underthrust


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underthrust

[¦ən·dər¦thrəst]
(geology)
A thrust fault in which the lower, active rock mass has been moved under the upper, passive rock mass.
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References in periodicals archive ?
The result shows that (1) beneath the southernmost portion of the profile there are two sets of strong north-dipping reflectors between 10 s-19 s TWT, which we interpreted to indicate that the LB may underthrust beneath the BNS; (2) there is a well-developed northward thrust beneath the shallow crust near the BNS; (3) there is a broad, gently folded reflection that presents close to the southern segment of the BNS at 10s and shallower to ca.
The figure on page 96 shows seismic reflection and drilling data for the Nankai accretionary prism, where coring penetrated the incoming sedimentary sequence completely, transecting the frontal thrust, the decollement zone (zone of detachment that separates accreted and underthrust sediments), and underthrust deposits to the ocean basement.
These seismic observations suggest that most of the plateau has been underthrust by high wave-speed Indian mantle from the south and possibly, to a lesser extent, high wave-speed Asian mantle from the north.
It was concluded that the convergence was absorbed due to (i) shortening of sedimentary strata in the foreland as India underthrusts its cover rocks, (ii) contraction within the collision zone by uplift in the high Himalaya and reactivation of interior thrust faults, and (iii) crustal shortening via thickening of the crust and escape-block tectonics along strike slip faults to the north of the collision zone [23, 24].
The underthrusted lower density masses of Miocene age, off-scraped from the ramp of Palaeozoic sediments, produced a higher topography of the Silesian nappe than one would expect from its simple stratigraphic thickness including tectonic repetition.