On 8 January 2006 (11:34 GMT) an earthquake of Magnitude Mw = 6.6 occurred close to the Northeast coast of Kythira Island (Southern Greece) causing some damages landslides and rockfalls. The hypocenter as estimated by the National Observatory of Athens, http://bbnet.gein.noa.gr/alerts_manual/2006/01/evman060108113454_info.html was calculated 36.214˚N, 23.406˚E, and the focal depth at 69 Km. This event is located in the Hellenic subduction zone which characterizes the Southern part of Greece. The shock was felt in a spatially extended area that covered Greece, Italy, Turkey, Egypt, Cyprus, Israel, Syria, Jordan, and Lebanon. This event is one of the largest earthquakes, after the event of 1903 (M = 7.3), which occurred in the same area. Previous works indicate the existence of a seismic gap in this region [10]. The major part of the seismic activity in this region is related to the active subduction zone along the Hellenic Arc, as well as the backarc area. Consequently, the area presents complex deformation, where the southern part of the Aegean region is moving towards the southwest at approximately 40 mm/yr [11] [12]. The area is characterized by active normal faults (Danamos, 1992) with an almost vertical orientation concerning the subduction zone. The main event was followed by a small number of aftershocks, as it appeared in Figure 1.

Thrust type faulting was revealed after applying moment tensor inversion. The obtained focal mechanism is strike = 205˚, dip = 48˚ and rake = 59˚ with a seismic moment equal to 8.4 × 10²⁵ dyn·cm, and a focal depth equal to 65 km (Figure 2).

The obtained focal mechanism calculated using data in regional distances is in agreement with the one proposed by the Harvard CMT solution, using teleseismic data.

Using manually locations of HRV, NOA and UOA and their respectively Moment Tensors (Table 1) with the varied depth we obtain H-C consistent solution.

The fault plane is the nodal plane with strike = 205˚, dip = 48˚ and strike = 59˚. The distance of the hypocenter from this plane is 7.5 km, while the distance from the other plane is 22.30 km. The distance between Hypocenter and Centroid is 33 km (Figure 3).

On January 6, 2008 (05:14, UTC) a strong earthquake happened near the Leonidio

town, Southern Peloponnesus. The geographical coordinates, as they calculated by National Observatory of Athens found, 37.114˚N, 22.775˚E and the depth at 86 km. There were no injuries or damages reported. The main event was followed by a small number of aftershocks since it is an intermediate-depth earthquake (Figure 4).

Three-component seismological data from stations belonging to the ORFEUS Institute were used. The inversion procedure provided a thrust type faulting with source parameters: strike = 114˚, dip = 75˚ and rake = 120˚. The depth is calculated at 85 km and the seismic moment M₀ = 1.6 × 10²⁵ dyn∙cm. The obtained result showed a good fit between the observed and the synthetic waveforms (Figure 5).

To apply the HC-plot method, the following 6 hypocenters manually locations (Table 2) were considered.

The fault plane is the nodal plane with strike = 225˚, dip = 36˚ and strike = 19˚. The distance of the hypocenter from this plane is 11.62 km, while the distance from the other plane is 26.30 km. The distance between Hypocenter and Centroid is 33.26 km (Figure 6). These results are in good agreement with this

one obtained by Zahradnik [2] [3].

On February 2008 an earthquake sequence including three strong events (Mw = 6.7, 6.1 and 6.0) occurred South of Methoni town, at a segment of the Hellenic arc which was not activated during the instrumental period. This sequence was followed by a large number of aftershocks, the strongest of which were processed to calculate their source parameters.

The first one occurred on 14 February 2008 (10:09, UTC) and the epicenter was located (36.50˚N, 21.78˚E) 230 km southwest of Athens. Two hours later (12:08, UTC) the second one occurred close to the first with epicenter (36.22˚N, 21.75˚E) and magnitude Mw = 6.1, according to the National Observatory of Athens. These two strong events were followed by another earthquake six days later on 20 February 2014 with a similar magnitude (Mw = 6.0). The moment tensor inversion indicates for the two first earthquakes the activation of a thrust-faulting type, while for the third event the inversion indicates a strike-slip type faulting.

Following we present the result of the inversion for the first event. For this purpose, the data of 6 stations from Hellenic Unified Seismological Network (HUSN) at epicentral distances less than 360 km, were used. Reverse type faulting was revealed after applying inversion. The obtained focal mechanism is strike = 290˚, dip = 16˚ and rake = 69˚. The seismic moment is equal to M0 = 1.56 × 10²⁶ dyn∙cm, for a focal depth equal to 29 km (Figure 7). The inversion

resulted in a DC equal to 90%, while the compensated linear vector dipole was equal to 10%. To determine the main fault four representative solutions selected, are presented in Table 3 and are plotted later in Figure 8.

