Velocity modelling of the lithosphere beneath south Finland

Abstract

The seismic structure of the upper lithosphere beneath southern Finland area was investigated by a series of seismic refraction and reflection surveys during the 1980s and 1990s. The resulting two-dimensional models of the crust from the deep seismic sounding (DSS) profiles were combined to image the region as a three-dimensional structure by interpolating and smoothing. Although, these models are reasonably accurate, the velocity structure between the profiles is truly unknown. In this study, the seismograms of the DSS shots at permanent seismic stations are used to estimate new depth points of reflections from the Moho between the profiles. The relief of the Moho boundary is reinterpolated by combining our depths with estimates along the DSS profiles. The detailed crustal model is discussed together with the geology and gravity anomalies of the area. The contradiction between the variation of the crust thickness in our model and the Bouguer anomaly support previously presented idea of mass surplus compensation. A simple three-dimensional seismic P wave velocity model is also constructed and presented as vertical and horizontal cross-sections. The variations of velocity in the upper crust correlate with surface geology unlike in the deeper crust. The velocity of the lithosphere beneath south Finland varies smoothly from 5.6–6.2 km/s on the surface to 7.8–8.6 km/s below the Moho.