Tectonic and seismological data collected in the field following the September 13, 1986, Kalamata earthquake (south Peloponnesus) are presented and analyzed to discuss the earthquake rupture process and the regional tectonics. The event occurred on the Kalamata normal fault whose trace was mapped with SPOT images and topographic and field observations. This fault is part of an approximately NNW‐SSE en échelon system cutting through the Hellenic nappes. The fault striking N15°E on the average, with a dip of about 50°, has a minimum cumulated Quaternary throw of the order of 1 km. The measured coseismic slip is 6–18 cm over a length of 6 km. The main shock focal mechanism obtained from long‐period waveform modeling (strike=201° (+10°,−20°), dip=45°±5°, rake=283° (+10°,−25°)) represents almost pure east‐west extension and is in good agreement with tectonic observations. The centroid depth is constrained to 5±3 km and the seismic moment to 7.0±2.5×1017 N m. Over 700 aftershocks, located by a 16‐station network installed after the earthquake for a period of 2 weeks, define two clusters separated by a “gap” of aftershock activity, from the surface to a depth of about 10 km. The main cluster, to the south, defines a 45° west dipping plane which lies on the downward extension of the fault mapped at the surface. Focal mechanisms of aftershocks on this fault plane are homogeneous and represent E‐W extension as the main shock. In contrast, the majority of focal mechanisms in the uppermost part of the foot wall show more or less E‐W compression, probably corresponding to postseismic stress release. The northern cluster of aftershocks is very dense and located away from the surface rupture, within a relay zone between the Kalamata and the next en échelon faults to the NW, the Thouria faults. There focal mechanisms represent extension from about N115° to N70° and N20°, corresponding mostly to fault reactivation in an area where nonrigid deformations prevail. The main shock probably initiated in this relay zone 3–4 s before the rupture front reached the main fault plane and released most of the energy there, the rupture presumably propagating southward. The focal mechanism of the Kalamata earthquake and that of the April 27, 1965, earthquake located to the northwest of Crete, as well as the regional active normal fault pattern, imply that E‐W extension oblique to the Hellenic arc is presently the dominant tectonic regime. E‐W stretching occurs partly on reactivated NW‐SE faults parallel to the Hellenic structures but mostly on newly formed N‐S normal faults across those structures. The latter faults are responsible for the apparent segmentation of the Hellenic belt from southern Peloponnesus to Crete. The existence of active E‐W extension in this region implies a recent change in the tectonic regime and consequently a change in boundary conditions at the subduction zone, probably in response to the incoming margin of Africa.

An earthquake catalogue for Greece is presented covering the period 1900-1985. It is based on a similar effort attempted a few years ago. The present version contains more than double the number of events, i.e. 4310 events compared with 1806 events, than in the previous papers. It also includes another 1711 events which took place in the region in an Appendix. The accuracy and completeness of the parameters of these shocks were insufficient for inclusion in the main catalogue without affecting the catalogue's homogeneity. For the new entries magnitudes are redetermined using Uppsala's reading as before, whereas the other parameters have been rechecked against local macroseismic information. The completeness of this catalogue varies according to the period of observation, but the lower threshold of completely reported magnitudes has been substantially decreased allowing for more detailed seismicity studies to be performed.

We compute crustal thickness in Epirus (NE Greece), from spectral analysis of the Bouguer gravity field.Moho depths were established from the slope of the log-power radial spectrum at the lower end of the wavenumber band and were found to vary from 31 to 38 km. This is in agreement with the results obtained by other investigators employing seismological methods of analysis.

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