The Vp/Vs relationship of the basement under the Trøndelag Platform, mid-Norway

Abstract

Two wide angle 3-Compnent Ocean Bottom Seismometer (OBS) profiles along with associated Land-Stations acquired during 2003 under the EUROMARGINS Program were analyzed during this M.Sc. Thesis. These profiles are named as PROFILE -3-03 & 4-03 & were aimed at studying the crustal structure beneath the Trøndelag Platform & adjacent areas, mid-Norway. Shear waves recorded on the horizontal components of the seismometers have been modeled using 2-D kinematic ray-tracing software RAYINVR, utilizing already generated p-wave velocity models. For shallower sediments (1-6 km depths) average Vp/Vs ratios are relatively high as expected i.e. 2.0-2.6 which indicate the presence of low consolidated sediments in the upper layers. The deeper sedimentary layers (6-11 km depth) present along NW side of both profiles exhibit lower Vp/Vs ratios i.e. 1.8-2.0 which represent further compacted sediments because of increased burial. The upper crust has an average Vp/Vs ratio in the range 1.75-1.78 which suggests that the crust under the Trøndelag Platform is felsic. Vp/Vs ratio increases to 1.80-1.85 in the lower crust which suggests the presence of mafic to ultra-mafic lower crust.