HR: 1340h
AN: T53B-0479    [Abstracts]
TI: Seismotectonics of the Caucasus and surrounding regions: source parameters and rupture histories of the recent destructive earthquakes
AU: * Tan, O
EM: tano@itu.edu.tr
AF: Istanbul Technical University Faculty of Mines Department of Geophysics, Ayazaga Campus, Maslak, Istanbul, 34390 Turkey
AU: Taymaz, T
EM: taymaz@itu.edu.tr
AF: Istanbul Technical University Faculty of Mines Department of Geophysics, Ayazaga Campus, Maslak, Istanbul, 34390 Turkey
AB: The complexity of plate interactions and associated crustal deformation in the eastern Mediterranean region is marked by the occurence of many destructive earthquakes throughout the recorded history. The wide range of deformational processes occuring in this region means that eastern Mediterranean provides a unique opportunity to improve our understanding of the complex kinematics of continental collision, including strike-slip faulting and crustal extension, as well as associated seismicity and volcanism. This presentation is concerned with the seismotectonics of Caucasus and surrounding regions that are prominent features in the collision zone between the African and Eurasian plates, and provides us with a complex pattern of continental deformation of the region. We have studied the tectonic characteristics of a comprehensive seismicity occurred in the region during the last 20 years, based on newly retrieved and obtained source mechanisms and rupture histories of $\sim$40 earthquakes, Mw$>$5.3, by using waveform inversion of teleseismic long-period P-, SH-, and broad-band P-waveforms recorded in the distance range of 30-90$\deg$. They all exhibit the characteristics and structural complexities associated with strike-slip, thrust and normal faulting as a result of ongoing crustal deformation. Earthquakes in the greater Caucasus mainly exhibit NW-SE thrust faulting mechanisms in general. The western part of the mountain belt has only one moderate size event and verifies that northward dipping shallow thrust fault is active beneath the southern border of the western greater Caucasus. In contrary, the Racha earthquake, and its four moderate size aftershocks, and earthquake of Barisakho indicate that most of the stress accumulation occurs within the central part of the Caucasus mountain belt. A series of earthquakes shows that northern boundary thrust faults of the eastern greater Caucasus dips southwards with a very shallow angle ($\sim$5-10$\deg$). Furthermore, the Lesser Caucasus is not capable of generating destructive earthquakes as the Greater Caucasus. However, Spitak earthquake indicates that right-lateral motion with thrust component active on the Pampak-Sevan Fault (PSF). In contrast to the field observations, preliminary reported parameters, and slip distribution of the Spitak earthquake exhibits that the rupture is not too complex. Furthermore, the energy release and rupture propagation also agree well with the field observations and aftershock distributions reported. The existence and active seismicity of the North-East Anatolian Fault (NEAF), and the Borjomi-Kazbeg Fault (BKF) that divides the Greater Caucasus has significant implications on the present study. The main active faults strike to the southwest end of the NEAFZ in the direction of $\sim$N45$\deg$E. On the other hand, right-lateral strike-slip faulting mechanism has not been clearly observed beyond Georgia-Turkey-Armenia border. This is the northeast end of the right-lateral strike-slip of NEAF zone, and the major events strike approximately in the direction of N60$\deg$E. The difference in fault strike angles ($\sim$15$\deg$) and slip vector orientations ($\sim$20$\deg$) between the both ends of the NEAF indicates that is bounded by block rotations clockwise along the strike: SW to NE. There is no further seismological evidence for a left-lateral strike-slip faulting, except the northerly dipping thrust faulting of Racha sequences in the region to the north of the Greater Caucasus. Although the large earthquakes in the Caucasus generally have uniform slip distribution, there are earthquakes with complex rupture mechanisms along the southern Caspian to NW Iran region.
DE: 7230 Seismicity and seismotectonics
DE: 8107 Continental neotectonics
DE: 8123 Dynamics, seismotectonics
DE: 7203 Body wave propagation
DE: 7215 Earthquake parameters
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting