Y10 Earthquakes Geological processes
Earthquake video • What is an earthquake? • What happens in an earthquake? • What is the effects of an earthquake on the community? • What should you do in an earthquake? • What shouldn’t you do?
Earthquake commission Fix. Fasten. Forget. • Secure hot water cylinders and header tanks • Check that your house is secured to its foundations • Secure your chimney with galvanised metal bands • Secure tall furniture to the wall studs • Secure wood burners to the floor • Store heavy objects low down • Use non-slip mats under smaller appliances and objects • Use plastic putty (Blu Tack) to secure ornaments • Push picture and mirror hooks closed • Have flexible gas and plumbing fittings installed.
What to do during an Earthquake • Follow this link for ideas what to do in an earthquake • FEMA: What to Do During an Earthquake
Te Anau Earthquake video • Click on the links below • Earthquakes - Earthquake damage, Te Anau - Te Ara Encyclopedia of New Zealand
Earthquake Definitions • An earthquake is vibrations of the Earth produced by the rapid release of energy. • Surface rocks of the Earth’s crust are brittle and can break when put under pressure. • Deeper rocks bend under pressure as they are not so brittle.
Focus, epicentre and fault • Focus – the point where the rock breaks in the Earth’s crust. • Epicentre – The point on the Earth’s crust directly above the focus. • Fault – break in the rocks of the crust where the two sides of the break have moved relative to each other.
Active faults • Many fault lines cut the ground’s surface in New Zealand; each past fault movement would have been accompanied by a large earthquake. • Those that are considered likely to move again in the future are called active faults. They are known to have ruptured the ground surface once or more in the last 120,000 years. • This map effectively shows the areas where future earthquakes are most likely.
Questions • Why do Earthquakes occur in the crust and not deeper in the mantle? • What is the difference between focus and epicentre?
Weblink to show NZ earthquakes • Click on the link below. • Earthquakes - New Zealand earthquakes, 1990–94 - Te Ara Encyclopedia of New Zealand
New Zealand regions at greatest risk of ground shaking • The difference between each level is 10%. • What do you notice about the distribution of more severe earthquakes?
The 1848 Marlborough Earthquake and 1929 Murchison Earthquake. • Click on the links below • Historic earthquakes - The 1848 Marlborough earthquake - Te Ara Encyclopedia of New Zealand • Historic earthquakes - The 1929 Arthur’s Pass and Murchison earthquakes - Te Ara Encyclopedia of New Zealand
Earthquakes - Seismic Waves • Waves travel outwards from the focus • Three types, in the order they arrive: • P Waves (primary) – longitudinal waves causing compression and extension of rocks. Moves through solid an liquid. • S waves (secondary) – transverse waves sideways and vertical shaking. Can’t move through liquids. • Surface waves – slow. Travel through crust like ocean waves. Cause most damage.
Earthquake wave animation • Earthquakes - Primary and secondary waves - Te Ara Encyclopedia of New Zealand#breadcrumbtop
Seismologists • Seismologist are scientists who study Earthquakes. • Seismographs are instruments which record seismic waves. • Seismograms are the recordings they make.
Finding an epicentre • Seismologist use the time interval between the arrival of the P and S waves to determine their distance from the epicentre. • When the arrival times of P and S waves from three seismographs in different locations are recorded, the epicentre can be calculated.
Measuring Earthquakes • Measured by Intensity and Magnitude • Intensity – Mercalli scale – based on people’s experiences and effects on buildings and the environment. • Magnitude – Richter scale – based on amount of energy released. Measurements of ground movements and seismographs.
Damage from Earthquakes • Depends on size, distance from focus, type of rock, strength of buildings and depth. • Richter scale – not linear, each step releases 30x more energy.
Make your own seismograph Make an earthquake and bring in your seismograph and seismogram
Structure of Earth • Crust - 6km thick under oceans – solid - up to 70 km thick under continents. Av: 30-40 km • Mantle - 3 000 km thick – plastic – flows - upper 100 km – rigid • Outer core – 2,300 km thick – liquid • Inner core – 1,200 km thick - solid
The bits • Continental crust is under the continents, its light and floats on the mantle. Oldest rocks. • Oceanic crust is heavier, thinner, less buoyant, sinks into mantle. • Mantle rock is hot and under pressure so isn’t actually melted. • Core is mainly iron and nickel. • Circulation of iron produces magnetic field.
Convection currents in mantle • Heat from the core heats the magma causing it to rise towards the crust in currents which push on the plates, moving them.
What happens when plates move? • Spreading zones – plates move apart at mid-oceanic ridges. Magma rises to form new crust in the gaps.
Where does the old oceanic crust go? • Collision zones – plates collide at boundaries. • Rocks can fold into mountains like the Southern Alps. • Earthquakes common • Subduction – a less dense oceanic plates goes in under a continential coast – east of the North Island.
Plate boundaries through New Zealand. • The pacific plate is subducting under the Australian in the north and colliding in the south.
Valley formed by the subsidence of a block of the Earth's crust between two or more parallel faults. • Rift valleys are steep-sided and form where the crust is being pulled apart, as at mid-ocean ridges, or in the Great Rift Valley of East Africa.
Gondwana • NZ was formed off the coast of the great southern supercontinent – Gondwana. • The oldest rocks in NZ are about 500 MY old.
150 mya • Rocks formed from sediments eroded off gondwana are uplifted due to a subduction zone forming.
This is the sediments that make the rocks building up off the coast of Gondwana. Greywacke forming at the edge of Gondwana
70 mya • Spreading ridge in future tasman sea starts NZ moving away on its long journey.
10 mya • NZ starts to take shape. • Land mass is large, one island. • Tectonic collisions are similar today.