Preliminary Observations on the August 14, 2003, Lefkada Island (Western Greece) Earthquake

EERI Special Earthquake Report — November 2003

Learning from Earthquakes Preliminary Observations on the August 14, 2003, Lefkada Island (Western Greece) Earthquake

Following the earthquake, EERI strongly felt in other Ionian Islands heavily affected by the strong members and their colleagues from (Kephalonia, Zakynthos, Ithaki, etc.) ground motion (settlements, hori- three institutions in Greece went into and in a large area on the mainland zontal displacements, lateral the field. Teams from the Institute of of Greece. The shock was also felt spreading, liquefaction, loss of Engineering Seismology and Earth- as far away as Athens (Δ=280 km). shear strength). The area affected quake Engineering (ITSAK), the The epicenter was located in the by the mainshock falls in Zone IV National Technical University of Ionian Sea, about 30 km east-north- of the Greek seismic code (EAK Athens (NTUA), and the University east of the town of Lefkada. Within 2000), with a design acceleration of of Athens (UoA) participated in this the next 12 hours, three major after- ag=0.36g, the highest for Greece. reconnaissance study. shocks were felt. Lefkada is third in size among the A few hours after the earthquake A peak ground acceleration of Ionian Islands at 302.5 km2. The and during the subsequent three ag= 0.42g was recorded at the ac- island is only 50 m from the main- weeks, teams of experts (seismolo- celerograph installed in Lefkada, land of Greece, and is connected gists and civil engineers of the re- close to the epicenter. Despite the by a pontoon bridge. According to search staff of ITSAK) visited the very strong ground motion recorded the 2001 national census, there are meizoseismal area. ITSAK teams in Lefkada, only one reinforced con- 22,506 permanent residents on the consisted of engineering seismolo- crete building collapse was reported. island. The capital is the homony- gists B. Margaris, C. Papaioannou, There were no deaths, and only a mous town of Lefkada. and N. Theodulidis; geophysicist A. small number of injuries. Moderate Savvaidis; geotechnical engineers damage was observed in villages Tourism is highly developed on the A. Anastasiadis, N. Klimis, and K. of the central and western part of island of Lefkada and it swarms with Makra; and structural engineers M. the island as well as in the town of thousands of visitors during the Demosthenous, C. Karakostas, V. Lefkada. summer months. The earthquake Lekidis, T. Makarios, T. Salonikios, happened during the culmination of and S. Sous. The primary and secondary road the tourist season. At the time of the network of the island was damaged main event, Lefkada had an esti- NTUA and UoA formed one team by landslides and rock falls. A num- mated combined population of about consisting of P. Carydis of the Labo- ber of ports were moderately to 80,000 residents and tourists. ratory for Earthquake Engineering of NTUA and E. Lekkas, S. Lozios, E. Skourtsos, and G. Danamos of the Laboratory for Tectonics and Geo- logical Mapping of UoA.

The publication of this report is supported by EERI’s Learning from Earthquakes Program under National Science Foundation grant # CMS-0131895.

Introduction On August 14, 2003 at 08:15 local time (05:15 GMT) a magnitude 6.4 earthquake struck close to the island of Lefkada in Western Greece (Fig- Figure 1. Location and tectonic setting of the August 14, 2003, Lefkada ures 1 and 2). The earthquake was earthquake.

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Repeated GPS measurements car- ried out between the northern Ionian Islands and Crete have shown rates of crustal motion of the Aegean reaching 35 mm per year, oriented SW relative to southern Italy (figure 1).

