A QPn STUDY FOR THE FREQUENCY BAND BETWEEN 0.3 AND 2.0 HZ IN TURKEY

A Q_PnSTUDY FOR THE FREQUENCY BAND BETWEEN 0.3 AND 2.0 HZ IN TURKEY

SUMMARY

The aim of this study is to calculate the QPn values for Turkey as a function of frequency. The data used in the study were recorded by Kandilli Observatory and Earthquake Research Institute (KOERI) and Belbaşı-Keskin Seismic Array (NDIM) which totally consists of 55 stations. The earthquakes recorded at epicentral distances from 200 to 1200 km, within a magnitude range of 4.5-6.4 (during 2000-2004) were selected. In this study, Extended Reversed Two Station Method (RTSM) which was developed by Chun (1986) was used. The method can be applied only when two seismic stations are aligned with two earthquake sources. The influence of source and station is eliminated by calculating the spectral ratios. Azimuthal variation of 10° or less was neglected. In order to calculate the approximate value of QPn for Turkey, 76 events and more than 3300 waveforms were collected. 1480 well-recorded Pn phases have been selected from these waveforms. The geometry of the source-station pairs enabled us to form 169 source- station combinations. Pn wave arrivals were best picked in the frequency band of 0-2 Hz. For consistency, we resampled the data to “40” sample/sec to uniform the sampling rates since different types of instruments were used. We used multitapering technique to estimate the power spectral density of the time series and in determining the QPn. In forming the source - station combinations we also determined an additional criteria for the signal to noise ratio. We set this ratio to “1” and eliminated the combinations if it is less than “1”. All things considered, frequency dependent spreading rate coefficient n(f) and attenuation coefficient γ(f) were derived. We used the Pn velocity values for Turkey which ranges between 7.6 – 8.4 km/sec during the calculation stages of the observed and synthetic QPn values as a function of frequency. Consequently, the average attenuation model for the average velocity of 7.8 km/sec takes the form of QPn (f): 28.380 f 1.1522.