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uprange structural uphft offset rim fauK

uprange structural uphft offset rim fauK

Fig. 4. Interpreted multi-channel (top three) and single-channel (bottom three) seismic reflection profiles stacked along the geometric crater center. In profile (a) selected reflector segments are connected to visualize the clear up-range structural uplift offset.
Table 1. Crater radii asymmetry factors (dimensionless) defined as the ratio of the two radii, on the left and right side, between the geometric crater center and the rim faults of each of the profiles (a-f) illustrated on Fig. 4

Profile (Fig. 4)

Asymmetry factor (direction)

a

1.33 (N)

b

1.12 (NW)

c

1.14 (NW

d

1.07 (N)

e

1.17 (NE)

f

1.15 (NW

The impact-induced seismic disturbance at Mjolnir has a parabolic bowl-shape at the center of the structure and turns into a shallow broad-brim towards the periphery (Fig. 2 and 4). This distinct shape evolved during gravitational collapse of the transient cavity wall and progressive outward expansion of the crater by inwards dipping fault-blocks floored on low-angle d├ęcollement surfaces (Tsikalas et al. 1998a). The crater radius asymmetry (Table 1) is directly translated to a similar asymmetry in the lateral extend of the shallow broad-brim part of the impact-induced seismic disturbance (Fig. 4). It also appears that the shallow part of the seismic disturbance is not only elongated but also slightly shallower in the same northward-direction (Fig. 4, profile a). Furthermore, the decompacted-thickness contour map of the intensely disturbed zone in Figure 5 is directly related to the transient cavity bounded approximately at the perimeter of the annular basin and reaches ~5 km in depth. It appears that the transient cavity maximum depth is offset by 2-2.5 km to the south-southwest relative to the geometric crater center (Fig. 5).

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