GIS@development May - June 1999; Application of Geodesy to monitor earthquake hazard: An overview

Application of Geodesy to monitor earthquake hazard: An overview

Prof. Madhav N. Kulkarni
Civil Engineering Department, IIT Bombay

With the rapid developments in the fields of modern geodesy and unprecedented accuracy achievable in geodetic measurements, the geodetic techniques have gained wider acceptance worldwide for monitoring crustal dynamics.

Geodesy, the science of measurements related to the Earth, includes in its vast scope the determination of the size, shape and gravity field of the Earth and accurate mapping of the Earth’s surface. The Earth and all the other celestial bodies are in continuous motion related to each other; undergoing translations, rotations and deformations; hence to monitor and describe their motions and positions in space and in time, a precise system of reference frame need to be established. Monitoring the crustal movements (Neotectonics) is an important aspect of the difficult and complex tasks of Geodesy & Geodynamics. These crustal movements include the global motion involving the different plates, the regional motions, and the local movements. Various geodetic observation systems are available for this purpose - classical geodetic techniques of triangulation and levelling, astronomical observations, Lunar Laser Ranging (LLR), Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), Global Positioning System (GPS) etc.

The recent earthquakes in Chamoli area, which caused extensive losses in terms of human lives and property, have once again highlighted the importance of monitoring the seismotectonic activities, not only in the earthquake-affected areas, but also in the entire country. The importance of monitoring the dynamics of the earth’s crust, in order to gain a better insight in to the earthquake mechanism, with the ultimate aim of predicting the occurrence of earthquake with high degree of reliability, can hardly be overemphasized. Several techniques are being used by scientists for this purpose, and large amount of data of diverse nature are being generated and analysed for such studies. These include seismic monitoring, geological studies, geophysical techniques, geodetic techniques, and few other methods such as animal behavior, etc. the geodetic techniques have gained wider acceptance for this application, due to their high accuracy and reliability.

The Geodetic & Research Branch (G&RB) of Survey of India is carrying out the geodetic surveys for over two centuries, for the primary purpose of national mapping. The extensive horizontal and vertical geodetic and geophysical control network established for this 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 been undertaken as extra-departmental tasks. During the period from 1984 to 1992, a small seismotectonic cell comprising about 15 technical personnel was also functioning, exclusively working in the Himalayan region. After 1993 Latur earthquake, geodetic investigations have been taken up in that area, and an extended plan to extend such studies, by Global Positioning System (GPS) surveys, to the Peninsular Shield of India, is being implemented.

Many different methods are being used in different parts of the world to monitor earthquake activities by monitoring the dynamics of the earth’s crust. The most common method is the employment of a dense network of seismographs to continuously monitor the seismic activities in the region. To supplement this monitoring, geological, geophysical, geodetic and other techniques are used to study the changes in the Earth’s crust. With the phenomenal advancements in the space geodetic techniques, and the high accuracy achievable through modern geodetic instrumentation like the Global Positioning System (GPS), Very Long Baseline Inferferometry (VLBI), Satellite Laser ranging (SLR) and Lunar Laser Ranging (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.

Geodetic Techniques:
The classical and modern geodetic techniques being used to establish horizontal, vertical, geomagnetic, and tidal control networks can be classified as below:

Terrestrial Techniques:

Geodetic Triangulation

Electronic Distance Measuring instrument (EDM)Traverse

Astrogeodetic Methods

Precision Leveling
Space Techniques:
- Doppler Satellite Surveying System
- GPS
- VLBI
- SLR
- LLR
- Other Space Geodetic Techniques like LORAN, DORIS,etc.
Geophysical Techniques in Geodesy:
- Gravimetric Surveys
- Geomagnetic Surveys
Tidal Observations and Prediction:
High Precision geodetic instruments including precision theodolites, precise levels, GPS receivers, EDMs Gravimeters, Magnetometers, Tide gauges, etc are being used by G&RB for such geodetic surveys, and proposals for procurement of VLBI, SLR etc are being pursued.

