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STRESS INVERSION FROM FOCAL MECHANISM OF MODERATE EARTHQUAKES IN ALBANIA

Edmond Dushi

Abstract

The present study seeks to relate the focal mechanisms of moderate earthquakes, regional tectonics and the tectonic stress distribution, in Albania. We have analyzed 33 moderate earthquakes (2.2 ? MW ? 4.9) recorded in the time period 2013-2015, by the Albanian broadband (BB) seismic network. Events were located within the upper crust, in the depth range 0 ? h ? 17 km, showing the present day active tectonics. Formal stress inversion of the focal mechanism data, support the variation in the direction of the actual stress field as well as of the stress index R?, between the outer and the inner tectonic domains in Albanian, respectively under a compressional and extensional tectonic regime. Both domains are connected through Vlora-Lushnja-Elbasani-Dibra (VLED) transversal source zone, characterized by normal faulting with a strong strike-slip component. Orientation of the stress axes, ?1, ?2 and ?3, vary according to the respective zones. Thus, along the Adriatic coastal region, stresses have the orientation ?1(2?/66?), ?2(20?/335?) and ?3(70?/162?) showing a compressional stress regime (R = 0.15) directed E-NE (N65?E), while in the Ionian region it changes to ?1(31?/260?), ?2(17?/159?) and ?3(53?/45?), showing a compressional stress regime (R = 0.5) directed to EW (N94?S); In the inner domain of an extensional regime (R = 0.98), stress axis results oriented ?1(55?/116?), ?2(2?/24?), ?3(34?/292?), having a NE (N22?E) direction; Along the transversal zone (VLED), of oblique displacements (R= 0.49), results support the orientation ?1(20?/1?), ?2(67?/152?), and ?3 (10?/267?), where the horizontal stresses are directed almost southward (N178?E). Focal mechanism solutions and horizontal stresses SHmax and SHmin, inferred from the formal stress inversion of focal mechanism data, show a good agreement with previous studies and support the continental collision mechanism between Adria microplate and Albanian orogen.

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DOI resolver: doi.org/10.5593/sgem2018/1.1/s05.123

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