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

Abstract

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.