A B C D E F G H I J K L M N O P Q R S T U V W X Y Z All
Lal, Babu
- Geophysics in Town Planning - A Case Study
Authors
1 Geophysics Division, Geological Survey of India, Jaipur - 302 004, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 43, No 1 (1994), Pagination: 67-73Abstract
Geophysical surveys as aid to urban evaluation in the Vidyadhar Nagar area adjacent to Jaipur city, Rajasthan, have been conducted. DC resistivity surveys over area covered by sand and dunes indicated the presence of a moderately thick surface layer underlain by a potable aquifer zone of substantial thickness over quartzite bedrock of even topography deepening towards southwest. The results of the magnetic survey show, in general, normal structural behaviour barring a high in the southwest part of the area. The high is explained as due to an intrusive feature at a considerable depth, hence inconsequential for town planning. Subsequently, Jaipur Development Authority has undertaken construction of urban complex with a high rise structure in the area. The paper presents the geophysical results along with chemical analysis of ground water and computer studies. The soundings reveal the suitability of the area for urbanisation, considering the presence of moderately thick surface horizon underlain by a promising aquifer formed over the quartzite bedrock of even topography and disposition. The order of the resistivity obtained and the chemical composition of ground water show the ground water to be of good quality for drinking purpose.Keywords
Geophysics, Hydrology, Groundwater, Jaipur, Rajasthan.- Seismic Survey for Delineation of Shallow Structures in the 2001 Earthquake-Affected Areas of Anjar and Bhuj, Gujarat
Authors
1 Geological Survey of India, Western Region, Jaipur - 302004, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 70, No 5 (2007), Pagination: 824-828Abstract
Shallow seismic refraction survey (Hammer source) was carried out by Geological Survey of India in Kutch distinct Gujarat after the devastating i e earthquake of 26thJanuary 2001. The aim of the investigation was to delineate different lithological units based on their P-wave velocities In earthquake-Affected areas of Anjar and Bhuj. The seismic survey camed out over 17 locations in township areas of Anjar and Bhuj has reflected two to three layer structures. In both areas, the P-wave velocity of first layer vanes from 476 m/s 1067 m/s while the velocity of second layer vanes from 1091 m/s to 1892 m/s. The third layer exhibits the velocity ranging from 1818 m/s to 4865 m/s. The first layer corresponds to loose soil, second layer to compact soil/weathered rock and third layer to weathered/bedrock.The depths given by two boreholes drilled in both areas of study are in excellent agreement with those obtained by seismic survey conducted at borehole locations. This lends additional credence to geophysical results obtained in the area. According to layer parameters deduced from shallow seismic survey, the foundation of houses in earthquake affected areas should be below first interface/or in second layer i e compact soil/weathered rock to be safer.
Keywords
Seismic Surveys, Shallow Structures, Layer Parameters, Anjar And Bhuj, Gujarat.- Observations on VMF Diurnal Inversion as Earthquake Precursor in Northeast Region of the Indian Plate
Authors
1 Geological Survey of India, 15-16 Jhalana Doongn, Jaipur - 302 004, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 70, No 6 (2007), Pagination: 987-992Abstract
A characteristic inversion in normal 'v'shape Vertical Magnetic Field(VMF) diurnal curve appears to be a good earthquake precursor on a tectonic region has been discussed elaborately along with field observations in western part of the Indian plate(Babu Lal, 2002). As stated, inception of excess stress energy on rock formation inside earth (the source of quake) simultaneously produces seismomagnetic field. This increases internal component of geomagnetic field, which results inversion in VMF diurnal variation. Magnitude of diurnal inversion increases Day-by-Day until on exceeding the threshold limit of rock strain, stress energy is released through weak geological structure of the region in form of earthquake event/tremor VMF diurnal precursory characters were also obtained in the northeast region of the Indian plate.Twelve VMF diurnal observations were taken time to time in connection with ground geophysical investigations during 1996-97 on Meghalaya Plateau of northeast region in India All the twelve observed VMF diurnal were analyzed for precursory character m view of the earthquake shock expenenced in field on 17-2-1996 and 8-5-1997 subsequent to the occurrence of inversion of Nongshram diumal of 12-2-1996 and Muktapur diurnal of 6-5-1997 respectively. The occurrence of VMF diumal inversion showing magnitude about 10-15 gamma is found with subsequent earthquake event in the region within a week time Further results show that the distance between epicenter and diurnal station is large in cases of longer wavelength of inversion curve of VMF diumal. The occurrence of mirror image inversion curve for long wavelength of about 60 hours (between 0900 and 1500hrs) and magnitude 55 gamma in Nongshram diumal dated 17-1-1996 is followed with an earthquake event on 18-1-1996 in the Molasses zone of India-Burma plate at distance about 350 km away Similarly VMF diumal inversion curve with shorter wavelength, the distance between epicenter and diumal station iS smaller Muktapur diumal inversion on 6-5-1997 for short wavelength about 3 0 hours (between 1000 to 1300 hrs) and magnitude 10 gamma is followed by an earthquake event on 8-5-1997 near Sylhet in Bangladesh at a distance of about 40 km from Muktapur diumal station.
Keywords
VMF Diumal Inversion, Earthquake Precursors, Meghalaya, NE India.- Vertical Magnetic Field Diurnal as a Precursor to Earthquakes with Field Study in Parts of Western India
Authors
1 Geophysics Division, Geological Survey of India, 15-16, Jhalana Doongri, Western Region, Jaipur - 302 004, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 60, No 4 (2002), Pagination: 455-463Abstract
Vertical magnetic field (VMF) component of geomagnetic diurnal variation governed by the ratio of internal and external fields exhibits a 'V' shaped curve with minimum amplitude of about -30 gamma around 1200 hrs in the low latitude regions of the Earth on a solar quiet-day. This normal shape is signified by its phase inversion during stress accumulation and, in contrast, by phase amplification on sudden release of energy, corresponding to the development and loss of rock seismomagnetic field, resulting in a magnetic event of increase and decrease of the internal field. The normal diurnal reversion occurs in a stabilized strain condition. This characteristic feature of VMF diurnal phase inversion may serve as a precursor to tectonism and help in forecasting earthquake occurrences by a few days in advance.Field studies carried out in parts of Western India in the area between latitudes 20°30" and 28°00"N during the years 1991 to 1995 show that VMF diurnal phase inversion attaining positive amplitude is invariably followed by earthquake occurrences within a few days in the region. These earthquakes are located in vicinity of the contact zone of Indian- Eurasian tectonic plates, Aravalli range, Delhi-Haridwar ridge and Western Ghat fault zone. Persistent prevalence of the diurnal phase fluctuation related to inversion-amplification-normal suggests that Western India is under strain due to tectonic forces acting upon it and, on exceeding the threshold limit of rocks, the stress energy is being released from time to time through geologically weak zones in form of tremorslearthquakes.