Thrust fault
Reverse fault in which the hanging wall moves upward relative to the footwall; many thrusts are low-angle.
Language and route: English technical use of ordinary word thrust, applied to low-angle reverse displacement; fault is inherited English geological vocabulary. English technical use of ordinary word thrust, applied to low-angle reverse displacement; fault is inherited English geological vocabulary
Literal gloss: pushed-over fault
The name and its history
Archibald Geikie according to BGS history, in Scottish mapping context · 1884 cited for geological thrust name
- What does the word literally mean?
- Immediate linguistic pathway: English technical use of ordinary word thrust, applied to low-angle reverse displacement; fault is inherited English geological vocabulary. Relevant original form: thrust + fault (thrust + fault); conventional gloss ‘pushed-over fault’. The linguistic gloss should not be mistaken for the original scientist’s stated motive unless directly demonstrated.
- What did the original author mean?
- At Loch Eriboll the usual assumed stratigraphic sequence was overturned when older metamorphic rocks were found structurally over younger rocks.
- Why was the name needed?
- Geologists needed a mechanism for large horizontal rock movements after map-based evidence defeated simple layer-by-layer succession.
- What evidence supported the original concept?
- Structural repetition, overriding contacts, displaced strata and mapped fault geometry.
- How has geology changed the concept?
- Thrusts are now interpreted within fold-and-thrust belts and plate-convergence systems; a thrust need not have been initiated in a textbook low-angle position.
Further historical context
At Loch Eriboll the usual assumed stratigraphic sequence was overturned when older metamorphic rocks were found structurally over younger rocks.
Geologists needed a mechanism for large horizontal rock movements after map-based evidence defeated simple layer-by-layer succession.
Structural repetition, overriding contacts, displaced strata and mapped fault geometry.
Thrusts are now interpreted within fold-and-thrust belts and plate-convergence systems; a thrust need not have been initiated in a textbook low-angle position.
Editorial qualification
The BGS retrospective attributes early tectonic thrust usage to Geikie 1884; do not claim this was first English use of ordinary “thrust.”
Related names
Sources
- BGS Loch Eriboll field guide — origin of thrust and mylonite — Historic sequence; Geikie thrust 1884, Lapworth mylonite 1885
- BGS geological conservation review, Lapworth and mylonite — Historical account identifying Lapworth 1885 and the Scottish thrust controversy
- The history of Alpine thrust nappes — academic book sample — Historical interpretation of Bertrand 1884 and later Alpine work; PDF excerpt not page inspected