Lefkada is 70% mountainous, with the highest peak being Stavrota (1182 m) in the center of the island. The western side of the island is very steep, with rather narrow sandy Figure 2. beaches, and the sea deepens rap- Location map idly. On the eastern side there are and fault plane large flat areas and the sea is shal- solutions of low with many islets. Inland there the main shock are narrow plateaus, fertile valleys, and the largest and deep ravines with opulent veg- aftershocks of etation. the Lefkada earthquake. The main tectonic structure of the island is an emplacement of carbon- ate rocks of the Ionian Unit over of more than 3000m. From marine the Pre-Apulian Unit, along a major The Seismotectonic Setting geophysical data it has been sug- N-S thrust fault (figure 3). Many gested that this trough represents neotectonic active faults, striking The tectonic setting of the wider a transform fault that demarcates to the NNE-SSW or E-W direction, area is determined by the continen- the northwestern end of the Hel- tal collision between northwestern lenic Subduction Zone. This has Greece in the east and the Apoulian been reinforced by earthquake focal platform in the west, as well as by mechanisms, microseismic studies, the subduction of the African plate and geodetic measurements that under the Aegean microplate along have shown that the KFZ is a right- the active Hellenic Arc in the south- lateral transform fault (figure 1). west (figure 1). The Ionian Islands are situated in a transitional zone Microseismic studies and GPS between the northwestern end of measurements (Yannick et al. 1998; this active subsidence and the con- Louvari et al. 1999) have shown that tinental collision in the north. This the horizontal movement continues transitional zone is characterized by in the sea area west of Kephalonia a high crustal deformation as re- and Lefkada (figure 2). This north vealed by the high seismicity of this segment of the KFZ was named the zone, which is the highest in the Lefkada segment and is character- Aegean. ized by dextral strike-slip motion with a thrust component. It strikes The main tectonic structure of this in a north-northeast direction, dips transitional area is the Kephalonia to the east-southeast, and has a Fault Zone (KFZ), which represents length of ~ 40 km. This fault length the active boundary between the corresponds to an earthquake mag- SW-moving Aegean microplate and nitude ~ 6.8, which is equivalent to the Apulian platform (figure 2). It is the magnitude of the largest event an offshore fault system to the west that struck Lefkada during the last of the island of Kephalonia, an area four centuries. The typical focal Figure 3. Alpine and neotectonic with a deep bathymetric trough, mechanism for an earthquake has structure and natural hazard map of striking at N20E, with water depths strike =14º, dip= 65º, rake =167º. Lefkada Island (Lekkas et al. 2001).

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cross-cut the island. They represent mainly normal or strike-slip faults. All the alpine rocks are highly fractured and deformed, especially along the active faults and the major neotectonic and alpine structures. The poor quality rocks and the steep slopes result in landslides and rock falls, which cause frequent damage to roads and the respective infrastruc- tural works (Lekkas et al. 2001).

Seismological and Strong- Motion Data Seismological Data. The area of planes are NP1: 11/60/165 and damage (Papazachos and Papaza- the three islands (Lefkada, Kepha- NP2: 109/77/31. chou, 1997). lonia, and Zakynthos) from north to south (figure 4) has the highest Table 1 summarizes the results for The aftershock sequence was ac- shallow seismicity in all of Greece the source parameters of the main tive during the first 24 hours, but and in the whole western Eurasia shock determined by various institu- diminished quickly over the follow- area (Papazachos 1990; Papaza- tions. The fault plane solutions of ing days. Within 12 hours of the chos and Papazachos 1997). Papa- these agencies indicate that the re- main shock, there were three major zachos and Papaioannou (2000) cent Lefkada earthquake was gen- aftershocks: the first was Mw = 5.3 separated the seismic activity in the erated by a right-lateral strike slip (ETHZ), the second Mw = 5.4 and islands into three seismogenic fault trending NNE-SSW. This is in the third Mw = 4.7. Surprisingly, the sources, Lefkada’s being character- agreement with the typical mecha- fault plane solutions of these major ized by high seismic activity with nism proposed by Papazachos et aftershocks, as provided by ETHZ, maximum magnitude M=7.1 and al. (1998). Since 1612, 16 strong correspond to thrust faults, which dominated by a strike-slip fault. The (M>6.0) earthquakes have been re- differs from the strike-slip solution of typical fault plane solution for this lated to this fault; the previous two the main shock (figure 2). seismogenic source has been pro- strongest ones during the instru- posed by Papazachos et al. (1998): mental period were in 1914 (M=6.3) Recorded Accelerograms and Re- the parameters of the two nodal and 1948 (M=6.5) and caused great sponse Spectra. Near the capital city, low-resolution digital accelerographs (Kinemetrics QDR-11 bits) had been installed by ITSAK, seven Figure 4. Perma- of which recorded the main shock. nent and temporary The triggering threshold of the net- strong motion array work instruments is 2%g, and all of ITSAK deployed in stations in the broader area were the broader epicentral found in operation. The station area (black squares: VAS1 was filled by noise and did permanent network; not record the earthquake. On Au- gray squares: tempo- gust 15, six digital high-resolution rary array deployed accelerographs (Guralp CMG-DM24 after August 15, 2003. with CMG-5 accelerometers) were Lefkada mainshock deployed on the island both to cap- is denoted by star. ture site effects within the town of Earthquakes with M>6 Lefkada and to increase the number are denoted with gray of instruments monitoring after- circles. The upper left shock activity. On September 1, inset shows the spe- three more digital accelerographs cial array deployed were added to the temporary within the town of strong-motion array (see figure 3). Lefkada.

