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ANNALS OF GEOPHYSICS, 56, 6, 2013, S0681; doi:10.4401/ag-6239 Special Issue: Earthquake geology Seismic intensity assignments for the 2008 Andravida (NW Peloponnese, Greece) strike-slip event (June 8, Mw=6.4) based on the application of the Environmental Seismic Intensity scale (ESI 2007) and the European Macroseismic scale (EMS-98). Geological structure, active tectonics, earthquake environmental effects and damage pattern Spyridon D. Mavroulis1,*, Ioannis G. Fountoulis1, Emmanuel N. Skourtsos1, Efthymis L. Lekkas1, Ioannis D. Papanikolaou2 1 National and Kapodistrian University of Athens, Faculty of Geology and Geoenvironment, Department of Dynamic Tectonic Applied Geology, Panepistimiopolis, Athens, Greece 2 Agricultural University of Athens, Department of Geological Sciences and Atmospheric Environment, Laboratory of Mineralogy and Geology, Athens, Greece Article history Received October 19, 2012; accepted November 14, 2013. Subject classification: Active faults, Earthquake environmental effects, ESI 2007 intensity scale, EMS-98 intensity scale, Strike-slip earthquakes. ABSTRACT ance design. Correlation of all existing data shows that the geological struc- On June 8, 2008, a strike-slip earthquake (Mw=6.4) was generated NE ture, the active tectonics, and the geotechnical characteristics of the alpine of the Andravida town (NW Peloponnese, western Greece) due to the ac- and post-alpine formations along with the construction type of buildings tivation of the previously unknown western Achaia strike-slip fault zone were of decisive importance in the damage and the EEE distribution. (WAFZ). Extensive structural damage and earthquake environmental ef- fects (EEE) were induced in the NW Peloponnese, offering the opportunity 1. Introduction to test and compare the ESI 2007 and the EMS-98 intensity scales in a Earthquake environmental effects (EEE) have been moderate strike-slip event. No primary EEE were induced, while second- increasingly disregarded in the literature and the prac- ary EEE including seismic fractures, liquefaction phenomena, slope move- tice of macroseismic investigations during the 20th cen- ments and hydrological anomalies were widely observed covering an area tury, while increasing attention has been directed of about 800 km2. The lack of primary effects and the relatively small towards the analysis of the effects on humans and man- surface deformation with respect to the earthquake magnitude is due to made structures. The European Macroseismic scale the thick Gavrovo flysch layer in the affected area that isolated and ab- (EMS-98), which is predominantly used in Europe, con- sorbed the subsurface deformation from the surface. According to the ap- siders three categories of effects: (a) on humans, (b) on plication of the EMS-98 scale, damage to masonry buildings ranged from objects and on nature and (c) damage to buildings grade 3 to 5, while damage in most of R/C buildings ranged from grade [Grünthal 1998]. Its basic advantage over previous 1 to 3. A maximum ESI 2007 intensity VIII-IX is recorded, while the max- macroseismic intensity scales is a definition of vulner- imum EMS-98 intensity is IX. For all the sites where intensity VIII has ability classes for buildings and more precise statistical been recorded the ESI 2007 and the EMS-98 agree, but for others the ESI treatment of collected macroseismic data [Grünthal 2007 intensities values are lower by one or two degrees than the corre- 1998]. This quantification is elaborated in details for the sponding EMS-98 ones, as it is clearly concluded from the comparison of effects on humans, objects and buildings, but not for the produced isoseismals. An exception to this rule is the Valmi village, the effects on nature which are rather briefly summa- where considerable structural damage occurs (IXEMS-98) along with the rized in a table in EMS-98 scale. This allows a large dis- lack of significant EEE (VESI 2007). This variability between the ESI 2007 crepancy between the EEE and the damage pattern. and the EMS-98 intensity values is predominantly attributed to the vul- Recent studies [Dengler and McPherson 1993, nerability of old masonry buildings constructed with no seismic resist- Serva 1994, Dowrick 1996, Esposito et al. 1997, Hancox S0681 MAVROULIS ET AL. et al. 2002, Michetti et al. 2004, 2007, Castilla and Au- [Guerrieri et al. 2007, Porfido et al. 2007]. Furthermore, demard 2007, Serva et al. 2007, Silva et al. 2008, Re- the EEE are not influenced by human parameters such icherter et al. 2009, Gosar 2012] offered new substantial as effects on people and the manmade environment as evidence that coseismic environmental effects provide the traditional intensity scales (MCS, MM, EMS 1992, valuable information on the earthquake size and its in- etc.) predominantly imply [Michetti et al. 2007]. tensity field, complementing the traditional damage- The integration of the ESI 2007 intensity scale based macroseismic scales. Indeed, with the outstanding with the other scales including EMS-98, provides a bet- growth of paleoseismology and earthquake geology, ter picture