The 6 september 2009 mw5.4 earthquake in Eastern Albania – FYROM border: focal mechanisms, slip model, shakemap

6 Eylül 2009 tarihinde (Greenwich saati 21:49) orta büyüklükteki (Mw5.4) bir deprem silsilesi, doğu Arnavutluk ile Makedonya’nın sınırlarını vurmuştur. Depremin ana şoku 30 Kasım 1967’de meydana gelen ve civar yerleşimlerde can ve mal kaybına neden olan Dibra (Debar) depremi (Mw6.2) episantırının yaklaşık 6 km kuzeyinde yer almaktadır. Odak çözümlerini hesaplamak ve kayma modelini elde ederek ana şok sarsıntı haritasını hazırlayabilmek için, komşu ağlardan gerçek zaman dalga formlarını alan Birleşik Helenik Sismik Ağı’nın (Hellenic Unifi ed Seismic Network) geniş band dalga formları kullanılmıştır. Zaman baskın ters moment tensör çözümleri ile elde edilen 18 kuvvetli olay dizisine ait odak mekanizmaları, deformasyonun Arnavutluk orojeni içerisinde yaklaşık D−B açılma ile uyumlu olan KKD− GGB yönlü normal faylar tarafından karşılandığını göstermektedir. Bu çalışma 2009 depremine ait ana şokun ~194°D doğrultulu ve ~45° batıya eğimli, kabaca 9 kilometrelik bir normal fayın 6 km derinlikte kırılması ile meydana geldiğini göstermektedir. Ana şoktaki kayma ~9 km × 6 km bir parça ile sınırlanmakta ve ortalama kayma 5 cm ve maksimum kayma 18 cm olmuştur. Yakın alandaki yer sarsıntısı dağılımını simule etmek için kayma modeli, ileri modelleme şeması ile birleştirilmiştir. Maksimum Yer İvmesi dağılımı temel alınarak oluşturulan Sarsıntı Haritası; Arnavutluk’un Dibra ve Bulqiza bölgelerindeki meso-sismik alanın makrosismik gözlemler ile uyumlu olduğunu ortaya koymuştur. 1967 Dibra depreminin sismojenik bölgesi ile 2009 silsilesinin meydana geldiği, kabaca KKD−GGB doğrultusundaki ve doğu Arnavutluk’un aktif sismotektonik zonu olan bu yapı, yakın yerleşim alanları için bir tehlike teşkil etmektedir

6 eylül 2009 mw5.4 Doğu Arnavutluk − Makedonya sınırı depremi: odak mekanizmaları, kayma modeli, sarsıntı haritası

On 6 September 2009 (GMT 21:49) a moderate Mw5.4 earthquake sequence burst at the eastern border of Albania with the Former Yugoslav Republic of Macedonia (FYROM). Th e main shock was located ~6 km north of the epicentre of the 30 November 1967 Mw6.2 Dibra (or Debar) earthquake, which caused loss of life and considerable damage to buildings. We use broad band waveforms recorded by the Hellenic Unifi ed Seismic Network (HUSN), which receives real-time waveforms from the neighbouring networks, to compute focal mechanisms, obtain the slip model and derive the ShakeMap of the mainshock. Th e focal mechanisms of 18 of the stronger events of the sequence, obtained through time-domain moment tensor inversion, indicate that deformation is taken up by NNE−SSW-trending normal faults, in agreement with the ~E−W extension previously identifi ed within the Albanian orogen. Our results show that the 2009 main shock ruptured a roughly 9 km normal fault at a depth of 6 km, which strikes at 194° and dips west at ~45°. Th e slip of the main shock was confi ned to a single patch of ~9 km × 6 km, the average slip was 5 cm and the peak slip was 18 cm. Th e slip model was incorporated in a forward modelling scheme to simulate the ground motion distribution in the near fi eld. Th e ShakeMap thus obtained, based on the distribution of Peak Ground Velocity at phantom stations, outlines the mesoseismal area within the Dibra and Bulqiza districts in Albania, in accordance with macroseismic observations. Th e region aff ected by the 2009 sequence, together with the seismogenic region of the 1967 Dibra event, form a roughly NNE−SSW-trending structure which is an active seismotectonic zone in eastern Albania constituting a threat for nearby urban areas.

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