INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET)

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1 INTERNATIONAL JOURNAL OF IVIL ENGINEERING AND TEHNOLOGY (IJIET) International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), ISSN (Print) ISSN (Online) Volume 3, Issue 2, July- December (212), pp IAEME: Journal Impact Factor (212): (alculated by GISI) IJIET IAEME UALITY FATOR OF SEISMI ODA WAVES IN GARHWAL HIMALAYAS Priyamvada Singh, J.N. Tripathi Department of Earth and Planetary Sciences, University of Allahabad, India Sushil Kumar Wadia Institute of Himalayan Geology, Deharadun ABSTRAT Seismic wave propagating through the earth experiences some reduction in the energy content. This decay in the wave energy is known as the seismic wave attenuation. The study of attenuation characteristics of these waves shed light on the heterogeneous nature of the Earth. Usually, seismic wave attenuation for local earthquakes is determined from the analysis of coda waves. Digital seismogram data of 75 earthquakes that occurred in Garhwal Himalaya region during 24 to 26 and recorded at different stations have been analyzed to study the seismic coda wave attenuation characteristic in this region. In the present study, 9 seismic observations from local earthquake events with hypocentral distance less than 25 km and magnitude range between 1. and 5. is used to study coda, i.e., using the single isotropic scattering model. Values are estimated at 1 central frequencies 1.5, 3, 5, 7, 9, 12, 16, 2, 24 and 28 Hz using a starting lapse-time LT=5 s and four coda window-lengths, WL= 1, 2, 3, 4 s. In n the considered frequency range, fit the frequency dependent power-law = f. The frequency dependent power-law for 5 sec lapse time with 1 sec coda window length is = 61.8 f and for 5 sec lapse time with 4 sec coda window length is = f. The ( at 1 Hz) estimates vary from about 61.8 for a 5 sec lapse time and 1 sec window length, to about for a 5 sec lapse time and 4 sec window length combination. The exponent of the frequency dependence law n ranges from 1.16 to.967, which correlates well with the values obtained in other seismically and tectonically active and heterogeneous regions of the world. It is observed for the study region that and frequency. The low c values increases both with respect to window length values or high attenuation at lower frequencies and high values 279

2 International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), or low attenuation at higher frequency may indicate that the heterogeneity decreases with increasing depth, in the study region. Keywords: Attenuation, oda, Single backscattering model, Lapse time window, Garhwal Himalaya I. INTRODUTION The attenuation of seismic wave is one of the basic physical parameter which is closely related to the seismicity and regional tectonic activity of a particular area. This is also important for seismic hazard measurement. In this work, the seismic attenuation in the Garhwal Himalayas is studied using local earthquakes. The amplitude of seismic waves decreases with increasing distance from the earthquake. This reduction of the energy content cannot be explained by geometrical spreading of the wave only. This decay in the wave energy is known as the seismic wave attenuation. Seismic wave attenuate because the earth is not a perfect elastic and homogeneous. Usually, seismic wave attenuation for local earthquakes is determined from the analysis of direct body waves, surface waves or coda waves. The dimensionless parameter,, is studied in the present work which is defined as a measure of the rate of decay of the coda waves within a specified frequency band. Aki (1969) referred oda as the tail part of seismograms of local earthquakes. Aki and houet (1975) suggested that the S oda of local earthquakes is superposition of incoherent backscattered S-wave and surface waves generated from numerous heterogeneity distributed randomly in the Earth s crust and upper mantle. The great variety of paths traveled by these waves provides information concerning the average attenuation properties of the medium instead of just the characteristics of a particular path (Aki and houet 1975). The, quality factor of oda wave has been estimated for different parts of the world (Aki and houet 1975; Sato 1977; Ugalde et al., 22; Tripathi and Ugalde, 24, Ugalde et al., 27, Pezzo et al., 211,). oda wave characteristics have also been estimated for different parts of the Himalayas (Gupta et al., 1995; Kumar et al., 25; Hazarika et al., 29; Sharma et al., 29; Mukhopadhyaya et al., 21; Padhy et al., 21; Tripathi et al., 212). In the present work the coda attenuation properties have been estimated in the Garhwal region of Himalayas using local earthquakes. The frequency dependence of coda wave is also estimated. II. STUDY AREA The Himalayas is the consequence of the collision of the Indian plate with the plates of central Asia during mid to late Eocene. The Outer Himalayas, Lower Himalayas and the Higher Himalayas are the three major terrains identified in the Garhwal Himalayas [Valdiya, (198)]. 28

