ALBERT

Description: The occurrence and the style of volcanic eruptions are largely controlled by the ways in which magma is stored and transported from the mantle to the surface through the crust. Nevertheless, our understanding of the deep roots of volcano-magmatic systems remains very limited. Here, we use the sources of seismovolcanic tremor to delineate the active part of the magmatic system beneath the Klyuchevskoy Volcanic Group in Kamchatka, Russia. The tremor sources are distributed in a wide spatial region over the whole range of crustal depths connecting different volcanoes of the group. The tremor activity is characterized by rapid vertical and lateral migrations explained by fast pressure transients and dynamic permeability. Our results support the conceptual model of extended and highly dynamic trans-crustal magmatic systems.

Description: The magma plumbing system of Merapi volcano is a key for understanding its eruptive activity and thus has received scientific interest for a considerable time. First detailed attempts to resolve the volcano’s internal structure and alleged magma reservoir were carried out at the beginning of the 1990s and included measurements of electrical conductivity, material density, seismic velocities as well as geodetic parameters and surface deformations. Major questions addressed were: (1) where do the fluids and magmas come from; (2) what are the magma ascent paths; (3) where are fluids and partial melts stored; and (4) what is the size and geometry of the magma and fluid reservoirs and the volcanic conduit? Here we review experiments and findings we made during various stages of investigation at Merapi volcano, and also discuss selected projects by other teams and projects. By using seismic methods different crustal zones could be identified with low-velocity values and high Vp/Vs ratios, which can be explained as fluid- and melt-hosting zones. Large-scale joint seismic experiments (MERAPI, MERAMEX and DOMERAPI) displayed seismic attenuation and scattering effects seen in the shallow portion of the edifice, revealed the presence of fluid percolation and subvertical fluid-magma transfer zones, and identified crustal and near-Moho magma reservoirs that are being off-centred to the north. The complementary results of these projects contributed to a new structural image and understanding of the deep structure of Merapi over a depth range of more than 100 km. These results are valid not only for Merapi but now serve as an important example of the crustal structure considered for subduction volcanoes elsewhere

Description: Subduction of the Neotethys Ocean resulted in collisions of continental plates, with formation of Cenozoic orogens. The different shapes and structures of various segments of these young orogens, such the Zagros Collisional Zone, suppose a complex interplay of shallow and deep structures, producing different degrees and styles of deformation. As part of the PRIN 2017 project, we analyze several types of recently acquired data (e.g., seismic tomography models of the crust and upper mantle, Moho depth, seismicity distribution, and surface topography). We find that the NW and central Zagros is characterized by a zone of thickened crust of variable width and overlain by topography that exhibits large height variations over small distances, in the central part of the collisional zone. These variations are accompanied by sharp lateral changes in the number of seismic events and velocities/temperatures at depths of ~100 km. We attribute these observations to relamination processes (i.e., the detachment of Arabian crust from the subducting lithospheric mantle and its underthrusting beneath the crust of the overriding plate), which are controlled by the variable geometry and stiffness of the overriding and subducting plates. This hypothesis is tested by performing a series of numerical experiments, using the numerical code I2VIS [1], that simulates relamination processes, occurring during continental collision. The consistency of the results is also verified through forward models of the static gravity field of the modelled structures, which are compared with the present-day observed gravity. References [1] Gerya, T.V., 2019. Cambridge University Press. ISBN 978-0-521-88754-0.