SEISMIC WAVE ATTENUATION CHARACTERISTIC OF CODA WAVES OF HIMACHAL HIMALAYA AROUND PROPOSED DUGAR HE PROJECT

Abstract

The earthquake recorded in the form of a seismogram is a combination of source, path, and site. To know the seismic hazard of a region it is necessary to know each of these factors. In this study, aim is to determine the seismic wave attenuation characteristic through the estimation of the quality factor, Qc, of Coda Wave for Dugar region of Himachal Himalaya around proposed Dugar HE project. Many studies have been done for the estimation of seismic wave attenuation in India and globally using Coda Wave part of local earthquake with the use of single backscattering model (e.g., Roecker et al., 1982; Pulli, 1984; REHA, 1984; IBANEZ et al., 1990; WOODGOLD, 1994; Akinci et al., 1994; Gupta et al., 1995, 1996,1998). The importance and objectives of coda Q is to determine the medium characteristics of the studied region. The Coda Q is also used as an earthquake precursory parameter along with other parameters. Qc estimates for this part has been determined partially by examining coda waves of 121 seismograms from 24 local earthquakes recorded digitally in the around Dugar HE Project between 07.10.2021 and 24.04.2022. The coda waves in a seismogram were studied at seven central frequencies using the single backscattering model for this purpose. With magnitude range 1.3< ML<3.0, the earthquakes had epicentral distances less than 50 Km and focal depths up to 25 Km. For several earthquake station pairs falling in the lapse time range of 30-60 s, Qc values were estimated at seven central frequencies of 1.5, 3.0, 6.0, 9.0, 12.0, 18.0, and 24 Hz for the 30-sec coda window length. Qc has a frequency dependency, ranging from 55 at 1.5 Hz to 4815 at 24 Hz indicating that attenuation at higher frequencies is less noticeable. The average frequency-dependence Qc relationship (Qc = Q0fn) based on this data set for the region determined as Qc = 93.73f1.05 and station wise Qc = 90.50f1.12 (BHU); Qc = 61.70f1.24 (DEV); Qc = 84.80f1.02 (KUT); Qc = 87.90f1.19 (MAN); Qc = 112.50f0.87 (PUR) and Qc = 113.80f0.89 (SNY) have been estimated. From the analysis it has been observed that seismic wave attenuation in the proposed Dugar HE Project region is low at lower frequencies, such as 1.5, 3.0, 6.0, and 9.0 Hz, but it is high at higher frequencies, such as 12, 18, and 24 Hz. Frequency dependence exponent ‘n’ decreases as Q0 increases.