3 International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), The major thrust fault striking parallel to the Himalayan arc, from north to south are the Main entral Thrust (MT), the Main Boundary Thrust (MBT) and the Himalayan Frontal Thrust (HFT) (Figure 1).The high grade metamorphic units of Higher Himalayas, situated north of MT, are considered to be inactive generally, due to no signs of break of uaternary deposits (Ni and Barazangi, 1984; Brunel 1986). The outer Himalayas comprises of Tertiary rocks that is underlain by the marine water to brackish origin subathu formation. This is followed upward by siwalik group. The siwalik group is overlain by uaternary gravel and sand. The Lower Himalayas are mainly made up of Precambrian sedimentary rocks with some outcrops of ambrian Tal formation. The Higher Himalayas are made up of high grade metamorphic rocks like amphibolites to granulites grade metasedimentary rocks, auger gneisses and intrusive leucogranite. In the Garhwal-Kumaon Himalayas region these groups of rocks are known as the vaikrita group (Srivastav and Mitra 1994) Figure 1: (a) Simplified map of the Himalya. (b) Map of the study area modified after Valdiya (198). 281

4 International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), III. METHOD AND DATA The single backscattering model of coda wave envelopes of Aki and houet (1975) considers the coincidence of source and receiver. So, for the practical application of the model, we have to consider lapse time t >2t s, where t s is the S wave travel time (Rautian and Khalturin, 1978). Sato (1977) proposed the single isotropic scattering model for non coincident source and receiver. Thus, we can analyse the coda window just after the S wave arrival. In this model, it is assumed that the elastic energy is radiated spherically, scatterers are distributed homogeneously and randomly, and the single scattering is isotropic in the media. Thus, the coda energy density E S at frequency f can be expressed as E ( f S 1 [ πft] W ( f ) g( f ) r, t) = K ( α )exp 2 4πr 2 (1) Where t is the lapse time measured from the origin time of the earthquake, t s is the S-wave travel time, r is the hypocentral distance, W is the total energy radiated from the source, g is the total scattering coefficient, and 1 α + 1 K ( α ) = ln, ( α > 1); and α = t / t s. (2) α α 1 The energy density is considered to be proportional to the mean square amplitudes of coda waves and taking natural logarithms of Eq.1 and reshuffling the terms, we get Aobs ( f r, t) πf ln = f t k r ln ( ) (3) (, α) where ( f r, t) represents the observed root mean square (rms) amplitude of the narrow band A obs. 5 pass filtered waveforms with central frequency ; k( r, α) ( 1/ r) K( α) Thus the f = and ( f ) is a constant. can be easily obtained from the slope b of the least square fit straight line to the measured ln[ A obs ( f r, t) / k( r, α)] versus t for a given central frequency, using the relation = πf / b. The frequency dependence law, different lapse time and window length, where is the value of dependent parameter (Table 3). n = f is also fitted to the data for at 1 Hz and n is frequency The digital waveform seismograms of 75 events used for coda attenuation in the present study were recorded at 2 stations of Garhwal Himalayas during 24 to 26 (Figure 2, Table 1). The MG 4T1 triaxial broadband seismometers were used for the digital data collection. The data is 282

