Abstract
On June 8, 2008, a strike-slip earthquake (Mw=6.4) was generated NE of the Andravida town (NW Peloponnese, western Greece) due to the activation of the previously unknown western Achaia strike-slip fault zone (WAFZ). Extensive structural damage and earthquake environmental effects (EEE) were induced in the NW Peloponnese, offering the opportunity to test and compare the ESI 2007 and the EMS-98 intensity scales in a moderate strike-slip event. No primary EEE were induced, while secondary EEE including seismic fractures, liquefaction phenomena, slope movements and hydrological anomalies were widely observed covering an area of about 800 km<sup>2</sup>. The lack of primary effects and the relatively small surface deformation with respect to the earthquake magnitude is due to the thick Gavrovo flysch layer in the affected area that isolated and absorbed the subsurface deformation from the surface. According to the application of the EMS-98 scale, damage to masonry buildings ranged from grade 3 to 5, while damage in most of R/C buildings ranged from grade 1 to 3. A maximum ESI 2007 intensity VIII-IX is recorded, while the maximum EMS-98 intensity is IX. For all the sites where intensity VIII has been recorded the ESI 2007 and the EMS-98 agree, but for others the ESI 2007 intensities values are lower by one or two degrees than the corresponding EMS-98 ones, as it is clearly concluded from the comparison of the produced isoseismals. An exception to this rule is the Valmi village, where considerable structural damage occurs (IX<sub>EMS-98</sub>) along with the lack of significant EEE (V<sub>ESI 2007</sub>). This variability between the ESI 2007 and the EMS-98 intensity values is predominantly attributed to the vulnerability of old masonry buildings constructed with no seismic resistance design. Correlation of all existing data shows that the geological structure, the active tectonics, and the geotechnical characteristics of the alpine and post-alpine formations along with the construction type of buildings were of decisive importance in the damage and the EEE distribution.
Highlights
Earthquake environmental effects (EEE) have been increasingly disregarded in the literature and the practice of macroseismic investigations during the 20th century, while increasing attention has been directed towards the analysis of the effects on humans and manmade structures
Five years after the event, we present some considerable data about the macroseismic characteristics of the earthquake and about the geology, tectonics and seismicity of the epicentral area (NW Peloponnese)
A maximum VIIIESI 2007 intensity has been assigned to several sites (Kato Achaia, Nissi and Pineios Lake areas) (Table 1, Figures 2, 4), where surface fractures up to 20 cm wide and up to hundreds meters long as well as impressive liquefaction phenomena were observed in post-alpine formations
Summary
Earthquake environmental effects (EEE) have been increasingly disregarded in the literature and the practice of macroseismic investigations during the 20th century, while increasing attention has been directed towards the analysis of the effects on humans and manmade structures. The integration of the ESI 2007 intensity scale with the other scales including EMS-98, provides a better picture of the earthquake scenario, because only EEE allow suitable comparison of the earthquake intensity both (a) in time: effects on the natural environment are comparable for a time-window (recent, historic and palaeoseismic events) much larger than the period of instrumental record (last century), and (b) in different geographic areas: environmental effects do not depend on peculiar socio-economic conditions or different building practices Despite these advantages, there are some limitations in the use of the ESI 2007 scale. They can be distinguished into Pliocene and Quaternary marine, lagoonal, lacustrine and terrestrial deposits and lie unconformably on the alpine basement [Christodoulou 1969, Tsoflias 1977, 1980, 1984, Kamberis et al 1979, Fleury et al 1981, Mariolakos et al 1990, Lekkas et al 1990, 1992, 2000, Mariolakos et al 1995]
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