A Workshop on Microzonation

26th & 27th June 2007


Microzonation has generally been recognized as the most accepted tool in seismic hazard assessment and risk evaluation. Making improvements on the conventional zonation maps and regional hazard maps, microzonation of a region generates detailed maps that predict the hazard at much smaller scales from one block of a city to another, for example. Damage patterns of many recent earthquakes around the world, including the 1999 Chamoli and 2001 Bhuj earthquakes India, have demonstrated that the soil conditions at a site may have a major effect on the level of ground shaking. For example, the Chamoli earthquake located more than 250 km from away from Delhi caused moderate damage to some of the buildings built on filled land or on soft alluvium. The Bhuj earthquake caused severe damage not only in the epicentral region, but even in Ahmedabad, about 200 km away, attributed to increased ground shaking on the soft alluvium.

In the modern urban planning and development, microzonation of seismic hazard is an important aspect, for seismic design, estimation of liquefaction potential, land use planning as well as for addressing insurance concerns. Thus, microzonation of major cities and other regions likely to be affected by future near or distant earthquakes is now regarded as an inevitable aspect of earthquake studies.

Mapping the seismic hazard at local scales to incorporate the effects of local ground conditions is the essence of microzonation. Earthquake damage is commonly controlled by three interacting factors- source and path characteristics, local geological and Geotechnical conditions and design of the structures. Seismic microzontaion is the process of assessment of the first two factors to provide a basis for estimating and mapping potential damage to buildings, which in other words is quantification of the risk. Obviously, all of this would require analysis and presentation of a large amount of data geologic, seismologic, engineering specifications etc. History of earthquakes, geometry and history of faults in the region, attenuation relationships, and ground amplification, liquefaction susceptibility are only few of the important inputs required. Presenting all of this information in the proper format, for the use of planners, developers, insurance companies etc. is another important aspect of microzonation. Considering the social and economic implications of this exercise, it is important that each of the parameters is carefully represented and the maps are presented with clarity, in appropriate scales and user friendly formats.

The existence of many earthquake source zones, associated with the northern Himalayan plate boundary and the seismogenic structures within the plate interiors (Narmada, Kutch rift basins etc) and other non rifted regions like Latur (Killari) that have generated damaging earthquakes, makes many urban and semi urban cities of India quite vulnerable to earthquakes. With the increasing pace of urban development, there is a compelling need to understand the effect of moderate/large earthquakes to the cities located close to, or with in the impact zone of such earthquakes.

Ever since the pilot study of microzonation of Jabalpur, various techniques of hazard assessment that would eventually lead to microzonation are being practiced in India. Under the DSTís Seismicity Programme, there have been several initiatives to do microzonation of major cities. These efforts are in various stages of progress, for the cities of Bangalore, Ahmedabad, Sikkim, Delhi and Gauwhati.

As implied above the procedures for microzonation involves various steps and analysis of a large amount of multidisciplinary data. It also requires many specialists to work together. Where data are not available (or if they just cannot be generated, like data on earthquake recurrence for Peninsular India), these limitations must be reflected.

Although several efforts are on for microzonation of selected regions in India, these studies are under development. The procedures are often modified or simplified and these are not adequately reflected in the final product. So also are the missing gaps in data, treatment of the data etc. There is also an increasing tendency to do a partial or incomplete analysis of some data available, prepare some maps using such data and refer to them as microzonation maps. Because of the possible inconsistencies between the procedures followed by various workers and the maps developed would be unacceptable to the end users. Thus there is a need to streamline the same and develop the standard procedures.

A 2-day workshop on microzonation, at IISc, Bangalore to discuss and finalize the following objectives:

1. The concepts behind microzonation and why it should be done in India.

2. The results of the ongoing projects.

3. Techniques and procedures followed elsewhere and how these can be used in the context of our studies.

4. To develop a set of standard procedures that may be followed by all those who are involved in these efforts.

5. Explore the possibilities of bringing out a special issue on this topic.

This workshop will be useful to and can be attended by National,state and local government agencies, Decision makers, Engineers, Planners, Emergency response organizations, Builders,Universities, and general public

Department of Civil Engineering
Indian Institute of Science
Bangalore - 560012