SEISMIC MICROZONATION OF A REGION BASED ON …...Microzonation studies in India, which is inadequate to represent local site effects. More importance shall be given to geotechnical

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International Journal of Advanced Research in Engineering and Technology (IJARET) Volume 8, Issue 6, November - December 2017, pp. 55–64, Article ID: IJARET_08_06_006

Available online at http://www.iaeme.com/IJARET/issues.asp?JType=IJARET&VType=8&IType=6

ISSN Print: 0976-6480 and ISSN Online: 0976-6499

© IAEME Publication

SEISMIC MICROZONATION OF A REGION

BASED ON SEISMOLOGY AND GEOLOGICAL

DATA

R. Manigandan

Department of Civil Engineering, College of Engineering Guindy,

Anna University, Chennai, Tamil Nadu, India

R. Thiyagarajan

Teaching Fellow, Department of Civil Engineering, College of Engineering Guindy,

Anna University, Chennai, Tamil Nadu, India

ABSTRACT

In current and past, massive earthquakes have leads to an huge loss of lives and

non-lives in the world (Armenia, 1988; Iran, 1990; US, 1994; Japan, 1995; Turkey,

1999; Taiwan, 1999, India 2001, Sumatra 2004, Pakistan, 2005, China 2008,) On

January 26, India’s 51 republic day 2001 at 08:46AM local time (3:16 UTC) Bhuj

Earthquake, one of the major devastating earthquakes ever to strike India occurred in

the Kachchh region of Gujarat in western India. The magnitude of 7.9(Mw) (6.9

Richter scale), and the depth of 16 Km(10mi), the damage was very big impact is

round the radius of 350kms. The epicenter was about 9km south-southwest of the

village of chobari in bhachau taltauka of kutch district of Gujarat, including major

cities like Ahmedabad, Bhavnagar and Surat at a distance of 240 km, 275 km and 350

km respectively. The damage incurred as well as past earthquake depends not only on

the intensity of the earthquake magnitude (source) but, in consideration to a large

extent, on the medium scale through which the seismic waves propagate (path of

waves propagation and site effects like soil condition) and the social-economic

development of the human settlement (Panza et al., 2001). Many huge cities in India

are situated in the severe earthquake hazard threat in the vicinity of Himalayan region

and even in peninsular shield. Macrozonation map in Indian seismic code 1893 is

frequently revised soon after a major earthquake. New revision was published in 2002

after Bhuj earthquake in 2001, which is of many recent earth quake is to be

considered in with adequate data at an new revision to contains four macro zones.

Revision of the map can efficiently be done by considering the geotechnical aspect

of the regions. Microzonation is an effective tool and a preventive step for reducing

the impact of earthquake in a particular region. The Microzonation map allows us to

characterize the seismic potential areas, which are important in the design of

structures. It is done by the sub division of region into micro zones.

The present study presents a review on the development of the seismic

microzonation studies. Seismic microzonation work has been carried out in India in

Seismic Microzonation of a Region Based on Seismology and Geological Data


some of the important mega cities that have the potential of being damaged from

future earthquakes. As part of the national level microzonation programme,

department of science and technology, Government of India has done microzonation of

63 cities in India. Some of them are finished and some of them are ongoing. As an

initial experiment, seismic hazard analysis and Microzonation was taken up for

Jabalpur city in Madhaya Pradesh. Further, for many other cities such as sikkam,

Mumbai, Delhi, North east India, Gauwhati, Ahmedabad,Bhuj and Chennai an

attempt has been made to carry out microzonation considering geomorphological

features and detailed geotechnical studies.

