Browsing by Author "Sohan Lal"

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Determination of site effect and anelastic attenuation at Kathmandu, Nepal Himalaya region and its use in estimation of source parameters of 25 April 2015 Nepal earthquake M w = 7.8 and its aftershocks including the 12 May 2015 M w = 7.3 event
(Springer Netherlands, 2018) Parveen Kumar; A. Joshi; Sushil Kumar; Sandeep; Sohan Lal
The destructive Mw = 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 of more than 300 m depth. Hence strong motion data recorded at Kathmandu station is strongly affected by site effect and anelastic attenuation. In this work, S-phase spectra recorded at Kathmandu station are corrected for site effect and anelastic attenuation to compute the source parameters of the events. The site effects and anelastic attenuation are estimated from inversion of strong motion data by using the inversion technique suggested by Joshi (Bull Seismol Soc Am 96:2165–2180, 2006a). The shear wave quality factor (Qβ(f)) is computed at Kathmandu station by using the inversion scheme as Qβ(f) = 68f0.58. The site effects and attenuation factor obtained by inversion technique are used to correct the spectrum for site effect and anelastic attenuation. The corrected source spectrum is compared with theoretical (Brune in J Geophys Res 78:4997–5009, 1970) spectrum to estimate various source parameters. Both horizontal component (North–South and East–West) are utilized to estimate the source parameters of 25 April 2015 Mw = 7.8 Nepal earthquake and its aftershocks. The best-fit theoretical spectrum provides final values of source parameters, i.e., stress drop, seismic moment, and source radius as 48.7 bars, 5.96 × 1027 dyne cm and 37.75 km, respectively, for the 25 April 2015 Mw = 7.8 earthquake and 1.40 × 1027 dyne cm, 44.7 bars, and 23.90 km, respectively, for the 12 May 2015 Mw = 7.3 earthquake. © 2018, Springer Science+Business Media B.V., part of Springer Nature.
Estimation of the source parameters of the Nepal earthquake from strong motion data
(Springer Netherlands, 2016) A. Joshi; Monu Tomer; Sohan Lal; Sumer Chopra; Sandeep Singh; Sanjay Prajapati; M.L. Sharma; Sandeep
Kathmandu and its surrounding region were rocked recently by a devastating earthquake on April 25, 2015. This is the largest earthquake that has occurred in this region since the past eight decades. This earthquake was recorded on strong motion stations located about 470–522 km away from its epicenter. Records of accelerographs from these stations have been used to determine the location of this earthquake using hypo71 algorithm given by Lee and Lehr (HYPO71, a computer program for determining hypocenter, magnitude and first motion pattern of local earthquakes. US Geological Survey Open file report, 100, 1975). The recorded accelerograms have been corrected for site effects using site amplification curve obtained from ambient seismic noise recorded at each station. Site effect has been computed using H/V ratio method given by Nakamura (Q Rep RTRI 30(1):25–33, 1989) using ambient noise data. The corrected record is further used to obtain source displacement spectra. The source spectrum obtained from strong motion data is compared with theoretical source spectrum obtained from Brune’s (J Geophys Res 75:4997–5009, 1970) model for the horizontal components. The long-term flat level and corner frequency from source displacement spectra are used to calculate stress drop, source radius and seismic moment of this earthquake. The present study indicates that the Nepal earthquake originated 12.0 km below the epicenter located at 27.93°N, 84.70°E. The source radius, stress drop and seismic moment of this earthquake estimated from source displacement spectra are 44.13 ± 3.85 km, 18.68 ± 5.93 bars and 3.53 ± 0.28 × 1027 dyne cm, respectively. © 2016, Springer Science+Business Media Dordrecht.
