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Çukurören-Çobanlar (Afyon) arasındaki deprem kaynaklarının (aktif fayların) belirlenmesi

Koçyiğit, Ali
Deveci, Şule
The Şuhut graben is an about 8-11 km wide, 24 km long, N-S-trending and actively growing extensional neotectonic structure located on the southern shoulder of the major AkşehirAfyon graben near the apex of outer Isparta Angle. The Şuhut graben developed on a pre-Upper Pliocene basement rock assemblage composed mostly of pre-Jurassic metamorphic rocks and Jurassic–Lower Cretaceous platform carbonates overlain with an angular unconformity by the Afyon strato-volcanic complex to its fluvio-lacustrine sedimentary cover of late Early-Miocene-Middle Pliocene age. Particularly, eastern margin of the Şuhut graben is dominated by the Afyon volcanics and their well-bedded fluvio-lacustrine sedimentary cover deformed by folding. This is strongly evidenced by a series of anticlines and synclines with the NNE-SSW-trending axes developed in this sequence. The stereographic plots of poles to bedding on the lower Schmidt hemisphere net reveal that this volcanosedimentary sequence have been deformed by a phase of compression (the latest phase of paleotectonic period) operated in an approximately WNW-ESE (N76°W) direction. This older and deformed (folded) volcano-sedimentary sequence is overlain with an angular unconformity by the nearly flat-lying modern graben infill of Plio-Quaternary age. Paleostress analyses of slip-plane data recorded in the lowermost unit of the modern graben infill and on the margin-boundary active faults indicate that the Şuhut graben continues to develop under the control of an extension operating in ENE-WSW direction since the latest Pliocene. Therefore, commencement age of the extensional neotectonic period, throughout Isparta Angle and particularly in the Şuhut area, is Latest Pliocene, even if, it has been previously reported that Isparta Angle has been experiencing a compressional neotectonic regime since Middle Miocene. All margins of the Şuhut graben are determined and controlled by a series of oblique-slip normal fault sets and isolated faults. Major and more active ones having a capacity of creating destructive earthquakes with magnitude of Mw = 6.3 and Mw = 6.5 are the Ağzıkara, Güneytepe, Çobankaya and the Yarışlı faults. This was previously proved by the occurrence of two devastative historical earthquakes, the 1766 and 1862.11.14 seismic events with intensity of VII-X. However, the Yarışlı fault still retains its nature of seismic gap. In addition, the finer-grained modern graben infill has also a high capacity of liquefaction. Therefore, these active faults and the finer-grained alluvial sediments have to be into account in both the earthquake risk analysis and design of city planning of the Şuhut County.