The trench site

At the trench site we found evidence for several fault strands reaching the surface.

A first small scale fault is located around 30 m along the profile on the cone penetration tests profile we noticed a 1 m displacement of the compact layer. The ground penetrating radar profiles, boreholes and a small break in the topographical profiles suggest that this fault runs up to the surface.

A second fault zone is situated between 70 and 100 m along our profile. The compact layer in the CPT profile is displaced by 6 m. The other geophysical methods show also an anomaly in this zone. On the radar profiles we saw that this is a fault zone near the surface and not one single fault.

The next fault is situated around 150 m. It can be observed in the electrical tomography . The base of the low resistivity layer is displaced by about 4 m.  The GPR profiles show that this fault also reaches the surface. In the CPT profile this fault is not evident because of the poor horizontal resolution .

Around 200 m the radar profiles show a clear fault near the surface. Also in the topography and the borehole profile a fault can be inferred at around 200 m along the profile. At depth the long electrical tomography shows that the base of the low resistivity layer is displaced by about 5 m. On the CPT profile this fault is again not evident.

Near the end of the long electrical tomography profile at 290 m a last fault can be interpreted. East of this position different deposits are present and also the base of the low resistivity layer seems to be displaced. If this were really a fault it would be an important one to investigate due to the more recent deposits. We will investigate this further with the other geophysical methods to confirm whether this is a fault.

It is not possible to investigate the more than 300 m of fault zone in one trench and in one month so we decided to excavate a 100 m long trench between 20 and 120 m along our profiles. This way we include the major fault zone of 70 to 100 m and also the fault at about 30 m. We also hope to find the lateral extension of the peaty layer that was encountered in hand boring 1 at 0 m along the profile and be able to date it using the c¹⁴ method.

It is important to know that in the trench only a part of the fault zone is exposed and that our observations and conclusions only apply for the investigated fault strands. The rest of the fault zone may be dug up and analysed in a later stage.