The volcanic center of Santorini Island is the most active volcano of the southern Aegean volcanic arc. Α dense seismic array consisting of fourteen portable broadband seismological stations has been deployed in order to monitor and study the seismo-

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PAGES 401,407Active tectonic processes along the AfricanEurasian collision zone are associated with catastrophic events including earthquakes, major volcanic eruptions, and tsunamis. Understanding how these processes can affect the eastern Mediterranean is of increas ing scientific and public interest. The region includes a frequently crossed international sea traffic corridor and dense population centers. Furthermore, most of the small vol canic islands in the Aegean are major tourist attractions that contribute significantly to the wealth of this region.One of these Aegean islands is Santorini, which is a major explosive volcano and pos sibly one of the most dangerous volcanoes in Europe. During the past 150 million years, Santorini has had 12 major eruptions, and several of them ejected large columns of ash and debris high into the atmosphere. It is widely believed that the eruption of San torini about 3600 years before present (B.P) destroyed the Minoan civilization of Crete.In addition to the volcanic island, there are several submarine volcanic seamounts in the Aegean Sea. One of them, the Columbo seamount, is about eight kilometers northeast of Santorini, and recently has attracted atten tion due to the high earthquake activity of the Hellenic subduction zone [Bohnhoff et al,2006].This activity is concentrated in an area northeast of Santorini, within the socalled Santorini-Amorgos zone.The earthquakes occurred in the upper crust at a depth of 3-15 kilometers and are considered to be related to evolving volcanism and related magma or fluid migration. Whereas the potential risk of future erup tions of the Santorini volcano is well recog nized by scientists and by Santorini residents, the Columbo underwater volcano never has reached a level of public risk perception The newly completed first phase of the 'Inspecting Columbo' project consisted of an extensive marine geophysical survey that was carried out in order to map active tec tonic and volcanic features. More than 1500 kilometers of seismic and magnetic data, as well as 2500 kilometers of gravity data, were collected in June 2006 during a cruise onboard the research vessel (R/V) Poseidon. On the basis of onboard processing, optimized loca tions for deploying five ocean-bottom seis mometers and four newly developed oceanbottom tiltmeters were determined.The retrieval of these instruments, scheduled for spring 2007, will initiate the second phase of the program. Volcanic Complexes of the Santorini-Amorgos ZoneAccording to previous findings, the San torini-Amorgos zone (SAZ) marks a major structural boundary in a dextral transtensional regime that subdivides the Hellenic volcanic arc into a seismically and volcanically quiet western and an active eastern part. The highest earthquake activity has been observed beneath the submarine Columbo volcano and northeast of it along the Santorini-Amorgos Ridge [Perissoratis, 1995], which terminates south of the island of Amorgos (Figure 1).The activity close to the Columbo seamount is considered to be linked dire...

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.

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