An attempt has been made to estimate the frequency dependent Qs value and its lateral variation over Ohchigata graven and surrounding area in Noto peninsula, Ishikawa prefecture, Japan by using the double spectral ratio method that is applied to the strong motion records of the KiK-Net. The Qs value in the central part is low as compared to the northern and the southern areas.
The earthquakes of magnitude above 3.0 and below 4.0 are used for analysis, as per the available strong motion records obtained by KiK-Net in the study area. These local shallow earthquakes, of which focal depth varies from 10.0 to 20.0 km, are well efficient to find out the lateral variation of Qs over the study area. The frequency dependent Qs are estimated in the frequency range from 0.5 to 10.0Hz for better consideration of signal to noise ratio and elimination of high frequency site effects.
The result obtained is that the Qs value at the central part is. In the wide spread northern part, three successive Qs are studied from extreme north towards the south that is closer to the western part of the graven:, respectively. In the southern part is obtained. The Qs value in the central part lower than the others may be due to the fractured material of upper crust under the graven