5 International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), acquired in continuous mode at 1 samples per second for three components at the stations. SEISAN (version 8.1) software package (Havskov and ottemoller, 25) was used to pick P and S wave arrival times of each earthquake recorded at the different seismic stations. The hypocentral parameters, viz, origin time, latitude, longitude and focal depth of these events were also computed using the SEISAN software. Most of the events are within the crust and local magnitude ranges from 1. to 5.. First of all we preformed a visual inspection of more than 45 seismograms, 9 waveforms with hypocentral distances less than 25 km have been finally processed for the present work. IV. DATA ANALYSIS AND RESULTS First of all the seismograms were band pass filtered for ten frequency bands, 1.5 ±.5 Hz, 3 ± 1 Hz, 5 ± 1 Hz, 7 ± 1 Hz, 9 ± 1 Hz, 12 ± 1 Hz, 16 ± 1 Hz, 2 ± 2 Hz, 24 ± 2 Hz, and 28 ± 2 Hz (Table 2), using eight-pole Butterworth filters. As the sampling rate was 1 samples per second, the maximum frequency for which reliable result could be obtained was 5 Hz. Then, the root mean squared amplitudes of the filtered seismograms were computed at an interval of.5 s with moving time windows of length t ± 2s for the first frequency band and t ± 1s for the next nine frequency bands. Then was estimated applying a least square regression technique to Eq.3 for one starting lapse time window length LT = 5 s from the S-wave onset, having Window Length WL=1, 2, 3 and 4s for ln[ A obs ( f r, t) / k( r, α)]. The estimates were computed only for the amplitudes greater than signal to noise ratios. The coda wave is analyzed only the vertical component, because it has been shown that the coda analysis is independent of the component of the particle ground motion analyzed (Hoshiba, 1993). The estimated values retained for further analysis which were having correlation coefficients greater than Stations Location Latitute Events Stations Longitude Figure 2: Station Locations (open circles) with events used in the Study. 283

6 International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), Table 1: Station code and their location Station Longitude Latitude DEO TZG UDA HT TSA UNA LGR BNK RJA BRM PAL GRG JKH PRT YOL AMB BEED NEL GYL NAD The frequency dependent oda relationship provides average attenuation characteristics of the medium. The average values of at different frequencies, one lapse time and four window lengths obtained from the mean values for the whole study area are given in Table.3. Table.2: entral frequencies and frequency range as low and high cutoff. entral frequency (Hz) Low cutoff (HZ) High cutoff (Hz) 284

7 International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), Table 3: The average numerical values of at different frequencies, lapse time (LT=5) and coda window length (WL=1, 2, 3, and 4 s). LT (s) WL (s) Values of at different frequencies 1.5 Hz 3 Hz 5 Hz 7 Hz 9 Hz 12 Hz 16 Hz 2 Hz 24 Hz 28 Hz For the study area it is observed that window length. It is observed that the value increases both with respect to frequency and increases with frequency. The average value of for the study region varies from 121 at 1.5 Hz to 179 at 28 Hz for lapse time 5s and window length 1s. When window length is 2, is 179 at 1.5Hz and 2611 at 28Hz. Higher values of are obtained at 3 and 4s window lengths. This observation of frequency dependence of is due to the degree of heterogeneity of a medium and level of tectonic activity in an area (Aki 198). The low values or high attenuation at lower frequencies may indicate a high degree of heterogeneity and decrease in rock strength at shallow parts. The high values or low attenuation at higher frequencies may be related to the comparatively less hetrogeneous deeper zones (Aki and houet, 1975)..95 Gupta et al. (1995) obtained a frequency relation = 126 f using records of seven micro earthquake in the adjoining southwestern part of Garhwali Himalayas for 3s coda window length. Kumar et al., (25) employed the time domain coda - decay method of a single - back scattering model to calculate frequency dependent values of coda. A total of 36 local earthquake of magnitude range have been used for estimation at central frequencies 1.5, 3.6, 6.9, 9., 12. and 18. Hz through eight lapse time windows from 25 to 6s starting at double the time of the primary S-wave from the origin time. The estimated average frequency 1.5 dependence quality factor gives the relation = 158 f while the average values vary from the relation 21 at 1.5Hz to 2861 at 18Hz central frequencies. The observed coda quality factor is strongly dependent on frequency, which indicate that the region is Seismic and tectonically active with high heterogeneity. Paul et.al., (23) estimated for Kumaun Himalayas using data from eight micro earthquake record by a five station array with epicentral distance range varying between 1 km to 8 km for (1.7±.23) 3 sec window length and obtained a = (92 ± 4.73) f analyzing the SH wave form data of 1988 Nepal - India border earthquake. 285

8 International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), 1 c= 61.75f c= 17.2f c 1 c 1 1 LT=5 WT=1 1 LT=5 WL= Frequency Frequency 1 c= 113.5f c= 161.1f.998 c 1 c 1 1 LT=5 WT=3 1 LT=5 WL= Frequency Frequency Figure 3: Frequency dependency power law for lapse time 5s and coda window length 1, 2, 3, 4, 5 s. Hazarika et al., (28) found that is very high i.e. coda at 1Hz frequency attenuates very 1 fast. They also found that and n values are different at Arunachal Himalayas, Shilong massif and Indo- Burma ranges with the former two being characterized by lower attenuation compared to the last one. 286