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Figure 5 shows the components of the accelerograms of the mainshock, with the highest peak ground acceleration recorded at the seven instruments of the permanent array of ITSAK (LEF1, PRE1, AMF1, AGR1, ARG1, ZAK1 and VAR2). Source-to-station epicentral dis- tances range from about 10km to 115km. The largest peak horizontal ground acceleration (PGA) recorded at the LEF1 station was 0.42g, hav- ing a period of about 0.5sec. The duration of strong ground motion was estimated at 18 seconds.

Table 2 compares data on a num- and values up to 114±18 cm/s/g quency content of the ground motion ber of earthquakes in Greece: Thes- indicate stiff soil conditions. The in relation to the built environment saloniki 20/6/1978; Corinthos 24/2/ recording station LEF1, where the and structural type. 1981; Kalamata 13/9/1986; Kozani strongest peak ground acceleration 13/9/1995; and Aigion 15/6/1995. A was observed, falls between the two In November of 1973, a magnitude characteristic parameter of seismic soil conditions. M=5.8 earthquake struck close to motion included is the ratio of peak the epicenter of the August 2003 ground velocity to peak ground ac- Response spectra for 5% damp- quake, with a recorded peak ground celeration. This ratio is a crude in- ing of the horizontal components acceleration of 0.49g (Theodulidis et dex of strong-motion frequency con- of Lefkada main shock are given in al. 2003). Despite the high values tent and local soil conditions. Ac- figure 6. The acceleration response of both earthquake recordings at cording to Seed et al. (1976), values spectra of the LEF1 station exhib- Lefkada, damage was less than of this ratio up to 66±7 cm/s/g are ited amplitudes Sa>0.9g for a period expected. indicative of rock soil conditions, range of 0.2 sec to 0.7 sec and reveal a peak of about 1.7g around 0.5 sec. For the LEF1 station, the Geotechnical Effects fundamental period was estimated Site effects in the town of Lefkada: around 0.5sec using strong-motion Damage surveys in the town did excitation (Dimitriou et al. 1999). not indicate locations of building This fact gives evidence of the influ- damage concentration that could be ence of local conditions on strong directly associated with the effect of ground motion. However, source local geology on earthquake ground effects (e.g., directivity) should not motion. This might be attributed to be completely excluded, since the quasi-uniformity of the underlying soil energy radiation pattern is not yet conditions or to building types. clear. Based on the average weighted val- Figure 7 shows a comparison ue of shear-wave velocity for the up- of the response spectra of the per 30m (V ) ranging between 230 Lefkada 2003 record (black lines) S30 and 250 m/sec, Eurocode 8 (2002) and the Bingöl, Turkey, 2003 places the subsoil of Lefkada in soil (www.deprem.gov.tr) record (gray category C (dense to medium density lines). Only the two horizontal com- sandy, gravelly, or stiff clay of a few ponents were considered. Even tens to hundreds of meters thick with though the two earthquakes were 180

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Figure 6. Elas- tic response spectra of the Lefkada mainshock (D=5%), recorded at the town of Lefkada, in comparison with the elastic design spectra of the old (AK) and recent (EAK-2000) Greek seismic codes, for different soil categories.

