Shear-wave velocity structure beneath Europe, the northeastern Atlantic and western Asia from waveform inversions including surface-wave mode coupling

摘要

Waveforms of 449 seismograms have been inverted for S-wave velocity structures beneath Europe, the northeastern Atlantic, and western Asia down to a depth of 670 km. Recorded waveforms were used in the time window starting at the S-wave arrival and ending after the fundamental-mode Rayleigh-wave arrival. The inversion method is based on the partitioned waveform inversion (Nolet 1990), with the difference that synthetic seismograms are calculated taking surface-wave mode coupling into account in order to model body waves in laterally heterogeneous media more accurately. The partitioning of the inversion procedure makes non-linear optimization feasible, even for inversions including surface-wave mode coupling. The non-linear inversion of the waveforms resulted in linear constraints on the 3-D velocity structure. In a second step, these constraints were used in a linear inversion for the 3-D shear-wave velocity model beneath Europe, the northeastern Atlantic and western Asia. The EUR-SC'95 model is presented, which is characterized by a wide range of length-scales of the velocity structures. In central Europe, where the ray density is highest, small-scale structures are recovered, such as the presence of high velocities associated with the Hellenic subduction zone. On the edges of the inversion model, where the ray density (and therefore also the resolution) is poorer, we find larger-scale features, such as the relatively laterally homogeneous high-velocity structure beneath the Russian Platform to a depth of 300 km. In this paper we discuss the inversion method, data processing, parametrization difficulties due to the introduction of surface-wave mode coupling, spatial resolution of the model, and structures in the EUR-SC'95 model