9 International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), For NW Himalayas Mukhopadhyay and Tyagi (28) found that coda and intrinsic attenuation decreases with depth, whereas scattering attenuation increases with depth. The mean values of reveals a dependence on frequency varying from at 1.5 Hz to at 18 Hz. In the hamoli region of the Himalayas Mukhopadhayay et al., (28) found that frequency ( 1.17±.3) ( 1.76±.5) relations for 1, 2, 3, 4, and 5s window lengths are (33 ± 2) f, ( 55 ± 6) f, (.98±.8) ( 1.7±.8) (.98±.7) (78 ± 2) f, (93 ± 18) f, (122±2) f, respectively. Mukhopadhayay and Sharma (21) analyzed the coda of local earthquakes to study the attenuation characteristics of the Garhwal - Kumaon Himalayas. It is observed that increases with frequency and also varies. Sharma et al., (29) estimated quality factor for P-wave, S-wave and oda- waves in hamoli 1.21 region, and estimated frequency dependent relations for quality factors are = 3 f, α = (44 ± 1) f (.82±.4) (.71±.3) and α = (87 ± 3) f. 1 1 Present study c LT=5 WL= Frequency Northwestern Himalayas Tripathi(212) Kumaun Himalayas Singh(212) Garhwal Himalayas Gupta(1995) Western HimalayaS Mukhopadhyay(27) Figure 4: omparison of estimated with other studies of Himalayas. Makhopdhyaya and Tyagi (27), analyzing the events from Northwestern Himalayas have shown that the region is highly heterogeneous and tectonically very active and heterogeneity decreases with depth in this area increases from 113 ± 7 to 243 ± 1 and n decreases from 1.1 ±.5 to.86 ±.3 when lapse time increases from 3 sec to 7 sec. Singh et al., (212) analyzed the local earthquakes in Kumaon Himalayas region to estimate lapse time dependence of coda waves and obtained that by increasing lapse time window from 287

10 International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), 2 to 5 s, increases from 64 to 23 while dependent parameter n decreases from 1.8 to.81. Tripathi et al., (212) estimated coda wave attenuation using the single isotropic scattering method for frequency range 1-3 Hz for the Garhwal region for other data set. They used several starting lapse times and coda window lengths for the analysis to study the variation of attenuation characteristics. Results show that the 1 c values are frequency dependent in the considered frequency range, and they fit the frequency power-law 1 ( f ) = 1 c n f. The estimates vary from about 5 for a 1 s lapse time and 1 s window lengths, to about 35 for a 6 s lapse time and 6 s window length combinations. The exponent of the frequency dependence law n ranges from 1.2 to.7; however, it is greater than.8, in general, which correlates well with the values of others in Himalaya region. The estimated coda attenuation values in the present study are comparable with that obtained from other regions of the Himalayas, as shown in Figure 4. Table 4: Frequency dependent power law n = f. For study region, increase in n LT WL = f with the window length is attributed to increase in with depth, as longer the time window the larger will be the sampled area of the earth s crust and mantle. This observation seems to indicate that there is a decrease in the level of heterogeneities with depth in the Garhwal Himalayas. This would imply that attenuation decreases with increasing depth. A strong correlation between the degree of frequency dependence, n value, and the level of tectonic activity was claimed (Aki 198). This is also observed by others, in Himalayan region, that n value is higher for tectonically active regions compared to the tectonically stable regions (Kumar et al., 25; Mukhopadhyaya et al., 21; Hazarika et al., 29; Sharma et al., 29; Tripathi et al., 212; Padhy et al., 21;). For Garhwal Himalaya Gupta et al., (1995) estimated as 126 and n as.9. Mukhopadhyay et al., (21) estimated as 119 and n as.99. The f f f f