Figure 7. Comparison of the response spectra of the Lefkada August 14, 2003, and Bingöl, Turkey, Figure 8. Geological and geotech- May 1, 2003, nical effects of the Lefkada earth- records caused quake. by strike-slip faults and open recreational spaces, tourist obtained in the facilities, and light construction. The near field. main fissures occurred at alluvial and coastal formations, located along the eastern coastal zone near to the Greek Seismic Code (EAK alignment of the damage coincides Nydri village between Aspropotamos 2000 (figure 6). In case where layers almost with the fault strike, a factor and Lagadi torrent, along the north- of loose fine sandy silts susceptible that may also influence the damage ern and northeastern coastal zone to liquefaction or densification are pattern (figure 8). near the town of Lefkada and Lygia present, the sires are classified as village, and near Vassiliki village soil category X (soils in need of Ground fissures: The main shock along the southwestern coastal special study) created a large number of fissures zone at the river mouth of Karouhas that caused minor damage to roads, torrent). Near the water, ground settlement and lateral spread were observed to a limited extent were directly related to liquefaction phenomena. Their effect (described in detail later in this Figure 9. Many report) was more pronounced on retaining walls seawalls, pavement, and fills behind leaned towards these structures than on buildings. the external side; the adjacent parts Damage surveys in the areas of As- of the roads sub- progerakata, Spanohori, Lazarata, sided, and cracks Kavallos, Pinakohori, and Karya appeared on the villages reveal building damage pavement (NTUA- concentration that may be related UoA team). to specific surface and subsurface topographic features. The rough

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drainage tubes served as funnels for the upward movement of the quicksand. The ejection resulted mainly in Figure 10. fine material deposits of sand and Ground subsid- silt. In other cases, no surficial out- ence of the fill flow was noticed, but the liquefied material of about material caused loss of support of 30 cm (NTUA- the overlying formations, which in UoA team). turn were deformed.

In the town of Lefkada, damage included uplifted, sunken or cracked concrete slabs, and distorted pavement and sidewalks (figure 11). Shallow subsurface materials at these sites probably consisted of uncompacted, miscellaneous fill. The length of the fissures varied differential seismic response of the Local residents reported that muddy from a few tens of cm to tens of m, various unconsolidated phases of water was ejected from cracks in their width was from a few mm to 10 the formations (figures 9 and 10). pavement surfaces. Observed cm, and their visible depth reached Most of them are also connected to ground cracking with lateral spread- 30 cm. A systematic study of the liquefaction phenomena and repre- ing, as well as silty-sandy boils trends of the fissures showed that sent lateral spreads and extensional along the waterfront in the town of there were two prevailing sets, one failures. parallel to the coast and one normal Lefkada and in Nydri village, were the primary surface evidences of to it. In addition, the pattern was Soil liquefaction: Ground settle- liquefaction, indicating high excess similar at the cracks located in the ment and lateral spreading had seri- pore pressure generation during river deposits; however, the primary ous consequences for port and ma- earthquake shaking. set ran parallel to the riverbed and rine structures (docks, seawalls, and the secondary ran normal to it. The breakwaters) in the north, east, and Densification of loose surface soil fissures and cracks had no genetic south parts of the island, namely at layers and of poorly compacted fills relationship with the fault deforma- the town of Lefkada and at Lygia, behind seawall facilities caused tion, but they were a by-product of Nydri, and Vasiliki villages (figures settlements and lateral spreading the seismic movement. Their occur- 11 and 12). These phenomena were towards the free face. The horizontal rence is exclusively controlled by related to local ground conditions as and vertical displacements varied the differential compaction of the well as to the depth of the water ta- between sites, but they were in the loose formations, the lateral insta- ble. They consisted of recent forma- range of 10-25 cm. Figure 13 shows bility of the ground masses at the tions of coastal, alluvial, and fluvial ground settlement near the coast- coastal or riverside area, and the deposits, where the depth of the line. Lateral spreading was prevent- water table was very high, almost ed due to the seawall, but an up-lift 0.7 m below the ground surface. of the ground just behind the sea- The ejection of quicksand occurred wall tilted the lampposts. through craters and fissures. It was also reported that boreholes and In some buildings near the coastal

Figure 11. In the town of Lefkada, distorted pavement and sidewalks due to ground settlement and lateral Figure 12. Area near the castle of Lefkada where soil liquefaction, lateral spread (ITSAK team). spreading, and ground settlement occurred (ITSAK team).

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(mainly sands, gravel, and cobbles with silt and clay intercalations) because of seismic shaking, (2) small- scale submarine landslides with si- multaneous loss of lateral support, or (3) liquefaction.

