DEVELOPMENT OF SPECTRAL ATTENUATION RELATIONSHIP FOR HORIZONTAL STRONG GROUND MOTION FOR HIMALAYAS, INDIA

Abstract

It is easy to design earthquake resistant structures by selecting ensemble of strong ground . motion recordings, if recordings are available in sufficient quantity. However, it is difficult due to lack of data. To overcome this problem, a predictive mathematical model has to be developed which is called Attenuation relationship In this study, a spectral attenuation relationship has been developed for five percent damped horizontal response spectra using strong ground motion data recorded in Himalayan region of India as well as Zagros region of Iran. The basic idea is that, if sufficient data is not available for a particular region, the data can be imported from other regions having similar regional characteristics. 11 earthquake records from Indian 1 region have magnitude ranges 4.9-6.8 and 12 earthquake records of Iranian region having magnitude ranges 5.2-6.9 have been collected and used in this study for the development of spectral attenuation relationship. Once the data is collected, all the efforts have been made on removing outliers and focusing on reliable and near field records rather than far field records (for this purpose, more weights are given to the near field records). Finally a set of 16 earthquake events consisting of 201 earthquake records with reliable data was chosen. Geometric mean of the horizontal component has been calculated and used for the development of attenuation relationship. The proposed spectral attenuation relationship (for time period 0.004) is given by, log (A) = 0.3098 + 0.08375 M- 0.7031 log (X+ e 016"3 M) - 0.01358 S+ 0.0274 H Where, A is Peak ground acceleration in terms of m/sec2, M is Moment Magnitude, b is y4 the decay parameter, X is JB (Joyner-Boore) distance in km. and S and H are the Site characteristics which represents soil or rock type and reverse fault or strike-slip fault respectively for other periods a table of co-efficient is proposed. S is 0 and I for soil and rock H is 0 and I for reverse and strike-slip fault respectively.