Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, N-0316 Oslo, Norway ([email protected])
Abstract. The 40-km-diameter Mjolnir crater is proposed to have resulted from an oblique impact from the south/southwest direction and at a -45° (possibly 30o-45o) angle from the horizontal. This is substantiated by several diagnostic structural and geophysical signatures related to obliquity and revealed through detailed re-assessment of Mjolnir's well-established structure, morphology, and gravity and seismic velocity anomalies. The diagnostic signatures include: (1) a dominant N-S/NNE-SSW crater diameter elongation, (2) a consistent northward asymmetry both in the crater radius and the shallow part of the impact-induced seismic disturbance, (3) a peak ring breached towards the N/NE, (4) an annular gravity low with a horseshoe-shape open towards the NE, (5) a transient cavity maximum-depth offset of 2 to 2.5 km towards south-southwest from the geometric crater center, combined with a similar structural uplift lateral offset towards the south, a similar central gravity high offset towards southwest, and an elongated traveltime central anomaly offset towards WSW. The oblique Mjolnir impact most probably generated a down-range sector/corridor of thicker ejecta deposits and faster travelling tsunami-waves, triggering short-term regional perturbations that are probably intensified within and adjacent to this sector.
thraw 100-50 m throw 50-20 m thraw 20-10 m
central high annular basin outer zone 4: platform
• borehoie 7430/10-U-Q1 O borehole 7329/Q3-U-Q1
Fig. 1. Seismic reflection profiles superimposed on the Mjelnir structure defined by its radial zonation boundaries and the impact-induced structural elements. MCS, conventional multichannel profiles; SSP, shallow multichannel and shallow high-resolution single-channel profiles. Hatched-raster denotes clear definition of the raised peak ring.
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