The National Observatory of Athens data center for the European Integrated Data Archive (EIDA@NOA) is the national and regional node that supports International Federation of Digital Seismograph Networks and related webservices for seismic waveform data coming from the southeastern Mediterranean and the Balkans. At present, it serves data from eight permanent broadband and strong-motion networks from Greece and Cyprus, individual stations from the Balkans, temporary networks and aftershock deployments, and earthquake engineering experimental facilities. EIDA@NOA provides open and unlimited access from redundant node end points, intended mainly for research purposes (see Data and Resources). Analysis and quality control of the complete seismic data archive is performed initially by calculating waveform metrics and data availability. Seismic ambient noise metrics are estimated based on power spectral densities, and an assessment of each station’s statistical mode is achieved within each network and across networks. Moreover, the minimum ambient noise level expected for strong-motion installations is defined. Sensor orientation is estimated using surface-wave polarization methods to detect stations with misalignment on particular epochs. A single data center that hosts the complete seismic data archives with their respective metadata from networks covering similar geographical areas allows coordination between network operators and facilitates the adhesion to widely used best practices regarding station installation, data curation, and metadata definition. The overall achievement is harmonization among all contributing networks and a wider usage of all data archives, ultimately strengthening seismological research efforts in the region.
The European Integrated Data Archive (EIDA) is the infrastructure that provides access to the seismic-waveform archives collected by European agencies. This distributed system is managed by Observatories and Research Facilities for European Seismology. EIDA provides seamless access to seismic data from 12 data archives across Europe by means of standard services, exposing data on behalf of hundreds of network operators and research organizations. More than 12,000 stations from permanent and temporary networks equipped with seismometers, accelerometers, pressure sensors, and other sensors are accessible through the EIDA federated services. A growing user base currently counting around 3000 unique users per year has been requesting data and using EIDA services. The EIDA system is designed to scale up to support additional new services, data types, and nodes. Data holdings, services, and user numbers have grown substantially since the establishment of EIDA in 2013. EIDA is currently active in developing suitable data management approaches for new emerging technologies (e.g., distributed acoustic sensing) and challenges related to big datasets. This article reviews the evolution of EIDA, the current data holdings, and service portfolio, and gives an outlook on the current developments and the future envisaged challenges.
On 8 June 2008 at 12:25 (GMT) an M w 6.4 strong earthquake occurred in the area of northwest Peloponnese, western Greece, causing the death of two people and extensive damage to the surrounding area. The main event and its aftershocks were recorded by one nationwide and three regional networks equipped with threecomponent broadband seismometers. Initial locations of the earthquake sequence comprising 438 aftershocks showed a linear northeast-southwest trend and that the mainshock was located at 22 km depth. After the relocation using catalog and differential travel times, most events form three distinct clusters at depths 15-25 km. Moment tensor solutions for the main event and its largest aftershocks exhibited a pure strike-slip mechanism with one nodal plane orientated northeast-southwest in accordance with the relocated seismicity. A parallel, nonnegative least-squares inversion technique utilizing multiple-time windows was used to derive the spatiotemporal slip distribution of the main event. The resulting slip distribution model revealed a large slip patch (maximum slip ∼150 cm) between 10 and 20 km depth at the northeast part of the fault that also coincides with the area that suffered most of the damage. Another patch exhibiting smaller amounts of slip (20-50 cm) is located to the southwest direction at the same depth range, and smaller patches exist at 25-30 km depth. Most aftershocks are located in areas of low slip (< 25 cm) filling the regions of slip deficit. The 8 June earthquake occurred at an area where no previous seismological or other observations indicated the existence of a seismogenic fault at that depth and with this strike. This, and the fact that the event nucleated in the middle to lower crust, may be interpreted as the reactivation of a fault structure that was inherited from previous tectonic phases.Online Material: Spatiotemporal evolution of the aftershock sequence of the 8 June 2008 mainshock, sensitivity tests to the mainshock slip inversion, color versions of figures, relocated aftershocks catalog, classification scheme for the moment tensor solutions, and moment tensor inversion description.
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