Evidence of large infrasonic radiation induced by earthquake interaction with alluvial sediments

The Mw 5.9 Ferrara earthquake that struck northern Italy on 20 May 2012 was recorded with an infrasound array at a source-to-receiver distance of 300 km. The infrasound record revealed early and late detections characterized by large backazimuth variations, suggesting the existence of an extended area of infrasound radiation. Unlike most previous studies, the modeled area of maximum infrasound radiation appears to mimic an extended flat area (plain of the Po River) with no significant contributions from nearby mountain ranges. The ShakeMap of the earthquake and the map of the reported acoustic boom are in good agreement with the modeled area of infrasound radiation, suggesting how the transition of seismic waves into acoustic atmospheric waves is efficiently exciting infrasound recorded at far distances from the source. Such a result is in agreement with the significant seismic amplification within the Po plain alluvial sediments.