Dictionary.net

• A throwing down: specifically, in geol. a fall or sinking of strata below the level of the surrounding beds, such as is caused by a great subterranean movement: also, the distance measured vertically between the portions of dislocated strata where a fault occurs: opposed to upheaval (which see) or upthrow.

1899 - The american dictionary of the english language.
By Daniel Lyons

• A local sinking in the strata of the earth; the distance to which it has sunk.

1914 - Nuttall's Standard dictionary of the English language
By Nuttall, P.Austin.