Aim-scope of work
Large scale kinematics of active tectonics in the Aegean sea
This transtensive shear zone (Fig. 2.2a, Fig. 2.3) crosses the older structures of the Hellenic thrust belt and connects them with the modern trench. The progress of upper plate deformation in the Aegean region is presented from Royden & Papanikolaou, 2011; from Miocene time to the present (Fig.2.3).
The role of low-angle detachment faults in Aegean back arc extension
Attica - Kifissos detachment fault
2004; presented the paleogeography of the Attica region during the recent geological periods (Fig. 3.2) after the compaction of the Alpine basement and the end of its intervening reformation. Since then, the format of the Athens plain has been similar to the current, with the exception of the Glacial Period of the Upper Pleistocene, which affected most of the Saronic Gulf which became land (Fig. 3.3), with Aegina and Salamina present islands that represented the continuation of Athens. Usual.
The role of the detachment fault in Northeastern Attica
These E-W trend faults, as already mentioned, are considered to be the most active faults in the entire region, next to the NW-SE trend faults that appear to be less active or inactive. The western part with unmetamorphosed rocks and E-W trend faults with high seismicity records, and the eastern part with metamorphic rocks and NW-SE trend faults with lower seismicity (Fig 3.6).
Seismicity in Attica
It is worth noting several features of active faults that have been identified and investigated in the Athens Metropolis area. From the above, it is clear that most reviewers have studied the tectonic structures that are geographically located west of the Kifissos detachment fault zone (Fig. especially in the intermediate zone by Papanikolaou & Lozios 1990; between the Megara and Oropos basins.
Study area
Methodology
Thus, we produced slope maps to highlight the main structure, the Dionysus fault zone, and other possible structures of the study area, in percentages (%) and degrees (º), ranging between 0°-47°. The classification and analysis of the Slope Map is presented in the Gemorphology chapter.
Geological regime of the study area
For the best illustration of the geological formations present in the study area, Dioysos NE Attica, the displayed data from field observations will be divided and presented in two parts with respect to the main tectonic. So, will be presented separately the geological formations, alpines or postalpines, which are located in the hanging wall and in the footwall of Dionysos fault zone. In the hanging wall of the Dionysos fault, as we have already mentioned, Dionysos town is located, and specifically in the foothills of the Dionysovouni hill at 650 m high (Fig. 5.4).
The lithological type of the Fyreza-Agios Georgios shales occurring in the area is similar to the system named from Lozios, 1993; ―Southern Pendeli shales‖ and are mainly represented by mica schists with well-developed cleavage (Fig. 5.8, 5.9). The dashed white lines represent the geological boundaries of the postalpine formations that extend in this area, view from the southeast. As in the hanging wall and the Dionysus fault, the alpine formations are marbles and slates.
According to the lithostratigraphic column that Lozios., 1993 built on the footwalls of the Dionysos fault, those alpine geological formations have local diversifications that led to their separation (Table 5.2 a). The postalpine sediments that crop out in the footwalls of the Dionysos fault are part of the Mesoge basin extending from the southern Pendel mountain. The third and last tectonic phase documented in Penteli is expressed by fractures and joints that are present in the study area and complement the tectonic setting.
The Dionysos Fault
Most of the fault slope is parallel to the 560 m elevation contours along the NW-SE direction. We could not distinguish striations at the base of the fault, nor striations resulting from the severely eroded fault surface. The lower escarpment is the main expression of the Dionysos fault and is a continuous escarpment with a length of 1 km.
The inclination of the fault plane was measured at an angle of about 55°-70° to the north, while vertical striations were observed in the iron crust (Fig. The end of the fault zone, which is covered by colluvial wedge scree (Fig. 5.36) We could not distinguish any striations on at the base of the lower scarp, a break in the white crust of calcite powder, which is common in scarp morphologies.
Another fault scarp was found in the hanging wall of the lower Dionysus fault plane, with the main difference between the other scarps. It should be emphasized that the slip is underestimated due to the existence of higher scarps, where it was not possible to make topographic profiles due to dense vegetation. In order to establish a correlation of the currently formed relief and morphogenetic processes in the wider Penteli region with the tectonic influence of the Dionysus Fault area and its extension towards the west or east, we focused on the analysis of morphological slopes and the drainage network.
