Reza Emami; Reza Rezaei
Abstract
In this study, for estimating of coda wave attenuation in the North of Sanandaj-Sirjan Zone the seismograms of earthquakes recorded at the seismic stations which located at the longitude of 48°-50° and latitude of 38°-40° have been used. The data with an epicentral distance less than ...
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In this study, for estimating of coda wave attenuation in the North of Sanandaj-Sirjan Zone the seismograms of earthquakes recorded at the seismic stations which located at the longitude of 48°-50° and latitude of 38°-40° have been used. The data with an epicentral distance less than 200 km and a signal to noise ratio equal to or greater than 3 were used. Due to the volumetric percolation of the coda waves from the medium, the variation in coda waves quality factor was investigated in both lateral and depth, and the results were compared with the values obtained for other regions of Iran and the world. After applying the intermediate filter on waveforms in 10 frequency bands, the quality factor was estimated, and finally, the mean values of the quality factor and frequency dependence factor in the region by using two single-back-scattering and single-isotropic-scattering obtained QC꞊149 ± 9f0.66 ± 0.03 and QC꞊152 ± 12f0.66 ± 0.03 respectively. The comparison of the results with the values have been obtained in Central Iran (Qc꞊94f0.97), Alborz (Qc꞊79f1.07) and Southeast Zagros (Qc꞊72f1.19) indicate more homogeneity in the shallow depth layers and seismicity is lower than Central Iran, Alborz and Zagros. Also, for investigating the depth variations of the quality factor in the region, 11 lapse time window lengths were used in 5 seconds increments. The window lengths are begin from 10 seconds. In the lower window lengths, the low Q0 values represent high heterogeneity in shallow depths of the earth.
S. M. Azhari; M. Rezapour; A. A. Mottaghi
Abstract
Northeastern part of Iran islocated in the Kopeh Dagh seismotectonic province. This province is part of the Alpine-Himalayan orogenic belt. In the last two decades, a number of earthquakes occurred in this region. Therefore, investigating and relocating these earthquakes with adequate precise play a ...
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Northeastern part of Iran islocated in the Kopeh Dagh seismotectonic province. This province is part of the Alpine-Himalayan orogenic belt. In the last two decades, a number of earthquakes occurred in this region. Therefore, investigating and relocating these earthquakes with adequate precise play a great role in seismicity research of the study area. Adequate crustal structure velocity has a key role in relocating the earthquakes. Since the earthquakes in this region are shallow earthquakes, the upper part of crustal structure can be acquired. So in this study, Mashhad and Quchan seismological networks data were used to determine the crustal structure velocity. In order to determine the velocity structure, Vp/Vs was first determined using the methods of Wadati and travel time of1.72 .Then by applying various filters and selection of several earthquakes 1D velocity structure of the arrival times was determined. Results reveal two velocity discontinuities approximately at 4 and 14 km depths. The resulting model consists of a 4-km-thick layer with VP = 5.9 kms−1 overlying a 10-km-thick layer with VP = 6.17 kms−1. Then the initial 1D velocity model was used to determine the three-dimensional velocity structure using LOTOS code. The results show significant changes in the vicinity of Mashhad. Two zones with higher velocity are observed in the north and south of Mashhad due to Kashaf Roud and Binaloud Faults. In the north of Mashhad, a change in velocity is observed, which might be due to the Tous fault. In the south of Mashhad, a sharp velocity discontinuity at the depth of 4 km is probably due to an alluvium cover above a bedrock of varying thickness. Also, the tomography results indicate that the area of Shandiz fault system in the south of Mashhad is associated with a lower velocity zone compared to its adjacent areas.
