SEISMIC MICROZONATION OF A REGION BASED ON SEISMOLOGY AND GEOLOGICAL DATA

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1 International Journal of Advanced Research in Engineering and Technology (IJARET) Volume 8, Issue 6, November - December 2017, pp , Article ID: IJARET_08_06_006 Available online at ISSN Print: and ISSN Online: 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 55 editor@iaeme.com

2 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 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 editor@iaeme.com

3 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 57 editor@iaeme.com

4 Seismic Microzonation of a Region Based on Seismology and Geological Data 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 subsurface 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 heads 2 : 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 58 editor@iaeme.com

5 R. Manigandan and R.Thiyagarajan 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) 59 editor@iaeme.com

6 Seismic Microzonation of a Region Based on Seismology and Geological Data 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 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 nondestructively 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 60 editor@iaeme.com

7 R. Manigandan and R.Thiyagarajan 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 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 (N 1 ) 60 = N x C N x C E x C B x C R x C S Where N = Actual N value, C N = Correction for overburden pressure, C E = Correction for energy ratio, C B = Correction for bore diameter, C R = Correction for rod length, C S = Correction for sampling method. The CRR 7.5 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 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 (C N ). The Automatic machine hammer was used in the SPT test. Therefore correction factor for energy ratio (C E ) is taken as 1. The Borehole of diameter 150 mm was driven for performing SPT test and hence the borehole diameter correction factor (C B ) is taken as Samples without liner were used and hence the sampling method correction factor (C S ) is taken as editor@iaeme.com

8 Seismic Microzonation of a Region Based on Seismology and Geological Data 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 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 (τ max ) = (γh/g) x a max x rd where τ max 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, a max 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 (τ av ) = 0.65 x (γh/g) x a ma 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= (τ av /σ`) = 0.65 x (σ/ σ`g) x a max 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 = ( z z z 1.5 ) 62 editor@iaeme.com

9 R. Manigandan and R.Thiyagarajan ( z z z z 2 ) 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 CRR 7.5 = Where (N 1 ) 60 is the corrected N values. This equation is valid only when (N 1 ) 60 is less than 30 i.e. (N1)60 < 30. But when (N 1 ) 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: [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. No: [4] K.S.Rao and D. Neelima Satyam, Liquefaction Studies For Seismic Microzonation Of Delhi Region, Current Science Vol. 92, Issuse No:5, 10 March 2007, Pg. No: editor@iaeme.com

10 Seismic Microzonation of a Region Based on Seismology and Geological Data [5] Ansal, M.Erdik, J. Studer, S. Springman, J. Laue, J. Buchheister, D. Giardini, D. Faeh, D.Koksal,] Seismic Microzonation for Earthquake Risk Mitigation in Turkey, 13 th World Conference on Earthquake, Vancouver, B.C., Canada, August 1-6, 2004, Paper No: [6] P. Revathi and K. Pandurangan, Seismic Hazard Analysis of Puducherry Region, International Journal of Earth Sciences and Engineering ISSN , Vol. 05, No. 02, April 2012, Pp [7] G.C.Kandpal, Biju John And K.C.Joshi, J. Ind. Geophys Geotechnical Studies in Relation to Seismic Microzonation of Union Territory of Chandigarh,. Union ( April 2009 ) Vol.13, No.2, Pp [8] S.Prathababu and P.D. Arumairaj Determination of Site Characteristics of Coimbatore for Microzonation Studies, Fourth National Conference on Recent Advancements in Geotechnical Engineering, April 2015, Pg. No: [9] Aminaton Marto, Tan Choy Soon, Fauziah Kasim A Correlation of Shear Wave Velocity and Standard Penetration Resistance, EJGE Vol. 18 [2013], Pg. No: ]. [10] Anbazhagan and T.G.Sitharam, J. Earth Syst. Seismic Microzonation of Bangalore, India. Sci. 117, S2, November 2008, Pp [11] Seed, H. B and Idriss I. M. (1971): Simplified procedure for evaluating soin liquefaction potential,.j soil mech. found.di., ASCE 97, Seed, H. B., Idriss, I. M. and Arango, I. (1983): Evaluation of liquefaction potential using field performance data, J. Geotech. Eng.- ASCE, 109, [12] Seed, H. B., Tokimatsu, K., Harder, L. F. and Chung, R. M. (1985): Influence of SPT procedures in soil liquefaction resistance evaluations. J. Geotech. Eng.-ASCE, 111, [13] Seed, H. B. and Harder, L. F. (1990): SPT-based analysis of cyclic pore pressure generation and undrained residual strength, in Proceedings of the H. G. Seed Memorial Symposium, BiTech Publishing, 2, [14] Sanjib Kalita, Uses of MEMS Accelerometer in Seismology. International Journal of Advanced Research in Engineering and Technology, 4(6), 2014, pp editor@iaeme.com