Earthquakes

Earthquake

Vibrations or tremors of the earths crust caused by a sudden release of energy along fault lines

Seismic activity

The frequency and intensity of tectonic movement

Focus

Point where an earthquake originates underground

Epicentre

Point on the earths surface directly above the focus

Shockwaves/seismic waves

Energy that radiates from the focus

Seismologist

Earthquake scientist

Seismograph

Instrument to measure earthquake intensity

Elastic rebound

Plates return to original position after an earthquake

Aftershock

Smaller tremors following the main event

Convergent/destructive earthquakes

Subduction zones, deep earthquakes eg Japan 2011

Or continental collisions eg himalayas

Divergent/constructive earthquakes

Plates pull apart, shallow earthquakes eg mid atlantic ridge

Transform/conservative earthquakes

Transform faults

Plates slide past each other, shallow but powerful quakes eg. San andreas fault

Methods of measurement

Richter scale: quantifies magnitude usually 1-10 seismometer

Modified Mercalli scale:describes effects based on human observation l to Xll

Moment magnitude scale: more accurate. Energy based

Tools of measurement

Strainmeter: this measures the stress and strain on a fault line

Tiltmeter: detect any changes in the angle of slopes .effective in monitoring volcanic eruptions where the side of a volcano may bulge before an erruption

Satellites: useful for producing images of surface changes, especially along coastlines before a tsunami

P-waves

Primary waves . Fast. Compressional (move back and forth) less damaging

S waves

Secondary waves. Slower. Shear waves. Become more intense as earthquake progresses. Damaging

Surface waves

Slowest but most destructive

Earthquake prediction

Historical records: can find earthquake prone zones

Animal behavior

Tiltmeters,strainmeters: can detect small changes

Radon gas emissions

Earthquake precautions

Deep foundations. Shock absorbers. Cross bracing. Earthquake resistant materials. Emergency drils. Strict building codes near fault lines

Effects of earthquakes

Immediate: death, infrastructure, collapse fires, tsunami, liquid, faction, and homelessness

Long term: disease .psychological trauma .economic loss .migration- cholera spreads, Fukushima leak

Liqufaction

Solid ground temporarily becomes a viscous liquid thick and sticky

Poorly drained fine grain soils such as silty gravity soils or sandy soil

Shockwaves travel through ground water so water makes its way upward through the earths layers soil particles lose contact with one another and secondary waves vibrate through the soil, causing it to behave like a liquid

Tsunamis

Caused by undersea earthquakes or volcanic activity

Fast moving

Eg.indian ocean 2004, japan 2011