Monitoring And Predicting Earthquakes Flashcards
Richter scale
. Monitors earthquake strength
. Unlike the Mercalli scale which looks at the damage caused by an event the Richter scale measures the ground deformation and energy release by an earthquake
. The scale is logarithmic and therefore 3 is 10x greater than 2
Mercalli intensity scale
. The effect of an earthquake on the Earth’s surface is intensity
. The intensity scale consists of key responses such as people awakening, movement of furniture, damage to chimneys, and total destruction
. The lower numbers of the intensity scale generally deal with the manner in which the earthquake is felt by people.
. The higher numbers are based on observed structural damage
. Structural engineers usually contribute information for assigning intensity values of VIII or above.
Seismometers
. In order to measure an earthquake as it occurs we use seismometers
. These machines are used to plot a seismograph
. Can be read to determine just how much shaking occurred
. A weight is suspended in a way to remain still when ground shakes (modern ones use electro magnets)
. Writing instrument is attached to the weight allowing it to record the movement
. Modern earthquake monitoring uses seismometers not seismographs and record earth movement digitally
. Theses wavelengths that represent earth’s movement are so small that they have to be amplified
Predicting earthquakes: past seismic events
. Seismic gap theory
. Regular pattern can help predict the next earthquake
. The seismic gap states that earthquake hazard increases with time since the last large earthquake on certain faults or plate boundaries
Radon gas emissions
. Radon gas escapes from cracks in the Earth’s crust
. Levels can be monitored and a sudden increase may suggest an earthquake
. Spikes in gas has been attributed to pre seismic stress or fracturing of the rock
. Radon is produced by radioactive decay of the trace amounts of uranium
. As it is radioactive is easily detected and has a short half life
Remote sensing
. A seismometer is used to pick up the vibrations in the earth’s crust
. Increase in vibrations indicate an earthquake
. Tilt metres can show ground deformation leading to an earthquake
. Have been replaced by modern and wider ranging satellite imagery
. Remote sensing uses satellites or aircraft
. Can detect the physical characteristics of an area by measuring its reflected and emitted radiation at a distance
Animals
. They may detect seismic activity and notice smaller vibrations and exhibit unusual behaviour
. They may sense ionisation of air caused by the large rock pressure in earthquake zones in their fur
. May smell gases
Lazar beams
Can detect plate movement by directing the beam across the fault line.
Pros + cons of mercalli scale
Cons:
. Can only measure earthquakes in inhabited ares
. Not very scientific
. Damage caused may not accurately reflect an earthquake’s strength
. Only measure effects not energy released
. Witnesses that scale is based on may not be accurate
Pros:
. Useful in determining damage caused to an area and responses can be planned
. Structural engineers contribute information for assigning values of VIII which is useful for rebuilding phases
Mercalli scale vs Richter scale
. Unlike the mercalli scale which looks at damaged caused the Richter scale measures ground deformation and energy released
. In richter as you move up the magnitude frequency decreases
. Large earthquakes are rare as it takes many years for the pressure and energy to build up
. Scientists prefer the Richter scale as it is more scientifically based, logarithmic scale, rather than human observation
Effects of earthquake: primary (immediate impact)
. Liquefaction of saturated soils
. Schools, universities destroyed
. Ground shaking will cause: building/bridges to collapse, power lines to collapse, water mains, gas mains and sewers to fracture
. Immediate deaths and injuries from crushing, falling glass, fire an d transport accidents
. Building foundations subside resulting in more collapses, possible deaths and injuries
. Damage to power stations
. Slope failures setting off landslides and avalanches
Effects of earthquake: secondary effects (as a direct consequence)
. Fires caused by broken gas pipes and power lines are difficult to put out, disease spread by contaminated water
. Flooding from blocked rivers creating
quake lakes
. Civil disorder, looting and direct intervention from civil authorities e.g. police, army
. Power cuts restrict emergency services including immediate medical care
. Panic, fear and hunger
. Repairs to buildings can be difficult and reconstruction expensive
. Education suspended for immediate future
Effects of earthquake: long term effects
. Bodies not buried/cremated spread disease such as cholera and injuries, may result in long term disability or death if not treated promptly
. Reconstruction of power stations is very expensive, hence it may take time before this is done
. Long term ‘lost generation’ to develop local/regional economy
. Permanent disruption of natural drainage patterns. Loss of farmland and food production
. Higher unemployment as not all businesses recover from damage, repair and reconstruction of
infrastructure may take months/years
. Disability and reduced life expectancy and trauma/grief may take months/years from which to recover from
. Problems restoring trust in neighbours and civil authorities
