## 7 Secondary Environmental Effects Induced by the 1953 Ionian Sea Earthquakes
### Far-Field Effects Induced by the 11 and 12 August 1953 Earthquakes  
Far-field effects were detected in several sites in the adjacent Aetoloakarnania area and in the Peloponnese by the 11 and 12 August earthquakes (Figure 13).  
Figure 12: Secondary environmental effects induced by the 12 August 1953 Ionian Sea earthquake in Zakynthos Island.  
Slope failures were generated by the 11 August earthquake in Kylini peninsula located at the northwestern coastal part of Peloponnese (Figure 13). They were reported at a distance of about 4 km from oil exploration drillings in the area and the mobilized material was several tons (PEDOPONNISOS, 12.08.1953).  
The 12 August 1953 earthquake induced also far fields effects including in tsunami, hydrological anomalies and slope movements (Figure 13). Moreover, environmental effects related to hydrocarbon release were also detected few days after the earthquake (Figure 13).  
More specifically, the Louros islet, located southwest of Aetoliko area in the adjacent Aetolioakarmania region (Figure 13), was covered by the sea waves during the earthquake (NEOLOGOS PATRON, 13.08.1953).  
Also, in Aetolioakarmania, the Aetheolos River diverted its course as a result of the earthquake and later returned to its normal bed (I IMERA, 14.08.1953; NEOLOGOS PATRON, 14.08.1953). The diversion was detected in the area between Palaeokastro and Aggelokastro (Figure 13) towards Katochi town and resulted extensive flooding of agricultural land, comprised of rice and vegetable crops.  
Slope failures were also generated along the slopes of the Foinikas River gorge located at the northern part of Panachaiko Mt in northern Peloponnese (Figure 13; NEOLOGOS PATRON, 15.08.1953). In particular, northwest of the Arravonitsa plateau (Figure 13), a large volume of unstable rocks detached and fell towards the Foinikas River, resulting in a wide opening. Slope failures were also generated closed to Lakka village located southeast of Arravonitsa village (Figure 13). Unstable material were detached from the bed rock and fell into the adjacent valley for 100 m. Ground cracks were also formed in the same area. Both sites affected by the slope movements are located along the seismogenic fault of the Southern Corinth Gulf, based on the Greek Database of Seismogenic Sources [39].  
Far field effects by the 12 August 1953 earthquakes were also reported in western Peloponnese (Figure 13). They comprised slope failures, ground cracks and hydrocarbon-related effects (AKROPOLI, 1953; NEOLOGOS PATRON, 20.08.1953).  
Slope failures were observed along slopes in Fragkopidima area located in the western Peloponnese, north of Vounargo village (Figure 13; AKROPOLI, 1953). Ground cracks were observed in the Kylini beach in western Peloponnese (Figure 13; AKROPOLI, 1953). Hydrocarbon related effects were observed in Katakolo area of western Peloponnese (Figure 13; NEOLOGOS PATRON, 20.08.1953; ELECTHERIA, 20.08.1953, 21.08.1953; Z2.08.1953; TAXY-DROMOS, 23.08.1953). Sulphureous gas emissions and subsequent flames about 1 m high  
Figure 13: Far field effects induced by the 11 and 12 August 1953 earthquakes.  
coming out of a pre-existing crater were observed in Psorochoma site 8 days after the 12 August 1953. The flames were observed during both day and night and illuminated an area with a radius of 200 m. These phenomena indicate combustion of natural gas, which escaped from the crater. Prior to these effects, a light stream of air came out of the crater, which extinguished a lighted match without ignition.  
Similar hydrocarbon-related effects were also triggered by historical earthquakes in Zakynthos Island, located west of the Katakolo area. Sulphureous gas emission and flames were also triggered by the 1633, 1791, 1809, 1820 and 1840 earthquakes in Zakynthos [15]. The occurrence of asphalt-pitch seepages and sulphureous gas emissions are associated with existing hydrocarbon deposits in both areas (Katakolo area and Zakynthos Island) [50,51].