Contemporary stress orientation features in bedrock, Trøndelag, central Norway, and some regional implications.

Abstract

Based on in situ rock stress measurements and contemporary stress orientation structures observed at diverse sites in Trøndelag, it can be shown that the Møre-Trøndelag Fault Complex marks an important structural divide separating crustal blocks with disparate, present-day stress fields. This supports earlier poposals reached by both field and numerical modelling studies; and, in one case, our data confirm published predicitions that constrasting contemporary stress fields should, theoretically, characterise the footwall and hangingwall blocks fo this major fault zone. The prevalent NW-SE horizontal compression recorded in coastal areas of central Norway northwest of the Møre-Trøndelag Fault Complex accords with borehole breakout and earthquake focal mechanism solution data acquired offshore, indicating that this patterns is likely to relate to a distributed ridge-push force arising from divergent spreading along the active axial ridge of the North Atlantic Ocean. Taken as a whole, the combination of in situ rock stress measurements and field observations of drillhole reverse-slip offsets and complementary stress patters existing in exposed bedrock.