TY - JOUR A1 - Lontsi, Agostiny Marrios A1 - Garcia-Jerez, Antonio A1 - Camilo Molina-Villegas, Juan A1 - Jose Sanchez-Sesma, Francisco A1 - Molkenthin, Christian A1 - Ohrnberger, Matthias A1 - Krüger, Frank A1 - Wang, Rongjiang A1 - Fah, Donat T1 - A generalized theory for full microtremor horizontal-to-vertical [H/V(z,f)] spectral ratio interpretation in offshore and onshore environments JF - Geophysical journal international N2 - Advances in the field of seismic interferometry have provided a basic theoretical interpretation to the full spectrum of the microtremor horizontal-to-vertical spectral ratio [H/V(f)]. The interpretation has been applied to ambient seismic noise data recorded both at the surface and at depth. The new algorithm, based on the diffuse wavefield assumption, has been used in inversion schemes to estimate seismic wave velocity profiles that are useful input information for engineering and exploration seismology both for earthquake hazard estimation and to characterize surficial sediments. However, until now, the developed algorithms are only suitable for on land environments with no offshore consideration. Here, the microtremor H/V(z, f) modelling is extended for applications to marine sedimentary environments for a 1-D layered medium. The layer propagator matrix formulation is used for the computation of the required Green’s functions. Therefore, in the presence of a water layer on top, the propagator matrix for the uppermost layer is defined to account for the properties of the water column. As an application example we analyse eight simple canonical layered earth models. Frequencies ranging from 0.2 to 50 Hz are considered as they cover a broad wavelength interval and aid in practice to investigate subsurface structures in the depth range from a few meters to a few hundreds of meters. Results show a marginal variation of 8 per cent at most for the fundamental frequency when a water layer is present. The water layer leads to variations in H/V peak amplitude of up to 50 per cent atop the solid layers. KW - Numerical modelling KW - Earthquake hazards KW - Seismic interferometry KW - Site effects KW - Theoretical seismology KW - Wave propagation Y1 - 2019 U6 - https://doi.org/10.1093/gji/ggz223 SN - 0956-540X SN - 1365-246X VL - 218 IS - 2 SP - 1276 EP - 1297 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Weidle, Christian A1 - Wiesenberg, Lars A1 - El-Sharkawy, Amr A1 - Krüger, Frank A1 - Scharf, Andreas A1 - Agard, Philippe A1 - Meier, Thomas T1 - A 3-D crustal shear wave velocity model and Moho map below the Semail Ophiolite, eastern Arabia JF - Geophysical journal international N2 - The Semail Ophiolite in eastern Arabia is the largest and best-exposed slice of oceanic lithosphere on land. Detailed knowledge of the tectonic evolution of the shallow crust, in particular during and after ophiolite obduction in Late Cretaceous times is contrasted by few constraints on physical and compositional properties of the middle and lower continental crust below the obducted units. The role of inherited, pre-obduction crustal architecture remains therefore unaccounted for in our understanding of crustal evolution and the present-day geology. Based on seismological data acquired during a 27-month campaign in northern Oman, Ambient Seismic Noise Tomography and Receiver Function analysis provide for the first time a 3-D radially anisotropic shear wave velocity (V-S) model and a consistent Moho map below the iconic Semail Ophiolite. The model highlights deep crustal boundaries that segment the eastern Arabian basement in two distinct units. The previously undescribed Western Jabal Akhdar Zone separates Arabian crust with typical continental properties and a thickness of similar to 40-45 km in the northwest from a compositionally different terrane in the southeast that is interpreted as a terrane accreted during the Pan-African orogeny in Neoproterozoic times. East of the Ibra Zone, another deep crustal boundary, crustal thickness decreases to 30-35 km and very high lower crustal V-S suggest large-scale mafic intrusions into, and possible underplating of the Arabian continental crust that occurred most likely during Permian breakup of Pangea. Mafic reworking is sharply bounded by the (upper crustal) Semail Gap Fault Zone, northwest of which no such high velocities are found in the crust. Topography of the Oman Mountains is supported by a mild crustal root and Moho depth below the highest topography, the Jabal Akhdar Dome, is similar to 42 km. Radial anisotropy is robustly resolved in the upper crust and aids in discriminating dipping allochthonous units from autochthonous sedimentary rocks that are indistinguishable by isotropic V-S alone. Lateral thickness variations of the ophiolite highlight the Haylayn Ophiolite Massif on the northern flank of Jabal Akhdar Dome and the Hawasina Window as the deepest reaching unit. Ophiolite thickness is similar to 10 km in the southern and northern massifs, and <= 5 km elsewhere. KW - Composition and structure of the continental crust KW - Asia KW - Body waves KW - Seismic anisotropy KW - Seismic tomography KW - Surface waves and free oscillations Y1 - 2022 U6 - https://doi.org/10.1093/gji/ggac223 SN - 0956-540X SN - 1365-246X VL - 231 IS - 2 SP - 817 EP - 834 PB - Oxford University Press CY - Oxford ER - TY - JOUR A1 - Freybourger, Marion A1 - Krüger, Frank A1 - Achauer, Ulrich T1 - A 22 degree long seismic profile for the study of the top D" Y1 - 1999 ER -