Landslides and rockfalls: The earthquake triggered landslides and rockfalls. The very steep morphology of the region is the result of the active tectonics and the rock mass that is highly fractured and deformed, representing in most cases a tectonic breccia or fault gouge material. The slides were mainly observed at the central and northern part of the island, as well as in the steep western coastal zone along the road join- ing the town of Lefkada with Tsouka- lades, Agios Nikitas, Kathisma, Kala- Figure 13. Part of the seawall has been laterally shifted and overturned mitsi, Chortata, Dragano, Komilio. (ITSAK team). The vast majority of slides on the island road network can be catego- rized as rock falls, rock sliding (plane area, observed damage indicates a Nydri, at the river mouth of the As- and wedge), and soil type sliding differential settlement between adja- propotamos torrent. The coastline with scree deposits (rock fragments) cent buildings of 5-10 cm. However, retreat of 1 m to 20 m damaged accumulated as cone deposits at those buildings did not suffer any some minor human construction and slope toes, with volume ranging from severe damage due to their relative- tourist and beach sport facilities. several cm3 to some (5 to 10) m3. ly small mass, their “flexible” wood- The most striking change took place Landslides were detected on both en frame, and, in cases of RC struc- at the coast of Kambos, where the natural and cut slopes, as well as tures, their foundation type (mat sea progressed inland for about 20 on downstream road embankment foundation, tie or foundation m, covering an area more than 50 m slopes. The most important slope beams). Figure 14 shows a plan wide. The coastline changes were failures were seen in limestones view of two adjacent buildings with a due to (1) rearrangement of the (thick bedded and thin bedded inter- common pipeline system that had a packing in the Holocene formations polated by thin layers of marly differential settlement of about 5 cm.

Coastline changes: The shock was accompanied by a coastline change (figure 15) in the northern part of

Figure 14. Plan view of two adjacent buildings with a common pipeline system that had a differential settlement of about 5 cm (ITSAK team). (Photo taken after repairing.) Figure 15. Coastline changes at Nydri beach (NTUA-UoA team).

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Figure 16. Rockfalls due to de- Damage to lifeline systems: Soil tachment and possible overturn at liquefaction, ground settlements, lat- the Agios Nikitas (left); Cars were eral spreading, landslides, and rock- buried under landslides near the falls caused some damage to life- same beach (right) (ITSAK team). line systems on the island. Just after the earthquake, there was a four- hour interruption in power, and con- sequently also in the central pump station of the water supply system in the town of Lefkada. Damage to the wastewater system, which impeded the transfer of waste from the town center to the central waste-process- ing unit, was reported at one point due to local soil failure. No damage was reported to the conventional telecommunication network, but local schists) located on steep cut slopes swimming and sunbathing, but they residents reported that the cellular (horizontal:vertical 2:1 to 3:1) and did not cause any casualties, thanks telecommunication network had with heights ranging from 20 to to the early morning hour of the problems due to overloading. 50 m, without any trench or other main shock. Figure 16 shows rock- preventive countermeasures. There falls and scree deposits due to over- Structures were also a considerable number turn, detachment, and sliding at of failures of embankment slopes, Agios Nikitas Beach. Buildings on Lefkada Island can be especially when lack of com-paction classified in four broad categories was obvious. Tsunami: A very small tsunami, no as shown in the chart below, accord- more than 0.5 m, hit in Vlychos Bay ing to their load-bearing system. Some of the slope failures took south of Nydri (Figure 8) and caused place along beaches suitable for minor damage to boats and coast- Strong ground motion compared line construction. to seismic code provisions: The

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first Greek Seismic Code (AK) was mate strength design, leading to code provisions, thus possessing issued in 1959 and revised in 1984. values of ε’ = 0.14, 0.21 and 0.27 high resistance to seismic actions. A major new revision took place in (Anagnostopoulos et al. 1986). Moreover, the existing buildings 1992 (EAK 1992), and upgraded possess a substantial amount of re- versions were published in 2000 and For seismic zone IV (Lefkada’s), serve strength (depending mainly on 2003. Until 1992, design was based seismic codes from 1992 onwards their redundancy and on the over- on maximum allowable stresses, establish a ground acceleration co- strength of individual structural and thereafter on ultimate strength. efficient ofα =0.36 and typical design members) as well as possible addi- Significant progress has been made spectra (with a spectral magnifica- tional energy dissipation mecha-