On June 8, 2008 (12:25 GMT) a strong earthquake with a moment magnitude M_w = 6.4 occurred in the region of Peloponnese, W. Greece close to Andravida city. The area is located between the Gulf of Corinth extensional province and the Eurasia-Africa plate boundary offshore Cephalonia and Zakynthos Islands. No surface rupture was observed.

The epicentral coordinates were 37.98˚N, 21.51˚E, after these events a large number of aftershocks were followed. Double-difference relocations of 370 aftershocks show a linear pattern of events and define a clear NE-SW striking mainshock fault plane (Ganas et al., 2009). The hypocenter was determined at 18 km depth beneath village Mihoi in SW Achaia.

The constrained focal mechanism solution indicates strike-slip faulting with source parameters strike = 290˚, dip = 70˚ and rake = 1˚, the seismic moment is equal to M₀ = 4.49 × 10²⁵ dyn·cm, while the focal depth was equal to 22 km (Figure 9). Taking to account the aftershock activity the fault plane is the one with the NE-SW direction.

To apply the HC-plot method, the following 6 hypocenters manually locations (Table 4) were considered.

The following CMT solutions were considered: HRV, USGS, ETHZ, INGV, AUTH and NOA (Figure 10). All these solutions are characterized by similar strike-dip-rake angles, with one nodal plane, strike~265˚, dip~85˚ and rake~4˚ plotted in green and hereafter referred to as the green plane and the other one, strike~300˚, dip~75˚ and rake~160˚ as the red plane (Figure 10).

The fault plane is the nodal plane with strike = 290˚, dip = 70˚ and strike = 1˚.

The distance of the hypocenter from this plane is 2.86 km, while the distance from the other plane is 9.52 km. The distance between Hypocenter and Centroid is 11.72 km (Figure 11). This result is in good agreement with those from other studies [2] [3] [13].

Following we present the inversions results for 28 events with magnitudes M_w > 3.5 that occurred in the same region (Table 5).

On 8 January 2013 at 14:16:08.3 UTC, a moderate earthquake of magnitude Mw = 5.7 occurred off the southern coast of Limnos island. The event was strongly felt in nearby north Aegean islands, the neighboring Turkish coasts and the northeastern Greek mainland but caused no damage [14]. The epicenter was manually located at 39.6663˚N, 25.5620˚E, depth = 31 km with a local magnitude M_L = 5.8 according to National Observatory of Athens, http://bbnet.gein.noa.gr/alerts_manual/2013/01/evman130108141608_info.html.

The location of the earthquake indicates that it ruptured a fault segment running south of the North Aegean Trough near the island of Limnos [15] [16] [17], where the main, northern branch of the North Anatolian Fault (NAF) enters

Aegean Sea [18] [19] [20].

The main event of January 8, 2013, was followed by a large number of aftershocks. For the next two months, a total number of 495 events (1 ≤ M_L ≤ 4.5) were recorded and analyzed. The main shock, as well as the aftershocks were relocated [21]. The aftershock distribution of the mainshock reveals a NE-SW stricking fault about 40 km offshore Limnos Island that extends from 2 km up to a depth of 14 km [21]. The next two months 7 events with magnitude M_w ≥ 3.7 occurred and the source parameters of them calculated and presented in Table 6.

We applied moment tensor inversion to calculate the source parameters of the main event (January 8, 2013 14:16, UTC). Seismological data from HUSN, of 8 stations at epicentral distances less than 350 km were used. A band-passed filtering at frequencies 0.05 - 0.08 Hz was used both of recorded waveforms of three components and calculated synthetics seismograms. The inversion indicated a strike slip faulting, and the source parameters were calculated: strike = 315˚, dip = 86˚, rake = 5˚ with a depth 8 km while the moment magnitude determined M₀ = 3.90 × 10²⁴ dyn∙cm. The calculated double couple found 95% (Figure 11).

To apply the HC-plot method, the followed 7 hypocenters manually locations (Table 7) were considered.

The following CMT solutions were considered: HRV, USGS, GFZ, INGV, AUTH and UOA (Figure 13). All these solutions are characterized by similar strike-dip-rake angles, with one nodal plane, strike~300˚, dip~80˚ plotted in green and hereafter referred to as the “green” plane and the other one dipping, strike~65˚ deg, dip~80˚ as the “red” plane. The distance of hypocenter from this plane is 6.11 km, while the distance from the other plane is 1.61 km. The distance between Hypocenter and Centroid is 6.89 km (Figure 12). The main fault is this with source parameters: strike = 45˚, dip = 85˚ and rake = −175˚ and it is in agreement with these from the study [13].

