Geography Reference
In-Depth Information
preference is given to geologically expressed tail-shaped anomalies rather than
to its topography because the impact-produced topographic lows have been
filled with sediments, and the "tails" expressed in the modern surface
topography (a lake contour) strike in a different direction.
Figure 31. Tail-shaped asymmetry of the Logancha impact crater expressed in Google
Earth satellite images (a), the ENDDB elevation model (b), and in the map of gravity
anomalies accommodating the Logancha astrobleme obtained according to [72] (c).
The scale shows gravity in mGal.
On the other hand, the probability of tail-shaped anomalies in an impact
structure may depend on the kinematics of crater formation: the speed of the
cosmic body (CB) and angle of its entry into the atmosphere. Particularly, for
the Logancha crater [1] (Figure 31), the CB entry at a relatively low angle
produced another morphological feature, a sort of braces on the frontal outer
side, with gaps between them filled with recent sediments. More geomorphic
evidence for the low-angle CB trajectory may come from its direction to a
chain of minor craters or from the frontal part of the crater being prominent
against the surrounding terrain, i.e. a shoe-shaped crater rim (e.g., in the
Erofeev crater [1], Figure 32).
Some tails have a bending geometry (e.g., the Karikkoselkä, Möckeln,
Korpinen, and Lasnamäe craters [1]). If they were produced by an energy
(gravitational) influence of a cosmic body [73], the latter would appear to have
"maneuvered" before falling. The same bends were observed also in the tail -
shaped zones of craters imaged in gravity anomaly maps [73]. They may result
either from the original gravity (density) heterogeneity of the target rocks, or
from density decrease by explosion-induced brecciation [74]. The latter
explanation is especially relevant to tails with prominent concentric anomalies
inside [73]. The brecciation and fracture of rocks are caused by shock waves
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