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6 Tectonic geomorphology
In order to correlate the current formed relief and the morphogenetic procedures in the wider Penteli region with the tectonic impact of the Dionysos fault zone and it’s westward or eastward prolongation , we focused on the analysis of the morphological slopes and the drainage network. For this purpose a wider area taken into consideration, thus a morphotectonic map for the area was extracted. Further, we studied the landscape evolution by morphometry, which is the quantative measurement of lanscape shape lengthwise of Dionysos fault that resulted valuable conclusions. The study of Geomorphic indices such as the mountain front sinuosity (Smf), facet slope-to- height ratio, percentage faceting (Lf/Ls) and assymetry factor (Af) are useful tools for active tectonics because they provide rapid insights into specific areas (here lengthwise of the Dionysos fault) in the study area that are adjusting to relatively rapid rates of active tectonic deformation ( Keller. 1986).
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Figure 6.1 Topographic map of the wider Penteli area.(GGRS87)
The morphological analysis that compiled through the slope value distribution are presented in the Slope Distribution Map (Fig. 6.2) , where the slope values have been subdivided into specific classes that mainly highlight the main tectonic structure of the study area. These are:
I. Areas of 0-5%, II. Areas of 5-15%, III. Areas of 15-25%,
IV. Areas of 25-35%, V. Areas more than 35%.
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Figure 6.2 Slope distribution map % of the study area (GGRS87). The slope values distinguished into 5 categories (see legend) in order to illustrate the clear zones where we have an abrupt change of slope.
The map is presented in Appendix II.
This classification of the slope values clearly illustrates the zones where we have an abrupt change of the slope which generally leed to the regognition of the tectonic structures (faults). The areas with slope more than 25% cover the 27% ( Fig. 6.3) of the overall study area which reflect abrupt zones that maybe are controlled by faults. Our first remark is that Dionysos fault has a clear geomorphic expression in a zone trending NW-SE, noting that there are anomalies in the extension of the Dionysos fault both in the west and in the east. The highest percentage is concentrated between 0-5% and 5-15% which are related to gentle relief (mainly 0-5%:31, 80%) and include the coastal area from Rafina-south to Agios Padeleimonas & Vranas-north, the Dionysos small basin, a part of the Kifissos basin at the west of the study area, and a part of the Mesogaia basin in the southern slopes of Penteli mt. Those gentle reliefed areas are directly related to their geological background. Thus, the easily erodible formations of postalpine sediments that are located in the areas that we have highlighted appear gentle slopes. Furthermore, we note some
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other abrupt zones that trend N/S, NE/SW and E-W which are in accordance with offshore trending faults in the southern Evoikos gulf (Fig. 3.14).
Figure 6.3 Graphical representation of the slope values distribution.
Those zones (morphotectonic features) that came from the slope map interpretation are expressed through sloap values from 25% and might represent low angle normal faults or high angle normal faults, such as Dionysos fault. A further representation of the slope distribution aiming to explore specific details lengthwise of the Dionysos fault were performed. The majority of the slope values correspond to gentle topographic relief (Fig. 6.4, 6.5) specifically 0-5° and 5°-15° while a rate of about 5% corresponds to slope values more than 25°. It is worth to observe that those slope values are developing mainly in the center part of the Dionysos fault where we have the maximum uplift and the maximum slip/rates.Furthermore, from the field observations the presence of triangular facets, that will be analyzed in a next paragraph, is recorded. Comparing the northern and the southern slopes of the Penteli mountain, we can have a clear picture of the differences on the tectonic force.
0.00%
10.00%
20.00%
30.00%
40.00%
0-5% 5-15% 15-25% 25-35% 35-100%
31.80%
25.80%
15.26%
12.76% 13.88%
Classified Slope Values %
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Figure 6.4 Slope distribution map (degrees) of the study area (GGRS87). The slope values distinguished into 5 categories (see legend) in order to illustrate the clear zones where we have an abrupt change of slope. The map is presented in Appendix II.
Figure 6.5 Graphical representation of the slope values distribution (degrees).
Aspect maps come from raster surfaced and predict the dowhslope direction of the maximum rate of change in orientation value from each cell to it’s neighbour. For the classification is used the trigonometrical circle and
0%
10%
20%
30%
40%
50%
0-5º 5 - 15º 15-25º 25-30º 30-47º 44.87%
29.95%
19.65%
3.80% 1.72%
Classified Slope Values (°)
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measured clockwise from 0° until reaching 359° representing the direction of the slope faces.
Figure 6.6 Aspect map of the study area (GGRS87), showing the downslope direction of the slopes. The different drainage basins are denoted with black dashed lines. The map is also presented in Appendix II.
In the (Fig. 6.6) NW part of the study area the Kifissos drainage pattern is present which is characterized by elongated slopes of S-SE and W-NW direction of the NE-SW main trending stream (Kifissos). The only area in the Kifissos drainage basin that disturbs this smooth impression is located at Dionysos basin where the impact of the Dionysos fault is imprinted. We note E-NE and N slopes direction of N-S trending streams that are clearly controlled by the Dionysos fault. By examining the neighboring drainage basin (central area) we note a local distribution that is resulted from changes in local geology conditions. Thus, we note a better development on the drainage network that is characterized by slopes of E-SE and N-NW direction of the N-S trending streams. On the other hand, in the southern Penteli Mt. the majority of slopes trend S-SE and W-NW of the NE-SW trending streams. This monotony changes to the southeast where elongated streams trending NW-SE with slopes in an E
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and S direction abruptly turn to the east. This change probably caused by the presence of a tectonic structure.
Figure 6.7 Graphical representation of the azimuth orientation of the slopes in the study area.
The data from the interpretation of the Slope distribution Map and the Aspect Map are presentesd in the Morphotectonic map in the next paragraph.