Sudati, Dario Ivano

In Italy, strong-motion monitoring was started in 1972 by different Institutions, although mainly through Ente Nazionale per l'Energia Elettrica (ENEL; Italian National Electricity Company) and Dipartimento della Protezione Civile (DPC; Italian Department of Civil Protection), with different purposes. These included permanent acceleromet- ric monitoring and temporary monitoring during seismic se- quences or before permanent installation. Today, the National Accelerometric Network (RAN; Rete Accelero- metrica Nazionale) [Gorini et al. 2010, Zambonelli et al. 2011] is operated by the DPC and consists of 464 digital sta- tions. These are distributed throughout the whole national territory, with a prevalence for areas of major seismicity. In 2006, the INGV began strong-motion monitoring, by installing 22 accelerometric stations in northern Italy (RAIS; Rete Accelerometrica Italia Settentrionale; Accelerometric Network of Northern Italy; http://rais.mi.ingv.it/). In 2008, the monitoring was extended to a national scale: this effort led to the installation of 105 accelerometers, collocated with the velocimetric sensors, in selected Rete Sismica Nazionale (RSN; National Seismic Network) sites [Amato and Mele 2008] that are managed by the Centro Nazionale Terremoti (CNT; National Earthquake Centre). Overall, the 127 strong- motion stations that form the INGV Italian strong-motion network homogeneously cover the whole Italian territory. The progress achieved in Italy in the field of strong-mo- tion monitoring and strong-motion data archiving and dis- semination was illustrated in a recently published special issue of the Bulletin of Earthquake Engineering [Luzi et al. 2010]. The strong-motion data recorded by the RAN have been distributed and are available on request to the DPC and to the Italian Accelerometric Archive (ITACA), as the Italian strong-motion database (http://itaca.mi.ingv.it/) [Pacor et al. 2011a], which has been updated with records to 2009. The INGV strong-motion data are archived in real-time and dis- tributed through the European Integrated Data Archive (EIDA; http://eida.rm.ingv.it/) web portal. Recently, an INGV working group developed the first version of a web portal with the aim of archiving, processing and distributing accelerometric data recorded by permanent and temporary INGV stations. This web portal (www.mi. ingv.it/ISMD/; Figure 1, top panel) is composed of two main modules: the former is known as the INGV Strong Motion Data (ISMD, www.mi.ingv.it/ISMD/ismd.h tml/; Figure 1, bottom left panel) and has as its main scope the analyse and distribution in quasi-real time (a few hours after event oc- currence) of the uncorrected accelerometric data, and the related metadata obtained after an automatic processing pro- cedure. This latter, known as the Dynamic Archive (DYNA, http://dyna.mi.ingv.it/DYNA-archive/; Figure 1, bottom right panel) is a dynamic database where manually post- processed accelerometric waveforms are provided, together with their metadata. Both of these archives are designed and structured in such a way that their compilations and updat- ing will be almost completely automatic. At the end of May 2012, a first prototype of the ISMD module was published, providing the uncorrected strong- motion data recorded by the INGV stations for the main events of the Emilia seismic sequence [Massa et al. 2012].

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.