## 7 Secondary Environmental Effects Induced by the 1953 Ionian Sea Earthquakes
### Secondary Effects Induced by the 12 August 1953 Ionian Sea Earthquake in Cephalonia Island
#### 7.3.1 Slope Failures
The 12 August 1953 earthquake triggered rockfalls in slopes above Agonas village (Figures 9e and 11), over the almost E-W-trending Ayia Kyriaki coast and from the mountain over Soitras beach (Figure 11). All sites are located along the eastern margin of the Thinia valley. The rockfalls affected the upper part of Agonas, while its lower part was protected by a series of olive trees, which acted as a barrier against down-rolling boulders [20]. The debris rockfalls in the Ayia Kyriaki area reached the sea, causing local disturbance and temporary change to its color (TAXYDROMOS, 16.08.1953). It is of significance that the eastern margin of Thinia valley was affected by slope failures induced by the early 2014 Cephalonia earthquake sequence and consisted of rockfalls, rock toppling failures and landslides [11]. Slope failures were also generated on the western slopes of Ayia Dynati Mt (Figure 11). This area is composed of Cretaceous limestones, karstified at a large scale, resulting in loose and highly weathered limestone blocks in surface and many hidden karst cavities, at depth. It is also characterized by intense relief, with steep slopes, large morphological discontinuities and gorges born of the synergy between uplift and incision [11]. The 12 August 1953 earthquake triggered rockfalls along the abrupt slopes of Tiganeto and Chalio Mts surrounding Kourouklata [20], which was the worst affected village (PELOPONNIOS, 16.08.1953). It was completely destroyed by falling boulders. Based on witnesses of prisoners in Argostoli prison, extensive slope failures occurred in the area north of Drapano [46]. Based on the geological and geomorphological structure of this area and the environmental effects induced in the same area by recent strong earthquakes in Cephalonia [11], it could be concluded that extensive rockfalls of unstable limestone blocks were generated along the western slopes of Ayia Dynati Mt, without impact on residential areas. These blocks ended up in the adjacent sea of the Argostoli Gulf according to the aforementioned description [46]. Rockfalls were also triggered along the western slopes of Avgo Mt (Figure 10a,b and Figure 11), in eastern Cephalonia [20]. They affected villages founded along the mountain front comprising Sami (Figures 10a and 11), Zervata (Figures 10b and 11) and Katapodata (Figure 11; TA NEA, 12.08.1953; Taxydromos, 14.08.1953, 19.08.1953; I I MERA, 13.08.1953). At a distance of about 50 m from Dichalia village, located almost 5 km northeast of Sami (Figure 11), failure of a coastal part with an area of 1000 m\({}^{2}\) took place before the August earthquakes. After the generation of the studied earthquakes, the failures were reactivated and the area was further subsided by 1 m [20]. In Sami area, extensive rockfalls were triggered along the western slopes of Avgo Mt (Figure 11). They formed a dust cloud, which was visible from the neighboring island of Ithaki, and looked like a dense cloud of fire (I MERA, 13.08.1953). These phenomena affected the town and the road network leading from Sami to the surrounding villages (TA NEA, 12.08.1953; TAXYDROMOS, 14.08.1953, 19.08.1953; I I MERA, 13.08.1953). Several mountainous villages were cut off for days by boulders that had accumulated on the road (TAXYDROMOS, 14.08.1953). In the Zervata area, where Alevrata, Zervata and Mouzakata villages were merged into Zervata village (Figure 11), rockfalls caused structural and non-structural damage to buildings, damage to the road network and effects on vegetation, including the destruction of olive trees and vineyards (TAXYDROMOS, 14.08.1953). Many buildings collapsed, while the traffic and communication with the surrounding villages and the rest of Cephalonia were disrupted for days. The village looked like an excavation, attributed to earthquake ground motion and its subsequent rockfalls. In Katapodata village, rockfalls resulted in further damage to some buildings [20].