A Comprehensive Site Response and Site Classification of the Garhwal-Kumaun Himalaya, Central Seismic Gap (CSG), India

ABSTRACT

We attempted a comprehensive site response study of Garhwal-Kumaun Himalaya in the Central seismic Gap (CSG) using the data collected from 97 strong motion, microtremor and broadband stations. Site response parameters such as predominant frequency (f_peak), site amplification (A_max) and average shear-wave velocity up to a depth of 30 m (V_S30) were estimated by adopting the Nakamura technique. Spatial maps of these parameters were prepared to show the distribution of site response functions across the region. The estimated parameters show a good correlation with site geology. Decreasing order of sediment thickness from foothills to Lesser Himalaya was observed in the region. The estimated V_S30 values were correlated with global V_S30 values as well as available field measurements and 1D velocity inversion results, it shows a good agreement. The sites were classified as per the NEHRP site classification scheme based on the V_S30 value. From this study, we inferred that the V_S30 values estimated from the Nakamura technique can be used as an alternate proxy for determining the average shear wave velocity up to a depth of 30 m in the absence of substantial field measurements due to challenging terrain conditions. Such results of site response analysis may be used for preliminary earthquake hazard assessment in the region.

KEYWORDS:

• Site response
• Nakamura technique
• predominant frequency and amplification
• v_S30

Acknowledgments

We are thankful to MoES, New Delhi for the funding support (MoES/P.O. (Seismo)/1(311)/2017 dated 27/09/2019) to Seismic Network in Kumaun Himalaya research project for proceeding with this work. Authors are highly acknowledged to Head, Department of Geology, Kumaun University, Nainital for providing the infrastructure facility for research work and other necessary support. The authors would like to thank Director NRSC/ISRO for the necessary support to carry out the Microtremor survey. We would like to express our sincere gratitude to PESMOS for providing earthquake strong motion data (http://pesmos.in/2011/). We acknowledge GEOPSY software for providing free access to us (http://www.geopsy.org/forum/). We sincerely thank the anonymous reviewers and the Associate Editor, Prof. Kazuhiko Kawashima, for their constructive comments and suggestions, which enabled the authors to improve the manuscript significantly.

Declaration of Interest statement

Authors declare that they have no conflict of interest.

Additional information

Funding

This work was supported by the Ministry of Earth Sciences (MoES), New Delhi, India [MoES/P.O.(Seismo)/1(311)/2017].