Strong Motion Modeling at a Near-Source Site in Avezzano, Italy

This paper describes the results of a seismic risk study at a near-source site in Avezzano, Italy. The goal was to quantify seismic hazard through the calculation of site-dependent response spectra and ground motion time histories. The methodology used consists in combining deterministic and stochastic modeling of radiated seismic energy from an extended fault. The use of an extended source is crucial as the site is in the near-source region of the Serrone fault, which is thought to have ruptured during the 1915 Avezzano earthquake (Ms = 6.9). In a first phase of the study, we determined plausible ranges for the parameters used in characterizing possible rupture scenarios on the Serrone fault. These parameters range from the purely geometrical (i.e., fault orientation and dimensions) to kinematic (i.e., plausible hypocenters, rupture velocity, seismic moment); and were subsequently used to generate a representative family of low-frequency synthetics. The simulation of high-frequency ground motion was based on the stochastic technique of Boore (1983). Since this method implicitly assumes a point source, we developed a hybrid technique which combines Boore’s method with elements of the isochron formulation of Spudich and Frazer (1984) and Bernard and Madariaga (1984), used to generate high-frequency synthetic waveforms. The isochron formulation, as used here, provides the physical basis for the generation of realistic waveform envelopes resulting from the rupture of an extended fault. In a final step, broadband synthetics were constructed by merging deterministic low-frequency and stochastic high-frequency waveforms. Response spectra for the site of interest were then calculated, along with bounds reflecting the different rupture scenarios considered.