The May 2012 Pianura Padano-Emiliana seismic sequence: INGV strong-motion data website

On May 20th 2012, 06:03:02 UTC, a ML 5.9 (Mw 6.0) earthquake struck the Northern Italy
(http://cnt.rm.ingv.it/tdmt.html). The epicenter was localized at 11.23° E and 44.89° N, in an area
among the cities of Ferrara, Modena and Mantova. The event occurred at a depth of about 6.30 km,
and was characterized by a reverse focal mechanism (http://cnt.rm.ingv.it/). From May 20th,
thousand of earthquakes, the strongest of which with a ML 5.8 (May 29th, 07:00:03 UTC), occurred
in the same area (http://iside.rm.ingv.it/).
This note presents a new web site, www.mi.ingv.it/ISMD/ that includes about 2.000 threecomponents
strong-motion recordings related to the events with 4.0 ≤ ML ≤ 5.9 occurred in the
central part of the Pianura Padano-Emiliana (Northern Italy) from May 20th to June 3rd. The data
come from all INGV strong-motion stations installed in Northern Italy (i.e. Strong-Motion Network
of Northern Italy, RAIS, http://rais.mi.ingv.it/, Augliera et al., 2011; strong-motion stations of the
National Seismic Network, RSN, http://cnt.rm.ingv.it) and selected with a minimum latitude of
43.5°N. The earthquake locations reported in the web site come from the National Earthquake
Center of INGV (preliminary location form: http://cnt.rm.ingv.it/).
An automatic procedure was developed in order to publish in the web site both metadata (processed
by an automatic system) and downloadable waveforms in ascii format (uncorrected version).
After each earthquake occurrence, the procedure downloads 5 minutes (starting from the event
origin time) of MINI-Seed waveforms from EIDA (http://eida.rm.ingv.it/) archive and applies a fast
processing and data analysis tool.
The automatic data processing includes: i) a first-order baseline operator applied to the entire
record, in order to have a zero-mean of the signal; ii) a baseline correction, in order to remove the
linear trend, computed with a least square method; iii) tapering of the signal through a cosine
function (0.01%) at the beginning and at the end of each selected window; iv) the application of a
4th order Butterworth band-pass acausal (Boore and Akkar, 2003; Boore and Bommer, 2005) filter
in order to remove the high and low-frequency noise: the filter cut-off thresholds were
automatically selected on the basis of the event magnitude (i.e., 0.1-40 Hz with ML ≥ 5.5; 0.2-35 Hz
with 4.5 ≤ ML < 5.5; 0.3-35 with 3.5 ≤ ML < 4.5).
Considering the available digital instrumentation (i.e. 24 bits Kinemetrics Episensor with a flat
response up to 200 Hz) the deconvolution for the instrument response was not applied. At the end
velocity waveforms were obtained through integration of the processed accelerometric data.
For each component of the automatically processed signals the following GM parameters are
evaluated: PGA (peak ground acceleration), PGV (peak ground velocity) and SA (5%-damped
acceleration response spectra) for periods up to 4 s were calculated. Moreover, the automatic system
provides PSV (5%-damped pseudo-velocity response spectra), Sd (5%-damped displacement
response spectra), Ia (Arias Intensity; Arias 1970) and Ih (Housner intensity; Housner 1952). In
correspondence of each recording site the horizontal-to-vertical spectral ratio (HVSR) was
automatically performed considering 5 s and 10 s of S phase (starting from 1s before the S-phase
onset).
At the end of the automatic procedure, for each single event, a web page is generated. On each web
page the results are published in terms of tables (text format) containing main strong-motion
parameters and generic plots (e.g., location of recording stations, HVSRs, response spectra,
accelerograms, comparison between recorded data and Italian Ground Motion Prediction Equations,
Bindi et al., 2011). For each event the strong-motion records, in uncorrected ascii-format, are
downloadable. Following the standards of the ITalian ACcelerometric Archive, ITACA
(http://itaca.mi.ingv.it, Pacor et al., 2011), the waveforms ascii files are composed of 43 header
lines followed by acceleration data in cm/s2.