Modeling of 2011 IndoNepal Earthquake and Scenario Earthquakes in the Kumaon Region and Comparative Attenuation Study Using PGA Distribution with the Garhwal Region
(Birkhauser Verlag AG, 2019) Sandeep; A. Joshi; S.K. Sah; Parveen Kumar; Sohan Lal; Sonia Devi; Monika
Kumaon and Garhwal regions are the chief terrains of Uttarakhand Himalaya. The present article simulates the strong ground motion of the 2011 IndoNepal earthquake in the Kumaon region using modified semi empirical technique (MSET). Acceleration records at ten stations in the near field region have been simulated which validates well with actual records and therefore confirms the reliability of MSET. In addition, MSET has been used to simulate strong motion records of future scenario earthquakes (Mw 7.0 and Mw 8.0) in Kumaon region by assuming the earthquake location same as that of 2011 IndoNepal earthquake. Isoacceleration maps are also provided, which reveals more than 400 gal value of PGA at epicentral distances less than 25 kms for an earthquake of magnitude 8.0. The comparison of isoacceleration map of future scenario earthquake (Mw 7.0) in Kumaon region has been done with isoacceleration map of 1991 Uttarkashi earthquake (Mw 6.8) in Garhwal region which suggests distinct attenuation characteristics of these two regions. © 2019, Springer Nature Switzerland AG.
Modeling of the strong ground motion of 25th April 2015 Nepal earthquake using modified semi-empirical technique
(Springer International Publishing, 2018) Sohan Lal; A. Joshi; Sandeep; Monu Tomer; Parveen Kumar; Chun-Hsiang Kuo; Che-Min Lin; Kuo-Liang Wen; M.L. Sharma
On 25th April, 2015 a hazardous earthquake of moment magnitude 7.9 occurred in Nepal. Accelerographs were used to record the Nepal earthquake which is installed in the Kumaon region in the Himalayan state of Uttrakhand. The distance of the recorded stations in the Kumaon region from the epicenter of the earthquake is about 420–515 km. Modified semi-empirical technique of modeling finite faults has been used in this paper to simulate strong earthquake at these stations. Source parameters of the Nepal aftershock have been also calculated using the Brune model in the present study which are used in the modeling of the Nepal main shock. The obtained value of the seismic moment and stress drop is 8.26 × 1025 dyn cm and 10.48 bar, respectively, for the aftershock from the Brune model.The simulated earthquake time series were compared with the observed records of the earthquake. The comparison of full waveform and its response spectra has been made to finalize the rupture parameters and its location. The rupture of the earthquake was propagated in the NE–SW direction from the hypocenter with the rupture velocity 3.0 km/s from a distance of 80 km from Kathmandu in NW direction at a depth of 12 km as per compared results. © 2018, Institute of Geophysics, Polish Academy of Sciences & Polish Academy of Sciences.
Modelling of strong motion generation areas for a great earthquake in central seismic gap region of Himalayas using the modified semi-empirical approach
(Springer, 2019) Sandeep; A. Joshi; S.K. Sah; Parveen Kumar; Sohan Lal; Kamal
Over the past decades, strong motion generation areas (SMGAs) have received significant attention in the modelling of high-frequency records. Herein, we propose the source model for a scenario earthquake (Mw 8.5) in the central seismic gap region of Himalayas. On the rupture plane, three SMGAs have been identified. Further, SMGA parameters are evaluated using available empirical relations. The spatiotemporal distribution of aftershocks is utilised to locate these SMGAs on the rupture plane. Further, the modified semi-empirical technique (MSET) is used to simulate the strong motion records. It has been observed that the study area can expect peak ground acceleration of >100cm/s2 and its distribution is mainly affected by the location of nucleation point in the rupture plane. Furthermore, the estimated peak ground acceleration (PGA) values are comparable with the earlier studies in the region. This confirms the robustness of generated rupture model with three SMGAs and the reliability of MSET to simulate high-frequency records. © 2019, Indian Academy of Sciences.
Simulation of Strong Ground Motion of the 2009 Bhutan Earthquake Using Modified Semi-Empirical Technique
(Birkhauser Verlag AG, 2017) Sandeep; A. Joshi; Sohan Lal; Parveen Kumar; S.K. Sah; Vandana; Kamal
On 21st September 2009 an earthquake of magnitude (Mw 6.1) occurred in the East Bhutan. This earthquake caused serious damage to the residential area and was widely felt in the Bhutan Himalaya and its adjoining area. We estimated the source model of this earthquake using modified semi empirical technique. In the rupture plane, several locations of nucleation point have been considered and finalised based on the minimum root mean square error of waveform comparison. In the present work observed and simulated waveforms has been compared at all the eight stations. Comparison of horizontal components of actual and simulated records at these stations confirms the estimated parameters of final rupture model and efficacy of the modified semi-empirical technique (Joshi et al., Nat Hazards 64:1029–1054, 2012b) of strong ground motion simulation. © 2017, Springer International Publishing AG.
