Preliminary report on the Mw:6.1 Cephalonia earthquake of 26th Jan 2014 (in English)

MINISTRY OF INFRASTRUCTURE, TRANSPORTATION AND NETWORKS EARTHQUAKE PLANNING AND PROTECTION ORGANIZATION

INSTITUTE OF ENGINEERING SEISMOLOGY & EARTHQUAKE ENGINEERING (ITSAK)

THE EARTHQUAKE OF 26/1/2014 (M6.1) IN CEPHALONIA (GREECE): STRONG GROUND MOTION, SOIL BEHAVIOUR AND RESPONSE OF

STRUCTURES (PRELIMINARY REPORT)

THESSALONIKI FEBRUARY 2014



THE EARTHQUAKE OF 26/1/2014 (M6.1) IN CEPHALONIA (GREECE): STRONG GROUND MOTION, SOIL BEHAVIOUR AND RESPONSE OF

STRUCTURES (PRELIMINARY REPORT)

This Report is redacted by the researchers of EPPO-ITSAK(in alphabetic order): Karakostas Ch., Civil Engineer, Researcher A Lekidis V., Civil Engineer, Researcher A Makra K., Dr. Civil Engineer, Researcher B Margaris B., Dr. Seismologist, Research A Morfidis K., Civil Engineer, Researcher C Papaioannou Ch., Dr. Seismologist, Research A Rovithis M., Dr. Civil Engineer, Researcher D Salonikios T., Civil Engineer, Researcher B Savvaidis A., Dr. Geophysicist, Researcher B Theodoulidis N., Dr. Seismologist, Researcher A Acknowledgements K. Konstantinidou, MSc IT and the staff of the Laboratory, S. Zacharopoulos Civil Engineer, A. Marinos, N. Adam technicians, contribute to effective operation of the EPPO-ITSAK strong motion network and assure its data transfer to the central computer facilities in Thessaloniki.

Digital data of the mainshock are open to the public at: http://www.itsak.gr/news/news/65 .



1. STRONG GROUND MOTION 1.1. Introduction In January 26, 2014, 13:55 GMT (15:55 local time) a strong earthquake with magnitude M6.1 (HVR) occurred at the southwestern coasts of the Cephalonia island, about 9km southwest of the Lixouri town. According to the Seismological Center of the Aristotle University of Thessaloniki, it was a shallow crustal event with epicenter 38.161N, 20.340E and depth 10km. (http://geophysics.geo.auth.gr/ss/station_index_en.html). At 18:45GMT (20:45 local time) a strong aftershock with magnitude M5.5 (HVR) followed the mainshock. From the focal mechanisms of both eartquakes it is deduced that they are related to the Cephalonia Transform Fault (CTF) (Scordilis et al. 1985). This is a dextral strike-slipe fault with a thrust component (Papazachos and Papazachou 1997, 2003).

Figure 1.1 Epicenter of the 26/1/2014 mainshock (M6.1, red star), aftershock (M5.5, pink star) and aftershock distribution (M≥4.0) during the first two days of the seismic sequence in Cephalonia (source: Geophysical Laboratory, Aristotle Univ. Thessaloniki). Accelerographs of EPPO-ITSAK in yellow squares and seismographs in pink triangles. Focal mechanisms are also shown.


INSTITUTE OF ENGINEERING SEISMOLOGY & EARTHQUAKE ENGINEERING (ITSAK) The seismic sequence of Cephalonia is related to the strike slip fault (Cephalonia Transform Fault: CTF) (Scordilis et al., 1985). In Fig. 1.1 the epicenter of the mainshock (13:55GMT) is shown by red star while for the aftershock (18:45 GMT) by pink star. Focal mechanisms determined by the Columbia University (www.globalcmt.org) are also given. From the aftershock distribution during the first two days following the mainshock a fault length around 18km appears that corresponds to a moment magnitude M6.1. The aftershock distribution of about 48 hours after the mainshock is shown in Fig. 1.1. Due to the moderate magnitude of the earthquake, the ground shaking was felt on the Cephalonia, on the islands of Ithaki, Lefkas and Zakynthos, as well as on areas of western Greece and Peloponnesos. According to the EMSC the ground motion was also felt in large part of continental Greece and in south Italy and Albania (Fig. 1.2).

Figure 1.2. Map of observed macroseismic intensities of the 26/1/2014 mainshock in Cephalonia (EMSC, 2014). On 27th of January scientific and technical staff of EPPO-ITSAK arrived on the Cephalonia island in order to install additional accelerographs and seismographs on the island and record effects of strong ground shaking on natural and built environment.


