Finneidfjord field laboratory
NGU has the equipment to perform very high-resolution seismic acquisition, combined with detailed seafloor topography. This equipment was used to study the causes of the 1996 Finneidfjord submarine landslide, in Norway.
In its final extent, the Finneidfjord slide involved some 1 million cubic meters of ground, of which about 90% was below sea level. Four people died, and several houses, a major section of highway, and a beach were destroyed. A bright reflector was identified on the seismic data and may correspond to free gas collected in relatively sandy layers. The free gas could have contributed to the generation of excess pore pressures and the initiation of the submarine landslide.
A US student, Eugene Morgan, is working further with the seismic data in order to extract an estimation of free-gas content and the consequent pore pressure based on amplitude and attenuation analyses. To better relate offshore and onshore structures in a coastal framework, near-surface geophysical methods were applied on land during the summer of 2007.
GPR, resistivity, and seismic (refraction tomography and surface waves) gave useful information about an intact site, with probable identification of remaining quick-clay (see reference list). Contacts are taken with the Norwegian Road Authority to possibly ground-proofed some of the identified geological units for calibration of the geophysical results.
This activity is part of the ICG Offshore Geohazards project.