Evidence of Rotational Macroseismic Effects in Greece

EVIDENCE OF ROTATIONAL MACROSEISMIC EFFECTS IN GREECE

Vasiliki KOUSKOUNA1, Georgios SAKKAS2 and Eleftheria PAPADIMITRIOU3

ABSTRACT

A considerable number of damaging earthquakes in Greece, have produced a variety of macroseismic effects to both built and natural environment. After a strong earthquake, rotational effects have been observed mainly on free-standing columns, statues, chimneys, tombstones and, more rarely, to buildings (permanent) or on heavy furniture (temporary). In the case of Greek and Roman free– standing columns and temples which have survived from collapse, rotation and lateral displacement between their drums is often observed, depending on the earthquake magnitude and epicentral distance. The phenomenon indicates that such simple and uniform structures appear to be more resistant to the near earthquakes, a fact that ensures their survival over the centuries. Regarding historical earthquakes, identifying, assessing and dating such distortions and explaining their preferential character is based on literary sources. For recent earthquakes, photographic and descriptive material is used. An assembly of rotational effects for historical and instrumental earthquakes in Greece is therefore performed, and presented after a thorough discussion.

INTRODUCTION

Macroseismic effects are the effects of earthquake shaking on buildings, infrastructure, human life and natural environment. Usually, the effects on buildings and different kinds of structures are the ones that define the macroseismic intensity of an earthquake in the aftermath. Macroseismic effects have been observed for centuries worldwide. It is important to notice that the macroseismic observations were the only means of scientific knowledge for the earthquakes until 1900, when the instrumental era of seismology begins. Macroseismic effects affect both to man-made and urban environment, with a variety of phenomena such as cracks or failure of walls, partial or total collapse, landslides or liquefaction. This paper deals with the effect of rotation around the vertical axis observed mainly in man-made structures, such as free-standing columns, statues, chimneys, tombstones and, more rarely, to buildings (permanent) or on heavy furniture (temporary). Rotational effects accompanying earthquake damage have been observed during time, worldwide and on different kinds of tectonic regimes, mainly in the area of maximum shaking. The phenomenon, described by Milne (1842) and Sieberg (1923) among others, has been related to the horizontal component of shaking. Such effects, when observed at one place –usually at the epicentral area- are expected to have similar direction, as a consequence of the direction of horizontal motion at the place. Westland and Heinrich (1937) have studied the 1937 Ohio earthquakes, where rotational

1 Associate Professor, Department of Geophysics – Geothermics, University of Athens, Greece, [email protected] 2 PhD Candidate, Department of Geophysics – Geothermics, University of Athens, Greece, [email protected] 3 Professor, Department of Geophysics, Aristotle University of Thessaloniki, Greece, [email protected]

1 displacement has been found on sixty seven (67) monuments/tombs in three cemeteries near the epicenter. Gupta et al. (1969) have observed rotational displacement on a pillar near the epicenter during the Koyna, India (December 10, 1967) earthquake. Sargeant and Musson (2009) have studied rotational earthquake effects from historical and recent earthquakes in the United Kingdom. They note that “from the historical observations it is not possible to determine whether they are due to true rotational shaking or are rotational effects caused by translation, particularly given the asymmetry of the structures”. Cucci and Tertulliani (2011) have mapped and related rotational macroseismic effects with site and source effects of the 2009 L’ Aquila, Italy earthquake. In the area of Greece, numerous rotational macroseismic effects have been observed from the 19th century until today. Most of the effects are twisting statuaries, rotated tombs and crosses in cemeteries, rotated drum columns and rotating feeling of ground motion during an earthquake. Unfortunately, no systematic record exists through these years despite the occurrence of such effects. Geordiades (1904) and Galanopoulos (1956b) consider that rotational effects observed in buildings are due to: a) the combination of horizontal and vertical motion, b) asymmetry of structure and c) differential friction of the base.

THEORETICAL BACKGROUND

Gutenberg (1927) and Richter (1958) have ignored rotational ground motion which they did not consider significant and due to difficulties occurring in their measurement. Instrumental seismology examines only the three components of translations, despite the fact that the complete analysis of ground motion requires the use of three additional rotational components and six components of strain (Aki and Richards 2002, Trifunac and Todorovska 2001). In the seismic wave equation, Eq. (1), displacement is the sum of the gradient of a scalar potential φ (x, t) and the curl of a vector potential Ψ (x, t) having specific assumptions (parts neglected). (1)

The part associated with the scalar potential has no curl (P-waves) or rotation while the part associated with the vector potential has zero divergence (S-waves). Bouchon and Aki (1982) calculated strain, tilt and rotation in the vicinity of the fault. They have shown that rotation, tilt and strain are much smaller than translational motions but are measurable especially in the direction of faulting. They have found that rotational motions appear with the S waves and also have discussed the issue that topographical and site effects may amplify the presence of rotation. Cochard et al. (2006) showed that rotation is related to displacement according to Eq. (2).

