GHC Ch 3: Earthquake Geology and Seismology Flashcards
What are earthquakes most commonly caused by?
Caused most commonly by movement of the Earth across a fault.
Fault
Complex zones of breakage in the Earth across which the two sides move relative to each other. Has irregular surfaces, and is many miles wide and long.
How does an earthquake occur?
Stresses build up until they are enough to cause rocks to fracture and shift, sending off waves of seismic energy, felt as earthquake.
Understanding faults begins with understanding what rock relationships, formalized by Steno?
Law of original horizontality and Law of superposition
Law of original horizontality
sediments are originally deposited in horizontal layers
Law of superposition
in un-deformed sequence of sedimentary rock layers, each layer is younger than the layer beneath it and older than the layer above it
Law of original continuity
sediment layers are continuous
If a sedimentary layer ends abruptly, it may have been…?
eroded by water action or truncated by fault passing through layer
Identifying truncated sedimentary layers and recognizing their offset continuation allows determination of…?
fault length
Length of fault determines size of…?
earthquake possible on fault
Longer fault ruptures create bigger or smaller earthquakes?
bigger earthquakes
Where does ‘jointing’ occur?
where brittle lithospheric rocks fracture and crack
Large stress differential on either side of a fracture results in movement, and then…?
fracture becomes a fault
Movement, ranging from millimeters to hundreds of kilometers, results in what?
tilting and folding of layers
Use strike and dip to describe what?
describe location in 3D space of deformed rock layer
Dip
angle of inclination from horizontal of tilted layer
Strike
compass bearing of horizontal line in tilted layer
Dip-slip faults are dominated by what movement?
vertical
Miners refer to the block beneath them as the…?
footwall (block beneath the fault)
Miners refer to the block above them as…?
the hangingwall (block above the fault)
what are dip-slip faults caused by?
pushing or pulling force
Strike-slip faults are dominated by what movement?
horizontal
right-lateral strike-slip fault
When straddling a fault, if right-hand side moved towards you
left-lateral strike-slip fault
When straddling a fault, if the left-hand side has moved towards you