Your search within this document for 'Nepal' resulted in 13 matching pages.
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“...site effect and anelastic attenuation at Kathmandu, Nepal Himalaya region and its use in estimation of source parameters of 25 April 2015 Nepal earthquake Afw = 7.8 and its aftershocks including the 12 May 2015 A/„ = 7.3 event Parveen Kumar* 1 • A. Joshi2 • Sushil Kumar1 • Sandeep3 • Sohan Lal2 Received: 18 October 2016 / Accepted: 27 December 2017 / Published online: 29 January 2018 © Springer Science+Business Media B.V., part of Springer Nature 2018 Abstract The destructive A/w = 7.8 Nepal earthquake happened in Nepal Himalaya, 80 km NW of Kathmandu city on 25 April 2015. A number of aftershocks in which one of them is Mw = 7.3 which occurred on 12 May 2015 are observed around the Kathmandu city of Nepal. In this paper, strong motion data of Nepal earthquake and its eight aftershocks having magnitude range 5.3-7.3, recorded at Kathmandu station is used to determine site effects and attenuation factor. Kathmandu city, capital of Nepal, is situated in a valley which consists of sediments...”
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“...source spectrum provides important information, which is used in strong motion prediction. The massive Nepal earthquake 41w = 7.8 happened on 25 April 2015, and its aftershocks including 12 May 2015 41w = 7.3 event are recorded on the strong motion accel-erograph situated in the Kathmandu city. In the present paper, strong motion data of this Nepal earthquake and its eight aftershocks are employed for estimation of source parameters of these earthquakes. Site effect and quality factor which denote anelastic attenuation are determined at Kathmandu station by using the inversion technique suggested by Joshi (2006a). Both horizontal components (NS and EW) of acceleration record are used in the present work. Obtained site effect and quality factor are further used to correct the source spectrum to determine various source parameters. 2 Seismotectonics The present study region lies in Nepal Himalaya, which is one of the most seismically active regions of Himalayan belt. During last 100 years...”
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“...Nat Hazards (2018) 91:1003-1023 1005 28.5° 27.5° 84.5° Fig. 1 Seismicity plot of Nepal Himalaya region illustrating seismicity around the Kathmandu. Grey circle shows the location of historical earthquakes occurred during 1971-2015 from USGS catalog. The tectonic is considered after Coleman and Hodges (1995) and MCT (Ni and Barazangi 1984; Seeber and Armbruster 1984), and it is observed from Fig. 1 that most of the historic earthquakes lie between the MBT and MCT. 3 Data A disastrous earthquake (Afw = 7.8) struck the Nepal region of central Himalaya on 25 April 2015. This main shock is followed by a number of aftershocks including 12 May 2015 41w = 7.3 event. The strong motion data of main shock of magnitude 7.8 (Afw) and its eight aftershocks having magnitude range 5.3-7.3 are recorded at Kathmandu station and used for the present work. This near-field data recorded in the hypocentral distance ranges from 21 to 85 km and as strong motion data recorded in desired passband without any clipping...”
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“...5500 5000 4500 4000 3500 I 3000 2500 2000 1500 I 1000 500 (a) Legends Mesozoic plutonic rocks a a Neogene Quaternary sediments MCT- MBT- ;□ Tethyan Himalayan sequences STDS- O ;□ High Himalayan Metamorphic rocks O ▲ Lesser Himalayan metasedimentary series Main Central Thrust Main Boundary Thrust South Tibetan Detachment system Epicenter of main shock (Nepal earthquake) Epicenters of after shocks Recording Station Fig. 2 a Location of events and recording station with the elevation map of the present study area. Elevation data is taken from NOAA National Oceanic and Atmospheric Administration, b Geological map of the Kathmandu, Nepal Himalaya region (after Yin and Harrison 2000). (Figure modified after Shanker et al. 2011) SD(f) = 5A(f)/(2^/)2. (4) In this work, circular model proposed by Brune (1970) is considered to estimate earthquake source size, and stress drop as a circular model is quite enough to compute these parameters (Madariaga and Ruiz 2016). The source strength of an earthquake...”