(2)

Also, Ferreira and Igel (2009) simulated Love waves from the Tokachi-oki 8.1 Mw earthquake with remarkable results. Newmark (1969) has shown the torsional and rocking effects even in symmetrical structures. Also, Hart et al. (1975) have studied the torsional response of high-rise buildings observed during the San Fernando earthquake.

ANALYSIS

In what follows, a number of earthquakes with evidence of permanent (P) and/or temporary (T) rotational effects in the area of Greece are presented.

T 1867 March 3, 18:00, Kloumidados Lesvos From the available information (Codex of Mytilini Diocese), earth was shaking in a rotated movement. The vice consul of Greece confirms the rotational feeling of the shaking (Taxeidis 2003), Kouskouna and Sakkas (2013).

V. Kouskouna, G. Sakkas and E. Papadimitriou 3

T 1867 March 28, 06:30, Mytilini Lesvos The only available information is from Mytilini with intensity 4 (EMS98). This earthquake is an aftershock of the main event that took place on March 3. In the text is reported that four (4) rotated movements were felt without any roar (Taxeidis 2003), Kouskouna and Sakkas (2013).

T 1877 October 17, 06:38, Kokkarion Samos Earthquake was strong enough with one rotational movement. Intensities: 4-5 at Avlaki, 4-5 at Kokkarion (Taxeidis 2003), Kouskouna and Sakkas (2013).

T 1881 April 03, 04:00, Chios One of the most destructive earthquakes happened in Chios. From the texts it is obvious that the earthquake had a direction from east to west followed by rotational movements from to right and vice versa (Taxeidis 2003), Kouskouna and Sakkas (2013).

P 1886 08 27, Philiatra Georgiades (1904) reports that the macroseismic observations revealed permanent effects of rotation in the area of Messinia struck by the earthquake, without providing any further details.

T 1893 January 31, 06:45 Corfou Weak shock with rotating movement of short duration (NOA bulletin).

T 1894 July 19, 06:50 Argostoli Weak shock with rotating movement with a long noise (NOA bulletin).

P 1895 January 12, 17:08 Patras The seismometer was making circles on its recording plate (NOA bulletin).

T 1896 July 03, 00:30 Patras Twisting shock of 2-3 seconds duration (NOA bulletin).

T 1897 May 29, 00:01:14 Kalavryta & Mazeica At Kalavryta wavy motion at first which was followed by strong twisting motion. The shock was felt by everyone. Its direction was W-E but immediately turned to mixed. After the shock, hanging objects were oscillating in a rotating manner to the direction East to South. Weak shock also felt in Mazeica (NOA bulletin).

T 1897 June 12, 00:17 Argostoli Strong rotating shock of short duration (seismic station) (NOA bulletin).

T 1898 June 02, 23:32 Egine Weak rotating shock with about 3 seconds duration (NOA bulletin).

T 1898 July 31, 08:20 Volos Rotating shock? The direction of motion was N-S (seismic station) (NOA bulletin).

T 1898 November 9, 20:15 Calamate Strong shock wave with duration of 15 seconds. Local observer Stassinopoulos, reports that this earthquake took place at 20h 19m 37s and was composed of three shocks. The second had a rotary motion and duration of 2 seconds.

T 1912 April 15, 23:23 between Cephalonia & Zakynthos At Argostoli felt rotating (NOA bulletin).

T 1914 November 23, 09:03, 09:06 Leukada (Western Greece)

At Leukada felt rotating (NOA bulletin).

T 1915 June 04, 17:22:27 Evrytania At Leukada felt rotating (NOA bulletin).

T 1924 November 13, 09:04, Valley of river Louros (Preveza) At Leukada felt rotating (NOA bulletin).

T 1926 June 26, 19:47 Between Crete and Cyclades (35,8 - 25,5) At Leukada felt rotating (NOA bulletin).

P 1941 March 01, 03:52:55.2, Larisa The earthquake took place at 03:52:55.2 (UTC) with magnitude 6.3. The epicentre is located at 39.73 – 22.46 with depth 25 km (Makropoulos et al., 2012) at a distance of 11km at NNE from Larisa. Damage was observed in some villages of the Thessaly plain. The statue of Kouma, located in the main square rotated around its vertical axes (Fig. 1). Larisa lies on alluvial Holocene deposits.

