculated using the box-counting technique. The results show significantly low value of fractal dimension of the Kachchh rift block consisting of the KMF compared to the other surrounding blocks, which also contain faults and rifts of higher fractal dimension. This indicates that the cause of earthquakes in this block may be asperities and barriers. However, the predominance of aftershocks over foreshocks signifies that barriers may be the main cause. The other results, such as the lower value of dimension of fault clustering show that the Kachchh rift block has faults which are distributed in a clustered manner. In this context, the seismicity of this block seems to be high. © Birkhäuser Verlag, Basel, 2005.
Interpretation of vertical magnetic anomalies due to inclined veins striking neither north nor east
(Birkhäuser-Verlag, 1971) Avadh Ram; H.S. Rathor
In the present paper an attempt has been made to interpret irregular vertical magnetic anomalies due to magnetite ore in the form of inclined thin veins, pods or lenses striking neither north nor east. A chart has been prepared for varying percentage of magnetite ore using arbitrary values of susceptibility contrast for Singhbhum and Palamau districts (Bihar), which would be helpful while interpreting magnetic anomalies to be found in these areas. Depth to width ratio against parameter c as well as two theoretical curves have also been presented. Further two field profiles are being matched with theoretical curves. The depths and widths of thin veins have been calculated using simple rules. An overall checking of these quantities is possible by curve-matching process. © 1971 Birkhäuser Verlag.
Nature of P-wave signals from Hindukush earthquakes
(1995) Avadh Ram; Jayant N. Tripathi; L. Yadav
Several causes for complexity of P-wave signals from earthquakes in the Hindukush focal region and recorded at Gauribidanur seismic array in southern India, have been investigated. Visual inspection of the records of these earthquakes revealed that most of the events occurring at shallow depths had complex signatures as compared to the deeper events. A positive correlation of complexity with magnitude is found. Spectral ratio measurements have demonstrated that complex signals are richer in low frequency energy. A number of theoretical seismograms for short period P-waves were computed and the analysis reveals that within certain constraints, complexity increases with focal fault area and decreases with focal depth. The structure of the fault rock in the source region, the source functions itself, and the ray-scattering in the crust-upper mantle near the source are the main responsibilities for the complexity of the Hindukush earthquake records at GBA since the transmission of the ray-tubes for all events studied is practically identical, with the exception of the very first near source part. © 1994.
On frequency magnitude and energy of significant Indian earthquakes
(Birkhäuser-Verlag, 1970) Avadh Ram; H.S. Rathor
Frequency, magnitude and energy of Indian earthquakes with magnitude greater than 5 has been studied. The Indian regions can be divided into three main seismically active regions, viz. 1. Delhi and Himalayan region, 2. Assam region and 3. Koyana region which includes southwest India. The relations between frequency-magnitude and energy-magnitude of earthquakes are shown in Fig. 3 and 4 respectively. Further a relationship, log N=p+q log E type has been established for frequency and energy of Indian earthquakes and the values of constants p and q have been determined for all the three seismic regions. The results thus obtained are good and satisfactory. © 1970 Birkhäuser Verlag.
On the seismic structure of Indian upper-mantle regions
(1982) Avadh Ram; Om Prakash Singh
Several velocity models on upper mantle regions of the world have been postulated during the last two decades. There has been a broad agreement amongst seismologists that upper mantle has got two transition zones, though the models differ in detail. These zones have been found to occur around '400 km' and '650 km' depth ranges with varying thicknesses of the zones. A limited number of such studies have been made on the upper mantle structure of the Indian subcontinent. High positive velocity gradients were reported to exist around the above depth range. Evidence for lateral heterogeneities has also been found. We address some problems like refinement of Indian upper mantle velocity models specially after considering the effect of scattering and attenuation on the short period P-waves. The study of proper positioning of the cusps of the travel-time branches and their extension is essential as well. In our opinion, analysis of such problems would help in the better understanding of the nature of propagation of seismic waves and mechanism of earthquakes. Complexity of seismic signatures observed is another major problem and may also be taken into consideration. © 1982 Indian Academy of Sciences.
Probabilistic assessment of earthquake hazards in the Indian subcontinent
(Birkhauser Verlag AG, 1999) Imtiyaz A. Parvez; Avadh Ram
The Indian subcontinent is one of the most seismic prone areas of the world. The Himalayan mountains in the north, mid-oceanic ridges in the south and earthquake belts surrounding the Indian plate all show that the subcontinent has undergone extensive geological and tectonic processes in the past. The probability of the occurrence of earthquakes with magnitude 6 < M(b) < 7 during a specified interval of time has been estimated on the basis of four probabilistic models namely Lognormal, Weibull, Gamma and Exponential distribution for the Indian subcontinent. The seismicity map has been prepared using the earthquake catalogue from the period 1963-1994, and six different zones have been identified on the basis of clustering of events. The model parameters have been estimated by the method of maximum likelihood estimates (MLE) and method of moments (MOM). A computer program package has been developed for all four models, which represents the distributions of time intervals fairly well. The logarithmic of likelihood (1n L) is estimated for testing the models and different models have been found to be plausible. The probability of different magnitude thresholds has been evaluated using the Gutenberg-Richter formula Log N = a - bM for magnitude distribution. The constants a and b have been computed for each region and found to be varying between 5.46-8.53 and 0.87-1.34, respectively.
Probabilistic assessment of earthquake hazards in the North-East Indian peninsula and Hindukush regions
(Birkhauser Verlag AG, 1997) Imtiyaz A. Parvez; Avadh Ram
The Himalayan region is one of the most seismic prone areas of the world. The North-East (NE) Indian peninsula and the Hindukush regions mark the zone of collision of the Indian and Eurasian plates. The probability of the occurrence of great earthquakes with magnitude greater than 7-0 during a specified interval of time has been estimated on the basis of four probabilistic models, namely, Weibull, Gamma, Lognormal and Exponential for the NE Indian peninsula and Hindukush regions. The model parameters have been estimated by the method of Maximum Likelihood Estimates (MLE) and the Method of Moments (MOM). The cumulative probability is estimated for a period of 40 years from 1964 and is ranging between 0.881 to 0.995 by the year 1995. using all four models for the NE Indian peninsula. The conditional probability is also estimated and it is concluded that the NE Indian peninsula would expect a great earthquake at any time in the remaining years of the present century. For the Hindukush region, the cumulative probability has already crossed its highest value, but no earthquake of magnitude greater than 7.0 has occurred after 1974 in this area. It may attribute to the occurrence of frequent shocks of moderate size, as seventeen earthquakes of magnitude greater than 6.0, including four greater than 6.4, have been reported until 1994 from this region.