Seismic Hazards

Question 1

earthquake

Answer 1

a tremor or movement of the earths crust

Question 2

cause of earthquakes

Answer 2

crust moves, slow build-up of stress between boundaries within rocks, pressure suddenly released, surface experiences intense shaking motion

Question 3

earthquakes link to tectonic theory

Answer 3

occur along plate boundaries so shaking motion suggests we have plates and they’re moving

Question 4

focus

Answer 4

breaking point at which pressure release from the earthquake occurs within the crust

Question 5

epicentre

Answer 5

point of pressure release directly above the focus on the earths surface with most intense ground shaking

Question 6

foreshocks

Answer 6

before, minor shocks- rocks beginning to move, become less frequent as rocks stick and lock

Question 7

aftershocks

Answer 7

minor shocks as rock masses settle into new positions

Question 8

liquefaction

Answer 8

occurs when water saturated soils lose strength and act like a fluid as the structure of a loose, saturated sand breaks down (very damaging to infrastructure as undermines foundations)

Question 9

why surface waves cause most destruction

Answer 9

confined to earth’s surface and cause ground to twist in side-to-side movements as well as rolling, up-and-down movements

Question 10

Primary effects of seismic hazards

Answer 10

Ground shaking along fault lines, ground rupture

Question 11

Secondary effects of seismic hazards

Answer 11

Liquefaction, landslides/avalanches, tsunami, fires, collapsed buildings, shock/seismic waves

Question 12

shallow focus

Answer 12

0-70 km deep, tend to cause greatest damage (account for 75% energy released)

Question 13

intermediate focus

Answer 13

70-300 km deep

Question 14

deep focus

Answer 14

300-700 km deep

Question 15

magnitude

Answer 15

amount of energy released by an earthquake (strength)

Question 16

tsunami

Answer 16

a series of very large waves created by undersea disturbance

Question 17

most at risk areas in the world to tsunamis

Answer 17

pacific ocean- ring of fire, north/east indian ocean, indonesia, east asia

Question 18

where are tsunamis found

Answer 18

subduction zones at destructive boundaries where shallow, large eq’s occur with large bodies of water

Question 19

drawback

Answer 19

where the first part of wave is a trough not crest so water along shoreline recedes dramatically exposing normally submerged areas

Question 20

why does drawback occur

Answer 20

tectonic plate on one side of faultline sinks during eq causing overlaying water to propagate outwards with trough at front

Question 21

run up

Answer 21

when the wave peak reaches the shore which is the temporary raise in sea level

Question 22

observations to predict seismic activity

Answer 22

crustal movement, changes in electrical conductivity, strange and unusual animal behaviour, historic evidence