INSTITUTE OF ENGINEERING SEISMOLOGY & EARTHQUAKE ENGINEERING (ITSAK) During the last three years the EPPO-ITSAK has installed throughout Greek a dense network of continuous recording accelerographs. Their accelerometers are broadband, of high resolution (24bits), with absolute GPS time. Recordings of this network are transferred in real time at the central computing unit of the EPPO-ITSAK in Thessaloniki. Consequently, strong ground motion parameters of the mainshock recorded at the Cephalonia and Ithaki islands (peak ground acceleration, velocity, displacement and spectral values) were provided in short time in the form of a preliminary report on the web site of EPPO-ITSAK (www.itsak.gr). In addition, in less than 10 minutes (almost real time) after the earthquake origin time, the preliminary shakemaps were generated and were available to the public (http://portal.ingeoclouds.eu/sitools/client-user/Shakemaps/project-index.html) . 1.2. Network of strong ground motion The permanent strong motion stations on the Cephalonia & Ithaki Regional Unity (digital instruments CMG-5TD-EAM) were installed in the town of Argostoli (ARG2: building of Regional Authority) and in the village of Vasilikades (VSK1: building for Sitizens’ Service Center) and in the village of Vathi (ITC1: building of Municipality Technical Department). A temporary network of three accelerographs was deployed in 27 and 28 of January, 2014, mainly within the area strongly affected by the mainshock around the town of Lixouri. More specifically, three accelerographs were installed; (i) in the townhall of Lixouri (LXR1), (ii) in the old school of the village Chavriata(CHV1) and (iii) in a private house of the Ag. Thekli village (AGT1). In addition, two seismographs one in the Fiskardo village (FSK1) and another south to Argostoli (VVA1) were also installed (Fig. 1.3). All these instruments are of continuous mode and from their data analyses significant information for the seismic source properties of the mainshock and its aftershock, ground motion prediction in the near field and influence of site conditions on ground motion will result. Data from the stations ARG2, VSK1, CHV1, LXR1 and AGT1 are transferred in real time to the seismological station of Thessaloniki to improve the hypocenter and magnitude accuracy of the aftershock activity for the national seismographic network. 1.3. Mainshock Strong Motion Recordings in Cephalonia Ground motion of the mainshock was recorded by the permanent accelerograph network on the islands of Cephalonia and Ithaki as well as throughout Greece. In near real time, in about 10 minutes after the origin time, preliminary shakemaps were produced and uploaded on the web (Fig. 1.4). These maps include distribution of instrumental intensity, peak ground acceleration, velocity and spectral acceleration values for natural periods T=0.3, 1.0, 3.0 sec.



Figure 1.3. Permanent (ARG2, VSK1, ITC1) and temporary (CHV1, LXR1, AGT1) accelerograph stations and temporary stations of seismographs (VVA, FSK1), installed by EPPO-ITSAK on the Cephalonia and Ithaki islands.

Figure 1.4. Shakemaps for the 26/1/2014(M6.1) earthquake in Cephalonia.


INSTITUTE OF ENGINEERING SEISMOLOGY & EARTHQUAKE ENGINEERING (ITSAK) High values of spectral acceleration (>1000cm/s/s) at the station ARG2 are observed in the range of low natural periods, T<0.3sec (Fig. 1.5). However, relatively high spectral accelerations (>500 cm/s/s) for periods up to 0.7sec are apparent in the N-S component. At the site of Vasilikades (VSK1), spectral values are up to four times lower than those of ARG2 but the spectral shape is different relatively enriched for periods T>0.5sec (Fig. 1.6). Strong ground motion bracketed duration, for ground acceleration >0.1g, was about 9sec in both horizontal components and 6sec in vertical component. In Figs. 1.7 and 1.8 acceleration, velocity and displacement time histories and their corresponding pseudo-velocity and acceleration response spectra (D=0.05) are also provided for the aftershock of 26/1/2014, 18:44GMT (M5.5). Peak ground acceleration at the station of Argostoli was 116cm/s/s while in Vasilikades 25/cm/s/s. For the accelerograms processing the software ViewWare was used (Kashima, 2005). In Table 1.1, recorded peak ground acceleration, velocity and displacement for the events of 26/1/2014 are given, along with corresponding epicentral distance from the recording stations of EPPO-ITSAK. Peak ground values were observed in horizontal components. For the same event, in the town of Lixouri, the accelerograph of the Geodynamic Institute of NOA, recorded a peak ground acceleration of 0.53g (Kalogeras I., personal communication).

Table 1.1. Ground motion parameters for the 26/1/2014 mainshock observed at Argostoli (ARG2) and Vasilikades (VSK1).

