3.a. earthquakes Flashcards
shallow focus depth
down to 70km
shallow focus charecterisitcs
fracturing is a common occurrence due to the stress and pressure
normally low energy (some are high)
more damage (less energy is dissipated)
limited warning (P waves arrive with other waves)
intermediate focus depth
70-300km
deep focus depth
300-700km
shallow focus plate boundary
transform/conservative
deep focus plate boundary
destructive boundary
oceanic is subducted
deep focus characteristics
less frequent
very powerful
depth and high pressure causes high temperatures
occur often in the Benioff zone
Benioff zone
an inclined zone in which many deep focus earthquakes occur
situated beneath a destructive plate boundary where oceanic crust is subducted
seismic primary (P) waves
body wave
longitudinal
fastest
least destructive
seismic secondary (S) waves
body wave
(squiggle/worm shape)
second fastest
slightly more destructive than P waves
seismic Rayleigh (R) waves
surface wave
cycling motion
slow
destructive
seismic love (L) waves
transverse
slow
very destructive
Richter scale
uses amplitude of seismic wave to determine magnitude (release of energy)
logarithmic
ground shaking is detected by seismometer/seismograph which produces a seismogram
no upper limit
moment magnitude scale
measures energy released more accurately than Richter scale
energy released is related to geological properties (e.g. rock rigidity, area of fault surface and amount of movement along the fault)
most accurate for large earthquakes- relies on physical movement caused by an earthquake which is a result of energy
not used on microearthquakes (2.0 or bellow) these are recorded locally and not felt by people
modified Mercalli intensity scale
measures earthquake intensity by its impacts and effects
qualitative and subjective assessment based on observations and descriptions
more meaningful to non scientists because refers to the effects on a place
scale of 1-12
tectonic faults
a fault is a break in the crust where slabs of crust slip past each other
caused by stress building on rocks causing rocks to shatter.
faults usually occur on plate boundaries where the forces of plate motion compress, pull or shear the crust too much so the crust ruptures
large geological time scale
Strike slip faults characteristics
Sheering creates this fault
Rocks on both sides of the fault slide past each other with little up and down motion
When a strike slip faults forms the boundary between two plates it becomes a transform boundary
Visible scar on landscape may appear
Strike slip faults tectonic activity
Earthquakes occur along faults as blocks of continental crust rotate or move sideways out of the principle collision zone
Remain tectonically active
Strike slip faults example
San Andreas fault: continental fault that extends 1200 km
Kunlun fault: formed on Tibetan plateau, successive earthquakes have caused visible scarring on the landscape
Normal fault
Caused by tensional forces on the crust
Formed on angle so one section of rock is raised
Movement along the normal fault chases the hanging wall to slip downwards
Normal fault example
Rio Grande Rift Valley in New Mexico
Two pieces of divergent crust
How rift valleys are impacted by earthquakes
Evidence of the impact of earthquakes in the morphology of the Earth’s surface
Fault scarps/escarpments are created when extensional forces put the lithospheric plate under tension and vertical faults form
Earthquakes occur as graben sinks
Scarps are eroded over time and blend until landscape
Reverse or overthrust faults
Compressional forces produce this fault
The fault has the same set up as a normal fault, but reversed
Just like a normal fault, one side of the reverse fault is at an angle of the other
This fault produced part of the Appalachian mountains in Eastern United States
Fold belts
Compression from tectonic activity produces folds in Rick strata. This creates mountain ranges such as the Himalayas
This may influence costal landforms
