← Back to Gallery

A Conceptual Seismological Model for the Norwegian Rifted Margin Drawn from the Perspective Hyperextension

We present a conceptual seismological model for Fennoscadia that is consistent with modern hypotheses of extended margin evolution, including post-breakup reactivation by footwall uplift in regions adjacent to sharp crustal taper. Fennoscandia’s seismicity reflects the benchmark domain boundaries of its Mesozoic rifted margin: Three distinct belts of earthquakes strike sub-parallel to the generalized line of breakup. The outermost seismic belt marks the Taper Break (TB), or the zone of flexural coupling/decoupling between the distal (seaward) and proximal/necking (landward) domains. A coastal belt follows the Innermost Limit of Extension, defined as the onset of 39 km-thick crystalline continental crust. An interior belt follows the landward limit of the Scandinavian uplift. Between each belt, large portions of the necking, proximal and hinterland domains are seismically quiescent.

As proposed by previous authors, a first-order spatial correlation between Scandinavia’s offshore earthquake belt and voluminous, geologically rapid, Neogene sedimentary loading is evident. However, the presence of thinned, faulted crystalline basement is also a very important factor behind Scandinavia’s offshore seismicity. Where the Neogene deposits are thickest the underlying crust is oceanic; released energy is lower per unit area there than where lesser Plio–Pleistocene loading impacts continental crust that was fully prepared by necking and hyperextension. These data suggest that the ‘strength’ of the TB and the continental margin’s distal domain is significantly less than that of relatively young (ca. 54 Ma) oceanic lithosphere. Our data also imply that ridge push does not contribute significantly to Fennoscandia’s seismicity. Rather, we find that thin-plate bending stresses stemming from offshore depositional loading conspire with unbuttressed Gravitational Potential Energy (GPE), onshore erosion and post-glacial isostatic rebound to generate Fennoscandia’s earthquakes.

Session: Tectonics and Seismicity of Intraplate Regions I

Type: Oral

Room: Cedar

Date: 4/20/2022

Presentation Time: 09:00 AM Pacific

Presenting Author: Tim F. Redfield

Student Presenter: No

Additional Authors