In this paper, the Microzonation studies carried out in different cities of India with

different methodologies used by various researchers will be discussed. Further, the

merits and limitations of these studies have also been highlighted. Seismic

Microzonation studies in India lack few aspects/issues which can be broadly classified

into three groups:

1. Seismology (features).

2. Grade and geology related (past and current data).

3. Geotechnical related issues.

Most of Microzonation studies do not have proper regional seismotectonic maps

for the study area. Seismic Microzonation maps published are based on deterministic

seismic hazard analysis for different possible scenario earthquakes. This may be

improved by considering uncertainties involved in the earthquake and produce the

hazard map with required probability and return periods. Seismic Microzonation

maps produced does not have a uniform scale, which may be generalized under the

uniform grade and scale of mapping. Importance of geology plays a major role in

Microzonation studies in India, which is inadequate to represent local site effects.

More importance shall be given to geotechnical

Key words: Microzonation, Mapping, Seismic, Geotechnical, Earthquake, Hazards,

Epicenter.

Cite this Article: R. Manigandan and R.Thiyagarajan, Seismic Microzonation of a

Region Based on Seismology and Geological Data. International Journal of Advanced

Research in Engineering and Technology, 8(6), 2017, pp 55–64.

http://www.iaeme.com/IJARET/issues.asp?JType=IJARET&VType=8&IType=6

1. INTRODUCTION

Seismic Microzonation is a subdividing of a region into smaller areas having different

potential for hazardous earthquake effects. The earthquake effects depend on ground

geomorphological attributes consisting of geological, geomorphology and geotechnical

information. The parameters of geology and geomorphology, soil coverage/thickness, and

rock outcrop/depth are some of the important geomorphological attributes. Other attributes

are the earthquake parameters, which are estimated by hazard analysis and effects of local soil

for a hazard (local site response for an earthquake). The Peak Ground Acceleration (PGA)

[from deterministic or probabilistic approach], amplification/ site response, predominant

frequency, liquefaction and landslide due to earthquakes are some of the important

seismological attributes. Weight of the attributes depends on the region and decision maker,

for example flat terrain has weight of “0” value for landslide and deep soil terrain has highest

weight for site response or liquefaction.

R. Manigandan and R.Thiyagarajan


Seismic zoning consists of subdividing a national territory into several seismic zones

indicating progressive levels of expected seismic intensity or peak ground acceleration for

different return periods based on historic and predicted intensity of ground motion. It is

common to see countries classified into three, four or more seismic zones and seismic design

requirements for buildings are generally the same within a defined seismic zone. Such maps

are small scale maps covering a large territory.

Seismic microzoning provides detailed information on earthquake hazard on a much

larger scale. It recognizes the fact that spectral acceleration values for sites within a seismic

zone vary in tune with the location specific geological conditions. It therefore consists of

mapping in detail all possible earthquake and earthquake induced hazards. It necessarily

involves seismological, geological, geotechnical and hydro-geological mapping and their

integration to provide a picture of levels of hazard distribution comprehensible to urban

planners, engineers and architects.

Levels of Seismic Microzonation generally float with the choice of scale of mapping as

also with the degree and scope of scientific investigation fashioned to minimize uncertainties

in seismic hazard evaluation for a specific set of objectives. The quantum and quality of basic

maps and information required for making a head with the mapping work are rarely available.

Since seismic microzonation work cannot wait for all the required information, a first cut

microzonation map is prepared based on a minimum programme of investigation. Choosing

an appropriate mapping scale and thinking to scale while mapping are the two challenges

common to every such programme. What is to be included and what is to be left out for future

investigation will have to be decided on a case to case basis. Degree of detailing and scrutiny

expands with increase of mapping scale.

Figure 1 Three Grades of Seismic Microzonation Recommended by the Technical Committee of

International Society of Soil Mechanics and Foundation Engineering [ISSMF]

Three levels of Seismic Microzonation expressed as Grade1: General Zonation; Grade 2:

Detailed Zonation and Grade 3: Rigorous Zonation were favoured by the Technical

Committee on Earthquake Geotechnical Engineering of the International Society of Soil

Mechanics and Foundation Engineering (1993). The recommendation essentially meant

making a beginning with relatively small scale mapping and move on to higher levels of

microzonation by obtaining added quality inputs that could justify large scale mapping.

