Seismic Hazards

• Seismic= ground movement
• Earthquakes occur at all plate boundaries as they all experience some degree of movement. Frequent movement means there is a constant release of energy and pressure, so earthquakes here are less severe
• Earthquake- as the crust of the earth is constantly moving, there tends to be a slow build up of stress within the rocks. When this pressure is released, parts of the surface experience intense shaking.
• Retrofitting is when, in earthquake prone areas, buildings and other structures can be fitted with devices such as shock absorbers and cross-bracing to make them more earthquake proof.
• A tsunami is a giant sea wave generated by a shallow focus under water earthquakes, violent volcanic eruptions, under water debris slides and landslides into the sea. It is a displacement of water.
• An epicentre is the point on the earths surface immediately above the focus of the earthquake.
• The focus is the point where the pressure release occurs withing the crust.
• Magnitude is the size of an earthquake using amplitude of seismic waves. This is measures with a seismometer.
• The Richter Scale is a logarithmic scale proportional to the magnitude. Mostly replaced by the moment magnitude scale (MMS) which identifies energy released
• The Mercalli Scale is a human scale which measures the intensity of an event and its impact using a 12-point scale
• Landslides and avalanches are slope failures as a result of ground shaking
• Liquefaction: when violently shaken, soils with a high water content loose their mechanical strength and behave like a fluid. The water particles move to the surface.
• P waves are vertical. Buildings are built to withstand vertical weight
• S waves are horizontal. These are more destructive, especially to buildings that have not been built/retrofitted to withstand this movement
• Tsunami- water is quickly vertically displaced which forms waves. These can reach 500-600 inland. P waves uplift under the sea. Wave gets taller is water shallows and wave slows. Generated by a shallow focus underwater.
• Drawdown is the reduction in sea level (tide goes out).
• Management of seismic hazards involves preparation, mitigation, prevention and adaptation
• Preparation includes securing things to the wall or floor and making a plan (where to meet, where emergency kit is and what's in it, emergency radio or beacon)
• Mitigation involves deploying the army (Gov), education (gov) and earthquake proof beds.
• Prevention cannot truly be done so it is better to prepare and mitigate. But, it can involve early warning systems of magnitude and location.
• Adaptation includes retrofitting (pendulums, deep foundations, early warning systems, making buildings flexible through dampeners)
• Examples of management: EQ drills, fire prevention, emergency services, land-use planning, insurance, aid, tsunami protection.