STATION Epicentral Distance

(km)

Peak Ground Acceleration

(cm/s/s)

Peak Ground Velocity (cm/s)

Peak Ground Displacement

(cm)

Argostoli (ARG2) 13 383.4 20.5 3.7

Vasilikades(VSK1) 34 95.0 8.4 2.1



Figure 1.5. Acceleration, velocity and displacement time histories recorded at Argostoli (ARG2) station and their corresponding pseudo –velocity and acceleration response spectra for the mainshockof 26/1/2014, 13:55GMT (M6.1) and damping D=0.05.



Figure 1.6. Acceleration, velocity and displacement time histories recorded at Vasilikades (VSK1) station and their corresponding pseudovelocity and acceleration response spectra for the mainshock of 26/1/2014, 13:55GMT (M6.1) and damping D=0.05.



Figure 1.7. Acceleration, velocity and displacement time histories recorded at Argostoli (ARG2) station and their corresponding pseudo–velocity and acceleration response spectra for the aftershock of 26/1/2014, 18:44GMT (M5.5) and damping D=0.05.



Figure 1.8. Acceleration, velocity and displacement time histories recorded at Vasilikades (VSK1) station and their corresponding pseudo–velocity and acceleration response spectra for the aftershock of 26/1/2014, 18:44GMT(M5.5) and damping D=0.05.


INSTITUTE OF ENGINEERING SEISMOLOGY & EARTHQUAKE ENGINEERING (ITSAK) According to information compiled by Papazachos and Papazachou (1997, 2003) since mid of 15th century AD the causative fault where the mainshock of 26/1/2014 occurred, produced events whose maximum magnitude reached M7.2. The most recent large event on the causative fault occurred in January 17, 1983 with magnitude M7.0. Despite its large magnitude this event caused a macroseismic intensity IMM=VI (Bulletin of Geodynamic Inst., NOA) while a peak ground acceleration of 0.17g was recorded at an epicentral distance of 35km in Argostoli (Theodoulidis et al., 2004). In Fig. 1.9, comparison of acceleration response spectra recorded at Argostoli of the 26/1/2014 (M6.1) earthquake with that of 17/1/1983 (M7.0), is presented. For periods less than 1.2sec, ground motion of the recent event is much stronger (two to three times) than that of 1983, which is probably due to shorter hypocenter-to-station distance.

Figure 1.9. Comparison of horizontal components acceleration response spectra of the 17/1/1983 (M7.0) and 26/1/1983 (M6.1), Cephalonia earthquakes.



2. GEOTECHNICAL ISSUES AND SEISMIC RESPONSE OF LIFELINES 2.1. GEOLOGICAL, GEOTECHNICAL AND GEOPHYSICAL CHARACTERISTICS OF THE BROADER ARGOSTOLI AREA 2.1.1 ARG2 strong motion site The broader area of Argostoli town is characterized geologically by pliocenic sediments. From a geotectonic point of view, the above sediments are part of the Paxos zone and are composed of sandstones, conglomerates, limestones, marly limestones and marls. Above those Pliocenic sediments, marine silty clay soils form the offshore zone along the present coastline of Argostoli town. The above soil formations which are rich in fosils and organics are characterized by low stiffness and high plasticity index whereas their thickness is at 30m approximately. The geological map of the broader area of Argostoli is given in Figure 2.1. An accelerometric station (marked as CH in Figure 2.2) had been installed in the telecommunications (OTE) building in the town of Argostoli. Since 2012, a new 24bit accelerometric station (code name: ARG2) is installed in a two-story building that houses the Prefecture of Ionian Islands (Figure 2.1) located in a close distance (approximately 200m) from the old CH station. ARG2 station is currently operated by ITSAK as part of the Greek National Accelerometric Network.

Figure 2.1. Geological map of the broader Argostoli area (Part of IGME map, scale 1:50.000) indicating the location of ARG2 accelerometric station.



Figure 2.2. ARG2 station installed at the Perfecture building of Argostoli as part of the Greek National Accelerometric Network operated by ITSAK and former CH station location where geotechnical survey was performed. The geotechnical and geophysical characteristics of the subsoil close to CH station were derived by means of in-situ tests (NSPT, Cross-Hole) performed in 1996 within a collaborative research project (AUTH, ITSAK and EEPO 1996). Figure 2.3 summarizes the obtained results in terms of soil classification, NSPT blows count, P and S waves propagation velocity. The latter leads to a mean Vs30 shear wave propagation velocity at 420m/sec corresponding to soil class Β (stiff preconsolidated clay of thickness larger than 70m) according to Greek Seismic Code ΕΑΚ2003 and EC8 (Table 2.1). Given the close distance and the comparable geological setting between ARG2 and CH stations the above geotechnical profile may be considered representative also for the subsoil conditions characterizing ARG2 station.

