ESTIMATION OF SOURCE PARAMETERS OF LOCAL EARTHQUAKES IN THE ENVIRONS OF TEHRI DAM SITE

Abstract

The objective of this study is to calculate Hypocentre parameters and source parameters of local events recorded at the seismological laboratory of IIT ROORKEE by employing 12 stations network around Tehri dam region. Hypocentre parameters of 3 local events around Tehri dam region are calculated using the HYPOCENTER program given in SEISAN software (Havskov and Ottemöller, 2005). The objective behind calculating earthquake source parameters is to work on the potential of the parameters in different areas and its application in seismology and earthquake engineering which broadly includes study of spatial and temporal variation of tectonic stress from the stress drops of earthquakes, study on process of earthquake rupture and developing various scaling laws. Earthquake source parameters are seismic moments, source radii, stress drops, displacements along the fault, and dimensions of the cohesive zones. To estimate earthquake source parameters , spectral parameters are calculated through fitted model. Source parameters of local have been estimated using Brune’s model and using real time data observed in seismology laboratory by adopting 12 different station instrument recordings deployed in Garhwal Himalaya around tehri dam region . Earthquake source parameters are estimated by using the code EQK_SRC_PARA in which source model is fitted in displacement spectra and acceleration spectra. For the Tehri dam region ,source parameters of small sized local earthquakes (1.3≤Mw≤3.2) are estimated. The seismic moments (Mo), Brune stress drop and source radii ranges from 2.2×1018 dyne-cm to 6.6×1020, 1 to 63 bars and 65.1 m to 667.4 m respectively. The maximum stress drop of 63 bars is observed at a source radius of 146.7 m The radiated seismic energy varies from 1.1×1014 to 3.9×1016. The radiated seismic energy follows the relationship with seismic moment as 𝐄𝐬(𝐞𝐫𝐠𝐬)=𝟑×𝟏𝟎−𝟓 𝐌𝐨𝟏.𝟎𝟏𝟑. The seismic moment shows the increasing trend with increase in source radius. The estimated values of fmax vary from 9.7 Hz to 39.6 Hz . The corner frequency fc follows the decreasing trend with the seismic moment. The relationship between corner frequency and seismic moment has been developed as fc =1.0E+06 𝐌𝐨−𝟎.𝟐𝟔𝟐. The fmax also follows the same decreasing trend with seismic moment similar to fc . The relationship between fmax and seismic moment has been developed as fmax =1.032 E+03 𝐌𝐨−𝟎.𝟎𝟗𝟏.