HIGH-RESOLUTION BODY WAVE TOMOGRAPHY BENEATH THE SVEKALAPKO ARRAY - II. ANOMALOUS UPPER MANTLE STRUCTURE BENEATH THE CENTRAL BALTIC SHIELD

Abstract

A number of different geodynamic models have been proposed to explain the early tectonic evolution of the Baltic Shield. To provide additional geophysical constraints on these models, we performed a teleseismic tomography traveltime inversion for the central part of the Baltic Shield. The SVEKALAPKO project is focused on the investigation of the lithosphere-asthenosphere structure down to 400 km depth under central Fennoscandia (Baltic Shield). A total of 143 stations were deployed including 15 permanent stations from the Finnish seismic network. The temporal network was composed of 40 broad-band and 88 short-period instruments distributed in a rectangular array of 1000 km by 900 km from 1998 August to 1999 May. The results are based on a non-linear teleseismic tomography algorithm. They reveal significant P-velocity variations (up to 4 per cent) throughout the SVEKALAPKO array. The most prominent feature is a positive anomaly that can be followed down to 250 km depth beneath the centre of the array.