Module 6: Hazards

The plates move apart and magma enters the crust. Shallow focus earthquakes (50-70km deep) and have a magnitude of below 5. Effusive eruption = mafic/ultramafic and low silica percentage (below 45%) Normal fault (hanging wall moves downward relative to footwall) 2 types: Continental-continental and oceanic-oceanic.

The plates move next to each other in a rubbing motion. Strike sip fault where rock strata can split and be carried in opposite directions parallel to the fault. Shallow depth (50km-70km) but have a high magnitude.

The plates move towards each other. There are 3 types: 1. Oceanic-oceanic 2. Oceanic-continental 3. Continental-continental The denser oceanic plate typically sub ducts beneath the continental plate (subduction zone = trench). Due to the intense heat and pressure, the sub ducting plate melts as it descends into the mantle. (Continental-oceanic) Shallow seismic activity but large magnitudes. At continental-continental zones, the plates fold within the compressed rocks, creating mountain like structures.

The more dense oceanic plate sub-ducts into the mantle and partially melts. This sedimentary material rises through the mantle and crust, creating volcanoes.

The dense oceanic plate sub-ducts beneath the lighter continental plate, creating deep ocean trenches and volcanic arcs.

P-waves (primary) - travel through both liquid and solid layers of the earth. They are the least damaging waves. S-waves (secondary) - travel through only solid layers of the earth. L-waves - Love (most damaging) and Rayleigh waves. Love = sideways movement. Rayleigh = rolling motion (up and down)

GSM can cause the foundations of buildings to subsidise, destabilise and break apart.

Foreshock: small magnitude shaking prior to the mainshock (occurs in the same spot as mainshock) Mainshock: main seismic activity Aftershock: continued tremors/seismic activity that can continue for days, weeks and months.

When the faults become stuck together, energy is stored from tension, and when the force snaps, energy is released as seismic activity.