tectonic hazards: earthquakes

Faulting

Slow due to friction, stressed rocks along the fault, rocks rupture and are displaced when stress exceeds the strength of the rocks

Stress

Force that results from plate tectonic movements : tensional, compressional and shearing forces

Strain

Change in shape or location of the rocks due to stress

Normal dip slip fault

Hanging wall moves relative to the footwall

Reverse dip slip

Hangning wall moves up relative to footwall

Low angle thrust fault

hanging wall moves up relative to footwall

Same movement as a reverse fault just at a shallower angle

Strike slip

Crust either side of fault moves horizontally (laterally) in opposing directions

Body waves

Primary and secondary waves.

Travel through the interior of the earth

Arrive before surface waves

Have a higher frequency (shorter wavelength) than surface waves

Surface waves

Travel only through the crust of the earth

Lower frequency than body waves

Easily distinguishable on seismographs

Almost entirely responsible for damage caused in earthquake

Damage reduced in earthquakes with a deeper focus

Richter scale

Recorded with a seismograph

First estimates of magnitude

Moment magnitude scale

Absolute size of earthquake

Measurement of actual energy released

Focus

Place within the earth where the earthquake starts (point of fault rupture)

Deeper earthquakes mean less dangerous earthquake.

Loss of energy is reffered to as attenuation.

Epicentre

Place on the earths surface directily above the focus, where shaking is most violent.

Liquefaction

Occurs on the surface when water saturated sand rapidly changes from a solid to a,liquid

Can cause buildings to float

Common in mag 5.5 earthquakes occurring in younger sediments

Landslides

Most common secondary effects during an earthquake

Can cause significant loss of human life

Fires

Earthquakes can cause pipe rupture and sparks leading to large scale fires

Retrofitting

Adapting current structures with new materials that can make them resistant to the shaking during an earthquake