An attenuation study in Southern Italy using local and regional earthquakes recorded by seismic network of Basilicata

• Main Authors: M. Mucciarelli, M. R. Gallipoli, R. R. Castro
• Format: Article
• Language: English
• Published: Istituto Nazionale di Geofisica e Vulcanologia (INGV) 2004-06-01
• Series: Annals of Geophysics
• Subjects: seismic attenuation; Southern Italy; Q
• Online Access: http://www.annalsofgeophysics.eu/index.php/annals/article/view/3362

We determined a set of empirical functions that describe the spectral amplitude decay of S-waves with distance in Southern Italy. We analyzed 32 earthquakes with magnitudes ML 2.0-5.4 and hypocentral distances ranging between 12 and 216 km. We obtained attenuation functions for 14 frequencies(1.0< f<20.0 Hz). We compared these functions with average non-parametric attenuation functions reported by Castro et al. (1999) for different regions of Italy, and we observe that at low frequencies (f<5.0 Hz) the spectral amplitudes from earthquakes in Southern Italy decay faster than the average. However, at high frequencies ( f > 5.0 Hz), the spectral amplitudes are above the average. At higher frequencies ( f > 10 Hz), the attenuation functions obtained for Southern Italy are slightly above the standard deviation of the average attenuation functions. It is possible that in this frequency range (10-20 Hz) site effects may influence the amplitude decay. In order to quantify the attenuation of the S-waves, we estimated the quality factor Q modeling the empirical attenuation functions using the following
 parametric form: A( f , r)=10/r b·e- pfR/Q ß; where 1.6 = f = 10.0 Hz is the frequency band with minimum effect of instrument
 and site response, r = 120 km is the distance range where the rate of decay of the spectral amplitudes is approximately constant, R=(r-10) and ß=3.2 km/s. We found that the exponent b=1.0±0.2 in the frequency
 band analyzed and Q shows a frequency dependence that can be approximated by the function Q=32.1 f 1.7.