Figure 1. Counterclockwise rotation due to the 1941 earthquake observed at a statue in Larisa: left Maravelakis (1943), right Critikos (1941)

P 1981 February 24, 20:53:37, Alkyonides On 24th of February 1981 at 20h 53 (UTC) Athens was shaken by a 6.6 magnitude (Makropoulos et al., 2012) earthquake located in the north east borders of Gulf of Corinth, near the Alkionides island. The epicentre was approximately 70 km WNW of Athens. The next day, on February 25, a second earthquake (aftershock) with magnitude 6.3 struck again. Because the largest aftershock occurred only some hours after the main shock the effects of the main shock only, cannot be easily distinguished. Khoury et al. (1983) estimated the maximum observed intensity (MM Scale) was equal to 9, north of Loutraki, while National Observatory of Athens estimated the maximum observed intensity (MM Scale) equal to 9-10 at Perachora (Corinth) and Prodhromos (Boiotia). In the city of Athens and its suburbs the observed intensity was varying from 5 to 7-8. Distance from the fault and especially local site conditions had a significant role in the macroseismic intensity estimation (Tilford et al., 1985). The only record of macroseismic rotational effects is reported from the Parthenon, where slips, twists and vertebrae chipping of the columns were observed. Most importantly, the SE column rotated anticlockwise about the horizontal axis (Zambas 1982, 1989).

V. Kouskouna, G. Sakkas and E. Papadimitriou 5

P 1986 September 13, 17:24:34.3, Kalamata The earthquake of Kalamata occurred the 13 September of 1986 with a magnitude 5.8, epicentral coordinates 37.08 – 22.15 and depth of 9 km (Makropoulos et al., 2012). The epicentre is located less than 10 km outside the city of Kalamata at the North-east. Papazachos et al. (1988) determined the fault mechanism to listric normal with strike NNE- SSW and dipping to WNW. Extensive damage was recorded to the city of Kalamata and also to surrounding villages of Amphia, Leika, Thouria, Giannitsi and Elaiochori (Gazetas et al. 1990). From all the damage very interesting phenomena of rotated effects were observed mainly in the cemetery of Kalamata. In Fig. 2, Fig.3, Fig.4 and Fig.5 the observed rotational effects are presented. It is worth noting that in Greek orthodox cemeteries, tombs are built in an east-west direction, where the cross is positioned facing east (Fig. 6), a fact which enables the identification of the direction of rotation.

Figure 2: Counter-clockwise rotation observed in cemetery of Kalamata

Figure 3. Clockwise rotation in the cemetery of Kalamata. Front view at the left, side, back view at the right

Figure 4. Counter-clockwise rotation at the cemetery of Kalamata

Figure 5. Counter-clockwise rotation at the cemetery of Kalamata

Figure 6. Orientation of Greek Orthodox tombs

V. Kouskouna, G. Sakkas and E. Papadimitriou 7

P 1999 September 07, 11:56:49.5, Athens The earthquake had a magnitude of Mw 6 and struck the city of Athens and its suburbs in September 07 at 15:00 (local time), located 20km NW of Athens at the Aspropirgos plain, and associated with Parnitha normal fault with an E-W strike. Papadimitriou et al. (2002) computed the strike at 105o, dip 55o and rake -80o. Damage (partial or total collapses) was focused mainly in the north-western suburbs of Athens (Ilion, Thrakomakedones, Acharnai, Nea Kifissia and Metamorphosi). At the cemetery of Nea Filadelfia the earthquake overturned tombs and caused rotational phenomena (Fig. 7).

Figure 7. Clockwise rotation at cemetery of Nea Liosia, Attika

In the center of Athens, the damage grade was low. However, in the Academy of Athens, the free standing columns of Athina and Apollo were rotated due to this earthquake (Ambraseys 2010). Measurements discovered a rotation of the base of the statues. Also, inside the building, in the main lamp post rotated and slid between the striata and no-striata parts of it (Ambraseys, 2010).

P 2014, 26 January, 13:55:42.55 – 3 February, 03:08:44.57, Cephalonia island Cephalonia island was struck twice, on January 26 by an earthquake of magnitude Mw 6.1 and again on February 3 by an earthquake of magnitude Mw 5.9. From the automatic solution of the University of Athens, the epicentres of both the observed earthquakes are located in the western part of the island. The peninsula of Palliki suffered the most. Total damage has not been fully recorded but the villages of Lixouri and Chavriata had the most serious damage recorded so far. In Fig. 8, observations of macroseismic rotational effects are presented.

