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The 8 January 2006 Earthquake (Mw 6.7) Offshore Kythira Island, Southern Greece: Seismological, Strong-motion, and Macroseismic Observations of an Intermediate-depth Event

Konstantinos I. Konstantinou, Ioannis S. Kalogeras, Nikolaos S. Melis, Moissis C. Kourouzidis, and George N. Stavrakakis

See also the publication in Seismological Research Letters, Vol 77, No 5 September/October 2006, 544-553

On 8 January 2006 at 11:34 GMT (13:34 local time), a strong earthquake with a moment magnitude of 6.7 occurred in southern Greece, off the eastern coast of the island of Kythira. The epicentral coordinates as estimated by the European Mediterranean Seismological Centre (EMSC-CSEM, were 36.31°N, 23.24°E, and the focal depth was 60 km. The shock was felt in a spatially extended area that covered Greece, Italy, Turkey, Egypt, Cyprus, Israel, Syria, Jordan, and Lebanon. Despite the large magnitude of the earthquake, the reported damage was not extensive mainly due to the intermediate focal depth. No casualties were reported and the structural damage to buildings was limited to the islands of Kythira and Antikythira and to the city of Chania, western Crete. Furthermore, landslides and/or rockfalls were reported only at the village of Mitata (Kythira island), where the main square and the road were damaged due to a landslide.

In this article we take advantage of a multitude of available observations to give a detailed report on this most recent large intermediate-depth earthquake. First, we describe the temporal and spatial distribution of the mainshock-aftershock sequence and summarize all available moment tensor solutions reported by various agencies. Then, we present preliminary analysis of strong-motion recordings in an effort to check the relationship between the shaking caused by such an event and the influence of both attenuation and local geological conditions. Macroseismic data collected from the whole of Greece also are included and utilized toward understanding the regional intensity attenuation pattern. Finally, we give an overview of the implications of such an event in terms of regional seismotectonics and seismic hazard.


Intermediate-depth earthquakes in the broader area of south-western Greece are related to the southern Aegean subduction zone, which is referred to as the Hellenic arc (figure).

The mainshock as well as several of its aftershocks (8 January to 20 May 2006) were recorded by the Institute of Geodynamics' seismological network. The results of the recordings analysis (manually picking of P- and S-phase arrival times and their inversion) are consistent with the results reported by several institutes/agencies, which show a predominently reverse slip component. In the map the circle The circle size is proportional to the local magnitude of each event, according to the scale shown at the right side of the plot. In a similar way, the focal depth follows the color scale shown at the right side. All available moment tensor solutions for the mainshock and two of its aftershocks also are plotted. The linked table shows the moment tensor solutions included in the study.


The strong motion recordings included in the study came from the accelerographs operated by the Institute of Geodynamics, ITSAK ( and PPC. The linked table gives information about the sites and the PGA recorded.

Some examples of strong ground motion recorded during the Kythira earthquake by a number of instruments in and around the Athens metropolitan area are showed in the figure. The star represents the epicenter of the mainshock and the different symbols indicate PGA values registered at those locations.

The linked table summarizes the PGA (g), PGV (cm/s) and PGD (cm) values calculated from the NOAIG strong motion instruments. Follow the number-links to view the respective graph.

Analysis of the accelerographs showed that the corresponding response spectra appear to be dominated by long period (up to 2.5s) strong ground motion, which is in contrast to observations of strong ground motions recorded during near-field events (dominant periods usually shorter than 0.5s). A comparison of near field (dashed line) and far field (continuous line) pseudoacceleration response spectra for PGA of the same order (around 20-30mg) was performed for 4 sites (PRSA, KORA, XLCA and ATHC) and showed the existence of the long period waves recorded by the strong motion instruments due to the Kythira earthquake in all situations, although the spectral accelerations do not vary much for the four cases.


According to first reports, the Kythira earthquake was felt in most parts of Greece, so questionnaires were sent to all the prefectures of the country. In total 666 questionnaires were sent and 304 were completed and returned by the local authorities. The reported answers clearly indicate that despite its large magnitude, the earthquake did not cause serious damage owing to its large focal depth. For example, at Potamos village (on Kythira island) situated only 35 km from the epicenter, the reported intensity was only V+. At the village of Mitata, where the most serious damage occurred (intensity VII+), local site amplifications appear to have been responsible for the relatively severe shaking, since similar observations also were reported after another intermediate-depth earthquake in 1903. A map of isoseismals curves derived from the macroseismic data following the methodology of Schenkova et al. (2006), based on a kriging method. Moreover some simple statistical diagrams concerning the macroseismic observations are presented.

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