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“...in present work, is expressed as (Brune 1970, 1971): r0 = 2.34/?/2tt/c. (6) Stress drop (Ac) is another important source parameter of an earthquake. Stress drop is defined as difference of shear stress before and after the occurrence of event (Ruff 1999). The relation between source radius and stress drop is utilized for calculating the stress drop, and the expression is denoted below (Papageorgiou and Aki 1983): Aa = 7M„/I6A (7) The acceleration data of Nepal earthquake and its aftershocks is recorded at the Kathmandu station in Nepal. The Kathmandu region is situated in the valley known as Kathmandu valley, and the spectral data of these events are affected by the layer of sediments (Paudyal et al. 2013). Hence spectral data of present work are influenced by site effect and anelastic attenuation factors. The spectral data are corrected for site effect and anelastic attenuation term in this work. The site effect and anelastic attenuation are enumerated by inversion of acceleration data...”
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“...triangle denote location of events and recording station, respectively and/c are considered for the Brune’s theoretical spectrum. The best match of Brune’s theoretical spectrum with the obtained corrected spectrum provides the value of Qo and/., which are further utilized to estimate seismic moment, stress drop, and source radius with the help of formulas proposed by Brune (1970) and Papageorgiou and Aki (1983). 4.1 Determination of site effect and shear wave quality factor The aftershocks of Nepal earthquakes are used to determine the site effect and gp(/) at Kathmandu station. The strong motion data is utilized for the present work, and in strong motion data, peak ground acceleration is associated usually with the arrival of S-wave (Hadley et al. 1982), so shear wave quality factor is estimated in this work. The inversion technique proposed by Joshi (2006a) and later modified by Joshi et al. (2012) and Kumar et al. (2015) is used to obtain site effect and gp(/). In this work, acceleration...”
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“...1014 Nat Hazards (2018) 91:1003-1023 100^- c/5 2 4 6 8 10 Frequency (Hz) Fig. 7 Obtained site effects at Kathmandu station. The black lines represent the site effects obtained by inversion for NS and EW component. The grey portion represents the area between // + o and //-r» of site effect obtained by Lermo and Chavez-Garcia (1993). The terms and V describe the mean and standard deviation, respectively 5 Results and discussion The source parameters of 25 April 2015 Nepal earthquake (Afw = 7.8) and its aftershocks are determined from both North-South and East-West component of strong motion records. Time window, covering complete S phase, is used to estimate various source parameters. This time window is cosine tapered and has 10% tapering for both ends (Sharma and Wason 1994). The FFT algorithm is used to obtain spectrum of this series and obtained spectrum is corrected for site effect and anelastic attenuation term. The site effects and shear wave quality factor are determined from the...”
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“...Nat Hazards (2018) 91:1003-1023 1015 Fig. 8 Comparison of observed source spectrum of NS component of the record of 25 April 2015 Nepal event (Afw = 7.8) with Brune’s (1970) theoretical spectra by using correction for a anelastic attenuation term only, b site effect term only and c both anelastic attenuation and site effect term. Blue line represents the theoretical Brune’s (1970) spectra Figure 8c suggests that best match is observed between the obtained and theoretical source spectrum when corrections of site effects and attenuation factors are introduced simultaneously in the computation. The iterative forward modeling method is applied to the theoretical Brune’s (1970) spectra for matching it with obtained corrected source displacement spectra. A number of possibilities of long-term flat level (f20) and corner frequency (fc) are considered for the Brune’s theoretical spectrum. The best match is obtained corresponding to the minimum root-mean-square error of theoretical and observed...”
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“...The final values of source parameters are calculated from the average values of NS and EW component. Source displacement spectra of Nepal earthquake and its aftershocks are compared with Brune’s (1970) theoretical spectra for both NS and EW component and shown in Figs. 10 and 11, respectively. The obtained values of seismic moment, stress drop, and source radius vary from 1.11 x 1024 to 5.96 X 1027 dyne cm, 9.5 to 48.7 bars, and 3.7 to 37.75 km, respectively. The various source parameters for both horizontal components of all the events are given in Table 3. Figure 12 represents the plot of hypocentral distance (R) versus seismic moment (Af0). The average value of seismic moment, source radius and stress drop obtained from both North-South and East-West component is 5.96 X 1027 dyne cm, 37.75 km and 48.7 bars, respectively, for the 25 April 2015 41w = 7.8 Nepal earthquake and 1.40 X 1027 dyne cm, 23.90 km and 44.7 bars, respectively, for the 12 May 2015 41w = 7.3 earthquake. The rupture area...”
