ENVS 112 Orogenies/Earthquakes

Rock deformation: Brittle

Low, Low, High

Rock Deformation: Plastic

High, High, Low

Evidence for Deformation

Displacement, Rotation, Distortion

Causes for mountain building

Subduction zones/continental collisions, convergent margins, continental rifting

Compression of subduction zones

Leads to uplift/rocks are squeezed upwards

Wrinkles in subduction zones

Little wrinkles on continent → big mountains for tiny humans, vertical exaggeration is cool

Rock cycle

Sedimentary→ burial of rocks- leads to metamorphic→ melting→ igneous→ erosion to transport to sedimentary

Plate tectonics and earthquakes

Lithospheric plates move: rocks move aganist each other

Cold + brittle

Brittle deformation

What does elastic deformation lead to?

Leads to fracture

What happens during elastic deformation

Rapid motion along fault, friction stops motion, rocks vibrate/oscillate for a while

Oscillations

seismic waves (ground movement)

Foreshocks

Initial small brakes along fault

What does the actual earthquake?

Main shock

Later readjustments

After-shocks (many)

How to record earthqaukes

Seismogram

Earth-quake predictions

Can’t predict if earthquakes will happen, statistical analysis helps

Types of seismic waves

P-waves, shear waves, r-waves

P-waves

Compressional waves-fast

Shear waves

Slower (than p-waves about 40% slower)

R-waves

slow- Large amplitude-do most damage

Richter scale

How much displacement is recorded on seismograph

Logarithmic scale

Mag. 3 is 10x shapes than Mag.2

Mercalli scale

Shows how severe/widespread damage can be

Moment magnitude

How much energy is released in earthquake

How fast do seismic waves move? Sed. rocks

P- wave (2200 m/s) S-wave (1500 m/s)

How fast do seismic waves move? Slate

P-wave (4300 m/s), S-wave (2900 m/s)

How fast do seismic waves move? Granite

P-wave (4000 m/s), S-wave (2700 m/s)

How fast do seismic waves move? Basalt

P-wave (5100 m/s), S-wave (3100 m/s)