Variation of Seismic Coda Wave Attenuation in the Garhwal Region, Northwestern Himalaya

Abstract

Seismic coda wave attenuation (Q À1 c ) characteristics in the Garhwal region, northwestern Himalaya is studied using 113 short-period, vertical component seismic observations from local events with hypocentral distance less than 250 km and magnitude range between 1.0 to 4.0. They are located mainly in the vicinity of the Main Boundary Thrust (MBT) and the Main Central Thrust (MCT), which are well-defined tectonic discontinuities in the Himalayas. Coda wave attenuation (Q À1 c ) is estimated using the single isotropic scattering method at central frequencies 1.5, 3, 5, 7, 9, 12, 16, 20, 24 and 28 Hz using several starting lapse times and coda window lengths for the analysis. Results show that the (Q À1 c ) values are frequency dependent in the considered frequency range, and they fit the frequency power law (Q À1The Q 0 (Q c at 1 Hz) estimates vary from about 50 for a 10 s lapse time and 10 s window length, to about 350 for a 60 s lapse time and 60 s window length combination. The exponent of the frequency dependence law, n ranges from 1.2 to 0.7; however, it is greater than 0.8, in general, which correlates well with the values obtained in other seismically and tectonically active and highly heterogeneous regions. The attenuation in the Garhwal region is found to be lower than the Q c -1 values obtained for other seismically active regions of the world; however, it is comparable to other regions of India. The spatial variation of coda attenuation indicates that the level of heterogeneity decreases with increasing depth. The variation of coda attenuation has been estimated for different lapse time and window length combinations to observe the effect with depth and it indicates that the upper lithosphere is more active seismically as compared to the lower lithosphere and the heterogeneity decreases with increasing depth.

Interpretation of Gravity Data using 3D Euler Deconvolution, Tilt Angle, Horizontal Tilt Angle and Source Edge Approximation of the North-West Himalaya

“…It can be concluded that the results obtained here are well correlated with the results of various scientists in this study area and neighboring areas (Tripathi et al 2012, Chamoli et al 2011, Arora et al 2007, Gokarn et al 2002.…”

“…Various authors (Tripathi et al 2012, Chamoli et al 2011, Arora et al 2007, Gokarn et al 2002 had carried out the depth estimation and provided their views. However, the present study provides better results and detailed information of source depth locations and structural boundaries with dip information.…”

“…Arora et al (2007) also studied the Deep Resistivity Sounding (DRS) along the western part of the northwestern Himalayas and suggest resistivity > 300 •m up to depth of 15 km. Tripathi et al (2012) suggested by coda wave attenuation analysis in the Garhwal region of north-western Himalaya that the earthquakes are mainly concentrated within depths from 10 to 15 km, which suggests that most of the crustal activation takes place within this particular depth. The coeval development of South Tibetan Detachment and the Main Central Thrust studies through simulation analysis and the thrusting dominating nature of Himalaya studies have been done by Shanker et al (2002).…”

Determination of high-frequency attenuation characteristic of coda waves in the central region of Nepal Himalaya

“…The coda waves in the local event, epicenter distance up to 100 km (less than twice the Moho depth), their power spectra, and coda duration are relatively independent of focal distance (Aki and Chouet, 1975). Coda waves are widely used to estimate the attenuation characteristics of a different region of the world (e.g., Aki 1969;Pulli, 1984;Canas et al, 1995;Gupta et al, 1995Gupta et al, , 1998Havskov et al, 1989;Kanao and Ito, 1991;Kosuga, 1992;Paul et al, 2003;Kumar et al, 2005;Tripathi et al, 2012;Naghavi et al, 2017). Coda wave attenuation is not well studied in Nepal Himalaya, but several studies have been carried out in adjacent regions of Nepal Himalaya.…”

Regional variation of coda Q in Kopili fault zone of northeast India and its implications

“…The attenuation of medium is inversely proportional to the quality factor (Q) which means that, seismic waves are highly attenuated for regions having lower Q values. There are many literatures available regarding the estimation of QC [9][10][11][12][13][14][15][16][17][18][19][20][21]. Adding to this, Aki (1969), Aki and Chouet (1975) and Sato (1977) suggested that by analyzing tail portion of earthquakes waveform data permits us to study the wave attenuation mechanism in the earth's interior.…”