Articles written in Journal of Earth System Science

    • Modelling of strong motion generation areas for a great earthquake in central seismic gap region of Himalayas using the modified semi-empirical approach

      Sandeep Joshi A Sah S K Parveen Kumar Sohan Lal Kamal

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      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 ($M_{\rm{w}}$ 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 >100 cm/s$^{2}$ 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.

    • Strong motion generation area modelling of the 2008 Iwate earthquake, Japan using modified semi-empirical technique


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      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.

    • Role of site effect for the evaluation of attenuation characteristics of P, S and coda waves in Kinnaur region, NW Himalaya


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      The site effect and attenuation studies are carried out for Kinnaur region of northwest Himalaya, India. A total of 109 local events happened in Kinnaur region of magnitude range 1.6–4.5, are utilized for present work. The earthquake records are influenced by the site effect depending on soft sediment thickness beneath the recording sites. Therefore, in the present study, records are corrected for site effects to estimate P ($Q_{p}$), S ($Q_{s}$) and coda ($Q_{c}$) wave quality factor. The regional frequency dependent attenuation relations, i.e., $Q_{p}$(f)$=$(29$\pm$1)$f^{(1.01±0.05)}$, $Q_{s}$ (f)$=$(38$\pm$5)$f^{(1.1±0.06)}$ and $Q_{c}$(f)$=$(74$\pm$11)$f^{(1.17±0.01)}$ are established for the Kinnaur region. The Kinnaur Himalaya mainly belongs to Higher Himalaya Crystalline (HHC) and Tethys Himalaya, where these two geological units are differentiated by the South Tibetan Detachment System (STDS). The resonance frequencies and attenuation characteristics are estimated for both regions, i.e., HHC and Tethys Himalaya. A comparison is made between HHC and Tethys Himalaya in the form of resonance frequencies and attenuation properties. The low value resonance frequency and high rate of attenuation towards the northern side of STDS, i.e., Tethys Himalaya support the presence of low-grade metasedimentary rocks. It suggests that Tethys Himalaya has high seismic hazard potential zone compared to HHC.


      $\bullet$Site effects have been incorporated to estimate attenuation characteristics of P, S and coda waves in Kinnaur region, NW Himalaya.

      $\bullet$The regional frequency dependent attenuation relations i.e., $Q_{p}$(f)=(29$\pm$1)$f^{(1.01±0.05)}$, $Q_{s}$ (f)=(38$\pm$5)$f^{(1.1±0.06)}$ and $Q_{c}$(f)=(74$\pm$11)$f^{(1.17±0.01)}$ are established for the Kinnaur region. The close resemblance of resonance frequencies with the geology of the study region has been observed.

      $\bullet$The Tethys Himalaya lies in present study region has high seismic hazard potential zone as compare to Higher Himalaya Crystalline.

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