Geodetic Studies to monitor Seismotectonics in India
The Geodetic and Research Branch of Survey of India has been carrying out crustal movement studies in various parts of the country mainly as extra-departmental tasks. The Seismicity & Seismotectonic cell (ST Cell) which functioned under an All India Coordinate Project from 1984 till 1993, carried out several such studies exclusively in Himalayas. After the 1993 Latur earthquake, geodetic investigations have been taken up to monitor the seismotectonic activities of Latur region, and also of the entire Peninsular Shield of India.
Geodetic Investigations for Latur area
After the 1993 Latur earthquake, Survey of India submitted detailed proposal for post-earthquake studies of the affected area as a short-term measure and monitoring the seismotectonic activity in the entire country as a long-term plan. Keeping in view the importance of the task, as also highlighted by the UN experts Committee and the World Bank experts, immediate geodetic studies in the area were taken up. Geodetic observations including precision levelling, GPS, gravimetric surveys were carried out in the region during the field seasons from 1992-94 and 1996-97, and reports based on preliminary analysis of the data collected have been submitted. The details of the work done, data collected, methodology used, data analysis, results obtained, and the conclusions drawn, etc are given in these reports. It is planned to continue these studies.
GIS & other Geodetic Studies for Peninsular Shield
The Peninsular Shield of India can no longer be considered to be seismically inactive, as shown by the Koyna & Latur earthquakes, it is necessary to monitor the crustal movements in this region on a regular basis. This was also emphasized by the UN Experts Committee after the 1993 Latur earthquake. This committee has recommended dense GPS and also vertical control for this region, to monitor the seismotectonic activities. Based on this (DST), Survey of India submitted a proposal for geodetic monitoring of the Peninsular Shield, with emphasis on GPS surveys. The proposal has been accepted, and work has been started in 1996. Major augmentation of resources, including instrumentation, manpower, budgetary allocation, etc has been done for this.
Proposed National GPS for Geodynamics Network
In order to evolve a ‘National Programme on GPS for Geodynamic Study 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 under the Chairmanship of the Surveyor General of India, in 1997. The Expert Group, comprising 14 scientists/experts from 10 institutions, has evolved an extensive National Plan as described in the Report submitted to DST in Feb 1998. The National GPS Network for Geodynamics, recommended by the Expert Group and now being implemented in a project by DST, consists of 27 permanent GPS stations to be established for this purpose, a total of about 280 semi-permanent GPS stations in NW and NE Himalayan regions, and many more field GPS stations to be established in project mode. A National GPS Data Centre is also proposed to be established at Survey of India, Dehradun, under this project. For details, see DST (1998).
Suggestions for Future Work
The following suggestions for future work in this direction are presented here:
- As outlined above, an integrated approach is required to understand & monitor the earthquake activities in the country. It is essential that co-ordination at all levels must be ensured to facilitate smooth functioning of the entire system, easy data exchange, and scientific co-operation. Frequent meetings of the agencies involved in the work, and close monitoring are essential for the purpose.
- It is important that the seismotectonic investigations in the entire country using GPS are monitored in a systematic manner, to include the establishment of :
  - few permanent GPS Reference Stations to monitor the inter-plate & intra-plate deformations.
  - a Zero Order GPS Network, and repeat observations of the same at suitable interval, to identify the active regions.
  - local dense networks in the areas identified as active zones.
- Resources augmentation for the short term plan as immediate measure and for the long term plan as a permanent measure is recommended, as required.
- It is recommended that as a long-term measure, an Institute/Directorate of Geodesy for Seismotectonic studies should be established for this task.
Conclusions
v An integrated approach to include input from several diverse techniques is a must for understanding and monitoring the earthquake activities. Geodetic techniques, due to their high accuracy and reliability, form a very important component of this earthquake monitoring mechanism. The Geodetic methods demand skilled manpower, experience, precise instrumentation, dedicated field work, detailed data analysis, and expertise in the field. Many organisations in India with their experience, and their extensive database, have a required expertise for this task, however, resource augmentation and co-ordinated efforts are required for this purpose. Reference
1. Bilham Roger, P. Bodin, M. Jackson (1995), Entertaining a Great Earth Quake in Western Nepal: Historic Inactivity and Geodetic Test……., Journal of Nepal Geological Society, 1995, Volume 11, pp 73-78
2. DST (1998) Report of GPS Expert Group on National Programme for GPS and Geodetic Studies.
3. Kulkarni, M. N. (1986). Geodetic Surveys for Dam Deformation Studies, Indian Surveyor, Jan.
4. Kulkarni, M. N. & B. C. Roy (1995) Geodetic VLBI to monitor Crustal Dynamics in India, International Workshop on Latur Earthquake, NGRI, Hyderabad, Oct.
5. Kulkarni, M. N. (1996). Monitoring Crustal Dynamics using GPS, Seminar on GPS, WIHG, Dehradun, March.
6. Kulkarni, M. N. (1997). Application of Geodesy to monitor earthquake hazard, Geomatics-97 Conference, IIRS, Dehradun, Sept.
7. Roy, B. C. and N. P. Sinha Roy (1993). Emergence of Reverse trend in Doon Valley, G&RB, Dehradun.
8. Roy, B. C. and Kulkarni, M. N. (1995). Geodetic aspects of Monitoring Seismotectonics in India, presented at International Workshop on Latur Earthquake, NGRI, Hyderabad.