Figure 2.3. Subsoil characteristics at CH station: Soil statigraphy and classification and variation of NSPT blows count, Vs and Vp velocities with depth (AUTH – ITSAK – EPPO 1996)


INSTITUTE OF ENGINEERING SEISMOLOGY & EARTHQUAKE ENGINEERING (ITSAK) Response spectra corresponding to NS and EW component of the M6.1 Cephalonia earthquake (26th Jan. 2014, 13:55 GMT) as recorded from ARG2 accelerometric station are compared in Figure 2.4 with the design elastic spectrum corresponding to soil type B according to EAK2003 and EC8, respectively. It is observed that the recorded spectral accelerations are higher than the code-defined values of EAK2003 between 0.1 and 0.3sec. On the other hand, EC8 design spectrum predicts higher spectral values closer to the recorded ones due to a soil amplification coefficient that is adopted by EC8 contrary to EAK2003. For the particular soil type (i.e. B) the above coefficient is equal to 1.20 which multiplies the peak ground acceleration (i.e. 0.36g for zone III) in rock conditions. Similar comparisons for the vertical component of seismic motion are plotted in Figure 2.5. In this case, ΕΑΚ2003 design spectrum predicts lower spectral amplitudes in the high frequency range and significantly higher values in the low frequency range with respect to the recorded response. On the contrary, EC8 design spectrum envelops the recorded motion in terms of both amplitude and frequency content.

Table 2.1. Eurocode EC8 – Description of soil class Β

Soil type

Description of stratigraphic profile

Parameters Vs,30 (m/s)

NSPT (blows/30cm) cu (KPa)

B

Deposits of very dense sand, gravel, or very stiff clay, at least several tens of meters in thickness, characterized by a gradual increase of mechanical properties with depth

360-800 >50 >250



Figure 2.4. Comparison of EAK2003 and EC8 elastic design spectra with response spectra of M6.1 earthquake (26/01/2014, 13:55 GMT) recorded from ARG2 accelerometric station: N-S and E-W components.

Figure 2.5. Comparison of EAK2003 and EC8 elastic design spectra with response spectra of M6.1 earthquake (26/01/2014, 13:55 GMT) recorded from ARG2 accelerometric station: Vetical (U-D) component.

MINISTRY OF INFRASTRUCTURE, TRANSPORATION AND NETWORKS EARTHQUAKE PLANNING AND PROTECTION ORGANIZATION


2.1.2. The bridge DeBosset Within the multidisciplinary project “Restoration and strengthening of the DeBosset bridge in Argostoli Cephalonia’ (Pitilakis and associates 2006, Rovithis and Pitilakis 2011), a set of geotechnical field tests were performed in properly selected locations along the bridge axis (Figure 2.6). The above field survey included sampling boreholes, SPT tests, Cross-Hole tests and microtremor array measurements complemented by laboratory tests on soil specimens to provide a detailed knowledge on natural, mechanical and dynamic properties of the foundation soil at the bridge site. Synthesis of the above geotechnical data allowed a detailed 2D cross-section of the bridge foundation soil in terms of soil stratigraphy and shear wave propagation velocity variation with depth (Figure 2.7). Of particular interest is the presence of a soft surface silty-clay layer (Vs=140-170m/sec) whereas at the depth of approximately 35m the stiff sandstone layer (Vs=1000m/sec) may be considered as the seismic bedrock. Based on the soil profile shown in Figure 2.7, the mean Vs30 shear wave propagation velocity is equal to 340m/sec. Thus, the particular subsoil conditions close to the shoreline of Argostoli town are classified as soil type D (soft clays of high plasticity index IP > 50 and thickness higher than 10m) and soil type C according to EAK2003 and EC8, respectively (Table 2.2).

Figure 2.6. Geotechnical and geophysical field tests in DeBosset bridge (Pitilakis and associates, 2006; Rovithis & Pitilakis, 2011)



Figure 2.7. 2D cross-section of the soil profile at the bridge site (Pitilakis and associates, 2006; Rovithis & Pitilakis, 2011) Table 2.2. Eurocode EC8 – Description of soil type C

Soil type




C

Deep deposits of dense or medium-dense sand, gravel or stiff clay with thickness from several tens to many hundreds of meters.

180-360 15 - 50 70-250

2.2. GEOLOGY OF THE BROADER VASILIKIADES AREA 2.2.1. VSK1 accelerometric station site Vasilikiades village (where VSK1 accelerometric station is installed) is located at the northern part of the Cephalonia Island. The geological setting consists of thin-bedded pelagic limestones of the upper Cretaceous era. From a geotectonic point of view, the above geological formations are part of the the Paxos zone. The geologic map of the area is given in Figure 2.8. The exact location of VSK1 accelerometric station is also shown. In the absence of other geotechnical – geophysical information, the VKS1 site may be classified as soil type A according to Greek Seismic Code EAK2003 (rocky or semi-rocky formations sufficiently extended in space and depth and conditioned by the fact that they do not present intense weathering) and Eurocode 8 (Table 2.3)


INSTITUTE OF ENGINEERING SEISMOLOGY & EARTHQUAKE ENGINEERING (ITSAK) The response spectrum of the horizontal ground motion (EW and NS components) recorded by VSK1 accelerometric station during the earthquake on January 26, 2014 (13:55 GMT) is significantly lower than the elastic design spectrum defined by EAK2003 or Eurocode 8 for soil type A (Figures 2.9 and 2.10).

