B. K. Rastogi

Ambient noise levels in Gujarat State (India) seismic network

The Gujarat state seismic network (GSNet), comprising of 50 broadband seismograph (BBS) stations and 40 strong motion accelerographs (SMAs), has been operated and maintained by the Institute of Seismological Research (ISR) since 2006. Nineteen permanent BBS stations are connected through VSAT and the rest are kept in an offline mode. The local geology beneath seismic stations varies from Mesozoic to Quaternary formations. The seismic background noise (SBN) at these stations was calculated and found that it varies widely as a function of period, time and geographic location. We have studied the SBN variation along these three parameters for 14 online BBS stations of the GSNet. It was found that the stations located on the Deccan trap and Mesozoic formations are good sites with low SBN while stations on Quaternary, Tertiary and soft soil are noisy. The comparison between day and night noise spectra shows that SBN increases during the daytime at most of the stations. Three typical noisy peaks at three different periods were recorded at all of the stations, which is a global phenomenon. The results of this study will be helpful in selecting sites for future earthquake observations.

A review of strong motion studies in Gujarat State of western India

AbstractThe present work reviews the strong motion studies done in Gujarat State of western India. Prior to the 2001 Bhuj earthquake, no strong motion instrument was in operation in Gujarat. After the earthquake, number of research institutes/universities from India and abroad deployed strong motion instruments to study aftershock activity, source dynamics, path and site effects. The strong motion recordings have enhanced the general understanding of the physics of earthquakes in the region. An attempt has been made to develop attenuation relationship for the Gujarat region from the actual ground motions recorded by the strong motion networks. The Government of Gujarat with the help from Asian Development Bank, World Bank (WB), Ministry of Science and Technology and Ministry of Earth Sciences, Government of India, has established a permanent dense network of strong motion accelerograph (SMA) all over Gujarat. In addition, the Institute of Seismological Research has been established in Gandhinagar, Gujarat, with the help of WB for carrying out seismological research. Recently, many important studies have been carried out using actual acceleration data obtained from a dense network of 54 SMA, as well as synthetic data generated using region-specific ground motion parameters. The recorded data are used to obtain region-specific ground motion parameters and ground motion prediction equation. A deterministic hazard analysis for the entire state of Gujarat has been carried out using site-specific ground motion parameters. The estimated peak ground acceleration and modified Mercalli intensity values have been used to estimate the vulnerability of the different types of buildings in 31 cities of Gujarat. As Gujarat has three distinct regions having varied geological conditions, the recorded strong motion data gave an opportunity to study the effect of geological and local-site conditions on the response spectra. This study for an intra-plate region like Gujarat is a pioneer work. Still, lots of research work need to be carried out as more and more data are available, such as development of more robust ground motion prediction equations and a 3D-velocity structure of Gujarat. Generation of shake maps in real time and a credible early earthquake warning system is need of the hour for disaster mitigation and management.