Seismic Hazard Assessment of Uttar Pradesh

Transcription

1 Seismic Hazard Assessment of Uttar Pradesh Shravan Kishor Gupta #1, Arvind Kumar #2, Amit Kumar Tomar #3 # M.tech 4 th sem Student, Department of Civil Engineering, Roorkee Institute of Technology, Roorkee , U.K, India Abstract This study deals with the estimation of spectral acceleration for Uttar Pradesh based on Probabilistic seismic hazard analysis (PSHA). In recent times, population of Uttar Pradesh has increased significantly. An earthquake near an urban cites of UP has the potential to cause severe damage. A comprehensive earthquake catalogue has been compiled from various sources for region ( E E latitude and N N longitude) that include historic and pre-historic events. The seismicity parameter has been estimated using past data in a control region. The completeness test is used to evaluated the collected data, farther, estimates seismicity parameters b-value, seismicity activity rate a and maximum expected magnitude (m max ) for low seismicity area like Uttar Pradesh based on Gutenberg-Richter relationship. Analyses were carried out using the earthquake catalogue available over a radius of 250 km around this state. Earthquake data were analyzed statistically and recurrence relationship has been obtained using Guttenberg- Richter (G-R) relationship. Probabilistic seismic hazard analysis were then carried out Uttar Pradesh considering known ten seismogenic sources. Results of the present investigation were presented in the form of peak ground acceleration and response spectra at bed rock level and considering the local site conditions. Ground motion prediction equations proposed by Douglas et al. (2012) and S. T. G. Raghukanth And B. Kavitha (2014) for the Himalayan region are used for estimating ground motion. Based on this, a response spectrum is generated, the Hazard curves of mean annual rate of exceedance for peak ground acceleration and spectral acceleration have been generated for the nine cities of Uttar Pradesh (Allahabad, Lucknow, Ghaziabad, Varanasi, Kanpur, Bareilly, Gorakhpur, Agra and Moradabad) for 0, 0.075, 0.1, 0.2, 0.75, 1, 2, 3sec time periods at rock level and also by taking into consideration the local site condition. Further, the uniform hazard response spectrum with 5% damping for these cities have been generated at 100-, 500- and year return periods from PSHA. A contour map of Peak ground acceleration over Uttar Pradesh is also presented for 100-, 500-, and year return periods. These results may be of use to planners and engineers for site selection, designing earthquake resistant structures and, further, may help the state administration in seismic hazard mitigation. Keywords Earthquake, Seismic hazard etc. I. INTRODUCTION India is currently penetrating into Asia at a rate of approximately 45 mm/year and rotating slowly anticlockwise. Due to this rotation and translation results in left-lateral transform slip in Baluchistan at rate of 42 mm/year and right-lateral slip relative to Asia in the Indo-Burman ranges at 55 mm/year. Deformation within Asia reduces India s convergence with Tibet to approximately 18 mm/year, and because Tibet is extending east-west, convergence across the Himalaya is approximately normal to the arc. Arcnormal convergence across the Himalaya results is the development of potential slip available to drive large thrust earthquakes beneath the Himalaya at roughly 1.8 m/century. The Indian subcontinent has a history of destructive earthquakes. The major reason for the high frequency and intensity of the earthquakes is that the Indian plate is driving into Asia at a rate of approximately 47 mm/year. Uttar Pradesh is very close to the boundary which makes the state vulnerable. In the present work an attempt is made to develop a new procedure for studying seismic scenario of Allahabad is a metropolitan city in the north Indian state of Uttar Pradesh (26.85 N E), Most of the state of Uttar Pradesh lies in the Gangetic Plain. This is a fore-deep, a downwarp of the Himalayan foreland, of variable depth, converted into flat plains by long-vigorous sedimentation. This is known as a geosyncline and the Gangetic Plain is the Indo- Gangetic Geosyncline. This has shown considerable amounts of flexure and dislocation at the northern end and is bounded on the north by the Himalayan Frontal Thrust. The floor of the Gangetic trough (if see without all the sediments) is not an