Figure 2.8. Geological map of northern part of Cephalonia Island (Part of IGME map, scale 1:50.000) indicating the location of VSK1 accelerometric station. Table 2.3. Eurocode 8 – Description of Soil type A

Soil type




A

Rock or other rock-like geological formation, including at most 5m of weaker material at the surface

> 800 - -



Figure 2.9. Comparison of EAK2003 and EC8 elastic design spectra with response spectra of M6.1 earthquake (26/01/2014, 13:55 GMT) recorded from VSK1 accelerometric station: N-S and E-W components.

Figure 2.10. Comparison of EAK2003 and EC8 elastic design spectra with response spectra of M6.1 earthquake (26/01/2014, 13:55 GMT) recorded from VKS1 accelerometric station: U-D component. 2.3 Geotechnical failures On 28th of January 2014 a group of researchers from ITSAK visited the affected area of Cephalonia Island to investigate earthquake-induced geotechnical failures.


INSTITUTE OF ENGINEERING SEISMOLOGY & EARTHQUAKE ENGINEERING (ITSAK) As a general comment, it may be stated that main M6.1 earthquake event of 26/01/2014 imposed extensive geotechnical failures. These were observed mainly in the Western part of the Island (peninsula of Paliki) and may be grouped in the following categories:

• Slope failures due to local landslides occurred in soil or rock formations. • Failures on stone retaining walls and soil settlement • Extensive cracks on the road network • Failures of quay walls and port marines

Figure 2.11 depicts the geographical distribution of the geotechnical failures recorded mainly along the perimeter of Argostoli bay. It is worth mentioning that most of the geotechnical failures were gathered along a North-South axis almost parallel to the fault rupture as defined by the distribution of the aftershocks epicenters (Figure 1.1).

Figure 2.11. Geographical distribution of geotechnical failures imprinted by ITSAK researchers during their in situ visit on January 28, 2014. 2.3.1 Landslides and rock sliding effects A large number of local landslides were observed in several locations along the road network of Paliki peninsula in the Western part of Cephalonia island. Most of the landslide phenomena occurred in cracked limestone formations (Photo 2.1). Large limestone segments of volume larger than 2m3 (Photo 2.2) were detached and collapsed due to the large natural slope in


INSTITUTE OF ENGINEERING SEISMOLOGY & EARTHQUAKE ENGINEERING (ITSAK) conjunction to the almost vertical tensile cracks (Photo 2.1). Local slope failures were also observed in rock type formations (consolidated red conglomerates and breccia) covering partially the road (Photo 2.3). In this case, it is assumed that the landslide mechanism was mobilized due to the combined action of vertical and horizontal seismic motion. 2.3.2 Failures on stone retaining walls and soil settlement Repeatable seismic induced failures on stone retaining walls were recorded. Of particular interest is the case of a stone wall along the road to Atheras village, that was damaged in two successive locations having an estimated failure length at 10m and 20m respectively (Photo 2.4). A direct effect of the above failure was the subsequent land sliding of the retained soil causing the closure of the road network. A similar type of failure was recorded at a stone retaining wall of a physical slope upon which a single-storey house was founded (Photo 2.5). It should be mentioned that heavy rainfall contributed to the evolution of landslide phenomena that were observed on site at the particular time period. Particularly extensive cracks were observed at the stone retaining wall supporting the foundation soil of a church located in the Chavriata village (Photo 2.6). Although, the above retaining wall didn’t collapse it is estimated that the evident disruption of the stone parts should have minimized the lateral strength of the wall leading to a particularly low safety factor against future seismic loading. The above failures may be attributed to significant lateral earth pressures imposed on the old stone walls during seismic shaking. Of course, possible structural deficiencies and poor condition of joint mortars should also have contributed to the observed damage. Foundation soil settlement in the range of 3 to 5cm was observed at a 2-storey building located in Ag. Dimitrios village (Photo 2.7).

Photo 2.1. Landsides of cracked limestone formations



Photo 2.2. Detachment of large limestone segments

(α) (β)

Photo 2.3. Landslides of rock formations

Photo 2.4. Extensive failure of stone retaining wall along the road network to Atheras Village



Photo 2.5. Retaining stone wall failure supporting the foundation soil of a single-story structure

Εικόνα 2.6. Chavriata village: Extensive cracks on a three-level retaining stone wall supporting the foundation soil of a church

Photo 2.7. Foundation soil settlement observed in a 2-storey building.


