A JOSHI
Articles written in Journal of Earth System Science
Volume 128 Issue 8 December 2019 Article ID 0202 Research Article
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.
Volume 131 All articles Published: 16 August 2022 Article ID 0180 Letter
PARUL BHARDWAJ A JOSHI MOHIT PANDEY MRITYUNJAY BHARGAV
The Uttarakhand Himalaya which lies in the central seismic gap region of Himalaya is divided into the Garhwal and Kumaon Himalayas. Several studies by different workers confirm differential attenuation behaviour of shear wave in the Garhwal and Kumaon Himalaya. In the present study, the shear wave velocity structure has been estimated using strong motion data and ambient noise data recorded in these two regions. In this study, the SH-wave transfer function of the Haskell–Thompson matrix has been calculated using the initial shear wave velocity model selected through the genetic algorithm (GA) approach and is compared with the HVSR curve obtained from strong motion data and ambient noise data. The total number of 38 strong motion records together with the ambient noise record that lies between the MBT and MCT has been used in the present study. The obtained velocity model has been used to prepare three-dimensional velocity surrounding Askot which confirms the presence of klippe in the region. The average shear wave velocity at different depths has been calculated for all investigated data in Garhwal and Kumaon Himalaya. The comparison of the average shear wave velocity model obtained for the Garhwal and Kumaon regions shows that the shear wave velocity in Garhwal Himalaya is comparatively higher than that in the Kumaon Himalaya. The average shear wave velocity at 30 m depth in Garhwal and Kumaon Himalaya is found to be in the range of 274–577 and 233–531 m/s, respectively. The results show that the region of Garhwal and Kumaon Himalaya that was taken in the present study fall under the C and D type site category according to National Earthquake Hazards Reduction Program (NEHRP) site classification. Low-velocity stioff soil mostly covers the Kumaon Himalaya region while in Garhwal Himalaya, the region is covered with high-velocity soft rocks. Most of the regions in Kumaon Himalaya are covered by high predominant frequency values as compared to that in the Garhwal Himalaya which indicates the presence of thin sediment layers overlying the basement rocks in Kumaon Himalaya. The average predominant frequency in Garhwal and Kumaon Himalaya ranges from 2.4–15 and 2.5–18.4 Hz, respectively. The anelastic attenuation factor has also been calculated using obtained shear wave quality factor and obtained shear wave velocities at different depths which supports the high attenuation of seismic energy in Kumaon Himalaya as compared to the Garhwal Himalaya.
Volume 131 All articles Published: 5 October 2022 Article ID 0216 Letter
A JOSHI MOHIT PANDEY MRITYUNJAY SAURABH SHARMA JYOTI SINGH RICHA RASTOGI ABHISHEK
Site and topography effects are integral part of strong ground motion recorded during an earthquake. Site effects due to shallow subsurface velocity and topographic changes have been clearly seen in the Gorkha earthquake, 25th April, 2015 ($M_w$ 7.8) at Kapkot and Berinag stations, which lies at an epicentral distance of 507 and 485 km, respectively. The high peak ground acceleration was recorded at Kapkot station that is at valley, while comparatively low peak ground acceleration was recorded at Berinag station that is at hill. This paper investigates the effect of site topography and shallow velocity structure on ground acceleration generated due to propagation of SH wave generated by a finite far-field rupture. The propagation of SH wave in a shallow subsurface earth model with the vertical variation of velocity can be modelled by finite difference (FD) method based on staggered algorithm that can effectively model the propagation of the seismic wave in isotropic as well as heterogeneous elastic medium. This paper discusses the role of staggered algorithm in the generation of particle motion at the surface of modelled earth characterized by surface topography and vertical distribution of elastic constants. The developed software for FD modelling of the medium has been tested for SH wave propagation in a purely elastic medium in terms of numerical stability, dispersion and boundary conditions. Numerical experiments show that the method effectively models the topography and thin surface velocity layers in the model for varying cases. The obtained surface acceleration records from the propagation of SH wave at Kapkot and Berinag clearly show that both the site amplification and topographic effects have played a vital role in shaping the accelerograms at these stations.
Volume 131 All articles Published: 28 October 2022 Article ID 0232 Research article
Three-dimensional attenuation tomography of Garhwal Himalaya, India obtained from strong motion data
MOHIT PANDEY A JOSHI SAURABH SHARMA JYOTI SINGH SANDEEP SINGH
This paper investigates the three-dimensional frequency-dependent attenuation structure of the Garhwal
Himalaya in the Indian subcontinent. Based on the distribution of earthquakes and recording stations in
the Garhwal Himalaya, the entire region of 152 ${\times}$ 94 km$^2$ is divided into 108 three-dimensional uniform
rectangular blocks. These blocks are assumed to be of thickness 5 km that extends to 15 km depth. Each
block represents the rock of different attenuation coefficients. The S-phase of strong motion records has
been used to estimate the shear wave quality factor in each block by the inversion of spectral acceleration
data. The inversion of spectral acceleration data is based on the modified technique of Joshi (2007) and
Joshi
Volume 132, 2023
All articles
Continuous Article Publishing mode
Click here for Editorial Note on CAP Mode
© 2023-2024 Indian Academy of Sciences, Bengaluru.