S wave attenuation and site effects in the region of Friuli, Italy

Abstract

We used strong motion records from the 1976 Friuli earthquake (M 6.4) and 10 of the biggest aftershocks recorded by the National Accelerograph Network of the Electrical Power Company of Italy to estimate the quality factor Q of S waves in this region. The wide distance range of the recordings (10 < r < 190 km) permits us to analyze the spectral amplitude decay of the records using a nonparametric approach [e.g., Anderson and Quaas, 1988; Castro et al., 1990; Anderson, 1991]. We obtained attenuation functions for a set of 18 frequencies ranging between 0.4 and 25.0 Hz. The values of Q retrieved from the attenuation functions obtained follow the frequency‐dependent relation Q = 20.4f. A test of the method was made using a second data set consisting of digital seismograms from the Friuli‐Venezia Giulia Seismograph Network. In spite of the different size of the volume sampled by these data (10 < r < 131 km), the frequency dependence of Q obtained (Q = 16.1f0.92) is similar to that obtained with the strong motion data set. The near‐surface attenuation was also estimated using the model proposed by Anderson and Hough [1984] and Anderson [1991]. We found that κ0 is smaller for the strong motion stations located on rock compared to stations located on either shallow or soft sediments. To estimate the site response of the strong motion stations, we corrected the spectral records for the attenuation effect and then inverted the corrected records to separate source and site effects using the inversion scheme proposed by Andrews [1986]. To verify the site amplification estimates obtained, we also calculated the transfer function of each site using Nakamura's [1989] method for S wave [e.g., Lermo and Chavez‐García, 1993]. In general, the shapes of the site functions obtained with the inversion are consistent with the transfer functions obtained calculating the horizontal to vertical component ratio.

Improved 2-D attenuation analysis for Northern Italy using a merged dataset from selected regional seismic networks

“…As stated in many studies (Mayeda et al 2003;Mayeda et al 1996) the stability of coda measurements with respect to the S amplitudes suggests that results from coda analysis may be more reliable. Moreover, they are consistent with Castro et al 1996 andConsole andRovelli, 1981 who observed low values of Q for this region.…”

“…Within Northern Italy, the Q parameter has been defined using one-dimensional models for different sub-regions (e.g., Morasca et al 2006 and, for the Western Alps; Thouvenot, 1983, Castro et al 2008 for the Central Alps; Malagnini et al 2002, Castro et al 1996and Console and Rovelli, 1981 for the Eastern Alps). The motivation for improving upon the 2-D attenuation model for Northern Italy is several fold.…”

Attenuation characteristics, source parameters and site effects from inversion of S waves of the March 31, 2006 Silakhor aftershocks

“…This evaluated apparent Q factor with low Q 0 and value of N near to 1 indicates high attenuation characteristics in this region and is similar to the results have been found for other tectonically active regions of Iran and the world [Rovelli 1982, Hellweg et al 1995, Yoshimoto et al 1993, Castro et al 1996, Bindi et al 2006, Motazedian 2006 amongst others].…”

“…Castro et al 1990Castro et al , 1996Dutta et al 2003;Oth et al 2011]. Here we provide a brief description of the GIT method and refer the reader to the above-mentioned papers for more in-depth details of this technique.…”

The updated crustal attenuation in North China using ML amplitude tomography

“…We therefore assume S i ( f ) is also independent of frequency. The geometrical spreading (Castro et al, 1996), G(R), is considered to be proportional to (1/R) k , where k is the geometrical spreading coefficient, which chiefly depends on wave type. k = 1.0 implies spherical spreading of body waves and k = 0.5 represents cylindrical spreading of surface waves.…”