INSTITUTE OF ENGINEERING SEISMOLOGY & EARTHQUAKE ENGINEERING (ITSAK) 2.3.3 Cracks along the road network Extensive cracks in the major part of the road network mainly within the Paliki peninsula were observed as direct result of the geotechnical failures described above combined with the old construction age of the road network . Significant problems with cracks of up to 20m long and up to 50cm wide were recorded at the road network joining Argostoli with Lixouri, Vilatoria, Kardakata and Zola villages (Photo 2.8) 2.3.4 Seismic response of port facilities at Argostoli and Lixouri. Extensive failures in the form of longitudinal cracks of jetties and displacement or/and rotation of quay walls were recorded at Lixouri port and (to a lesser extent) at Argostoli port. At the Lixouri port, the earthquake-induced horizontal displacement of the concrete quay walls was measured in the range of 5cm to 15cm followed by a rocking deformation towards the waterfront thus demonstrating a 3-dimensional pattern of their seismic response (Photo 2.9a and 2.9b). The above response mechanism in combination with possible liquefaction phenomena (although obvious signs of extensive soil liquefaction were not observed) and consequent lateral spreading of the liquefied soil led to extensive cracks in several parts of the port’s jetties parallel to the coastline (Photo 2.9c and 2.9d). At the Argostoli port, the observed failures were less extensive with small displacement and rocking deformation of the quay walls , as shown in Photos 2.10a and 2.10b. In the above type of failure, the material discontinuity between concrete quay walls and the debris embankment should be taken into account. For this case, liquefaction phenomena were less extensive due to the clayey composition of the soil formations close to the DeBosset bridge (Pitilakis et al., 2006). Finally, it is worth noticing that despite the extensive damage, both ports remained functional.



(a) (b)

(c) (d)

(e) (f)

Photo 2.8. Cracks on the road network: (a) Argostoli – Lixouri (b) Argostoli - Kardakata (c-d) Lixouri - Vilatoria (e) Ag. Dimitrios – Livadi (f) Argostoli – Zola



(a) (b)

(c) (d)

Photo 2.9. Lixouri port: (a-b) Lateral transposition and turn of seawalls (c-d) Long cracks at the port’s jetties parallel to the seashore



(a) (b)

Photo 2.10. Argostoli port: (a-b) Seawall detachement along the seashore close to DeBosset bridge. 2.4. Preliminary Conclusions on Geotechnical Engineering Aspects From a geotechnical point of view, the main earthquake-induced geotechnical failures may be summarized as follows: • The road network was significantly affected by the earthquake triggered landslides at

slopes composed mainly of limestone formations • A large number of stone retaining walls failures were observed that may be attributed to

significant lateral earth pressures during seismic shaking imposed on the old stone walls. • Significant displacements and rocking motion were recorded on the quay walls of Lixouri

port and (to a lesser extent) Argostoli port combined with extensive cracks on the jetties parallel to the shoreline that should be associated with liquefaction and lateral spreading phenomena.


INSTITUTE OF ENGINEERING SEISMOLOGY & EARTHQUAKE ENGINEERING (ITSAK) 3. RESPONSE OF STRUCTURES 3.1. Type of structures The types of structures that are located at the stricken areas were mainly constructed after the 1953 Cephalonia earthquake. These are divided in four major categories in relation to the type of the load bearing system. In the wider meisoseismal area where structures were strongly affected by the 26/01/2014 earthquake the structural systems are grouped as follows: • One to two storey masonry buildings: These buildings are further subdivided according

location criteria. There are masonry buildings that were constructed by clay or stone or concrete bricks and by higher quality mortar, which are mainly located at Argostoli and Lixouri. Also there are one storey masonry buildings that are located at small villages. These buildings have walls that are composed by roughly treated stones and low-strength clay mortar . These buildings are of secondary use serving as barns or stables and are not numerous, since most were destroyed during the catastrophic earthquake that took place in the island in 1953.

• Reinforced concrete buildings: These buildings are located at the whole island and were constructed mainly after the 1953 earthquake, till nowadays. These buildings are of one to four storeys, they have well reinforced concrete frames, as well as shear walls that were qualified as such under Eurocode standards . Also there are many reinforced concrete buildings that were constructed after 1953 and are characterized as monuments. The most important towns on the island are Argostoli and Lixouri and the main building stock there belong to the present category.

• Monumental and other cultural heritage masonry buildings: These buildings serve mainly as churches or schools (at country villages) and have one or two storeys. They were constructed by adopting traditional antiseismic techniques and in most cases their construction was financed by benefactors.