The population of the country is crossing leaps and bounds and a great revolution is taking

place in the human living standards. The developments are seen in various fields, but when

we come across the natural disasters that have been occurred in the past history, we can see a



great destruction in the society. India has been facing the threat of earthquake quite from

ancient time. Earthquake is one among the major natural disasters that are been created due to

the seismic waves generated from plain bed region.

Earthquakes come up with a devastating scene for both public and government. Today

tall raise building is being in trend, hence the design of such structure should be made by

considering the seismic action of the region. The effect of the earthquake depends upon the

local site condition. It is found that the presence of an unconsolidated soil profile can amplify

the seismic waves at the time of earthquake. They are highly prone zones to earthquake. The

presences of a hard stratum can reduce the magnitude and frequency of the seismic waves.

The seismic hazard analysis can be made by using the ground motion at the time of

earthquake and liquefaction of the soil present. The dynamic site characterization of a sub-

surface soil in a region helps us to determine the average dynamic behavior of the subsurface

at the time of the earthquake. The liquefaction of the soil happens when the vibration or the

water pressure within the soil causes the particles to come in contact with one another. This

condition is caused because of seismic waves that propagate through soil and makes it loose

layer resulting with the loss of support. After the bhuj earthquake at Gujarat in 2001, the

government has encouraged for the microzonation of the cities. A serious thinking is

necessary on the account of town planning and designing of structures based on the

microzonation in order to reduce the effect of earthquake hazard. Microzonation map is now

a foremost tool that acts as a preventive measure for determining seismic hazard on land mass

usage.

2. METHODOLOGY

A general methodology in doing the seismic microzonation of a region can be divided into the

following four major heads2:

Estimation of the ground motion parameters using the historical seismicity and recorded

earthquake motion data which includes the location of potential sources, magnitude,

mechanism, epicentral distances.

Site characterization using geological, geomorphological, geophysical and geotechnical

data.

Assessment of the local site effects which includes site amplification, predominant

frequency, liquefaction hazard, landslides, tsunami etc.

Preparation of the seismic microzonation maps



Figure 2 General Frame Work for Seismic Microzonation Studies

These are the method to analysis to determine the soil properties of the location

Multichannel analysis for surface waves(MASW)

Spectral analysis of surface waves (SASW)

Microtremor analysis(MA)

Standard penetration test(SPT)

penetration test(CPT)

Beeker penetration test(BPT)



2.1. Multichannel analysis for surface waves (MASW)

An illustration of the overall procedure and main advantage of MASW method. Complicated

nature of seismic waves is carried over into the measurement.

Figure 3 Schematic of a Prototype Field System Recently Developed and Tested in future MSAW

Survey.

2.2. Spectural analysis of surface waves (SASW)

This tests allow the user to determine the different profiles in pavement layers or soil layers,

including the depth, velocity and also the condition of each of these layers. It is all done non-

destructively from the top surface of the pavement.

Figure 4 Thypically views on Velocity Transducers with Sub-layers

In SASW tests, two receivers are placed on the surface and a hammer is used to generate

the wave energy. Short receiver. Spacing are used to sample the shallow layers while long

receivers. spacing is used in sampling the deep materials Two profile, a forward profile and a

reverse profile, are typically obtained in SASW measurements where the accessible surface is

struck by a hammer on two opposite Sides of the receivers. A singal analyser is used to collect

and transform the receiver outputs to the frequency domains.

3. PRINCIPLS AND PROCEDURE

A. Ansal et. al. discuss in Seismic Microzonation discuss in turkey by taking two pilot areas

[1] Adapazari [2] Golcuk. The first part of the paper deals with the soil properties of the

location, geological data of each area in the specific location, it also deals with geotechnical

data. The data are collected by the institute The data of nearly 97location in which data [bore



log] details through which they found an N values by conducting the SPT test. The project is

developed and controled by Disaster Risk Management (DRM), and funded by the Swiss

Agency for improving the city Development and Cooperation (SDC).