even plain, but shows corrugated inequalities and buried ridges (shelf faults). Beneath Uttar Pradesh, run the Delhi-Haridwar Ridge (DHR), trending NNE-SSW along New Delhi to the Gharwal region. The Delhi-Muzaffarnagar Ridge (DMR), which trends east to west, running from New Delhi to Kathgodam, in Nepal. The last ridge is the Faizabad ridge (FR), which runs in a curved manner, first east to west from Allahabad to Kanpur and then starts to bend towards the north-east towards Lucknow and carries on in this direction towards the Himalayas in Nepal. The depression that forms between the DMR and the FR, forms the West Uttar Pradesh shelf in the west and the Sharda Depression in the east. The region to the south of the FR, forms the East Uttar Pradesh shelf. There are several faults in ISSN: Page 11

2 the region, among them the Moradabad Fault which trends NE-SW and the Bhairwan Fault in the vicinity of Allahabad. Apart from these there are east-west running tear faults in the region that control the courses of the main rivers. Earthquakes have occurred in mostly all parts of Uttar Pradesh. Major earthquakes in the neighboring states of New Delhi, Uttaranchal, Bihar and from across the Indo-Nepal border have also shaken many parts of Uttar Pradesh. However, it must be stated that proximity to faults does not necessarily translate into a higher hazard as compared to areas located further away, as damage from earthquakes depends on numerous factors such as subsurface geology as well as adherence to the building codes. The districts of Saharanpur, Muzaffarnagar, Bijnor, Moradabad, Meerut, Etah, Hardoi, Sitapur, Agra, Mainpuri, Farukhabad, Unnao, Lucknow, Bara Banki, Rae Bareli, Sultanpur, Faizabad, Azamgarh, Ballia, Pratapgarh, Jaunpur, Ghazipur, Varanasi and Mirzapur lie in Zone IV. The districts of Etawah, Kanpur, Jalaun, Jhansi, Harimpur, Banda, Fatehpur, Allahabad and Lalitpur lie in Zone III. Since the earthquake database in India is still incomplete, especially with regards to earthquakes prior to the historical period (before 1800 A.D.), these zones offer a rough guide of the earthquake hazard in any particular region and need to be regularly updated. Earthquake Catalogue Prerequisite of seismic hazard analysis is to compile a reliable earthquake catalogue of past earthquakes in the control region around the Uttar Pradesh which is a exigent assignment. For past few decades after installation of data recorder the complete instrumental data are available for short periods of time. To understand the frequency of occurrence of large events the information is not that sufficient. The most accurate and complete information on instrumental earthquakes for India is from permanent global seismic network observations. The International Seismological Summary (ISS) is the most comprehensive global earthquake catalog for the time period between 1918 and 1960, in 1964 and data from 1900 till date is available on the ISC website. The USGS ( website also contains information for location, date, origin time and magnitude. This is considered to be one of the reliable data repositories since Apart from these global databases, the IMD data base is comprised of historical and instrumentally recorded earthquakes. Only local magnitude M L is assigned to the recorded earthquakes. In the present study the data has been collected from all the sources and they are converted to uniform scale of Moment magnitude using Equation 1. All together 483 events of magnitude M w 4.0 for the study region for the region ( E E latitude and N N longitude) starting from 1800 to The time scale plot in Figure 3 shows that before 1964 the density of earthquake < 5 is less, which is due to lack of instrument facility, after 1964 the same were recorded and capture almost all events and hence it is required to perform completeness test on data set for different magnitude ranges using procedure give by Stepp (1972). Figure 1: Timescale plot of earthquakes The Fault map of India prepared from GSI (2000) is shown in Fig1. A total of ten number of major faults, which influence seismic hazard in Uttar Pradesh, can be identified from the above map. Some of the faults in Uttar Pradesh are viz., LUCKNOW SUBSURFACE FAULT, ALLAHABAD FAULT, MORADABAD FAULT, GREAT BOUNDARY FAULT, AZAMGARH FAULT, GORAKHPUR FAULT, SHAHJAHANPUR FAULT, DEORIA FAULT, MAIN CENTRAL THRUST(MCT), MAIN BOUNDARY THRUST(MBT). The NE-SW trending Great Boundary fault displays a left lateral sense of movement. The Moradabad Fault has an E-W trend in the western part. TABLE 1: Details of faults in Uttar Pradesh S NO NAME OF FAULT LENGT H (KM) COORDINATES IN DEGREE LAT. LONG. 1 LUCKNOW FAULT ALLAHABAD FAULT 60 3 GREAT BOUNDARY FAULT MORADABAD FAULT AZAMGARH FAULT GORAKHPUR FAULT SHAHJAHANPUR FAULT DEORIA FAULT MAIN CENTRAL THRUST(MCT) MAIN BOUNDARY THRUST(MBT) ISSN: Page 12