• Other buildings: During the in situ inspections some wooden buildings were found, as well as some stone and reinforced concrete bridges.

3.2 Type of damage on structures at the stricken area The earthquake of 26 January 2014 at Cephalonia cause limited damage to the structures of the island. In less than 24 hours after the main event, five EPPO-ITSAK researchers arrived at the island. Among others, extensive inspections were performed and the damage on buildings and other structures was recorded. Next day after the earthquake there was not significant available information about the range of the damage throughout the meisoseismal area, so was decided to inspect buildings in the two main towns of Argostoli and Lixouri on foot and asking the citizens to show the damaged buildings. Two days after the earthquake important information was available about the situation at the villages, so was decided to inspect these


INSTITUTE OF ENGINEERING SEISMOLOGY & EARTHQUAKE ENGINEERING (ITSAK) areas. It was deduced that the damaged structures were mainly located at the Paliki peninsula, which is the part of Cephalonia where Lixouri is located. Inspections were performed at the villages of Agios Dimitrios, Livadi, Vilatoria, Agia Thekla, Kalata, Monopolata, Kaminarata, Mandourata, Favata, Havdata, Havriata, Vouni and Manzavinata. Bellow, follows the description of damage that were observed on the load bearing systems of buildings according to the aforementioned categories. Also photos are given from the most important types of damage. • One to two storey masonry buildings: These buildings were not constructed according to

any seismic code and are located mostly at the small villages. Diagonal cracks and/or partial collapses where observed for buildings of this category. These are low importance buildings, of secondary use or occasionally habitable and inadequately maintained. In some cases, cracks that were formed due to previous earthquakes and which were inadequately repaired with different type of mortar opened further. Also some buildings were totally abandoned and had partially collapsed. The number of these buildings was significantly limited and it is not possible to define a specific area where many damaged buildings of this type are concentrated.

• Reinforced concrete buildings: The majority of the existing building stock in Cephalonia pertains to this group. The most common type of damage was the detachment of the infill walls from the surrounding concrete beam – column frames. This type of damage was observed in numerous cases, and was a reason for concern of the population since it was the main type of observed damage to structures. After detailed inspections no cracks were observed at the reinforced concrete elements of almost every building that was checked. Also, in most cases no diagonal cracks were observed at the infill walls. This fact indicates that the infill walls were well constructed. Also it was observed that typically, along the height of the infill wall two concrete wall ties were constructed. Due to the good construction practices that were applied to the infill walls, the reinforced concrete frames were supported and the developed inter-storey drift was significantly limited. This way it is possible to deduce that the absence of diagonal cracks at the infill walls is related with the absence of cracks at the reinforced concrete elements. Of course, some exceptions were observed. In some reinforced concrete (R/C) buildings significant damage to structural elements or/and in infill walls were observed. These structures, with significant damage at the structural elements and infill walls are mainly located along the road at the north of Lixouri (towards Agios Dimitrios and Livadi). The most serious damage was observed in the village of Livadi, where the second floor of a three storey building totally collapsed, coming to rest on the ground floor. However, in most cases it was found that concrete buildings were reinforced with adequate number of steel bars and stirrups and no failures due to the inelastic elongation of steel bars were observed. Observed failures were mainly due to concrete crashing and diagonal tension. Also there is a subcategory of public and museum R/C buildings that were constructed after the 1953 earthquake. These buildings have local failures at their structural element that can be attributed to the reduced strength



due to the reduced durability and the intensity of the earthquake. Through corrosion of the reinforcement due to carbonation of concrete, the strength of the R/C structural elements is significantly reduced and the most common type of damage is the loss of concrete cover. These buildings were built half a century ago and were not properly maintained to preserve their strength capacity, which was significantly reduced by the pass of time.

• Monumental and other cultural heritage masonry buildings: The temples and other cultural heritage buildings were one or two storey masonry structures. Some of these buildings had no damage or light damage. Many of them had cracks at the exterior walls (no detailed inspection was performed). More specifically, the temples churches at the south of the Paliki peninsula had suffered significant damage. In some cases strengthening techniques were applied to these buildings in the past and local failures at the top of the temples were observed. The bell towers were not constructed in touch with the temples in order to avoid impact phenomena of the bell tower to the main structure. In masonry buildings that were constructed at the villages through funding by benefactors damage at the exterior walls were observed.

