Ground motion modeling for site effects at L’Aquila and middle Aterno river valley (central Italy) for the MW 6.3, 2009 earthquake

Abstract

Ground motion for the 6 April 2009 (Mw 6.3) earthquake is computed along 2-D cross-sections at L’Aquila by a hybrid method (modal summation plus finite differences) and validated with recordings at AQU, AQK, AQG, AQA and AQV stations. Parametric studies of S-wave velocities of the shallowest lithotypes allow to get a general agreement between synthetic and observed response spectra, despite the scaled point-source approach and the lack of detailed geological and seismic studies. It results that the megabreccia covering on lacustrine soils, characterizing the historical center of L’Aquila, is responsible of spectral amplifications along the vertical (2–7) and horizontal components (2–3) at a wide frequency range (0.6–7Hz). The covering of alluvial soils in the middle Aterno river valley is responsible of amplifications at 2–7Hz both in the horizontal and vertical planes of the motion. Such amplifications evidence that site effects might have been responsible of structural damages.