نوع مقاله : مقاله تحقیقی (پژوهشی)
1 پژوهشگر پسادکتری، پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله ، صندوق حمایت از پژوهشگران و فناوران کشور، تهران، ایران
2 دانش آموخته کارشناسی ارشد زلزله شناسی، پژوهشگاه بین المللی زلزلهشناسی و مهندسی زلزله، تهران، ایران
3 دانشیار، پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله، تهران، ایران
عنوان مقاله [English]
In this study, coda wave decay parameter, coda Q, is evaluated using waveform data of three networks in the east and northeast of Iran based on the single-scattering method. The database includes 300 earthquakes with magnitudes in the range of 2.5-6.0 recorded in 2012 to 2020. The waveforms were gathered from the Iranain Seismological Center (IRSC) of the University of Tehran, National center of Broadband Seismic Network of Iran (BIN) at the International Institute of Earthquake Engineering and Seismology (IIEES) and Seismological Earthquake Research Center of the Ferdowsi University of Mashhad (FUMSN). The coda Q for the east-northeast of Iran was calculated as Qc = 125f 0.76 for a lapse time of 40s and optimal parameters of our database. We also evaluated coda Q based on parameters proposed by Havskov et al. (2016) as Qc = 90f 0.87 and as can be seen, the difference in the parameters leads to the different results. Furthermore, the effect of different parameters in estimating the quality factor of coda waves was investigated. The frequency dependence of the wave attenuation coefficient is evident in this region. Considering the 10-year interval of earthquakes used in the east and northeast of of Iran in this study, the obtained results indicate high seismicity rate and continuous seismic activity in the study area.
Recently some studies have been conducted to study the seismic wave propagation effects in this region. For example, Safari et al. (2020) investigated the attenuation of seismic waves in the Fariman region based on 122 local earthquakes recorded in a temporary dense seismic network of IIEES. Based on this research, the frequency relationship Qc = 66f 0.84 for a lapse time of 20s was obtained.
The results of the quality factor studies depend on tectonic regime of the study area and various proccesing factors, such as: the lapse time, filter bandwidth, the window length, etc. Therefore, accurate comparison is only possible when similar parameters are considered in different studies.
We compared our results with several studies in different regions of Iran and other parts of the world. The estimated values of Q0 in this area are in the same range of active regions of the world (Q0 <200) and is near to the results of studies conducted for another active regions of Iran. The results of our study are in good agreement with previous studies and indicate the strong frequency dependency in attenuation of seismic waves in northeast of Iran Plateaue. The observed small differences in coda Q estimates originate from differnet tectonic rigions and processing parameters.