11 International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), obtained values of n is close to 1 in the present study which indicate that the region is highly hertogeneous and tectonically very active. V. ONLUSION In the present study, the values have been estimated for Garhwal Himalayas region, using 9 seismograms from 75 local earthquakes recorded digitally at 2 different stations and analyzed for one lapse time (e.g. 5 s), four window lengths ( e. g. 1, 2, 3, and 4 s) and at 1 frequency bands with the central frequency in the range of 1.5 Hz to 28 Hz. The estimated values for the lapse time 5 s vary from 121 to 279 at 1.5 Hz and from 179 to 52 for 28 Hz where the coda window varies from 1 to 4 s. It is clear from the results (Table 3) that is a function of frequency in this region. The value increases as frequency increases. A frequency dependent relationship has also been obtained for the region (Table 4), which shows that there is a significant increase in values with increasing window length, while there is a nominal decrease in the degree of frequency dependence, n. This can also be interpreted that the scattering effect in the region exhibits a decreasing trend with increasing depth (Aki 198). This may be due to decrease in the heterogeneities level of the medium. The general trend of the present coda attenuation study is similar to seismically and tectonically active region (Figure 4). Attenuation parameter is an important factor for understanding the physical mechanism of seismic wave attenuation in relation to the composition and physical condition of the Earth s interior and it is also an essential parameter for the quantitative prediction of strong ground motion for the viewpoint of engineering seismology. Hence numerous studies of have been carried out worldwide by using different methods and concentrate on seismically active zones and densely populated area. AKNOWLEDGEMENT Authors are very thankful to the Director, Wadia Institute of Himalayan Geology, Dehradun for providing us the data for this study REFERENES [1] Aki, K (1969), Analysis of the seismic coda of local earthquakes as scattered waves, J. Geophys. Res., Vol.74, pp [2] Aki, K (198), Scattering and attenuation of shear waves in the lithosphere, J. Geophys. Res., Vol. 85, pp [3] Aki, K, and houet, B (1975), Origin of the coda waves: source, attenuation and scattering effects, J. Geophys. Res., Vol. 8, pp [4] Brunel, M., (1986), Ductile thrusting in the Himalayas: Shear sense criteria and stretching lineation, Tectonics, Vol. 5, pp

12 International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), [5] handrasekhar, A. R. and Das J. D.(1992), Analysis of strong motion accelerograms of Uttarkashi earthquake of October 2, 1991, Bull. Indian Society of Earthquake Technology, Vol. 29, pp [6] Fehler M., Sato H., (23), oda, Pure and Applied Geophysics, Vol. 13, pp [7] Gupta A K, Sutar A K, hopra S, Kumar S, Rastogi B K (212), Attenuation characteristics of coda waves in mainland Gujarat, India, Tectonophysics, Article in Press, available online. [8] Gupta S, Kumar A, Shukla A K, Suresh G, Baidya P R, (21), oda in the Kachchh basin, western India using aftershocks of the Bhuj earthquake of January 26, 21, Pure and Applied Geophysics, Vol. 163, pp [9] Gupta S, Singh V N, Kumar A, (1995), Attenuation of coda waves in the Garhwal Himalya, India,. Earth. Planet. Inter., Vol. 87, pp [1] Gupta S, Teotia S S, Rai S S, Gautam N, (1998), oda estimates in the Koyna region, India, Pure and Applied Geophysics, Vol. 153, pp [11] Hazarika D, Barauh S, Gogoi N K, (29), Attenuation of coda waves in the Northeastern region of India, Journal of Seismology, Vol. 13, pp [12] Herraiz M, Espinoza A F, (1987), oda waves: A review, Pure and Applied Geophysics, Vol. 125(4), pp [13] Havskov, J., and Ottemoller, L.,(25), SEISAN (version 8.1): The earthquake analysis software for Windows, Solaris, Linux, and Mac OSX Version 8., pp 254. [14] Hoshiba, M (1993), Separation of scattering attenuation and intrinsic absorption in Japan using the Multiple Lapse Time Window Analysis of full seismogram envelope, J. Geophys. Res.,Vol. 98, pp [15] Kumar D, et al., (25), Estimation of the source parameters of the Himalaya earthquake of October 19, 1991, average effective shear wave attenuation parameter and local site effects from accelerograms, Tectonophysics, Vol. 47, pp [16] Kumar D, Teotia S S, Kahtri K N (26), The representability of attenuation characteristics of strong ground motions observed in the 1986 Dharamshala and 1991 Uttarkashi earthquakes by available empirical relations, urrent Sciences, Vol. 73(6), pp [17] Kumar N, Parvez I A, Virk H S (25), Estimation of coda wave attenuation for NW Himalayas region using local earthquakes, Physics of the Earth and Planetary Interiors, Vol. 151, pp [18] Mukhopadhyay S, et al., (28), Lapse time dependent of coda in source region of 1999 hamoli earthquake Bull. Seismol. Soci. America, Vol. 98(4), pp [19] Mukhopdhyay S, Sharma J, (21), Attenuation characteristics of Garwal-Kumaun Himalyas from analysis of coda of local earthquakes, Journal of Seismology, Vol. 14, pp [2] Mukhopdhyay S, Sharma J, Del- Pezzo E, Kumar N, (21), Study of attenuation mechanism for Garwhal-Kumaun Himalyas from analysis of coda of local earthquakes, Physics of the Earth and Planetary Interiors, Vol.18, pp [21] Mukhopdhyay S, Tyagi, (27), Lapse time and frequency-dependent attenuation characteristics of coda waves in the North Western Himalayas, J. Seismology, Vol.11, pp