in Greece, especially during the last tion factor βο=2.5). In figure 6, the nisms. Experience in this and previ- 20 years, in improving both codes response spectra of the Lefkada ous seismic events suggests that and practices. main shock are compared with the seismic protection of Greek urban elastic design spectra of the new areas relies also on several alterna- According to the 1959 Greek Seis- seismic code (EAK) provisions (for tive factors (such as infill walls, reg- mic Code, the base shear seismic soil types B-medium and C-soft). In ular configuration of the structural design coefficient for Lefkada was the same figure, the pre-1992 provi- system, proper material, and con- ε = 0.08, 0.12 and 0.16, for firm, sions (AK) are also plotted. struction quality) (Bertero 1988). medium, and soft soils, respective- ly. This coefficient was constant, in- It is obvious that low-rise buildings Damage in the meisoseismal dependent of the building’s period, with relatively small mass and fun- area: The main shock caused most and applied uniformly to all build- damental period (T<0.15÷0.20sec), damage on the island of Lefkada. ings. Since the 1959 Code was which comprise the majority of the Also minor damage was reported in based on the allowable-stress de- building stock in Lefkada, were not the nearby prefectures of Thesprotia sign method, the coefficient has heavily stressed, due to the particu- and Aitoloakarnania as well as in the been modified to correspond to ulti- lar shape of the response spectrum neighboring island of Kephalonia. of the main shock. The ductility de- The town of Lefkada had the most mands imposed on buildings in this damaged buildings and churches. specific range were not too high, Most damage was concentrated in thus explaining the limited damage the old town district, while minor observed. Taller buildings were in damage was reported to the more general built according to modern modern Neapoli and Bei districts.

Figures 17a, b, and c. The traditional earthquake-resistant system of Lefkada. The undamged structure in Fig. 17a was built at the end of the 19th century. In Fig. 17b the wooden columns and beams (w) with wooden corners (c) are visible. In Fig. 17c the special earthquake system is shown 17a▲ 17b▼ under construction (NTUA-UoA team).

17c▼

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Figures 20a and b. In a building with a market and mezzanine on the ground floor: insufficient stirrups with poor detailing (a). In the mezzanine: damaged columns on the surface between phases of concrete and the lower part of the arches, formed Figure 18. Partial collapse of ma- with brickwalls (b) sonry wall in a category B building (NTUA-UoA team). 20a 20b (ITSAK team). “Yellow”: Buildings in this category dual structural system (category B) Less severe damage was reported have decreased seismic capacity behaved in a rather satisfactory way, in villages throughout the rest of the and should be repaired. Usage is given the intensity of the main event island. not permitted on a continuous base. (ITSAK 2003). In this composite sys- “Red”: Buildings in this category are tem, a wooden frame has special For a proper explanation of the dis- unsafe and entry is prohibited. Deci- carved corners (figure 17) that tribution and intensity of damage in sion for demolition will be made on strengthen beam-to-column joints, relation to the recorded acceleration the basis of more thorough inspec- and wooden stiffening walls with x- at the town of Lefkada, an extensive tion. braces. In the plane of these stiffen- vulnerability study is needed, com- ing walls, various masonry materials plemented with a soil response Damage according to structural may be added in order to increase study. A preliminary estimation of the system: Traditional stone masonry the stiffeners and the energy ab- intensity for the main event in the buildings (category A), usually with sorbing capacity of the whole sys- old town of Lefkada is between VII one or two stories, constitute a small tem. On the ground floor, the wood- and VIII on the modified Mercalli percentage of the building stock on en frame comes in contact with the scale. The inspection of 3165 build- Lefkada Island. Observed damage external masonry wall, with which it ings on the island resulted in 1544 to such buildings (partial collapse of is well connected. The carved cor- “green,” 1495 “yellow,” and 126 “red” stone walls) can be attributed main- ners are also put in the lower part of tags. The classification of damage is ly to lack of sufficient seismic resis- the columns that are fixed to the briefly described as follows (Lekidis tance, as well as to their poor condi- foundation. In some cases, there et al. 1999): tion (old age, inadequate mainte- was partial collapse of masonry nance). A significant percentage of walls (figure 18), but the structural “Green”: Original seismic capacity such buildings is found in villages stability of the building was ensured has not been decreased, the build- outside the town of Lefkada. by the activation of the secondary ings are immediately usable and en- (redundant) wood frame on the try is unlimited. Traditional buildings with the special ground floor level.