• Other buildings: During the in situ inspections some wooden buildings as well as some stone and reinforced concrete bridges were found. No damage to stone or reinforced concrete bridges were observed during the inspections. Also, a wooden building that was examined had no any damage. Additional remarks: During the inspections the detachment and displacement of many tiles from the roof of many buildings was observed mainly at Argostoli and Lixouri and less at the other villages. This is explained by the fact that wooden roofs were constructed without any wooden board panel under the tiles. In contrast, the tiles were resting on wooden rafters placed at 20 to 30cm distance. In addition to the repair cost, this detachment and displacement of tiles had the consequence of allowing the entrance and flow of the rainwater on furniture, electric devices and inside the electric wires, causing short circuits. Also in many temples ceiling decorations under the wooden roof were constructed. By the detachment and displacement of the roof tiles, these decorations were exposed to rain water and should be repainted or repaired or possibly reconstructed. During the main seismic event many household belongings, furniture, commercial goods and museum contents fell at the floor and some of them were broken. For the museum contents the damage happens through the detachment at the interfaces where the exhibits previously bond.

3.3. Preliminary Conclusions on Seismic Response of Structures

• In general, recorded intensity of the 26/1/2014 (M6.1) earthquake (acceleration, energy, response spectra) does not correspond to the observed damage of the buildings on the island. Certainly, there is damage, mainly on stone masonry buildings and on buildings that were designed by older codes. No cases were observed in which hysteretic damping was developed through the flexural cracking of concrete structural



elements and through a high level of inelastic deformation of steel bars. This is also justified by the fact, that there were not observed cracks at the R/C structural elements, with few exceptions.

• It is noted that existing buildings possess a substantial amount of strength reserves (depending mainly on their redundancy and on the over-strength of individual structural members), as well as possible additional energy dissipation mechanisms, which contribute to a significant increase of their behavior factor. Experience gathered from this and previous seismic events suggests that the seismic protection of Greek urban areas relies also on several alternative factors (such as infill walls, regular configuration of the structural system, proper material and workmanship quality, etc.). Due to high level of recorded accelerations, soil-structure interaction phenomena probably developed with positive effects on structural response. The aforementioned remarks show that there are additional mechanisms activated for the dissipation of the imposed seismic energy when a strong earthquake occurs. In this way, the response of structures subjected to strong ground motion can be improved.

• Through the accumulated experience from past earthquakes as well as from the present one, it is concluded that seismic protection, not only in Cephalonia but also in other seismic regions, is additionally improved by other parameters such as the correct arrangement of the load carrying structural elements, the use of shear walls, the well constructed infill walls and the use of high quality construction details and materials. Additionally, the high construction quality applied at the most of the buildings in Cephalonia, together with the long lasting experience of local construction personnel to aseismic construction contributes to positive response of the built environment.

• Additionally to the structural damage, the earthquake generated secondary damage to commercial wares and household contents. Also, due to damage on tile-roofs it is possible for rain water to enter the house, causing damage to furniture, electric devices and electric networks. In these cases it is important to repair tile-roofs immediately and if this is not possible, to cover temporarily the openings on roof. In masonry wall buildings special and immediate measures should be applied after an earthquake, since rain water may deteriorate the mortar between bricks as well as may cause damage to paintings, museum contents etc.

• Finally, it is suggested that buildings constructed according to the 1959 Greek Seismic Code or before, should be carefully checked, evaluated and when necessary strengthened according to modern techniques. In addition, school buildings designed according to older codes of 1959 or 1985(same coefficients as 1959), should be checked and strengthened according to new Greek code for building strengthening.



Photos 3.1, 3.2. Two neighbor masonry buildings at the villages. The building with strong R/C ties at top had no damage.



Photos 3.3, 3.4. Partial collapses of masonry buildings of secondary use.



Photos 3.5, 3.6. Multistorey buildings with detachment of infill walls from the R/C frames. No damage to the structural elements were observed.



Photos 3.7, 3.8. Cracks between structural element and infill walls of the elderly people nursary (up) and the hospital (bottom) at Argostoli. These buildings were temporarily abandoned.



Photos 3.9, 3.10. Damage at the Labour houses at Lixouri.



Photos 3.11, 3.12. Damage at a two storey building in Agios Dimitrios.



Photos 3.13, 3.14. Three storey building severely damaged in Livadi. Total collapse of second floor coming to rest on the ground floor.



Photos 3.15, 3.16. Two storey building with damage, at the Northern road from Lixouri.



Photos 3.17, 3.18. Flexural cracks at the ends of R/C columns at the Northern road from Lixouri.



Photos 3.19, 3.20. Two temples at the southern area close to Lixouri.



Photos 3.21, 3.22. Temple at the southern area close to Lixouri.



Photos 3.23, 3.24. Cultural heritage masonry building and temple, with damage, at the center of Paliki peninsula.

Photo 3.25. Damage at glass panes.

Photo 3.26. Damage on tile - roofs.

Photo 3.27. Damage of commercial wares.

Photo 3.28. Damage of commercial wares.

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Preliminary report on the Mw:6.1 Cephalonia earthquake of 26th Jan 2014 (in English)