Upper crustal structure of Iceland

Abstract

This report contains the results of the seismic measurements made by a Swedish-Icelandic expedition in Iceland during the months of August and September, 1960. This is a continuation of work started a year earlier and is the first detailed investigation of the deeper structure of the lava beds on Iceland. Measurements were made at eight locations, each with a refraction profile from 20 to 41 km long, in order to obtain values on thickness and structure of the lava layer which covers the whole island. The profiles were laid near a line in a southwest-northeast direction across central Iceland. The lava layer was found to consist of three sections with longitudinal wave velocities of 3.7±0.3, 4.95±0.2, and 5.55±0.05 km/sec. The 3.7-km/sec section was found mainly in southwest Iceland, where the other two sections were not found. In north Iceland the 4.95-km/sec section was found near the surface and the 5.55-km/sec section at a depth of about 2 km. The total lava thickness ranges from 1.73 to 4.81 km; it is thin in the southwest and thick in the northern part of Iceland. Below the lava layers, the longitudinal wave velocity is about 6.2 km/sec, increasing to 6.7 km/sec at a depth of about 5 km. Shear waves were clearly recorded on three profiles in north Iceland, but were recorded not at all or only faintly on other profiles.