Figure 8. a) Left: from Lekkas et al. (2014) to the village of Chavriata, clockwise rotation of the base and counter-clockwise rotation of the monument, b) right: from Bouckovalas et al. (2014) counter-clockwise rotation

Rotational effects on free standing columns in Athens

1. Thiseion The columns of the temple of Hephaistos (Thiseion) in Athens, built c. 415 BC, have been distorted over the years. The drums of the columns of the north face and some of the south face (to a lesser degree) have been rotated and displaced. This observation (Fig. 9) is reported by Ambraseys (2009) and Galanopoulos (1956b) in Fig. 10, but none of them defines when this rotation appeared.

Figure 9. Rotated drums at the temple of Hephaistos (Thiseion) in Athens. Photo from Ambraseys personal archive (University of Athens)

V. Kouskouna, G. Sakkas and E. Papadimitriou 9

Figure 10. Rotated drums at the temple of Hephaistos (Thiseion) in Athens. Left: from Galanopoulos (1956b), right: modified (digitized) of Galanopoulos (1956b) where the dislocation of the vertical axis of the columns is apparent

2. The choragic columns of Thrasyllos The two choragic marble columns at the southern slope of the Acropolis, above the choragic monument of Thrasyllos and the theatre of Dionysos are dating most probably between the end of the classical and the beginning of the Hellenistic period, with exceptionally high standards of structural design. During the detailed survey and documentation of the two choragic columns on the south slope of the Acropolis, above the Monument of Thrasyllos, aiming to contribute to the research of the seismic past of the center of Athens, analysis of their seismic behavior and its correlation with past earthquakes were performed. The two choragic monuments must have suffered at least one strong seismic action during their past, which caused them a significant deformation (Fig. 11). However, the 1981 and 1999 events did not cause any damage to the two choragic columns (Zambas et al., 2011).

Figure 11. The capital and the subsequent displaced and rotated plinth of the western Thrasyllos choragic column (Zambas 2011)

3. The Academy of Athens columns and statues of Athena and Apollo The Pentelic marble columns situated in the front right of the Academy of Athens bear the statues of Athena and Apollo mounted on them (Fig. 12 and Fig.13). Since their erection, the column/statue systems have experienced a number of strong earthquakes, apparently with no damage. However, the Parnitha 1999 earthquake produced significant sliding and rotation of the statues bases (mainly in the

case of the Apollo statue), which rest rather loosely on the columns (Ambraseys, 2010, Ambraseys and Psycharis, 2011).

Figure 12. The statue of Athina at the Academy of Athens. Rotation observed at the base of the statue (Ambraseys, 2010)

Figure 13. The statue of Athina at the Academy of Athens. Clockwise rotation observed at the base of the statue (Ambraseys, 2010)

V. Kouskouna, G. Sakkas and E. Papadimitriou 11

CONCLUSIONS

As it has been shown above and in many cases worldwide, rotational macroseismic effects are observed on specific structures. Monuments, statues, free standing columns, chimneys and even furniture suffer more from rotation during the seismic motion. It seems that cylinder, pyramid or obelisk shaped structures seem to suffer the most from rotational movements/dislocations. It is without a doubt that rotational motions may appear in structures which lack of symmetry. Bouchon and Aki (1982) have shown the existence of rotational motions in the vicinity of the fault area and Newmark (1969) the existence of torsion even in symmetrical buildings. Although several destructive earthquakes have occurred in Greece with a variety of macroseismic effects, it is very difficult to trace rotational effects mainly for three reasons: a) rotational effects seem to be more intense at specific structures, b) they are observed mainly in the vicinity of faults and c) no systematic recording of this kind of effects has been kept since the prevailing theory for generation of these effects was due to translational motions. From the examples presented in the present study, it is generally difficult to identify whether these effects were due only to the rotational component of seismic wave. It seems that the distance from the fault (Bouchon and Aki, 1982) and the geological setting (Cucci and Tertilliani, 2011) at the site have a specific tendency to a higher rotational component. Most of the examples are located in a distance of about 10 km from the epicentre, based on Holocene sediments.

ACKNOWLEDGMENTS

The present study was co-funded through the Synergasia 2011 (NSRF 2007 - 2013) project “Greco- Risks - Hellenic Natural-Hazards Risk-Management System of Systems”.

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