The second part of the paper deals with the major work by evaluation of the earthquake

hazard parameters for the microzonation study. In this part, both pilot areas were sub divided

into approximately 500m x 500m cells to evaluate earthquake hazard parameters in forms of

spectral acceleration ordinates for each forms of subdivided cells. They determinated the

regional hazard for the pilot areas, it is the major contributions of this study to the state-of-the

practice of microzonation in Turkey. Basically two types of assessment were carried out. The

first assessment was the estimation of the hazard parameters with respect to the Poisson

model for a probability of exceedance of 10% and 40% in 50 years. The second assessment

was the estimation of the hazard parameters with respect to time dependent probability by a

renewal model taking into account the recent earthquakes of 1999.

Figure 5 Comparison of Ground Shaking Map with Geological formation which Author determined

using GIS

The liquefaction susceptibility is found by equation developed by Iwasaki et al. and Youd

et al. First CSR is calculated from Seed and Idriss equation and corrections are made on this.

From this the factor of safety is calculated. Based on the factor of safety the liquefaction

potential index is calculated

(N1)60 = N x CN x CE x CB x CR x CS

Where N = Actual N value, CN = Correction for overburden pressure, CE = Correction for

energy ratio, CB = Correction for bore diameter, CR = Correction for rod length, CS =

Correction for sampling method.

The CRR7.5 can be found much effectively using SPT’s or CPT’s N values. The Table 5.1

gives the correction values to the SPT listed by Robertson and Wride in 1998.

For this study the overburden pressure correction is being calculated and if it exceeds 1.7,

then 1.7 has been taken as overburden correction factor (CN). The Automatic machine

hammer was used in the SPT test. Therefore correction factor for energy ratio (CE) is taken as

1. The Borehole of diameter 150 mm was driven for performing SPT test and hence the

borehole diameter correction factor (CB) is taken as 1.05. Samples without liner were used

and hence the sampling method correction factor (CS) is taken as 1.2



The Assessment of liquefaction potential framed by Seed and Idriss (1971). This

procedure is being used as a standard practice for the determination of the liquefaction

potential. Often liquefaction refers to the phenomenon of seismic generation by which large

pore pressure causes softening of granular soils. The liquefaction potential of the soil varies

from location to location. Based on the resistance offered by the soil against the liquefaction,

a map can be plotted denoting the liquefaction potential of soils.

Liquefaction potential denotes the liquefaction resistance of a soil. Liquefaction is the

state at which soil change from solid to liquid form due to the increase in the pore pressure.

The cyclic stress tends to increase in the pore pressure of the soil, which in turns reduces the

effective pressure. Hence the strength and the stiffness of a soil get decreased. The increase in

the pore pressure is due to compaction of the granular medium of the soil. When the soil has a

good resistance against the liquefaction it is understood that the soil is less prone to

liquefaction by cyclic stresses offered by the seismic waves at time of earthquake and vice

versa. The effect of liquefaction is very much higher in loose soil; therefore the layer tends to

lose its shear strength due to large shear deformation. This will result with failure of the

ground, reconsolidation of soil, ground settlement or arising of sand boils. In medium or

dense soil, the liquefaction tends to soften of the layer only. But in case of high cyclic

stresses, the large deformations are produced and it causes major loss of shear strength in soil

and failure of the medium.

Seed and Idriss coined a simplified procedure for the evaluation of liquefaction resistance

of the soil in the year 1971. It contains two terms like Cyclic Stress Ratio (CSR) and Cyclic

Resistance Ratio (CRR). The seismic demand of the soil is usually expressed in terms of

cyclic stresses. The shear stress in a soil can be determined using the equation proposed by

Seed and Idriss

(τmax) = (γh/g) x amax x rd

where τmax is the maximum shear stress on the soil element, γ is the unit weight of the soil,

h is the depth at which the actual shear stress acts, g stands for acceleration due to gravity,

amax is the peak ground acceleration and rd denotes the stress reduction factor.

