Tectonics Earthquakes and seismicity

Quantitative measurement measures a number and is objective (Richter) whereas a qualitative measurement measures an opinion and is subjective (Mercalli)

The amplitude of the waves, the greater the magnitude the greater the shaking

On the Richter Scale or by moment magnitude on a seismograph or seismometer

Each number on the scale is a 10x increase to the previous number

A reliable indication of the size of an earthquake. Combines the amount of movement on the fault, rock strength and the size of the rupture area.

• The degree of surface shaking
• Measured on the Mercalli Scale - qualitative

• Soil liquefaction
• Landslides
• Avalanches 
• Tsunamis

• Disease
• Famine
• Infrastructure collapse
• Loss of life
• Economic downturn
• Fire

Partially saturated soils lose strength and structure as a consequence of applied stress from the earth shaking. The soil is caused to behave like liquid.

• They can over-turn people and structures, cause building damage or collapse, break underground pipes and block roads
• E.G. In Alaska 1964, 56% of all damage was caused by landslides

• Destabilized snow and ice asa result of the sudden shaking of the ground. 
• Snowfall, temperature, wind direction, slope angle and terrain all influence the risk of an avalanche
• E.G. mount everest as a consequence of Nepal earthquake

Earthquakes cause subsidence of the sea floor. This displaces water, which tries to regain its equilibrium. The wave compresses as it reaches the shore and the amplitude increases

• Location of epicentre
• Depth of focus 
• Geology 
• Duration of shaking 
• Time of day

• Building style and land use
• How people react before, during, after quake 
• Community preparedness
• Emergency and relief services - availability and organisation
• Economic and social structures

• avoidance 
• Modify event 
• modify vulnerability 
• modify loss
• do nothing

• The time it takes from the first signs of the event to its peak
• can range from seconds to years

The land area affected by the hazard

The extent of which the location of a hazard can be predicted.

No we cannot control earthquakes, but can try and reduce man-made earthquakes through hazard-resistant designed buildings

• Through warning systems, such as in Japan
• Correct preparation, eg drills so people are less likely to panic
• Taking accounts of earthquake survivors to see whether they had an observations before it happened
• Monitoring the change in groundwater levels, release of radon gas or unusual animal behaviour
• Keep emergency supplies in community and private stock
• Land-use planning

• Immediate international disaster aid
• Life insurance - payouts made to families to help them if a family member dies - not realistic in LEDCs

• Primary waves (P-waves)
• Secondary waves (S-waves)
• Rayleigh waves
• Love waves
• Co-seismic elevation
• Ground rupture

• P waves 
• S waves

• Love waves
• Rayleigh waves

• P waves
• S waves
• Love waves
• Rayleigh waves

• S waves
• Love waves

• Two plates have equally pressured and stable position on slope.
• Sudden movement on the fault line creating an imbalance and the plates to slip

A fracture or zone of fractures between two blocks of rock

A dip-slip fault in which one block above the fault has moved downwards

• The upper block moves up and over the lower block. Common in subducting plate areas (e.g. Japan) 
• 

• Two blocks slide past one another 
• e.g. San Andreas Fault
• 

The direction determines the displacement of the far block

Movement of blocks underground but land above doesn't 'crack' it just bends 

Along conservative or destructive plate margins

• Earthquakes that do not occur on the plate boundary
• Rarer
• May be caused by man (mining, creating dams or reservoirs)

Destructive

• The Ring of Fire
• 80% of energy

• The point on the surface directly above the focus
• Shock waves radiate out from the focus like ripples

The hypocentre

No, they can only travel through solid material

Shallow

Giant sea waves caused by large scale and sudden disturbance of the seawater

Objects such as boats and vehicles, and structures like wooden buildings, are lifted and carried inland by the wave. The backwash of the wave may have a similar effect, carrying objects offshore

tearing buildings apart, washing away soil, undermining foundations of buildings, bridges and harbour structures

battering by debris carried in the wave. Human deaths as a consequence of drowning, or being lifted or battered by moving debris

Around the Pacific Basin, particularly at plate boundaries

• The cause of the tsunami (earthquake, mass movement etc)
• Distance travelled from source
• Water depth
• Profile of coast
• Orientation of coast

increase the height

Over 500mph

• 150-250km
• (normal waves = 100m)

• Thrust fault earthquakes in water (Japan)
• Volcanic explosion that releases large amount of debris into sea (Alaska, 1964)
• 'Ping' effect of a movement on destructive plate boundary
• Glacial calving due to global warming

75%

The minimum/lowest part of the wave

• The wave is compressed, meaning speed decreases to below 50mph and wave length is shortened to less than 20km. This increases amplitude 
• 

• A strong tide that pushes up rivers, as a consequence of a tsunami, against the current.
• May cause flooding