Understanding the background to seismic hazards Flashcards
What causes seismic hazards?
A build up of stress within rocks. When the pressure is suddenly released, parts of the surface experience an intense shaking motion that lasts for just a few seconds.
Where is the pressure released during a seismic hazard?
The focus
What is the epicentre?
The point immediately above the focus on the crust
What is defined as a shallow focus?
0-70km deep
What is defined as a intermediate focus?
70-300km deep
What is defined as a deep focus?
300-700km deep
How is the magnitude of an earthquake measured?
The Richter scale, a logarithmic scale
What is more commonly used to measure earthquakes?
MMS - moment magnitude scale
What does the MMS measure?
Identifies the energy released
What was the Mercalli scale?
Measures intensity
How do we predict seismic hazards?
Monitor groundwater levels
Measure local magnetic fields
Areas can be mapped on the basis of geological information and studies made into ground stability - predict the impact of an earthquake - product hazard zine map - used by national planners
How do we prevent earthquakes?
It is pretty much impossible, however there have been studies into lubricating the movement of plates, to stop ‘sticking’ then releasing
How do we protect ourselves from seismic hazards?
In USA, FEMA follows certain objectives: educate people of EQ effects and risk, improve construction, encourage planning policies
How can buildings be designed to be aseismic?
Putting a large concrete weight on the top of the building which will move, with the aid of a computer programme, in the opposite direction to the EQ to counteract stress
Large rubber shock absorbers in the foundations
Adding cross-bracing to the structure to hold it together
How does education protect us from earthquakes?
Instruction can be issued on how to secure homes, appliances, and heavy furniture, and assembling ‘EQ kits’.