In the upper floors, the load-bearing Figure 19. Collapse wood frames suffered no damage, of R/C building in the but cracking to the brick infills was town of Lefkada. On observed. These cracks were diffi- the right side, there cult to notice at first, since the exter- are no brickwalls nal walls at the upper stories are on the ground floor, typically clad with zinc sheets (for where the build- rain protection). Damage could be ing collapsed. The observed only on the interior face of remaining part on the the walls, which are usually plas- left side has partitions tered with lime. Due to the use of down to the founda- extended wood footings or piles tion (NTUA-UoA described above, and the small team). weight of these buildings, no foun-

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frames, out-of-plane collapses). Figures 21a and b. A • A uniform foundation settlement four-story building with a was observed in several build- mezzanine was heavily ings at the seafront in the town damaged in the ground of Lefkada. Since no differential floor columns. The col- settlements were involved, no umns seem to have swol- imminent danger to the structur- len in the center due to al safety of the buildings was unsufficient transverse present. reinforcement (NTUA-UoA • A systematic oxidation of steel team). reinforcement was observed at the base of ground floor columns, due to the high under- ground water level. In some cases, the oxidation was very dation settling was observed, de- ground level. severe, a serious vulnerability spite the poor soil conditions in the • Damage to vertical structural factor for structural safety. old district of the town of Lefkada, elements at ground floor levels where the majority of such building due to non-symmetrical distribu- Middle-age and later era monu- types are found. The severe or total tion of infill walls. ments (category D) also suffered damage to a limited number of build- • Flexure-shear failure of poorly serious damage. It was reported that ings of this type can be attributed to designed columns. more than 40 churches all over the old age and poor maintenance. • Failure of short columns that island (with the majority in the town Common to all types of buildings were originally not designed to of Lefkada) have been put out of was the detachment of tiles from act as such (e.g., noncontinuous service until restoration measures roofs. infill walls on either side due to are taken. The churches are typically openings). built with stone masonry walls and A total collapse occurred in a three- • Failures at beam-column joints have a rectangular floor plan and a story R/C building (category C) with due to unpredicted local action wooden roof. Serious damage was short columns on the ground floor at of the infill walls. observed at the perimeter walls (fig- the front and thick brick infill walls at • Shear failure of R/C shear walls ure 22) as well as at the corners of the back. The building was poorly due to inadequate web rein- adjoining walls (figure 26). No col- designed with inadequate stirrups at forcement. lapses of bell towers were reported, the columns (figure 19). • Flexural cracking at R/C beam ends. It should be noted, how- Other serious damage to R/C build- ever, that this type of failure has ings was due to the following condi- a beneficial contribution to the tions, some of which are shown in overall building stability since figures 20 and 21: the formation of plastic hinges at columns is avoided. • Severe damage to poorly • Cracking of infill walls (diagonal designed columns and walls shear cracks, detachment of in buildings with soft stories at the wall from the surrounding

Figure 22. Churches built of stone masonry suffered heavy damage. In various parts of Lefkada, the tiles at the center of roofs moved. This might be explained by the vertical flexibility of the roof at its center (NTUA-UoA team). Figure 23. Cracking of masonry walls of Agios Minas church (town of Lefkada) (ITSAK team).

