We estimated the quality factor Q of S waves traveling through the crust in the southern region of Italy. For that purpose 65 regional earthquakes with magnitudes ML 2.0-5.3 and hypocentral distance ranging between 7 and 375 km were analyzed. To estimate Q we first calculated a set of empirical functions that describe the S-wave spectral-amplitude decay with distance for 15 frequencies between 1 and 25 Hz. Within the distance range of the recordings, the average Q can be approximated as Q=25.7f(1.4). To separate the effect of upper and lower crust in the total Q, we used the first 50 km of the attenuation functions to estimate Q of the upper crust, and found that Q= 18.8 f(1.7). Then, using the 50-100 km segment of the attenuation functions we estimated that Q= 17.8(1.3) for the lower crust We also found that at high frequencies (f>10 Hz) the upper crust Q increases considerable relative to lower crust Q, being a factor of nine greater at 25 Hz. This higher attenuation in the lower crust may be the effect of deep structures as reported by Menardi-Noguera and Rea (2000) that were subjected to brittle-ductile deformation during past tectonic events
Crustal Q in Southern Italy determined from regional earthquakes
Gallipoli MR;
2008
Abstract
We estimated the quality factor Q of S waves traveling through the crust in the southern region of Italy. For that purpose 65 regional earthquakes with magnitudes ML 2.0-5.3 and hypocentral distance ranging between 7 and 375 km were analyzed. To estimate Q we first calculated a set of empirical functions that describe the S-wave spectral-amplitude decay with distance for 15 frequencies between 1 and 25 Hz. Within the distance range of the recordings, the average Q can be approximated as Q=25.7f(1.4). To separate the effect of upper and lower crust in the total Q, we used the first 50 km of the attenuation functions to estimate Q of the upper crust, and found that Q= 18.8 f(1.7). Then, using the 50-100 km segment of the attenuation functions we estimated that Q= 17.8(1.3) for the lower crust We also found that at high frequencies (f>10 Hz) the upper crust Q increases considerable relative to lower crust Q, being a factor of nine greater at 25 Hz. This higher attenuation in the lower crust may be the effect of deep structures as reported by Menardi-Noguera and Rea (2000) that were subjected to brittle-ductile deformation during past tectonic eventsI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
