Local earthquake tomography of the Tjörnes Fracture Zone / North Iceland
Proposers:
Prof. Dr. Torsten Dahm
Members:
Dr. Carsten Riedel, Martin Hensch, Michael Schnese
Abstract:
The Tjörnes Fracture Zone (TFZ) is composed of three major lineaments of seismicity linking the fissure zones of Northern Iceland to the ridge crest of Kolbeinsey Ridge (Einarson, 1976). It is generally thought of as a transform zone, i.e. a continentally influenced transform structure rather than a simple transform fault, which is typical for the more oceanic Mid Atlantic ridge. In that regard it should function in a way similar to the better known San Andreas fault system or New Zealand's Alpine Fault. In some structures they mirror each other, e.g. active volcanism, hydrothermalism, Riedel faults and pull-apart basins, which have been outlined onshore by Gudmundsson et al. (1993) and offshore by Riedel et al. (2001). However, the continental influence in Iceland originates in the hot spot origin of the Icelandic crust which thickens the crust to more than 40 km thickness near the hot spot centre underneath Vatnajökull. North of Iceland, where the crust is made up of apparently "normal" oceanic crust produced by a "normal" slow-spreading ridge as Kolbeinsey Ridge the thickness rapidly decreases to around 10 km. A local earthquake tomography study was initiated to shed more light on the processes involved in the transition area spanned by the TFZ by highlighting low velocity zones and providing a better hypocenter localization, which can then be used to assess hazards associated to the activity of the fault system cropping out at the surface and can give valuable clues on the interplay of fractures and fluid reservoirs in the subsurface and their transport in dikes and hydrothermal convection cells to the crust-ocean boundary.
Duration:
2002-2004
Funding:
DFG
Figure 1 shows a 2D result of the local earthquake tomography oriented subvertical to the strike of the main seismic lineaments, Husavik-Flatey fault (HFF) and Grimsey Lineament (GL). High shear wave velocity (Vs) and low compressional wave velocity (Vp) mark these fracture zones.