13 International Journal of ivil Engineering and Technology (IJIET), ISSN (Print), [22] Mukhopdhyay S, Tyagi, (28), Variations of intrinsic and scattering attenuation with depth in NW Himalayas Geophysics J. Int., Vol. 172, pp [23] Mukhopdhyay S, Tyagi, Rai S S, (26), The Attenuation mechanism of seismic waves in northwestern Himalayas, Geophysics J. Int., Vol. 167, pp [24] Ni J, Barazangi M, (1984), Seismotechtonics of the Himalayan collision zone: Geometry of the underthrustic India plate beneath the Himalya, Journal of Geophysical Research, Vol. 89(B2), pp [25] Padhy S, Subhadra N, Kayal J. R.(211), Frequency dependent attenuation of body and coda waves in the Andaman Sea Basin, Bull. Seismol. Soci. America,, Vol. 11(1), pp [26] Padhy S, Subhadra N,(21), Frequency dependent attenuation of P and S waves in the Northeast India, Geophysics Journal of International, Vol. 183, pp [27] Padhy S, Subhadra N,(21), Attenuation of high frequency seismic waves in northeast India, Geophysics Journal of International, Vol. 181, pp [28] Paul A, Gupta S, Pant,(23), oda estimates for Kumaun Himalaya, Proc. Indian Acad. Sc.(Earth Planet Sci.), Vol. 112(4), pp [29] Pezzo E D, et al., (211), Depth dependent intrinsic and scattering seismic attenuation in the North central Italy, Geophys. J. Int., Vol.186, pp [3] Rautian T G et al., (1978), Preliminary analysis of the spectral content of P and S waves from local earthquakes in the Garw Tadjikistan Regions Bull. Seismol. Soci. America, Vol.68 (4), pp [31] Sato H, (1977), Energy Propagation including scattering effects single isotropic scattering approximation, J. Phys. Earth, Vol. 25, pp [32] Sharma B et al., (29), Attenuation of P and S waves in the hamoli region, Himalaya, India Pure and Applied Geophysics, Vol. 166, pp [33] Singh et. al., (212), Frequency dependent body wave attenuation characteristics in the Kumaun, Himalaya, Tectonophysics, Vol. 524, pp [34] Singh., Bharathi V.K.S., hadha R.K. (212), Lapse time and frequency dependent attenuation characteristics of Kumaun Himalayas, Journal of Asian earth sciences, available online, March 212. [35] Srivastava P and Mitra G, (1994), Thrust geometries and deep structure of the outer and lesser Himalaya, Kumaon and Garhwal ( India): Implications for evolution of the Himalayan fold and thrust belt, Tectonics, Vol. 13, pp [36] Tripathi J N, Singh P, Sharma M L, (212), Variations of seismic coda wave attenuation in the Garhwal region, Northwestern Himalaya, Pure and Applied Geophysics, Vol. 169, pp [37] Tripathi J N and Ugalde A., (24), Regional estimation of from seismic coda observation by the Gauribidanur seismic array (southern India, Phys. Earth. Planet. Inter., Vol. 145, pp [38] Ugalde A., Tripathi, J.N., Hoshiba, M. and Rastogi, B.K., (27), Intrinsic and scattering attenuation in western India from aftershocks of the 26 January, 21 Kachchh earthquake, Tectonophysics, Vol. 429, pp [39] Valdiya K S., (198), Geology of Kumaun lesser Himalaya, Wadia Institute of Himalayan Geology, Dehradun, pp