On August 7, 2013 (09:06, UTC) a moderate earthquake, Mw = 5.4 occurred in central Kallidromon Mountain, in the Pthiotis region of central Greece. The event was manually located at 38.7012˚ N, 22.6950˚E, and the depth calculated at 8 km, using recordings of the HUS Network. Four minutes before at 09:02, (UTC) a foreshock of M_w = 4.3 has occurred. For the next three months, eleven aftershocks with M_L = 4.0 happened in the same area with the largest of these on September 16, 2013 (15:01, UTC) with M_w = 5.3. For the same time interval, 2270 aftershocks (1 < M_L < 5.2) were recorded and relocated [22]. The moment tensor solutions for events with magnitudes, M_w ≥ 3.7, were calculated and presented in the following table (Table 8).

Regional waveforms at epicentral distances less than 3˚ were used to determine the source parameters of the main event as well as all the aftershocks.

The inversion indicated the activation of a normal fault for all the studied events with a variation of the dip value between 30˚ and 40˚ and a focal depth varied between 8 - 13 km. For the first event (August, 7 2013 - 09:06 UTC) the regional data from 8 stations with good azimuthally coverage was used. The source parameters as they calculated applying the moment tensor inversion method found: strike = 270˚, dip = 45˚, rake = -80˚ the seismic moment M₀ = 1.2 × 10²⁴ dyn·cm for a depth of 12 km. The calculated double couple was found equal to 96%, while the compensated linear vector dipole (CLVD) to 4%. The results of the applied procedure are presented in Figure 13.

To apply the HC-plot method, the followed 5 hypocenter manually locations (Table 9) were considered (Figure 14).

The previous solutions were considered: HRV, INGV, GFZ, AUTH and NOA. All these solutions are characterized by similar strike-dip-rake angles, with one nodal plane, strike~265˚, dip~50˚, plotted in green and hereafter referred to as the “green” plane and the other one dipping, strike~75˚, dip~50˚, as the “red” plane.

On January 26, 2014 (13:55, UTC) two strong earthquakes of magnitude M_w = 6.1 and M_w = 5.2 (18:45, UTC) occurred on the island of Kefallinia, Ionia Sea. These events inducing extensive structural damages, mainly in the western and central parts. Eight days later on February 3, 2014 (03:08, UTC) a second strong event with a magnitude similar to the first (M_w = 6.0) happened at the north section of Lixouri town. These two earthquakes (M_w = 6.1 and M_w = 6.0) occurred in the same island as the destructive events of 1953. Between August 9^th and 12th of 1953, three earthquakes of magnitude 6.4, 6.8 and 7.2 took place in Cephalonia leading to hundreds of casualties and strong damages all over the island, but also in Zante and Ithaca.

These events were followed by a serious number of aftershocks. We noted that

two months after the main event was recorded and analyzed more than 4000 events. The three large earthquakes, as well as all the aftershocks were relocated [1] [22] [23]. The source parameters for the strongest of these earthquakes (M_w ≥ 4.0) were calculated, using the moment tensor inversion and presented in Table 10.

Follow, we will present the focal mechanism for January 26, 2013 (13:55, UTC) earthquake, M_w = 6.1 (Figure 15). The data of 6 stations at regional data in epicentral distances less than 370 km were used and inverted, as it appeared in Figure 10. The inversion indicated the activation of a strike-slip faulting with source parameters strike = 23˚, dip = 68˚, rake = 175˚ the depth calculated at 13 km and the moment magnitude M₀ = 1.51 × 10²⁵ dyn∙cm. The fit between observed and synthetic waveforms and the misfit/CLVD versus depth diagram presented in Figure 15.

Six hypocenters manually locations were considered from NOA, HARV, GFZ, INGV, UOA and AUTH (Table 11).

The following CMT solutions were considered: HRV, GFZ, INGV, AUTH, UOA and NOA (Figure 16). All these solutions are characterized by similar strike-dip-rake angles, with one nodal plane, strike~20˚, dip~70˚, plotted in green and hereafter referred to as the “green” plane and the other one, with strike~130˚, dip~80˚, as the “red” plane.

The distance of the hypocenter from this plane is 3.46 km, while the distance from the other plane is 3.87 km. The distance between Hypocenter and Centroid is 8.05 km (Figure 17). A preliminary result, about the activation of the main fault, is this with source parameters: strike = 23˚, dip = 68˚ and rake = 175˚. As it appears in Figure 16 the distance between the plane and the Hypocenter-Centroid is similar.