of the earthquake scenario, because only nowadays the effects on the environment can be de- EEE allow suitable comparison of the earthquake in- scribed and quantified with a remarkable detail com- tensity both (a) in time: effects on the natural environ- pared with that available at the time of the earlier scales. ment are comparable for a time-window (recent, historic Therefore, today the definition of the intensity degrees and palaeoseismic events) much larger than the period can effectively take advantage of the diagnostic charac- of instrumental record (last century), and (b) in differ- teristics of the effects on natural environment. ent geographic areas: environmental effects do not de- Earthquake environmental effects (EEE) are any pend on peculiar socio-economic conditions or different effect produced by a seismic event on natural environ- building practices. ment [Michetti et al. 2007]. Several decades of research Despite these advantages, there are some limita- on earthquake geology and paleoseismology have tions in the use of the ESI 2007 scale. The ESI 2007 scale pointed out their crucial role in seismic hazard assess- may not accurately describe the damage in the far field ment, due to their relations with the earthquake size [Papanikolaou et al. 2009]. It is important to establish and the location of seismogenic sources [Dengler and that this scale should be used predominantly in the epi- McPherson 1993, Serva 1994, Wells and Coppersmith central area and thus may not accurately describe dam- 1994, Esposito et al. 1997]. The coseismic environ- age in the far field. mental effects considered diagnostic for intensity eval- Also, in deep nonlinear morphogenic events [Ca- uation can be categorized in two main types [Michetti puto 2005], where ruptures cannot reach the surface, et al. 2007]: (a) Primary effects, which are directly the ESI degrees should be correlated with the area, linked to the earthquake energy and in particular to where severe EEE have been recorded. However, in the surface expression of the seismogenic source, in- such cases uncertainties are expected to be higher, im- cluding surface faulting, surface uplift and subsidence plying that the assignment of the ESI 2007 intensities and any other surface evidence of coseismic tectonic should probably be considered less precise for deep deformation; (b) Secondary effects including phenom- events [Papanikolaou et al. 2009]. ena generally induced by the ground shaking. They are Intensive EEE have not been expressed or even conveniently classified into eight main categories that recorded in some earthquakes even though high grades are hydrological anomalies, anomalous waves includ- were assigned using other macroseismic scales, due to ing tsunamis, ground cracks, slope movements, trees the strictly localized area of damage and its limited ge- shaking, liquefactions, dust clouds and jumping stones ographical coverage. However, it is argued that this in- [Michetti et al. 2007]. consistency is probably due to the structural response The use of EEE for seismic intensity assessment of multistorey buildings, the bedrock geology and the has been recently promoted by the ESI 2007 scale, local site effects in accordance with the long distance which evaluates earthquake size and epicenter solely from the epicenter. from EEE. The application of ESI 2007 scale (i) allows This paper focuses on the June 8, 2008, An- the accurate assessment of intensity in sparsely popu- dravida earthquake (Mw=6.4) that affected the NW lated areas, (ii) provides a reliable estimation of earth- Peloponnese (western Greece) causing 2 fatalities and quake size with increasing accuracy towards the highest 214 injuries. The earthquake produced both extensive levels of the scale, where traditional scales saturate and damage and significant EEE in the Ilia and the Achaia ground effects are the only ones that permit a reliable prefectures. estimation of earthquake size, and (iii) allows compar- Five years after the event, we present some con- ison among future, recent and historical earthquakes siderable data about the macroseismic characteristics [Michetti et al. 2004]. In addition, some environmental of the earthquake and about the geology, tectonics and morphogenetic effects (either primary or secondary) seismicity of the epicentral area (NW Peloponnese). can be stored in the palaeoseismological record, allow- This paper offers: (a) a view of the geotectonic and the ing the expansion of the time window for seismic haz- seismotectonic regime of the region affected by the ard assessment up to tens of thousands of years earthquake based on previous works and new field ob- 2 ESI 2007 AND EMS-98 FOR A STRIKE-SLIP EVENT servations, (b) the description of the active faults and lacustrine and terrestrial deposits and lie unconformably fault zones that pose seismic hazard for the residential on the alpine basement [Christodoulou 1969, Tsoflias parts of the region, (c) the evaluation of the seismic in- 1977, 1980, 1984, Kamberis et al. 1979, Fleury et al. 1981, tensities based on the guidelines of the ESI 2007 scale Mariolakos et al. 1990, Lekkas et al.