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“...Nat Hazards (2018) 91:1003-1023 1017 0.01 0.1 10 100 0.001 0.01 0.1 10 100 0.001 0.01 0.1 10 100 Frequency Fig. 11 Corrected source displacement spectra of EW component for 25 April 2015 Nepal event (Afw = 7.8) and its aftershocks with Brune’s (1970) theoretical spectral. The theoretical spectrum is shown by blue line (1994) for all events. The following empirical relation is used to compute the rupture area (Wells and Coppersmith 1994): log(A) = a + b X M, (13) where the terms ‘A’ and W represent the area of rupture and magnitude of particular earthquake, respectively. The terms 'a' and ‘Z?’ denote the coefficient having value, a = - 3.49 and b = 0.91 (Wells and Coppersmith (1994)). The standard errors suggested by Wells and Coppersmith (1994) for the terms 'a' and ‘Z?’ are ± 0.16 and ± 0.03, respectively. The rupture area values calculated by the obtained source radius and empirical relation are given in Table 4. It is observed that the rupture area values calculated in present work lie...”
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“...Nat Hazards (2018) 91:1003-1023 1021 Fig. 13 Comparison of obtained value of seismic moment with the seismic moment values reported by other sources (USGS and CMT Harvard) o O Legend O Present work A A A USGS + + + CMT Harvard 6 Conclusions In this paper, frequency-dependent shear wave quality factor (Q^(/)) and site effects are computed by using the strong motion data recorded at Kathmandu station in Nepal Himalaya. The inversion algorithm is used to obtain g^(/) = 68 f° 58 relationship at the Kathmandu station. The low Qp(f) relation suggests presence of high attenuating earth medium below the Kathmandu region. The obtained Qp(f) and site effects are used to correct the spectrum, and this corrected spectrum is further utilized to compute various parameters, i.e., stress drop, seismic moment, and source radius. The best-fit Brune’s (1970) theoretical spectrum with the observed corrected spectrum provides these source parameters for the earthquakes of magnitude range 5.3-7.8 used in present...”
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“...RK (2012) Determination of Qp(f) at different places of Kumaon Himalaya from the inversion of spectral acceleration data. Pure appl Geophys 169:1821-1845 Joshi A, Kumar P, Arora S (2014) Use of site amplification and anelastic attenuation for the determination of source parameters of the Sikkim earthquake of September 18, 2011, using far-field strong-motion data. Nat Hazards 70:217-235 Katel TP, Upreti BN, Pokharel GS (1996) Engineering properties of fine grained soils of Kathmandu Valley Nepal. J Nepal Geol Soc 13:121-138 Ko YT, Kuo BY, Hung SH (2012) Robust determination of earthquake source parameters and mantle attenuation. J Geophys Res 117:B04304. https://doi.org/10.1029/2011JB008759 Kumar D, Sarkar I, Sri Ram V, Khattri KN (2005) 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 407:1-24 Kumar A, Kumar A, Gupta SC, Mittal H, Kumar R (2013)...”
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“...Dahal RK (2013) Basement topography of the Kathmandu Basin using microtremor observation. J Asian Earth Sci 62:627-637 Ruff LJ (1999) Dynamic stress drop of recent earthquakes: variations within subduction zones. Pure appl Geophys 154(1999) :409-431 Sakai H, Fujii R, Kuwahara Y (2002) Changes in the depositional system of the Paleo-Kathmandu Lake caused by uplift of the Nepal Lesser Himalayas. J Asian Earth Sci 20:267-276 Seeber L, Armbruster JG (1984) Some elements of continental subduction along the Himalayan front. Tec-tonophysics 92:335-367 Shanker D, Paudyal H, Singh HN (2011) Discourse on seismotectonics of Nepal Himalaya and vicinity: appraisal to earthquake hazard. Geosciences 1(1): 1-15 Sharma ML, Wason HR (1994) Occurrence of low stress drop earthquakes in the Garhwal Himalaya region. Phys Earth Planet Inter 34:159-172 Singh SK, Ordaz M, Dattatrayam RS, Gupta HK (1999) A spectral analysis of the 21 May 1997, Jabalpur, India, earthquake (Afw = 5:8) and estimation of ground motion...”