Seismic Hazards Flashcards
What are seismic hazards?
Earthquakes, tsunamis, landslides and liquefaction
What is seismicity?
The earth’s shaking, can be human, induced or natural
How are seismic waves formed?
Pressure builds up at a point where plates meet
Sudden release due to rock failure creates waves
The waves cause the ground to shake
Intensity of the shaking is dictated by the depth of focus and energy release
What are tsunamis caused by?
Earthquakes under the sea, moving a column of water above it, displacing it
What are the characteristics of tsunamis?
Waves less that 3ft tall, but are compressed towards land, gaining height. A wave train which propagates from the earthquake.
What is liquefaction?
The mixing of sand or soil with groundwater during the shaking of a moderate or strong earthquake. Ground becomes very soft and similar to quicksand
When is land susceptible to landslides?
It has experiences heavy rain
Fractured or unconsolidated rock
Fold mountains, unstable plate boundary
Steep relief
How can earthquakes be predicted?
Past seismic events
Remote sensing
Radon gas emissions
How can past seismic events be used to predict earthquakes?
Looking into past frequencies and magnitudes to infer future events can be used for prediction
How can remote sensing be used to predict earthquakes?
GPS can be used to monitor the smallest of movements by the plates, stationary plates suggest build up of pressure
How can radon gas emissions be used to predict earthquakes?
Radon escapes from cracks in the earth’s crust and a sudden increase may suggest that an earthquake may be imminent
Are earthquakes predictable?
NO
What type of boundary do most earthquakes originate from?
Destructive - at subduction zones
Where is liquefaction a particularly dangerous hazard?
In areas where groundwater is near the surface and the soil is sandy
What is subsidence?
When the ground surface is lowered often during earthquakes
