Application of GPS for studies of the earthquake - Affected areas in Gujarat
Madhav N. Kulkarni Civil Engineering Department, Indian Institute of Technology, Bombay. Mumbai Application of Geodesy for Earthquake Studies in India With the rapid developments in the field of modern geodesy, and with the unprecedented accuracy achievable in geodetic measurements using advanced techniques, the geodetic methods have gained wider acceptance world-wide for monitoring crustal dynamics for earthquake studies. Starting with the classical geodetic techniques like triangulation, astronomic & gravimetric surveys and precision levelling, the introduction of Electronic Distance Measuring (EDM) instruments, and more recently, the space geodetic techniques, the scope of application of geodesy for this important purpose has widened. With the phenomenal advancements in the space geodetic techniques, and the high accuracy achievable through modern geodetic instrumentation like the GPS, VLBI, SLR, LLR etc., the Geodetic techniques have gained importance for monitoring the crustal dynamics. Thus, due to their accuracy and reliability, the geodetic techniques have become an important component of the integrated studies to understand the earthquake mechanism. However, the need for an integrated approach by combining data from these diverse techniques in an integrated analysis to understand this complex process must be stressed here, as none of these techniques alone can yield a complete insight into the earthquake generating mechanism. In India, an extensive high precision Geodetic & Geophysical control network has been established by Survey of India (SOI), the national mapping agency of Govt. of India, for the primary purpose of national mapping, through dedecated efforts of over two centuries. More recently, various national organisations and institutions, including Geological Survey of India (GSI), National Geophysical Research Institute (NGRI), Indian Institute of Geomagnetism (IIG), Indian Institute of Technology Bombay (IITB), Centre for Mathematical Modelling & Computer Simulation (CMMACS), Bangalore, etc. have taken up geodetic, geophysical and geological surveys for specific purposes. The extensive horizontal and vertical geodetic and geophysical control network established through these collaborative efforts, and the huge amount of valuable data thus generated, have contributed significantly towards monitoring the crustal dynamics of the Indian sub-continent. Several specific projects for geodetic monitoring of local and regional crustal deformations in the entire country have also been undertaken in earthquake-affected areas. In the past, the geodetic studies were carried out using the conventional terrestrial techniques, mostly by SOI, which consisted of establishing a dense high precision geodetic survey control network of survey pillars, bench marks and bases, around the location of the active fault under investigation, using conventional geodetic instruments and techniques. Repeat observations over this network, carried out periodically, would provide precise estimates of the crustal deformation vectors and velocities, rotations, etc. in horizontal as well as vertical directions, between the observation epochs. During the period from 1984 to 1992, an inter-disciplinary national programme for seismotectonic studies in the Himalayan region, involving 11 Government institutions, which was functioning under the Department of Science & Technology (DST), Government of India, has collected valuable data for such studies. After the 1993 Latur earthquake, extensive geodetic and GPS investigations have been taken up in that region, and a comprehensive plan to extend such studies, by GPS surveys, to the Peninsular Shield of India and the Himalayan region, is also being implemented by DST. In order to evolve a 'National Programme on GPS for Geodynamic Studies in India', by integrating the GPS control network for Peninsular Shield, and other existing GPS stations, to cover the entire country, DST set up a GPS Expert Group, which evolved an extensive programme. This National GPS Network for Geodynamics, recommended by the Expert Group and now being implemented in a Project by DST, consists of permanent, semi-permanent, and many field GPS stations to be established in campaign mode, to monitor the crustal deformations. Several GPS research groups are engaged in studies of specific regions under this National programme. The GPS teams of IITB, CMMACS and IIG have now undertaken GPS studies for monitoring the post-earthquake deformations in the Gujarat area, after the Jan. 2001 earthquake. Introduction The tragic earthquake that struck Gujarat on 26 Jan. 2001, destroying lives & property, has once again highlighted the need and importance of the contribution of engineers and scientists to social and national cause, during such national calamities. Keeping in view the urgent nature of the work, and our responsibility as a Department of an Institute of national Importance, faculty members and students of Civil Engg. Department took up immediate work in the area. The satellite-based geodetic technique of Global Positioning System (GPS) has evolved as an important technique for Earthquake studies. GPS is being used by all the earthquake-affected countries for studying crustal deformations due to seismic activity. As a part of the National GPS for Earthquake Studies Programme of Dept. of Science & Technology (DST), Govt. of India, under a DST-funded project, with Prof. Madhav N. Kulkarni of Civl Engg. Dept., IIT Bombay as Principal Investigator, GPS studies have been taken up in the Koyna area. It is important to study the post-earthquake related crustal deformations in the tragic earthquake which took place in the Bhuj area of Gujarat on 26 Jan. 2001. For this purpose, GPS field data collection has been taken up by a team of research fellows and students of the Dept., under the guidance of Prof. M. N. Kulkarni, are carrying out GPS work in the area on priority basis, as a DST-funded project. Work Plan A collaborative work, involving the GPS teams from IIT Bombay, Centre for Mathematical Modelling & Computer Simulation (CMMACS), CSIR, Bangalore, and Indian Institute of Geomagnetism (IIG), Mumbai, has been taken up, to carry out immediate GPS observations in the earthquake-affected area of Gujarat near Bhuj, to understand the post-earthquake crustal deformation pattern, and for monitoring crustal dynamics in this earthquake-affected region in the future. GPS teams from University of Colarado, USA, and University of Tokyo, Japan are also carrying out GPS observations in the area, and the joint work is being co-ordinated by Prof. M. N. Kulkarni. It is proposed to establish about 25-30 GPS stations in the area, and few reference stations outside the earthquake affected region. The aim of establishing these stations is to monitor the deformations of the region from a reference point outside the region, and to monitor the deformations of the region near the epicentre. These observations will be useful in estimating the crustal deformations in the region, using GPS repeat observations in the future also. Personnel & Instrumentation
The post-earthquake GPS studies, and the repeat observations subsequently, is expected to yield valuable data related to this tragic earthquake. Detailed results will be presented after data processing and analysis. References:
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