Morphological slope analysis
The morphological analysis constructed through the distribution of the slope values is shown in the slope distribution map (Fig. 6.2), where the slope values are divided into specific classes that mainly highlight the main tectonic structure of the study area. This classification of the slope values clearly illustrates the zones where we have an abrupt change of the slope, which generally led to the recognition of the tectonic structures (faults). Further representation of the slope distribution was carried out, with the aim of investigating specific details in the length of the Dionysos Fault.
The majority of slope values correspond to slight topographic relief (fig. specifically 0-5° and 5°-15°, while a rate of about 5% corresponds to slope values of more than 25°. Comparison of the northern and southern slopes of Penteli mountain, we can get a clear picture of the differences of the tectonic force In (Fig. 6.6) NW part of the study area, Kifisso drainage pattern is present, which is characterized by elongated slopes in S-SE and W-NW direction. of the NE-SW main stream (Kifissos).
The only area in the Kifissos basin that disturbs this smooth impression is in the Dionysos basin, where the impact of the Dionysos fault is imprinted. We thus observe better development on the drainage network characterized by slopes in the E-SE and N-NW directions of the N-S trending flows. The data from the interpretation of the Slope Distribution Map and the Aspect Map are presented in the Morphotectonic Map in the next section.
Drainage pattern analysis
Drainage basin N.1 (Fig. 6.8) covers an area of 97 Km2 in the SE and drains the southern slopes of SE Penteli to the Evoikos Gulf in the east. Drainage basin N.2 (Fig. 6.8) covers an area of 45 Km2 in the central part of the study area, draining the central-northern slopes of Penteli to the north, where a third-order stream and a fourth-order stream join the Kimpitougios . current (fourth order current). Drainage basin N.3 (Fig. 6.8) covers an area of 65 Km2 in the south-western part of Penteli and drains the SW slopes to the SSW.
Drainage basin N.4 (Fig. 6.8) covers an area of 7 Km2 in the Petroti Hill, draining the slopes of Evoikos Bay. Quantitative analysis of the river profiles showed significant differences in convexity along the Dionysos fault. The data from the interpretation of the drainage pattern will be presented in the morphotectonic map in the next section.
The planning surfaces that develop in the study area are divided into two different types with angles between 0-5. The geometry and erosion of the river network is the result of the strong uplift caused by the Dionysos fault on Mount Pentel. In particular, deep shear zones are directly related to the tectonic regime of the region and mainly develop vertically on the Dionysos fault (Fig. 6.12).
Morphotectonic regime
The combination of erosion with active faulting can cause landslides or instability. During fieldwork east of Rea, a mica slide was identified (see geological map - Fig. It is worth noting that most of these features are presented for the first time and are not included in the geological map of I.G.M.E.
In the hanging wall of the Dionysus fault, the number of tectonic elements is greater than in the foothills. Two antithetical faults identified on the basis of morphotectonic interpretation bounding the small NW-SE trending Dionysus Basin to the north. These antithetical features are reinforced by the presence of a small Holocene basin that develops between them (Fig. 5.16.
The rest of the morphotectonic features vary in direction from east to north-south and NE-SW, which may correspond to active faults that appear to be consistent with the offshore faults of the southern Evoikos bay (Fig. 3.14). In conclusion, the local tilting of the tectonic blocks that emerged from the drainage disturbances is realized (Fig. 6.13.
Geomorphic indices
Also, geomorphic indices with their results can show the continuity or not of the Dionysos fault. We notice a more active part in the central and the western part of the Dionysos fault and a decrease of the tectonic potential towards the eastern part of the fault zone. The mountain front in the western part of the Dionysos fault is expressed geomorphologically as a trace of northern scarps that cut the northern slopes of the Penteli Mt.
Thus, these elements strengthen the possibility of the western continuation of the Dionysos fault in the Kifissos drainage basin. The worst-case scenario for Dionysus breaking would mean the entire 16 km of its length being torn off. The highest macroseismic intensities on a possible future rupture will be recorded on the hanging wall of the Dionysos fault (Fig. 7.3 – X intensities in red).
Four km west of Dionysos town, Drosia village will suffer greater damage (intensity IX) than Dionysos town due to the geological background (Holocene deposits). Especially deep incision zones are directly linked to the tectonic regime of the region and develop mostly vertically in the Dionysos fault. We notice a more active part in the central and the western part of the Dionysos fault and a decrease of the tectonic potential towards the eastern part of the fault zone.
The highest macroseismic intensities on a possible future rupture will be recorded in the hanging wall of the Dionysos fault. We see a more active part in the western and central sector of the Dionysos Fault and a decrease in tectonic potential in the east.
