Methodology for Seismic Hazard and Microzonation

Seismic Microzonation falls into the category of applied research. That is why it needs to be upgraded and revised based on the latest information. In Indian context, definition is Microzonation is subdivision of a region into zones that have relatively similar exposure to various earthquake related effects. This exercise is similar to the macro level hazard evaluation but requires more rigorous input about the site specific geological conditions, ground responses to earthquake motions and their effects on the safety of the constructions taking into consideration the design aspects of the buildings, ground conditions which would enhance the earthquake effects like the liquefaction of soil, the ground water conditions and the static and dynamic characteristics of foundations or of stability of slopes in the hilly terrain DST Expert Group on Microzonation of Delhi Chaired by Dr. A.S. Arya in 1998 and the definition was endorsed by the DST subcommittee on Microzonation, chaired by Mr. P.K. Narula in 2001. For the present investigation the seismic microzonation has been subdivided into three major items:

Evaluation of the expected input motion

Local Site effects and ground Response analysis

Preparation of microzonation maps.

The microzonation is graded based on the scale of the investigation and details of the study carried out. The technical committee on earthquake geotechnical engineering (TC4) of the International society of soil mechanics and foundation engineering (TC4-ISSMGE 1993) states that the first grade (Level I) map can be prepared with scale of 1:1,000,000-1:50,000 and the ground motion was assessed based on the historical earthquakes and existing information of geological and geomorphological maps. If the scale of the mapping is 1:100,000-1:10,000 and ground motion is assessed based on the microtremor and simplified geotechnical studies then it is called second grade (Level II) map. In the third grade (Level III) map ground motion has been assessed based on the complete geotechnical investigations and ground response analysis with a scale of 1:25,000-1:5,000.

Even though the step involved seismic hazard analysis and microzonation grouped in to three major groups as discussed in previous section, it need to adopt step by step procedure to arrive at the final map of microzonation. The steps followed in seismic hazard and microzonation of Bangalore in the present investigation is illustrated in the form of a flow chart in below Figure. The present investigation was carried out with a scale of 1:20,000 and ground motion are arrived based on the detailed geotechnical/geophysical investigations and ground response analysis. Hence, this study can be graded as third grade (Level III) seismic microzonation.

Department of Civil Engineering

Indian Institute of Science, Bangalore

Geology data

Seismology data

Seismotectonic data

Deep Geophysical data

Remote sensing data

Regional Attenuation law

Geology and Geomorphology

Soil Mapping

Geotechnical data

Shallow Geophysical data

Rock motion data

Geotechnical Data

Dynamic Properties

Experimental Study

   -Microtremor

Ground PGA

Magnitude of EQ

Soil properties with corrected “N” value

Experimental studies

Geology

Hydrogeology

Topography

Geotechnical data

Pre-existing stability

Geology and Seismology

Rock depth

Soil characterization

Response results

Liquefaction hazard

Landslide hazard

Tsunami hazard

Tsunamigenic Source map- longer distance

Tsunamigenic Earthquake estimation

Tsunamigenic Source parameter calculations

Only for hilly area

 

Flowchart: Alternate Process:

Only for coastal  area

 

Methodology followed for specific regions

 

Webpage is maintained by

Dr P Anbazhagan

Lecturer

Department of Civil Engg

Indian Institute of Science

Bangalore, India 560012

Input

 

Output

 

Suggestions and queries may be directed to Dr P Anbazhagan

Copyright  All Rights Reserved.

This page was last updated on August 25, 2011