2 DefinitionEarthquakes – the shaking of the ground caused by the release of energy waves as rocks in the earth’s crust move suddenlySeismology – The study of earthquakesSeismologist – Scientists who study earthquakes
3 Where Do Earthquakes Occur? Near edges of tectonic platesTectonic plates can move toward each other, away from each other or slide past each otherThese movements create faults in the Earth’s crustA fault is the break in the Earth’s crust along which blocks of the earth's crust slideEarthquakes occur along these fault lines
4 What Causes Earthquakes? As tectonic plates move along faults, stress builds up as the rocks get stuck togetherThis causes the rocks along the fault to change their shape or deformElastic deformation leads to earthquakesRocks can stretch but eventually they will unstick and move suddenly into a new positionWhen the rocks unstick they release energy in the form of seismic waves. These waves of energy cause earthquakes
5 Seismic Waves Waves of energy that are released during an earthquake. These waves are able to travel through the Earth’s interior and along the Earth’s SurfaceIt is these waves that cause damage during an earthquake
6 P and S Waves P Waves are the fastest seismic waves Also known as Primary WavesThey are able to travel through both liquids and solids so they can reach across the entire planetS Waves travel at half the speed of P WavesAlso known as Secondary WavesThey can only travel through solids so they can not travel through the Earth’s outer core
7 Locating an Earthquake Seismologists use seismographs. These instruments can detect and record seismic wavesBased on the arrival times of P and S waves to the seismograph, seismologists can determine the location of the earthquake.
8 Epicenter and FocusEpicenter is the point on the Earth’s surface directly above an earthquakes starting pointDamage done during an earthquake will usually be the most severe at and around the epicenterFocus is the point inside the Earth where an earthquake beginsSeismographs and the timing of the S and P waves can help to locate the epicenter and the focus of an earthquake
9 Measuring Strength and Intensity Strength of an earthquake is measured using Richter ScaleStrength also known as magnitudeMeasure of ground motionBased on a scale of 1 to 10Each unit increase equals ground motion becomes 10 times largerIntensity of an earthquake is measured using Mercalli ScaleMeasure of how people feel the earthquake and how much damage it causesBased on numbers I to XIII is not felt at all, XII is total damage to area