But the above equation gives the value of the maximum shear stress induced in the soil

during earthquake. The average shear stress in soil is about 65% of the maximum shear stress.

Hence the average shear can be given as

(τav) = 0.65 x (γh/g) x ama x rd

Seed and idriss showed that the cyclic stress ratio acting on the soil could be calculated by

relating the average shear stress with the effective pressure in the soil. Hence the cyclic stress

ratio can be written as

CSR= (τav/σ`) = 0.65 x (σ/ σ`g) x amax x rd

Where σ` = Effective overburden pressure, σ = γh [Total overburden pressure], rd

represents the stress reduction coefficient whose value should be less 1. There are many

relations for finding the stress reduction coefficient but T.F.Blake found the mean curve for

stress reduction coefficient based on the mean and range values proposed by Seed and Idriss.

The equation for the purposed mean curve of T.F.Blake is always known as the most

generalized equation for calculating the stress reduction factor. The equation for stress

reduction coefficient can be given

rd = (1.000 – 0.4113z0.5

+ 0.04052z + 0.001753z1.5

)



(1.000 – 0.4177z0.5

+ 0.05729z – 0.006205z1.5

+ 0.001210z2)

The second term for determining the liquefaction potential is the evaluation of the cyclic

resistance ratio. The evaluation of liquefaction resistance CRR can be found using the

equation of the curves as given by Youd et. Al

CRR7.5 =

+

+

+

Where (N1)60 is the corrected N values. This equation is valid only when (N1)60 is less

than 30 i.e. (N1)60 < 30. But when (N1)60 is greater than or equal to 30 the soil is considered

to be too dense to liquefy and are usually said to be non-liquefiable soil.

4. CONCLUSIONS

Microzonation is an efficient tool to mitigate earthquake risk by hazard-related land use

management. However, microzonation does not replace the existing building and construction

codes. Seismic microzonation maps do not provide detailed hazard parameters at the level of

the specific building site, but they do provide guidance on required site-specific

investigations.

The national seismic zonation maps are mostly at small scales, while seismic

microzonation for a town requires larger scale studies. There are incompatibilities regarding

differences among map scales adopted for estimating earthquake hazards and site

characterization. Therefore, a major purpose of the seismic microzonation is to supply

structural design input by replacing national macrozonation maps. However, the applicability

of this approach is uncertain because there is no assurance of the reliability and uniformity of

these microzonation studies.

A reason for this weakness is the necessity for interdisciplinary interpretation. Unlike

seismic macrozonation, seismic microzonation requires input from civil engineering and

engineering geology, especially in the field of geotechnical engineering.

There is demand from international, national, regional and municipal administrations for

seismic microzonation maps to be included in urban planning, seismic codes and civil

protection procedures.

Guidelines and recommendations for seismic microzonation have been produced in many

countries, and including these documents in the framework of seismic regulations is highly

desirable.

REFERENCES

[1] T.G.Sitharam, P. Anbazhagan, K.S.Vipin- “Principle And Practice Of Seismic Microzonation:

Case Studies In India” Fifth International Conference on Recent Advance in Geotechnical

Earthquake Engineering and Soil Dynamics and symposium in honor of Professor I.M.IdrissJ.

[2] Anbazhagan, K. Premalatha, “Microzonation of Liquefaction factor of safety of Chennai

City”, IGC- 2004, Pg. No: 227 – 230.

[3] Karthic Kumar, K.K. Aneesh “Seismic Microzonation Of Coimbatore Using Remote Sensing

And GIS”, International Journal of Remote Sensing and GIS, Volume 1, Issue 2, 2012, Pg.

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[4] K.S.Rao and D. Neelima Satyam, “Liquefaction Studies For Seismic Microzonation Of Delhi

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[5] Ansal, M.Erdik, J. Studer, S. Springman, J. Laue, J. Buchheister, D. Giardini, D. Faeh,

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