Attenuation of Coda Waves in the Nubra-Siachen Region, Himalaya, India

Abstract

ABSTRACT The attenuation properties have been estimated in the Nubra-Siachen region situated in the highly mountainous region of Himalayan belt. Coda wave quality factor (Qc) has been determined for this virgin region by using the single backscattering method. A total of thirty earthquakes recorded in this region, which fall in the epicentral distance range of 3 to 115km have been used for the present work. A 30 sec window length of coda waves at different central frequencies 1.5, 3.0, 6.0, 9.0, 12.0, 18.0 and 24.0 Hz have been studied to determine Qc at different recording stations. The frequency dependent coda wave quality factor relationships of the form Qc(f) = Qof n, have been computed at each recording stations separately: BASE: Qc(f) = (137 ± 4.2) f (0.99 ± 0.12), CHALUNKA: Qc(f) = (116±3.8)f (1.0±0.05), PARTA: Qc(f) = (122±3.0)f (1.0±0.02) , and SASOMA: Qc(f) = (111±4.1)f (1.0±0.03). A regional Qc relation has been developed for the Nubra-Siachen region by using the average value of Qc at different frequencies obtained at each recording station of the form Qc(f) = (121±7.2)f (1.0±0.04). The average Qc values vary from 183 at 1.5 Hz to 3684 at 24 Hz central frequencies. The present regional relation developed for Nubra-Siachen region indicates heterogeneous and tectonically active region.