3 GSI (2000) Geological Survey of India. Figure 2: Details of Faults and Earthquakes II. METHODOLOGY Seismic Hazard Analysis The specification of ground motion parameter for a particular site due to the near by seismic sources is one of the most important problems of earthquake engineering. This is achieved through seismic hazard analysis (SHA). It involves the quantitative estimation of ground- shaking hazard at a particular site. This assesses the ground motion to which the site and the facilitates may undergo during an earthquake. With the help of quantified hazard, design and modification of structures can be undertaken for the possible future ground motion. Seismic Hazard Analysis are of two types (i) Deterministic Seismic Hazard Analysis (ii) Probabilistic Seismic Hazard Analysis Deterministic Seismic Hazard Analysis (DSHA) A DSHA involves the development of a particular seismic scenario upon which a ground motion hazard evaluation is based. The scenario consists of the postulated occurrence of an earthquake of a specified size occurring at a specified location. DSHA provides no information on the likelihood of occurrence of controlling earthquake, the likelihood of it occurring where it is assumed to occur, the level of shaking that might be expected during a finite period of time or the effects of uncertainities in the various steps required to compute the resulting ground motion characteristics. Because of these limitations DSHA is not often used for Hazard Assessment. Probabilistic Seismic Hazard Analysis (PSHA) Probabilistic seismic hazard analysis (PSHA) provides a frame work in which uncertainties which were not quantified by DSHA, to be identified, quantified and combined in a rational manner to provide a more complete picture of the seismic hazard. Typical input parameters for PSHA include: 1) Definition of earthquake sources, either as faults or as area sources of diffused seismicity not directly attributed to a known fault. 2) A probability distribution of earthquake magnitude for each source. 3) A definition of earthquake ground motion attenuation, including uncertainty. Steps involved in PSHA: Step 1 Characterization of spatial uncertainty of the seismic sources. In addition to the identification of seismic sources PSHA needs to characterize the uncertainty in spatial description of each sources. Step 2 Characterization of magnitude uncertainty. The distribution of the rate of occurrence of future earthquakes for each source has to be described as a function of magnitude. In addition estimation of the maximum magnitude for each source is required. Step 3 Determination of uncertainty in ground motion attenuation. For the controlling region around the site, determination of the relation that expresses how the amplitudes of ground motion parameter varies with earthquake magnitude and source to site distance, associated with certain probability of exceedence is an essential step in PSHA. Step 4 Calculation of the seismic Hazard using the mathematical model and presentation of the results. Each combination of inputs determined in steps 1 through 3 is to be integrated to calculate a seismic hazard and to plot a curve expressing the annual probability that a given value of ground motion will be exceeded. The integration for all combinations of inputs to incorporate the variability of input estimates is the most delicate part of the seismic hazard curves, which show the annual probability of exceedence of a given hazard (PGA) value at the site. Probabilistic analysis allows the uncertainties in the size, location, rate of recurrence and effect of earthquake to be explicitly considered in the evaluation of seismic hazard. There are some advantages in using probabilistic seismic hazard analysis: a) A probabilistic seismic hazard analysis (PSHA) allows the designer to balance risk and cost for a project in a manner similar to that used for other environmental loadings such as flood or wind loadings. The reduction in risk by selecting a lower probability level (longer return period) and correspondingly higher seismic loading may be compared to the increased project cost involved while designing for the higher loading. b) The frequency of occurrence of earthquakes is explicitly incorporated in PSHA. As such, regions of greater seismic activity (thus higher probabilities of earthquake ISSN: Page 13

