ALBERT

Beschreibung: A large consortium of European and North American institutions—28 in all—recently completed a huge active source seismic experiment focused on Central Europe. This experiment is called Central European Lithospheric Experiment Based on Refraction, or CELEBRATION 2000. It targeted the structure and evolution of the complex collage of major tectonic features in the Trans-European suture zone (TESZ) region, as well as the southwestern portion of the East European craton (southern Baltica), the Carpathian Mountains, the Pannonian basin, and the Bohemian massif (Figure 1). The TESZ region (Caledonides-Tornquist Teisseyre zone area, Figure 1) can be thought of as a broad zone of deformation that extends across Europe from the British Isles to the Black Sea region.

Beschreibung: True amplitude processing of the Urals Seismic Experiment and Integrated Studies (URSEIS) vibroseis deep reflection seismic data acquired by the URSEIS consortium shows the southern Uralide crust to be composed of four major blocks with distinctive reflection characteristics. These blocks are juxtaposed along crustal-scale boundaries. The foreland thrust and fold belt, developed from the East European craton crust, is imaged as subhorizontal to east dipping reflectivity that can be related to its Paleozoic and older tectonic history. The Moho beneath the foreland thrust and fold belt is not imaged in the vibroseis data set. The Main Uralian fault (the major arc-continent suture) is unreflective, but its subsurface location can be inferred by the truncation of the reflection pattern of the East European craton and its contrast with that of the Magnitogorsk arc. The Magnitogorsk arc reflectivity is characterized by patchy, noncoherent to coherent reflections in the upper ∼10 – 15 km that are interpreted to be related to the arc volcanic rocks. Below this, reflectivity is diffuse, or the arc crust is transparent, and the Moho is not imaged. The East Magnitogorsk fault zone, which juxtaposes the arc against the East Uralian zone, is not imaged by the data. The upper 5 to 6 km of the East Uralian zone, corresponding to the Dzhabyk granite, is transparent. Below the granite the crust is characterised by east dipping patches of moderately coherent, high-amplitude reflections that in the east become shallowly west-dipping. A ∼10 km thick, west dipping band of coherent, high amplitude reflections between 12 and 35 km depth, corresponding to the Kartaly Reflection Sequence, extends beneath almost the entire East Uralian zone. The crust beneath the easternmost East Uralian zone reaches 53 km in thickness. The upper and middle crust of the Trans-Uralian zone is characterized by a series of east and west dipping, concave upward, moderately coherent, high-amplitude reflections. The lowermost middle and lower crust displays thin bands of west dipping, coherent, low-amplitude reflectivity. The Moho is imaged as a sharp transition from reflective lower crust to transparent upper mantle at ∼49 km depth, and the lower crustal reflections appear to merge with it. The URSEIS vibroseis data are integrated with results from the explosion source reflection data, the wide-angle reflection data, and the surface geology to place constraints on the crustal architecture of the orogen and on the timing of its assemblage.

Beschreibung:  — Observations based on relatively limited data recorded by sparsely distributed stations have indicated that regional seismic phase propagation (Lg and Sn) is very complex in the Middle East. Accurate characterization of regional seismic wave propagation in this region necessitates the use of a large number of seismic stations. We have compiled a large data set of regional and local seismograms recorded in the Middle East. This data set comprises approximately four years of data from national short-period networks in Turkey and Syria, data from temporary broadband arrays in Saudi Arabia and the Caspian Sea region, and data from GSN, MEDNET, and GEOFON stations in the Middle East. We have used this data set to decipher the character and pattern of regional seismic wave propagation. We have mapped zones of blockage as well as inefficient and efficient propagation for Lg, Pg, and Sn throughout the Middle East. Two tomographic techniques have been developed in order to objectively determine regions of lithospheric attenuation in the Middle East.¶We observe evidence of major increase in Lg attenuation, relative to Pg, across the Bitlis suture and the Zagros fold and thrust belt, corresponding to the boundary between the Arabian and Eurasian plates. We also observe a zone of inefficient Sn propagation along the Dead Sea fault system which coincides with low Pn velocities along most of the Dead Sea fault system and with previous observations of poor Sn propagation in western Jordan. Our observations indicate that in the northern portion of the Arabian plate (south of the Bitlis suture) there is also a zone of inefficient Sn propagation that would not have been predicted from prior measurements of relatively low Pn velocities. Mapped high attenuation of Sn correlates well with regions of Cenozoic and Holocene basaltic volcanism. These regions of uppermost mantle shear-wave attenuation most probably have anomously hot and possibly thin lithosphere.

Beschreibung: In this thesis the subduction zone of the Central Andes is studied. The Andes have formed in a complex interplay of subduction related and tectonic processes. The Central Andes with the associated Altiplano-Puna high plateau constitute the second largest continental land-mass on earth, rivaled only by the Tibetan highland. Whereas in the case of the Himalayas , where two buoyant continental plates collide, crustal thickening and uplift is quite intuitive, processes leading to formation of a plateau above a subduction zone are puzzling.