Please use this identifier to cite or link to this item: http://localhost:8081/xmlui/handle/123456789/739
Title: ON SEISMOLOGICAL INVESTIGATIONS OF THE KUMAON HIMALAYA USING LOCAL EARTHQUAKE DATA
Authors: Sarkar, Irene
Keywords: SEISMOLOGICAL;KUMAON HIMALAYA;EARTHQUAKE DATA;EARTH SCIENCE
Issue Date: 1983
Abstract: Microearthquake investigations have been carried out in the Kumaon Himalaya in the hope tiiat they would provide information not obtainable from the existing network of seismograph stations at regional and teleseismic distances. The results of analyzing data recorded during three separate spells are provided. During the first spell, the largest dimension of the array was 90.77 Km while during the next two spells an array with the largest dimension of M+.03 Km was operated in the north western corner of the earlier array. The smaller array was comprised of stations located in the valleys of the Yamuna and Bhagirathi rivers in the vicinity of the Main Central Thrust. One station was located further east of the Bhagirathi valley. P and S wave arrival times were read to determine hypocentral parameter estimates of 252 microearthquakes. The sense of first P motion was examined in all these cases but only US readings were considered adequately reliable to be used in the composite focal mechanism solutions. A computer program was developed to determine hypocentral parameter estimates using the least square error criterion. Notable features of the program include: (a) use of penalty functions to incorporate inequality constraints (b) use of the non-linear optimization procedure based on the Newton - Raphson technique in conjunction with tile sequential unconstrained optimization technique of Fiacco and McCormick ( c) a fixed-end-point ray tracing algorithm for seismic velocity models comprising of constant velocity layers with interface of arbitrary orientation in a three dimensional space ( d) estimation of joint confidence region at 95 percent confidence level, based on the theory of Flinn. The algorithm has been successfully tested on synthetic data as well as against the HYPO 71 program of the US Geological Survey. Hypocentral parameter estimates were obtained in this study assuming a homogeneous half space model with a P_wave velocity 5 Km/s. Subsequently, it was estimated that a velocity of $.kl Km/s would be a better estimate of the local upper crust velocity although revised hypocentral parameters were not obtained in view of the expected small changes. Based on tests conducted on synthetic data, it was concluded that great focal depths obtained for 58 microearthquakes were a direct consequence of using the half space velocity model for those earthquakes, where head waves wouid arrive first in layered velocity models. Among the major conclusions from the exercise on hypo central parameter estimation for 252 microearthquakes are the following. Microearthquakes in the Kumaon Himalaya occur in specific belts. One of these belts is well defined by the located hypocentres over a distance of 70 Km. where it lies distinctly to the south west of the north-eastward dipping Main Central Thrust (MCT) as it crosses the Yamuna valley. 19*f microearthquakes were assigned focal depths less than 20 Km. A majority of the remaining microearthquakes would also have been assigned shallow focal depths, had a more complicated vi velocity model been used. Using our data, a bodywave magnitude (m, ) 5 earthquake was lot ited 23 Km northeast of the NOAA estimate, so that this earthquake also forms a part of the seismic belt. The composite focal mechanism solution yields two nearly vertical nodal planes with strike slip motion on whichever of them is the fault plane. The compression axis is nearly horizontal and normal to the local trend of the MCT. The seismological data throw up among other problems, the following: (a) the observed relationship of the seismicity belt vis-a-vis the MCT. (b) the strike-slip focal mechanism in the vicinity of a major thrust fault and also observation of thrust fault type focal mechanism from teleseiomic data in regions not very far from the one investigated in this study (c) constancy of maximum compressive stress direction from geological times to the present.
URI: http://hdl.handle.net/123456789/739
Other Identifiers: Ph.D
Research Supervisor/ Guide: Khattri, K. N.
Gaur, V. K.
Chander, R.
metadata.dc.type: Doctoral Thesis
Appears in Collections:DOCTORAL THESES (Earth Sci.)

Files in This Item:
File Description SizeFormat 
ON SEISMOLOGICAL INVESTIGATIONS OF THE KUMAON HIMALAYA USING LOCAL EARTHQUAKE DATA.pdf28.89 MBAdobe PDFView/Open


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.