ABSTRACT A complex seismic sequence characterised by two thrust earthquakes of magnitudes
ML 5.9 and ML 5.8 occurred on May 20 and 29, 2012, respectively, and activated
the central portion of the Ferrara Arc structure beneath the Po Plain in northern Italy. The
sequence, referred to as Emilia 2012, was recorded by the Italian Strong Motion Network,
the Irpinia Network, the Friuli Venezia Giulia Network and 15 temporary stations installed
by the Civil Protection Department. In this study, we compile and analyse a large dataset that
contains 3,273 waveforms from 37 ML ≥ 4.0 seismic events. The main aim of this paper is to
characterise the ground motion induced by the Emilia 2012 seismic sequence and compare
it with other data in the Italian strong motion database and to the recent Ground Motion
Prediction Equations (GMPEs) developed for northern Italy, all of Italy and Europe. This is
achieved by (1) the computation and analysis of the strong motion parameters of the entire
Emilia Strong Motion Dataset (ESMD) and (2) a comprehensive investigation of the May 29
event recordings in terms of time–frequency analysis, the ground motion parameters and the
response spectra. This detailed analysis was made possible by the temporary Civil Protection
Department stations that were installed soon after the May 20 event at several municipalities
in the epicentral area. Most of the recordings are characterised by low-frequency content and
long durations, which is a result of the thick sedimentary cover that is typical of the Po Plain.
The distributions of the observed horizontal peak ground accelerations and velocities (PGAs
and PGVs) with distance are generally consistent with the GMPEs. This is particularly true
for the data from ML ≥ 5.0 (MW ≥ 5.0) events, though the data are scattered at distances beyond approximately 60–70km and show faster attenuation than the European GMPEs. The
horizontal components for the May 29 event at two near-fault stations (Mirandola and San
Felice sul Panaro) are overestimated by all of the analysed GMPEs. In contrast, the vertical
components, which played an important role in the shaking near the source, are underestimated.
The May 29 event produced intense velocity pulses on the horizontal components
and the highest peak ground acceleration ever recorded in Italy on the vertical component of
the Mirandola near-fault station. The ground motion recordings contained in the ESMD significantly
enrich the Italian strong motion database. They contribute new information about
(1) the possibility of exceeding the largest recorded PGA in Italy, (2) the development of a
spectral design that takes into account the role of the vertical component and the extreme variability
of the near-fault ground shaking, and (3) the characterisation of the ground motions
in deep sedimentary basins.
Strong motion recorded during the Emilia 2012 thrust earthquakes (Northern Italy): a comprehensive analysis. Available from: https://www.researchgate.net/publication/261961294_Strong_motion_recorded_during_the_Emilia_2012_thrust_earthquakes_%28Northern_Italy%29_a_comprehensive_analysis [accessed May 28, 2015].
