from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A depression of the strata on one side of a fault
from the GNU version of the Collaborative International Dictionary of English
- n. The sudden drop or depression of the strata of rocks on one side of a fault. See throw, n.
from The Century Dictionary and Cyclopedia
- n. In mining, a dislocation of the strata by which any bed of rock or seam of coal has been brought into a position lower than that it would otherwise have occupied. See dislocation and fault.
Sorry, no etymologies found.
For the sake of the illustration, the displacement is here shown as very slight; but, in some cases, these elevations and depressions of the strata extend to many hundreds of feet -- as, for instance, at the mines of the British Iron Company, at Cefn-Mawre, in North Wales, where the downthrow of the fault is 360 feet.
This is termed the upthrow of the fault, as at B; and the downthrow, as at A.
Professor Ramsay has published an account of a downthrow in Anglesea of 2,300 feet; and he informs me that he fully believes that there is one in Merionethshire of 12,000 feet; yet in these cases there is nothing on the surface of the land to show such prodigious movements; the pile of rocks on either side of the crack having been smoothly swept away.
A normal fault with a hade of 50 degrees, the original fault scarp worn away, showing cliffs caused by harder strata on the downthrow side.
After the upthrown block has been worn down to this level, differential erosion produces fault scarps wherever weak rocks and resistant rocks are brought in contact along the fault plane; and the harder rocks, whether on the upthrow or the downthrow side, emerge in a line of cliffs.
A fault of recent date may be marked at surface by a scarp, because the face of the upthrown block has not yet been worn to the level of the downthrow side.
Normal faults, of which Figure 184 is an example, hade to the downthrow; the hanging wall has gone down.
A thrust fault with a hade of 30 degrees, showing cliffs due to harder strata outcropping on the downthrow.
The escarpments, however, are due in a large degree to the erosion of weaker rock on the downthrow side.
In Figure 184 the right side has gone down relatively to the left; the right is the side of the downthrow, while the left is the side of the upthrow.