## 4 Discussion
### Pockmark Field Activation  
The Patras pockmark field displayed strong evidence for activation at least twice during two major earthquakes of magnitude 5.4 and 6.4 R on 14 July 1993 and 8 June 2008, respectively [39; 40]. Several pockmarks were found to be active for a few days after the 1993 earthquake, of which the epicentre was located near the pockmark field. Similarly, the field was activated by the 2008 major earthquake, which occurred 32 km SW of the field at the Northwestern Peloponnese. In both activations, the number and intensity of the gas flares showed a gradual decrease over time, in a period of 15 to 30 days. Post-earthquake pockmark venting has been reported in several places worldwide [30; 32; 33; 34; 35; 36]. The long-term Gas Monitoring Module (GMM), which was deployed inside a composite pockmark of the southern sector, showed the normal behaviour of a pockmark during a period with no major earthquakes [55]. Gas seeps exhibit significant temporal variations in venting behaviour, and few studies have been conducted using visual census [111] or acoustic methods [112]. The GMM recorded 60 \"pulses\" of CH\({}_{4}\) increase, associated with T-P drops, in a period of almost six months, using an METS methane sensor [42; 55]. Based on direct evidence and long-term monitoring data, the PGPF is characterised by a normal activity consisting of micro-emissions (1 event/3-4 days), which is interrupted by episodic and vigorous venting triggered by major earthquakes. The earthquake-induced vigorous venting seems to last for 15 to 30 days after the mainshock. In the present study, acoustic flares (gas seepage) in the water column, immediately above a few pockmarks, have been detected for the first time during a period of calm seismic activity in the area. In addition to the seepage pulsation that has been recorded by GMM, the water column data indicate gas seepage above the pockmarks, implying ongoing pockmark activity. The acoustically imaged gas flares extend in the water column from the centre of the pockmarks to the sea surface, suggesting a continuously flowing--rather than a pulsing--nature [75]. Similar pockmark field behaviour has been reported by [PERSON] et al. [103] in the Concarneau Bay pockmark field. Ongoing gas venting activity in the field could be due to the repetitive action of the short-term pressure-controlled process superimposed on longer-term temperature-controlled processes and episodically on earthquake occurrence. The acoustic data collected from the water column above the pockmarks of PGPF after the mainshock of two major earthquakes (1993 and 2008) were reprocessed and plotted onto the new bathymetric map (Figure 18). The spatial distributions of gas flares triggeredby two earthquakes showed different patterns. The 1993 earthquake flares are concentrated in the northern sector of the field and at the proximity of AT.F. On the contrary, the 2008 earthquake flares are widespread over the entire field. Although the earthquake mechanism in both events is similar (strike slip), the locations and distances of the epicentres of the main and post-earthquake events (Figure 18b) could explain the different spatial distribution patterns of gas flares in the PGPF obtained in these two seismic events. The 1993 Patras earthquake was located in the eastern city outskirts, roughly 6 km east of the pockmark field, at the city's harbour. The earthquake had a shallow depth (~10 km) and caused a complicated aftershock sequence that is described in detail by [PERSON] et al. [115]. The aftershocks extended in a NNW direction to the north of Patras. The focal mechanism of the mainshock suggests a strike-slip fault, with one nodal plane in the NNW direction, i.e., similar to the aftershock sequence. Although of medium size, the event caused significant damage to buildings near the AT.F fault and activated the pockmarks localised near the AT.F's offshore extension. The Movri earthquake in 2008 (6.4 Mw) ruptured an NNE right lateral fault; its epicentre was ~30 km south of Patras [56; 114].