Estimation of Coda‐Wave Attenuation in the Central and Eastern Alborz, Iran

Abstract

The quality factor of coda (Q c ) waves has been estimated by using single backscattering and single isotropic scattering models. The earthquakes used were recorded by three permanent and one temporary network located in the central and eastern Alborz, Iran. The database was composed of 746 local earthquakes with local magnitude from 1.1 to 5.7. The estimated Q c has been found to be similar for lapse times greater than twice the S-wave travel time (2t S ) for both methods.The estimated Q c for central frequencies < 1:0 Hz shows less frequency dependency compared with the higher frequencies. By using a Q 0 f n relation, the average frequency dependence of Q c for the whole area has been estimated as 59f 1:03 , 69f 0:97 , 78f 0:97 , 105f 0:93 , 123f 0:89 , 159f 0:79 , and 203f 0:68 for central lapse times 30, 40, 50, 65, 85, 110, and 155 s, respectively. We found the value of Q 0 decreases at an average depth of 78 km, which may be the result of high dissipating media at this depth. The average Q c values, estimated for central and eastern Alborz and their frequencydependent relationships are similar to those of tectonically active regions.

CodaQin Different Tectonic Areas, Influence of Processing Parameters

“…This value is normally never changed. Other studies use a fixed rms window (e.g., Farrokhi et al, 2015) of 2-5 s. It should be long enough to smooth out the envelope but not so long as to completely ruin the shape of the envelope. Tests were made with three and seven cycles as well as fixed lengths (Table 6) and it can be observed that the length of the rms window affects Q 0 but less so Q 10 .…”

“…This coda Q method can give quite different results depending on the processing parameters used. Many papers have been published that claim a close relationship between tectonics and coda Q by comparing results from different regions in which Q has been studied by different authors using different or unknown parameters, for example, Woodgold (1994), Bianco et al (1999), Zelt et al (1999), Yun et al (2007), Dobrynina (2011), andFarrokhi et al (2015). However, because all the processing parameters are rarely, if ever, given, and different parameters can lead to different results, there might not be much substance to those claims.…”

“…The envelope is obtained by calculating the root mean square (rms) values in a running window of a given length starting at a given time, the lapse time, and after the origin time. Alternatively, the envelope is sometimes calculated using the envelope definition with the Hilbert transform H (e.g., Farrokhi et al, 2015) as E Q -T A R G E T ; t e m p : i n t r a l i n k -; d f 3 ; 5 5 ; 6 1 3 Envelopef; t HAf; t 2 Af; t 2 q :…”

“…3 This method of using the coda Q decay envelope is called the coda wave decay (CWD) method and it is the most commonly used approach for determining coda Q, applied in many publications, both presently (e.g., Farrokhi et al, 2015;Khan et al, 2015;Singh et al, 2015) and for the last 30 years (e.g., Zelt et al, 1999;Bianco et al, 2002;Mak et al, 2004;Yun et al, 2007;Mukhopadhyay et al, 2008;Carcole and Sato, 2010;Rahimi et al, 2010;Calvet and Margerin, 2013). Gusev (1995) in his review article provides many references up to 1994.…”

Estimation of Quality Factor (Qβ) Using Accelerograms of Ahar-Varzaghan Earthquakes, Northwestern Iran

“…Motaghi and Ghods (2012) studied the attenuation of ground-motion spectral amplitudes and its variations across the central Alborz Mountains. Rahimi et al (2010) and Farrokhi et al (2015) estimated coda-wave attenuation in the central and eastern Alborz. Farrokhi and Hamzehloo (2016) investigated body wave attenuation…”