Lithospheric structure and stress field orientations in the northern Libya and east-central Mediterranean region
This thesis is a combination of three studies including tomography using surface wave group velocities, stress orientations from focal mechanisms, and receiver functions. The study area covers northern Libya and the east central Mediterranean region. I utilized new data from the Libyan National Seismic Network to better understand the crustal thickness and stress orientation of northern Libya as well as the east central Mediterranean region. In the first study, I conducted surface wave group velocity tomography implementing the Gaussian beam method for obtaining 2-D velocity variations assuming an isotropic model. I constructed surface wave group velocity maps over a range of periods for both Love and Rayleigh waves on a 2.0° x 2.0° grid. The results resolved the main geological features in the central Mediterranean and northern Libya. Crustal thickness variation of the Libyan margins shows a gradient (South to North) interpreted as a change from continental to oceanic crust. A thinner crust was resolved in the central Mediterranean beneath the Ionian Sea and Abyssal Plan. The Hellenic subduction zone and the Calabrian Accretionary prism were imaged as zones with very low group velocities. In the second study, 10 new focal mechanism solutions are presented and a total of 26 focal mechanisms from local earthquakes in northern Libya were used in an inversion to determine the variation of principles stress of the northern Libya area. The results indicate that there are two different regional stress orientations. In Zone I (north central Libya) the maximum principal stress orientation (?1) has a strike 95° and plunge of 22°. The orientation of the greatest principal stress (?1) in Zone II (northeastern Libya, Cyrenaica region) has a strike of 327° and plunge of 13°. In Zone III (northwestern Libya), ?1 has a strike of 129° and plunge of 16°. These results show a rotation of the maximum principal stress orientation from southeast in northwestern Libya to northwest in eastern Libya. This confirms the existence of at least two different stress regimes in the area, which has been suggested by previous studies. In the third study, I analyzed waveforms from 66 teleseismic events (distances of 4000 km to 15700 km and magnitudes of 0.1 to 4.5) to compute receiver functions using a frequency - domain method that is based on the deconvolution of the vertical components. Unfortunately, due to the lack of well-recorded data I was not able to obtain viable receiver functions results. More data are required to adequately determining these receiver functions. ^
Agail, Abdusalam Ali, "Lithospheric structure and stress field orientations in the northern Libya and east-central Mediterranean region" (2015). ETD Collection for University of Texas, El Paso. AAI10000758.