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respond to earthquakes and natural but most towers were recently built hazards. Because Lefkada Island Lekkas, E., Danamos, G., and Lozios, (with R/C or steel elements), indicat- has experienced several destructive S., 2001. Neotectonic structure and ing collapse of the original ones dur- earthquakes in the past, much has neotectonic evolution of Lefkada Island. ing past earthquakes. The castle of Bull. Geol. Soc. Greece, XXXIV/1, 157- been learned. Agia Mavra, at the entrance of the 163. town of Lefkada from the mainland, Acknowledgments Louvari, E., Kiratzi, A., and Papazachos, suffered no damage to its exterior B., 1999. The Cephalonia Transform walls. At its interior, partial collapse Fault and its extension to westwern Lef- The contribution of the technical of some building ruins as well as kada Island (Greece). Tectonophysics, some permanent displacements of staff of ITSAK to the network readi- 308, 223-236. stone parapets and decorative ele- ness and the field work should be Margaris, B., Papaioannou, C., Savaidis, ments were observed. acknowledged. Special thanks are also due to the people of the local A., Anastasiadis, A., Klimis, N., Makra, authorities and the Prefecture of K., Dimosthenous, M., Karakostas, Emergency Management C., Lekkidis, B., Makarios, T., Sous, I., Ionian Islands for their support. 2003. The Lefkada earthquake (M-6.4), The emergency response was rapid 14 August 2003. Preliminary report of and well-managed, although the References the consequences of the earthquake event did not cause heavy damage in the built and nonbuilt environment, to structures and, therefore, few Anagnostopoulos, S., Rinaldis, D., Leki- ITSAK, Thessaloniki, August 2003. casualties (only 50 injuries). The de- dis, V., Margaris, V., and Theodoulidis, mand for search and rescue re- N., 1987. The Kalamata, Greece, earth- Papaioannou, C., Papazachos, A. and sources was minimal, and the medi- quake of September 13, 1986, Earth- B.C., 2000. Time independent and time cal system was able to treat the quake Spectra, 3, 365-402. dependent seismic hazard in Greece based on seismogenic sources, Bull. injured within hours of the strong Bertero, V., 1988. State-of-the-art report: Seism. Soc. Am., 90, 22-33. shaking. Because of the extensive Ductility based structural design. Proc. landslides and rockfalls, human of 9th World Conference on Earthquake Papazachos, B.C., 1990. Seismicity of losses would have been heavier had Engineering, Aug. 1988, Tokyo-Kyoto, the Aegean and surrounding area, Tec- the earthquake struck two to three Japan, VIII, 673-686. tonophysics, 178, 287-308. hours later when the roads and the Dimitriou, P., Kalogeras, I., and Theodu- Papazachos, B.C. and Papazachou, C. beaches were filled. lidis, N., 1999. Evidence of nonlinear B., 1997. The earthquakes of Greece. site response in horizontal-to-vertical Ziti Publications Thessaloniki-Greece, Emergency response to the disaster spectral ratio from near-field earth- 304pp. was underway immediately after the quakes. Soil Dyn. & Earthq. Engin., 18, Papazachos, B.C., Papadimitriou, E. E., earthquake, supported by all levels 423-435. Kiratzi, A. A., Papazachos, C. B., and of local and governmental authori- Eurocode 8, 2002. Design of structures Louvari, E. K., 1998. Fault plane solu- ties, with the collaboration of the pri- for earthquake resistance. Part 1: Gen- tions in the Aegean Sea and the sur- vate sector and the affected popula- eral rules, seismic actions and rules rounding area and their tectonic impli- tion. Sixty-four civil engineers from for buildings (Draft No 4) CEN/TC250/ cation, Boll. Geofis. Teor. Appl., 39, the Greek Ministry for the Environ- SC8/N317, European Committee for 199-218. ment, Physical Planning, and Public Standarization, Brussels, BELGIUM. 345pp. Seed, B., Ugas, C., and Lysmer, J., Works formed 32 inspection teams 1976. Site-dependent spectra for earth- to proceed with visual assessments EAK 2000. Greek Seismic Code. Earth- quake-resistant design, Bull. Seism. of buildings, providing the basis for quake Planning & Protection Organiza- Soc. Am., 66, 221-243. determining which structures re- tion, Athens-Greece, 72 pp and 7 ap- quired more thorough examination. pendixes (in Greek). Theodulidis, N., Kalogeras, I., Papaza- chos, C., Karastathis, V., Margaris, B., The inspection was performed in ITSAK, 2003. A preliminary report on Papaioannou, C., and Skarlatoudis, A., two stages — a rapid one and a earthquake consequences of the 2003. HEAD v1.0: A unified HEllenic more detailed one — and was com- August 14, event M=6.4, Thessaloniki- Accellerogram Database. Seism. Res. pleted about 20 days after the main GREECE, 61pp (in Greek). Letters, (in press). shock for all buildings of the island. Lekidis, V., Karakostas, C., Dimitriu, P., Yannick, P., Kahle, H., Cocard, M., Veis, Margaris, V., Kalogeras, I., and Theodu- G., Felekis, S., and Paradisis, D., 1998. The readiness and competence of lidis, N., 1999. The Aigio seismic se- Establishment of a continuous GPS net- responders can be attributed to a quence of June 1995: seismological, work across the Kephalonia Fault Zone, number of factors. One of these is strong-motion data and effects of the Ionian Islands, Greece. Tectonophysics, the Greek Civil Protection system, earthquakes on structures, J. Earthq. 294, 253-260. which has specialized teams to Engin 3, 349-380.