4 occurrence) will have higher ground motion levels for given probabilities or return periods. c) The uncertainty or randomness in earthquake location is explicitly incorporated in PSHA. Thus, the conservatism of assuming that the earthquake occurs at the closest location on the source to the site is not necessary in PSHA. d) Uncertainties in the earthquake occurrence and ground motion estimation process are explicitly considered in PSHA. In the past 20 to 30 years the use of probabilistic concepts has allowed uncertainties in the size, location, and rate of recurrence of earthquakes and in variation of ground motion characteristics with earthquakes size and location to be explicity considered in the evaluation of seismic hazards. All title and author details must be in single-column format and must be centered. Where, m 0 and m u are the lower bound magnitude and maximum magnitude. β is equal to the 2.303b, where b is the slope of recurrence curve. N (m 0 ) is the frequency of occurrence of events of magnitude m 0 and larger. m 0 is the threshold magnitude taken as 4.0. The frequency of occurrence of events can be computed from the following expression as λ k (m i ) = N k (m i - m/2) N k (m i + m/2) (2) In the expression (1), b- value is needed for its computation. So an accurate estimation of b- value will produce good results. III. ANALYSIS AND RESULTS Seismic hazard curves The seismic hazard curves have been obtained by (using seismic parameter viz., a and b value estimated in Chapter 3 and attenuation relationship from chapter 4 computing mean annual rate of exceedance for different specified ground motion values. The procedure for carrying out seismic hazard to obtained the seismic hazard curves are as follows; 1) identifying of seismic sources around Uttar Pradesh. 2) evaluating earthquake recurrence and magnitude distributions. 3) estimating ground motion using attenuation model and 4) computation of seismic hazard curves for all the ten faults to estimate the aggregate hazard at the site. Figure 3: Steps of a probabilistic seismic hazard analysis a) Identification and Characterization, b) Recurrence relationship, c) Uncertainty Inherent in predictive relationship, and d) Parameter Exceedance value in particular time Figure 4 (a): Seismic hazard curves at the cities of Moradabad T=-t/ln (1-p) Where P= probability of exceedance in t years; T= Return period Now as in step2, The number of earthquakes per year of magnitude m and above is given by N(m)= N(m 0 ) (1) Figure 4(b): Seismic hazard curves at the cities of Lucknow ISSN: Page 14

5 Figure 4(c): Seismic hazard curves at the cities of Varanasi Figure 4(f): Seismic hazard curves at the cities of Bareilly Figure 4(d): Seismic hazard curves at the cities of Kanpur. Figure 4(g): Seismic hazard curves at the cities of Allahabad Figure 4(e): Seismic hazard curves at the cities of Agra Figure 4(h): Seismic hazard curves at the cities of Gorakhpur ISSN: Page 15

6 Figure 4(i): Seismic hazard curves at the cities of Uttar Pradesh at rock level (5% damping) for Ghaziabad PGA contours The seismic hazard maps of Uttar Pradesh for return periods of 100, 500, and 2500 years at PGA are shown in Figures 5 a-c, PGA value= contour value/981 From figure 5 a-c it has been observed that near about Gorakhpur and Moradabad PGA values are 0.01g. whereas other cities are has much lesser PGA values comparison to IS It may be noted that Indian code of practice (IS-1893, 2002) considers the most part of Uttar Pradesh on seismic zone (Zone iii) with PGA value of 0.16g, without specifying any return period. Figure 5. (a) PGA contours with 100-year return period. Figure 5(b) PGA contours with 500-year return period Figure 5 (c) PGA contours with 2500-year return period. Results:- The Regional Recurrence, established based on past earthquake data, show that [a= and b=0.8976] Uttar Pradesh is in lower seismic region. Using the results of seismic hazard curves, UHRS (Uniform Hazard Response Spectra) have been derived for 100-, 500- and 2500-year return periods. Results obtained from the UHRS were