Source model estimation of the 2005 Kyushu Earthquake, Japan using Modified Semi Empirical Technique
(Elsevier Ltd, 2017) Sandeep; A. Joshi; S.K. Sah; Parveen Kumar; Sohan Lal; Vandana; Kamal; R.S. Singh
The 2005 Kyushu earthquake (MW 6.6, MJMA 7.0) occurred northwest of Fukuoka, Japan causing much damage and injuries. Here, we model the earthquake's source using the data recorded at surrounding field stations. Two isolated strong motion generation areas (SMGA) are identified on the rupture plane. The parameters of each SMGA are estimated using source displacement spectra and then used the spatiotemporal distribution of aftershocks to identify possible locations of SMGAs on the rupture plane. A modified semi empirical technique (MSET) simulated the records for the estimated rupture model. We then compared the observed and simulated acceleration records from eight regional stations. A comparable match between the observed and simulated records confirms the robustness of two SMGA rupture model and ability of MSET to simulate strong ground motion. © 2017 Elsevier Ltd
Strong ground motion simulation techniques—a review in world context
(Springer, 2020) Sandeep Arora; A. Joshi; Pushpa Kumari; Parveen Kumar; Shashi Kant Sah; Sohan Lal; Nagendra Pratap Singh
Strong motion studies continue to be a very active field in seismology, and the use of simulation techniques in this context will continue to be an important endeavour in the coming years. Therefore, this review summarizes the recent progress and also pioneering efforts for the most prevalent simulation techniques including stochastic simulation technique (SST), empirical Green’s function technique (EGFT), composite source modelling technique (CSMT) and semi-empirical technique (SET). Attempts are also made to analyse the impact of each and every technique in terms of input parameters, output, advantages and limitations. The detailed analysis of trends we discussed herein indicates that every technique has its own metiers and flaws; hence, it is very difficult to select a simulation technique for a particular task. In conclusion, we hope that this overview would help the seismologists and earthquake engineers to look at this area of study from different angles to reveal some hidden opportunities. This will serve as an inspiration to improve the existing techniques for seismic hazard analysis and modelling of future earthquakes. © 2020, Saudi Society for Geosciences.
Strong motion generation area modelling of the 2008 Iwate earthquake, Japan using modified semi-empirical technique
(Springer, 2019) Sandeep; A. Joshi; Sonia Devi; Parveen Kumar; S.K. Sah; Sohan Lal; Kamal
The Iwate–Miyagi earthquake (Mw 6.9) of 14 June 2008 is one of the largest intraplate earthquakes that struck north-east Japan. This earthquake has produced the largest peak ground acceleration (PGA) ever recorded. The acceleration values 4022 and 1036 gal were observed at the surface and borehole accelerometers of IWTH25. To understand the cause of this extremely large acceleration, it is highly essential to obtain the detailed rupture process of Iwate–Miyagi earthquake. The present paper estimates the rupture model for this earthquake using the modified semi-empirical technique (MSET). The detailed analysis proposes one strong motion generation area (SMGA) in the rupture plane and nucleation point in the extreme western corner of the SMGA. Using this estimated source model, a satisfactory match is observed between the simulated and actual records. The quantitative analysis of these waveforms provides an almost 1:1 match for PGA values. Furthermore, the variation of these PGA values with epicentral distance shows similar attenuation rate. These results confirm the reliability of MSET and the estimated source model of this earthquake. To the best of our knowledge, this study is the first to model SMGAs in the rupture model using MSET and provides sufficiently reliable information which will be useful for seismic hazard prevention management. © 2019, Indian Academy of Sciences.