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EXTREME NATURAL EVENTS 1 Earthquakes - Processes 1 EARTHQUAKES WHAT WILL WE BE LEARNING? Natural Processes the produce ENE’s How natural and cultural characteristics/features of an environment make them vulnerable to the ENE’s The effects of the ENE on the natural & cultural environment 1 Earthquakes - Processes 2 The impacts of ENE’s on different groups of people and how they respond Earthquakes Geographical Terms 1 Earthquakes - Processes Tsunami Wave Noisy Rumbling Epicentre Fault Focus Friction Hazard Lateral Magnitude Seismic Stress Subterranean 3 Convulsing Cracking Crunching Devastating Vibrating Trembling Fracturing Frightening Gaping Grinding Mercalli Scale Richter Scale Shaking Shattering NATURAL PROCESSES THAT PRODUCE ENE’S Large earthquakes are usually connected with plate boundaries. Seismometers record earth movements. An earthquake is a sudden shockwave caused by rocks being under stress from movements of plates at plate boundaries. Eventually the stress in the rock builds up enough to deform and reach breaking point. 1 Earthquakes - Processes 4 At that point, the stored up energy is released in the form of a shockwave. 5 1 Earthquakes - Processes EARTHQUAKES & FAULTS A fault line is a fracture along which the crust has moved Stresses in the crust along NZ’s plate boundary have broken it into separate fragments or blocks that move relative to each other along fault lines. 1 Earthquakes - Processes 6 Plate tectonics was developed in the mid 1960’s as a theory to explain processes and events such as quakes and vulcanism. SEISMIC WAVES Seismic waves are generated when the two sides of the fault rapidly slip past each other. For most earthquakes, the faults do not break the surface, so the faults can only be “seen” through analysing the seismic waves. Faults can be anywhere from metres to a thousand kilometres long. 1 Earthquakes - Processes 7 Link: Different types of faults WHERE EARTHQUAKES HAPPEN Most earthquakes occur along the edge of the oceanic and continental plates. All but the very deepest earthquakes (deeper than 600km) occur on faults. The plates under the oceans are called oceanic plates and the rest are called continental plates. The plates are moved around by the motion of a deeper part of the earth (the mantle) that lies underneath the crust. These plates are always bumping into each other, pulling away from each other, or past each other. Plates usually move at about the same speed that your fingernails grow. 1 Earthquakes - Processes 8 Earthquakes usually occur where two plates are running into each other or sliding past each other. WHERE EARTHQUAKES HAPPEN Earthquakes can also occur far from the edges of plates along faults. Faults are cracks in the earth where sections of a plate (or two plates) are moving in different directions. Faults are caused by all that bumping and sliding the plates do. 1 Earthquakes - Processes 9 They are more common near the edges of the plates. 10 1 Earthquakes - Processes 1 Earthquakes - Processes 11 FLYOVER OF THE GREENDALE FAULT 12 1 Earthquakes - Processes MAJOR FAULTS IN NZ There are major fault lines running the length of New Zealand The Alpine fault carries most of the total plate boundary strain 1 Earthquakes - Processes 13 It is a very distinct feature along most of its length because o f the Southern Alps that have been uplifted along the eastern side making it clearly visible from space. HIKURANGI TRENCH This is a broad, deep-sea trough (or subduction zone) that lies less than 100km off the east coast of the North Island and runs south to the waters off Kaikoura It marks the boundary between two crustal plates and the margin where the Pacific Plate (to the east) is being dragged underneath the Australian Plate. 1 Earthquakes - Processes 14 Large tsunamis, such as the 2004 Indian Ocean tsunami, are most frequently caused by earthquakes on plate boundaries where subduction takes place. 15 HIKURANGI TRENCH 1 Earthquakes - Processes 1 Earthquakes - Processes 16 WHERE TWO TECTONIC PLATES COLLIDE 17 1 Earthquakes - Processes 1 Earthquakes - Processes 18 CHRISTCHURCH 19 1 Earthquakes - Processes HOW DO YOU MEASURE IT? Question - How are earthquakes measured? The Richter Scale • On this scale, the magnitude of an earthquake is expressed in whole numbers and decimal fractions. It is not used to express damage. The modified Mercalli Scale This is the intensity value assigned to a specific site after an earthquake and has a more meaningful measure of severity to a non scientist than the magnitude because intensity refers to the effects actually experienced. ! 1 Earthquakes - Processes 20 • MEASURING EARTHQUAKES Earthquakes were traditionally measured on the Richter scale. Now they are measured using the Moment Magnitude Scale (Magnitude scale) • This measures the size of the seismic waves during an earthquake. The amount of damage caused by an earthquake is measured by the Mercalli Scale. 1 Earthquakes - Processes 21 • This is a measure of intensity ! ! ! 1 Earthquakes - Processes 22 Using the guide on the next page, illustrate the impacts of an earthquake at each magnitude on the Richter Scale. SEISMIC WAVES Earthquakes produces shock waves that cause damage. There are two types of seismic waves * P-waves (longitudinal/faster/travel through solids and liquids) – like sound waves * S-waves (transverse/slower/travels through solids only) – like light waves 1 Earthquakes - Processes 23 Seismometers can detect these waves and provide evidence of the Earth’s surface 24 1 Earthquakes - Processes BODY WAVES These waves travel through the Earth P-waves are the fastest type of seismic wave. As P-waves travel, the surrounding rock is repeatedly compressed and then stretched. S-waves arrive after P-waves because they travel more slowly. 1 Earthquakes - Processes 25 The rock is shifted up and down or side to side as the wave travels through it. SURFACE WAVES These travel over the Earth’s surface Rayleigh waves (also called ground roll) travel like ocean waves over the surface of the earth moving the ground surface up and down. They cause most of the shaking at the ground surface during an earthquake. 1 Earthquakes - Processes 26 Love waves are fast and move the ground from side to side. MAPPING THE DEADLIEST EARTHQUAKES You will be given a table of earthquakes and a world map Use the map to present the information in the table. Your final map should: 1 Earthquakes - Processes 27 • Be easy to understand. This includes usin g coloured pencils, rulers, horizontal labels etc • Contain all the relevant information in the table • Follow mapping convensions • Title, key, orientation, scale Once complete, answer the questions on the separate handout