Project S 6 – Data base dei dati accelerometrici italiani relativi al periodo 1972-2004 Coordinators :

The Italian strong-motion data base includes 2182 three component waveforms relative to 1004 earthquakes with maximum magnitude 6.9 (1980-11-23 Irpinia earthquake) in the period range 1972 – 2004 and is devoted to engineering and scientific communities. During this time span, the strong motion data have been acquired by different institutions, namely ENEL (Ente Nazionale per l’Energia Elettrica, Italian Electricity Company), ENEA (Ente per le Nuove tecnologie, l’Energia e l’Ambiente, Italian Energy and Environment Organization) and DPC (Dipartimento della Protezione Civile, Italian Civil Protection) with different purposes (permanent strong motion monitoring of the Italian territory and temporary monitoring during seismic sequences or before permanent installation). In the 18 months of the S6 project the data have been collected, homogenized and processed according to the defined standards. Acceleration, velocity, displacement and acceleration response spectra have been calculated, together with the most used engineering parameters. In order to increase the data quality, the parameters relative to the seismic events have been included after a careful revision, through the use of the most updated seismic catalogues and data bases. The data relative to the recording stations have also been added, not only collecting existing data, but also promoting new field investigations of various type (borehole geophysical tests, seismic refraction, seismic reflexion, SASW, geological and geo-mechanical surveys). The data set has been organized in a relational data base, which is made of four main “blocks”, relative to waveforms, seismic events, recording stations and references. The data base is distributed in a stand-alone format, which can be downloaded on a PC and explored through the MS Access software, or it can be accessed via the web at the address: http://itaca.mi. ingv.it. The on-line data base can be interactively searched by the user according to personal needs through user friendly data queries, which allow the identification of waveforms with particular characteristics. A range of display and download options allow users to view data in multiple contexts, extract and download metadata, time series and spectra files. The documentation relative to data collection, data format, data base structure, processing standards and waveform metadata is contained in the project web portal at http://esse6.mi. ingv.it. Progetti sismologici di interesse per il DPC – Rendicontazione conclusiva 2 1. Results of the project: general description The project goals have been almost entirely fulfilled. The minimum expected result, represented by the mere collection of existing data has been reached. In addition, the data base has been enriched by a huge amount of metadata, some of which have been collected during the project, promoting new investigations. The data base, unlike existing ones, is characterised by the care spent in increasing the metadata quality, which cost time and financial efforts. Another notable feature of the project is the data distribution policy. Two approaches of data distribution were adopted: a MS Access file, that can be directly downloaded on the PC, or the web portal, where the data base can be interactively searched by the user according to personal needs, through user friendly data queries. In order to help users, a wide range of display and download options were planned in order to display data in multiple contexts, extract and download metadata and time series. Another relevant result is the interaction of the S6 project with other seismological DPC-INGV ones. In particular, there was a collaboration with project S3 for the study of the Gubbio area, where two boreholes were drilled and geophysical tests were performed to obtain the Vs and Vp profiles. A collaboration was carried on with the S1 project for the verification of the Italian hazard map (MPS04) with the peak ground acceleration values recorded in the last 30 years. Two of the research units, officially included in S4 and S3 projects, collaborated to this project receiving an integration of funds for performing field activities. Finally there was a collaboration with the EC project NERIES at two tasks, namely NA5 Improving accelerometric data dissemination, for the exchange of experiences acquired in the data base structure and the strategies of data dissemination, and JRA4 Geotechnical site characterization, for the exchange of soil velocity profiles and the definition of the relevant soil geotechnical and geophysical parameters to be stored in the data base. The project has a prevalent technological imprint and no research advances have been reached. The potential of the data base is the research that can be carried on with it in the immediate future. Many applications in seismology and earthquake engineering make use of strong motion data, from the evaluation of the empirical attenuation relationships, to the verification of shaking scenarios, hazard maps and real time shake-maps, among others. These 18 months spent in collecting data, defining standards and designing data distribution facilities, represent an investment made by the scientific community. The challenge for the future is the use of the data for research advances. As preliminary result, the data set used by Sabetta and Pugliese (1987) to derive the Italian empirical ground-motion attenuation relation has been revised and integrated with the records of the most relevant earthquakes occurred since 1984. A new set of coefficient has been obtained using the same functional form. The comparison between the new attenuation relation and the Sabetta and Pugliese (1987; 1996) shows the tendency of the latter to overestimate the PGA on rock sites (Bindi et al., 2007), as shown in Figure 1. Progetti sismologici di interesse per il DPC – Rendicontazione conclusiva 3 Figure 1: Comparison between the Sabetta and Pugliese (1996) attenuation relation (green) and the model obtained with the new data set (red). The areas represent the mean value ± one standard deviation. Black dots are observations for a Mw 6.9 earthquake (top) and 5.2 (bottom), respectively. On the left attenuation for rock sites, on the right attenuation for class1 sites (shallow alluvium). However, at the conclusion of the project many issues remain opened and not solved, at least definitively. The data collection stops at 2004 and a huge amount of data has been gathered by the Department of Civil Protection in the time span 2004-2007. The quality of recording instruments increased, in accuracy and precision and the same amount of strong-motion data as in the 19722004 period has been collected. In addition, in the last decade new strong motion networks have been installed, managed by different institutions than DPC, whose data have not been included in the S6 data base. The issue of the recording site characterization is still open, as only few sites were investigated during this project. But this task cannot be carried on routinely by scientific institutions, so field investigation standards should be defined in order to outsource this activity to private companies which should work under a strict scientific supervision. Progetti sismologici di interesse per il DPC – Rendicontazione conclusiva 4 2. Results of the project: detailed description by single tasks The project was carried out in four main tasks: Task 1 – Data base structure definition and data base control Task 2 – Waveform collection and processing Task 3 – Verification of seismic events, station and instrument metadata Task 4 – Data base implementation and data dissemination The activity 1 regarded the definition of the data base architecture and the selection of a software for the data base management. The data base is handled through two different relational data base management system: Ms Access® 2003, of major use among research institutions and public administrations, for CD-ROM release, and MySQL for the web distribution. The selection of the former product is driven by the simplicity of the software, the worldwide diffusion and the possibility of being linked to software’s for the management of spatial data, such as ESRI ArcGis® and Arcview®, and software for the scientific calculation such as Matlab®. 48 tables were created in order to store the information regarding the seismic events, the recording stations, the installed instruments and the strong-motion parameters. They are connected through a relational structure in order to avoid data redundancy. Figure 2 exemplifies the recording station “block” of the data base. The waveform format has been unified according to one standard. The file name is composed of 33 characters which include the event time, the recording network, the recording site, the component, the correction flag and the time series type (acceleration, velocity, displacement or acceleration spectrum). This structure was thought in order to be managed with simple OS commands. The waveform file in ASCII format contains a 43 row header of metadata which regard the event, the recording site and the instrument characteristics. The processing information are also added, for a correct data use. This structure makes each record self-consistent. The waveforms are also available in SAC format, which is mainly used by the seismological community and can be handled by many softwares. The data are distributed in processed and raw format, so that each expert user can reprocess the data according to his needs. Progetti sismologici di interesse per il DPC – Rendicontazione conclusiva 5 Figure 2: example of the recording site “block” of the data base Progetti sismologici di interesse per il DPC – Rendicontazione conclusiva 6 The second task mainly regarded the establishment of a standard for data processing. It is well known that strong-motion records require processing, as they contain a variable noise level which depends on different causes. Neverth