Unit 14 Flashcards
Plate tectonics & earthquakes
•Continents seem fixed from human perspective. Until the mid-twentieth century, scientists believed Earth’s continents were rigid
Continental Drift
continents move on Earth’s surface; Alfred Wegener proposed this idea in 1912; Pangaea
Plate Tectonics
Theory behind motion of lithospheric plates; plates float on the ATHENOSPHERE
(get tectonic plates image form slides)
Convection
transfer of heat through a fluid; the asthenosphere bubbles up and encounters the crust which leads it to fracture the crust.
mid-oceanic ridges
formed by magma rising up from mantle
sea floor separates
new basaltic crust created
ocean trenches
sea floor comes together; older lithosphere descends into the asthenosphere where it is recycled
Plate Boundaries
the border between two plates
Divergent
moving away from each other; constructive; mid-oceanic ridge; youngest crust
Convergent
moving towards each other; destructive; collisions
oceanic-continental (destructive)
A) oceanic plates sink since it is more dense
B) forms oceanic trench and continental mountains (cascades &Andes)
C) earthquakes occur along margin
D) volcano formation along the plates (continental volcanic arc)
E) forms metamorphic rocks-blueschist
oceanic-oceanic (destructive)
A) subduction results in undersea trench formation
B) deep and shallow earthquakes
C) island volcanic arc
continental-continental
A) no subduction since two plates are highly buoyant
B) builds huge mountain ranges
C) volcanoes are rare
D) shallow earthquakes are relatively common
E) examples: Himalayan mountains
Transform (Stripe-slip)
slide against one another; neither creates nor destroys crust; commonly produce shallow earthquakes; San Andreas fault line (right lateral transform boundary)
Fault
a crack in the Earth’s surface
Earthquakes
The shaking and trembling of the Earth’s surface caused by sudden releases of stress within the crust; can happen near the surface, deep in the crust, or even in the upper mantle
•generate pulses of energy known as seismic waves
Body waves
A)p waves: travel faster and can move though any material; can travel through entirety of Earth
B)S Waves: travel slower and can only pass through solid material
Surface Waves
waves you feel and shake the surface
•Seismograph
Focus
the actual center of the earthquake; source of shaping
Epicenter
the point on the Earth’s surface directly above the focus
Magnitude
is energy that is actually released, and it is measured by Richter scale (logarithmic), there is only 1 rating per earthquake;1-10
Intensity
is the severity of shaping and it is measured by the Mercalli scale; multiple Mercalli ratings (highest at the epicenter) 1-12
Tsunamis
- seismic sea wave
* Produced when ocean water is suddenly displaced by movement of the crust in an earthquake or by a large land slide
San Francisco Earthquake of 1906
occurred April 18, 7.8 earthquake occurred at 5 am with an 11 on the Mercalli scale; 3000 people died and 80% of san Francisco was destroyed due to the fires
