Subsoil non-linearity effect during the 2016 mw 6.5 central Italy mainshock?

Abstract

This paper focuses on the high-frequency pulses observed in some recordings of temporary seismic stations during the largest mainshock (Mw 6.5, 30 October 2016) of the 2016-2017 Central Italy sequence. Such pulses are characterized by a spike shape and are particularly evident in the horizontal components producing peak acceleration values (PGA) that largely exceed the estimation of ground-motion prediction equation usually adopted in Italy. Similar spikes were already observed in literature for very strong earthquakes in the world, and were ascribed mostly to subsoil nonlinearity. In this work we present the raw recordings affected by the spikes of the Mw 6.5 Central Italy event, and we try to interpret these anomalous signals also invoking possible equipment malfunctions.