4 The Geography of Earthquakes Earthquake activity – how, why and where it occurs How earthquakes and their effects may be predicted The effects of earthquake activity on different worldwide examples

Chapter 4: The Geography of Earthquakes What is an earthquake? Occur due to the movement of tectonic plates Shaking or vibration of the Earth’s crust Sudden release of energy along a fault line Seismic waves/tremors are known as shocks Three types of shocks: Fore shock Main shock After shock

Chapter 4: The Geography of Earthquakes What are the causes of earthquakes? Plate movement fuelled by convection currents Sometimes the plates get stuck Stress and pressure builds up in the rocks of the plates Rocks bend under this pressure Plates slip along the fault line Energy is suddenly released Shock waves sent to the Earth’s surface resulting in an earthquake

Chapter 4: The Geography of Earthquakes The Richter scale Used to measure the intensity of an earthquake Point scale, measuring 1 to 10 Each point on the Richter scale is a 10-fold increase in power

Chapter 4: The Geography of Earthquakes The Mercalli scale Measures earthquake damage Scale of 12 points 1 means no damage 12 means complete devastation

Chapter 4: The Geography of Earthquakes Categories of earthquake Shallow earthquakes Intermediate earthquakes Deep earthquakes

Chapter 4: The Geography of Earthquakes Shallow earthquakes Focus is close to the surface Most common type Great loss of life and destruction Occur at plate boundaries Result of a plate sinking becoming stuck and then releasing

Chapter 4: The Geography of Earthquakes 2. Intermediate earthquakes Lower depths Associated with melting plates

Chapter 4: The Geography of Earthquakes 3. Deep earthquakes Focus is deep in the Earth Associated with changes in chemical or mineral composition

Chapter 4: The Geography of Earthquakes Where do earthquakes occur? Commonly associated with destructive plate boundaries. They occur: when two continental plates collide when a continental and oceanic plate collide

Chapter 4: The Geography of Earthquakes Three types of fault are associated with earthquake activity: Normal fault Thrust fault Transform fault

Chapter 4: The Geography of Earthquakes 1. Normal faults Crust of the Earth has vertical movement Rocks are stretched and pulled apart Area of crust moves downwards along the fault line e.g. Great African Rift Valley

Chapter 4: The Geography of Earthquakes 2. Thrust faults Occur where rocks of the Earth’s crust push over one another Forms an area of block mountains e.g. Ox mountains, Sligo

Chapter 4: The Geography of Earthquakes 3. Transform faults Plates slide past each other horizontally e.g. San Andreas Fault, California, USA

Chapter 4: The Geography of Earthquakes Seismic waves The waves that shake the Earth’s crust. There are three types: P-waves Primary waves and are the first to be recorded Fast-moving waves Compress and expand the material resulting in vibrations forward and backward

Chapter 4: The Geography of Earthquakes Seismic waves (continued) 2. S-waves Secondary waves and are second to arrive Slower-moving waves that move through rock Causes a right-angled movement/vibration

Chapter 4: The Geography of Earthquakes Seismic waves (continued) 3. Surface waves Travel close to the surface and are the last waves Slowest waves Arrival is noted by vibrations of the Earth’s crust in an upward and sideways motion

Chapter 4: The Geography of Earthquakes Earthquake prediction Seismologists study the history of earthquake activity Patterns of earthquake activity along a fault line Greater the time since the last earthquake striking, the more imminent is the next

Chapter 4: The Geography of Earthquakes Seismic gaps The time gap between earthquakes Period of inactivity Tiltmeters record changes that occur to levels of land Tell-tale signs, e.g. animal behaviour

Chapter 4: The Geography of Earthquakes Damage caused by earthquake Depends on a number of factors: Time of the earthquake Magnitude of the earthquake Depth of the focus Distance from the epicentre Duration of the earthquake Type of rocks and soils Population within the affected region Building structures Utilities of the region

Chapter 4: The Geography of Earthquakes The effects of earthquakes Loss of life Damage to property Gas leaks Power cuts Liquefaction Fires Tsunami Damage to sewage system Landslides

Chapter 4: The Geography of Earthquakes Ways to limit earthquake damage Linked to level of development Developed economies more earthquake-proof Less developed or developing economies are most affected Earthquake-proof buildings Made of materials that can withstand the pressure of earthquake activity

Chapter 4: The Geography of Earthquakes Ways to limit earthquake damage (continued) Columns which are flexible to allow for movement of the building Rollers to allow for movement from side to side Flexible materials Fire-proofing Build on stable ground Liquefaction Emergency plans in place

Chapter 4: The Geography of Earthquakes Indian Ocean Earthquake, 2004 Occurred under the sea at 00:58 (UTC) on December 26 2004 Recorded as 9.1 on the Richter scale Epicentre was off the west coast of Sumatra, Indonesia Caused by subduction For approximately 1600 km the fault slipped about 15 m along the subduction zone where the Indian Plate subducts under the Burma Plate

Chapter 4: The Geography of Earthquakes Indian Ocean Earthquake, 2004 Resulted in a rise of the ocean floor and the displacement of large volumes of water, resulting in the tsunami striking the Indian Ocean coastlines Generated tsunami waves of some 30 m in height Affected many countries in south-east Asia and further afield, including Indonesia, Sri Lanka, India, Thailand, the Maldives and Somalia