GEOSCIENCES 2008

Fault-generated landforms in the eastern part of Simitli graben (SW ): a tectonic geomorphology approach Ðàçëîìíî ñâúðçàí ðåëåô â èçòî÷íàòà ÷àñò íà Ñèìèòëèéñêèÿ ãðàáåí (ÞÇ Áúëãàðèÿ): îïèò çà àíàëèç íà òåêòîíñêàòà ãåîìîðôîëîãèÿ Ianko Gerdjikov1, Svetoslav Dimitrov2 ßíêî Ãåðäæèêîâ1, Ñâåòîñëàâ Äèìèòðîâ2

1 University, Dept. of Geology and Paleontology; E-mail: [email protected] 2 ESRI Bulgaria

Key words: Simitli graben, tectonic geomorphology, fault zones.

Simitli graben is being intensively studied during the in accordance with the published data about the last years, but dispite this there are no tectonic geo- active Krupnik fault. In this area we were able to morphological researches for this seismically active differentiate another fault zone, situated SE of the area. Our approach uses quantitative data and met- trace of the Krupnik fault which also could be char- rics extracted from digital elevation models, analysis acterised as youthful or even active structure. This of sub-meter resolution satellite imagery (Digital- tectonic zone is traced from N 41.8391 E 23.21669 Globe data at Google Earth), as well as field surveys. to N 41.899727 E 23.236047. It was informally named The purpose of our study is to assess how the relief “zone of Topographic front 2” (ZTF2) and approx- in the eastern part of Simitli graben was influenced imately coincides with the southern part of Osen- by the reported active faults and also to check gra- ovski fault of Zagorcev (1975). Significantly, the high- ben bounding faults (e.g. Zagorcev, 1975; Dobrev, est values of IAT index have been calculated for the 2005; Tranos, 2008). basins that are crosscut or situated next to these faults. We processed two sets of digital elevation models The ZTF2 fault has an overall strike of 25° and an (DEMs) with resolution of 15 m and 30 m. They were average dip of about 45° NW. Despite the deeply created after digitalization of 50 000 and 25 000 scale incised valleys and steep slopes the fault slip sur- topographic maps. Twenty three drainage basins were face was observed just in a single spot (N 41.84507; delineated using the ArcGIS Spatial analyst tools. E 23.2209). The surface itself is polished, but it lacks They cover the traces of reported active faults — Krup- striations and tool tracks. The hanging wall is se- nik, and Elovitsa (Ganas et al., 2005). Mor- verely deformed, hydrothermally altered and it is cut phometric analysis included calculation of region- by deeply incised gulleys. ZTF2 is a nice example of al geomorphic indices using the two DEMs and the tectonic inheritance because the fault is exploiting delineated watersheds. The calculated geomorphic the pronounced anisotropy related to the solid-state indices are the Stream Length — Gradient Index (“SL fabric within the granitoids of North pluton. Index”), hypsometric integral, basin elongation, ba- Despite the lack of kinamatic data, geomorphology sin assimetry, basin shape, ratio of valley floor width of the area is unambiguously indicating that ZTF2 to valley height. We also used recently introduced is a normal fault. IAT index (Hamdouni et al., 2008) to categorise stud- Our research is also focused on the faults within ied watersheds to four classes of relative tectonic the basin of Gradevo river. There are opposite views activity. All basins are characterized with values of on the position, geometry and kinematics of SW-NE the ratio of valley floor width to valley height index trending fault/s usually named Gradevo fault and hypsometric integral that are indicative of deep (Zagorcev, 1975; Dobrev, 2005; Ganas et al., 2005; valley incisement and young relief. Local peaks in Tranos et al., 2008).The reason to focus on this area SL indices are observed in all of the basins. They are is also a “weak signal” we received from the analysis common in the uppermost reaches of the streams of metrics and the landscape. Except probably some (Keler and Pinter, 2002) but anomalously high SL local deviations, geomorphic indices point to low to indices are also found where rivers cross some prom- moderate tectonic activity that can well be explained inent fault zones. The analysis of derived metrics is with regional uplift during Quaternary.

95 We also put all the old map data in GIS and formed and the width of the damage zone is reach- checked the DEM of the area and its derivatives ing tens of meters. In exposures around the village of (shaded relief, slope map, etc.) for possible linea- Dolno Osenovo a principal movement zone is well- ments. Detected features were delineated and export- defined by up to 2 m thick grey matrix-supported ed to KML file format and further explored with breccia and ultracataclasite/gauge layer. These tec- Google Earth. tonites display consistent dip to the west and rarely This procedure allowed us to pin down the plac- observed Riedel shears in the gauge indicate westward es where there was strong possibility to find fault- shear. Despite the local control on the geometry of the related rocks. The coordinates of these places were Miocene-Quaternary cover the described extensional transferred to hand-held GPS receiver and checked zone is inactive — in the village of Dolno Osenovo the during the field work. Despite our efforts, we were associated tectonites are displaced by late strike-slip unable to confirm the existence of Gradevo fault in fault. Nevertheless high SL indices as well as knick the vicinities of the village of Gradevo. But further points, aligned saddles are indicating pronounced geo- to the NE we found major and yet not described morphological expression of this fault zone. fault zone which was traced for several kilometers (N 41.9248 E 23.22408 — N 41.96004 E 23.24117). Acknowledgements: The study is supported by The zone is built by tectonic breccia, ultracatacla- the grant 209/2008 by the scientific fund of Sofia sites and a gauge layer. Its footwall is severely de- University.

References Dobrev, N. 2005. Registered movements of active faults lomb stress triggering of the 1904 earhtquake se- in SW Bulgaria. — Rev. Bulg. Geol. Soc., 66, 1—3, 115— quence. — Journ. Geodynamics, 40, 316—333. 124 (in Bulgarian). Keller, E. A., N. Pinter. 2002. Active Tectonics: Earthquakes, El Hamdouni, R., C. Irigaray, T. Fernández, J. Chacón, Uplift and Landscape. New Jersey Prentice Hall. E. A. Keller. 2008. Assessment of relative active Tranos, M. D., V. N. Kachev, D. M. Mountrakis. 2008. tectonics, southwest border of the Sierra Nevada Transtensional origin of the NE-SW Simitli basin (Southern Spain). — Geomorphology, 96, 1—2, alont the Strouma (Strymon) Lineament, SW Bul- 150—173. garia. — Journ. Geol. Soc. London, 165, 499—510. Ganas, A., S. Shanov, G. Drakatos, N. Dobrev, S. Sbo- Zagorchev, I. 1975. On the Fault Bundle and ras, Ch. Tsimi, G. Franov, S. Palvides. 2005. Active the Fault-Block structure of the Vlahina block. — fault segmentation in southwest Bulgaria and Cou- Geotect., Tectonophys. and Geodyn., 3, 3—16.

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