used to draw the variation of seismic hazard in Uttar Pradesh, showing that a major portion of Uttar Pradesh is vulnerable to mild seismic hazard. The highest level of hazard has been observed for the Gorakhpur districts of Uttar Pradesh. The design spectra developed here incorporate uncertainties in the location, magnitude and recurrence of earthquakes. IV. CONCLUSION This study is of importance for the reason that we evaluate hazard parameters and maps utilizing the maximum possible seismological information available. Here we have applied a procedure utilizing both the complete part of the catalogue as well as extreme part of catalogue having extreme values of magnitudes. The reliability of result for seismic hazard parameters estimation in a given region depends on the methodology and information input used, also it depends on the threshold magnitude value used for analysis. The b- value obtained using 4.0 as threshold magnitude are within acceptable range ( ) mentioned by various researchers all over the world. The regional recurrence established based on past earthquake data with the value of a (=5.15 ) and b= (0.89). The attenuation relations proposed by RaghuKanth and B. Kavitha (2014) has been used to compute spectral acceleration hazard curves. The seismic hazard curves for PGA, 0 sec, 0.075s, 0.1s, 0.2s, 0.75s, 1s, 2s and 3s spectral acceleration for all nine cities are given in figure. Using the results of seismic hazard curves, UHRS have been derived for 100-, 500- and year return periods. It has been observed that near about Gorakhpur and Moradabad PGA values are 0.01g. whereas other cities are has much lesser PGA values comparison to ISSN: Page 16

7 IS Further, it has been found that at PGA, predicted S a are found to be on the lower side as compared to the value (0.16 g) recommended by IS: REFERENCES [1] Abrahamson, N. A., and Silva, W. J., (1997), Empirical response spectral attenuation relation for shallow crustal earthquake, Seismological Research letters, 68, [2]Abrahamson, N. A., and Somerville, P.G., (1996), Effects of the hanging wall and foot wall on ground motions recorded during the Northridge earthquake, Burma., Bulletin of Seismological. Society America, 86, [3]Adams, J., and Atkinson G., (2003), Development of seismic hazard maps for the 2003 National Building Code of Canada, Canadian Journal of Civil Engineering, 30, [4] Algermissen, S. T., & Perkins, D. M., (1976), A probabilistic estimate of maximum acceleration in rock in the contiguous United States, United State Geological Survey, Open-file Report, [5] Ambraseys, N. N, Simpson, K. A., and Bommer, J. J., (1996), Prediction of horizontal response spectra in Europe, Earthquake Engineering and Structural Dynamics, 25, [6] Ambraseys, N., and Bilham, R., (2003), MSK Isoseismal intensities evaluated for the 1897 Great Assam Earthquake, Bulletin of Seismological Society America, 93, [7] Agarwal, P., and Shrikhande, M., (2006), Earthquake resistant design of structures, PHI Learning Pvt. Ltd., New Delhi. [8] Gutenberg, B. and C. F. Richter (1944). Frequency of earthquakes in California, Bull. Seism. Soc. Am. 34, [9] GSI (2000) Seismotectonic Atlas of India and Its Environs. Geological Survey of India. [10] IS: 1893 (Part 1)-2002, Bureau of Indian Standard (BIS) (2002) revised its code of practice, Criteria for Earthquake Resistant Design of Structures. [11] IMD [12] Kijko, A. (2004). Estimation of the maximum earthquake magnitude, mmax, Pure and Applied Geophysics, 161, [13] Kumar Pallav (2010), Seismic Microzonation of Imphal city and Probilisitc Hazard Assessment of Manipur State, Ph.D. Thesis, Indian Institute of Technology Guwahati, India. [14] Kumar Pallav, S T G Raghukanth and Konjengbam Darunkumar Singh (2012), Probabilistic seismic hazard estimation of Manipur, India. [15] S. T. G. Raghukanth and B. Kavitha (2014), Ground Motion Relations for Active Regions in India [16] Stepp, J.C. (1972). Analysis of Completeness of the Earthquake Sample in the Puget Sound Area [17] and Its Effect on Statistical Estimates of Earthquake Hazard, Proceedings of the International [18] Conference on Microzonation, Seattle, U.S.A., Vol. 2, pp [19] USGS website ( [21] RaghuKanth, S. T. G., (2008), Modeling and synthesis of strong ground motion, Journal Of Earth System Science, 117, [22] RaghuKanth, S. T. G., (2010), Estimation of Seismicity parameters for India, Seismological Research letters, 8, ISSN: Page 17