EARTHQUAKES EARTHQUAKES WHAT IS AN EARTHQUAKE Earthquake movement

EARTHQUAKES

EARTHQUAKES

WHAT IS AN EARTHQUAKE • Earthquake – movement of Earth’s lithosphere that occurs when rocks in the lithosphere suddenly shift, releasing stored energy • Energy released during an earthquake is carried by vibrations called seismic waves

STRESS IN EARTH’S CRUST • Stress – force that squeezes rock together, stretches or pulls them apart, or pushes them in different directions • As tectonic plates move, they cause stress in the crust, which in turn produces faults & folds. • Fault – break in a mass of rock along which movement occurs. • many occur along plate boundaries • e. g. San Andres fault

STRESS IN EARTH’S CRUST • Fold – bend in layers of rock • form where rocks are squeezed together, but do not break • rock tends to fold rather than break when under high pressure & temperature

EARTHQUAKES & SEISMIC WAVES • Earthquakes occur because stress forces exceeded the strength of the rock • Focus – where earthquake begins • Epicenter – location on Earth’s surface directly above the focus • As earthquake occurs, seismic waves move out in all directions from the focus

EARTHQUAKES

EARTHQUAKES

EARTHQUAKES & SEISMIC WAVES Earthquakes and seismic waves produce 3 main types of seismic waves • P waves • Surface waves

EARTHQUAKES & SEISMIC WAVES • P waves (primary waves) – longitudinal waves similar to sound waves • Particles in material vibrate in direction of waves’ motion • Fastest of seismic waves so first to be detected • CAN travel through both solids & liquids

EARTHQUAKES & SEISMIC WAVES • S waves (secondary waves) – Transverse waves • Particles in material they pass through vibrate at right angles to direction wave moves ** CAN’T travel through liquids

EARTHQUAKES & SEISMIC WAVES Produce 3 main types of seismic waves • Surface waves – develop when seismic waves reach Earth’s surface • Move more slowly than P waves & S waves but usually produce larger ground movement & greater damage

EARTHQUAKES & SEISMIC WAVES

EARTHQUAKES & SEISMIC WAVES

EARTHQUAKES & SEISMIC WAVES • To measure earthquakes and pinpoint their epicenter, geologists record seismic waves using seismographs • seismographs – device that can detect & record seismic waves • Most earthquakes are too small to be felt by humans

MEASURING EARTHQUAKES • Richter Scale – rates earthquakes based on measurements of times & amplitude of seismic waves by seismographs • most well known but no longer used by geologists • Moment Magnitude Scale – gives measure of amount of energy released by an earthquake • Modified Mercalli Scale – based on observations of the intensity of ground shaking & damage in areas affected by an Earthquake, 1 -12

SEISMOGRAPHIC DATA • cannot predict earthquakes yet but can map earthquakes around the world & map the interior structure of Earth • Most earthquakes are concentrated along plate boundaries, where many faults are found

http: //www. nbcnews. com/id/7807001/ns/technology_and_science/#. Ul 9 Z 9 Civm 5 c

http: //www. nbcnews. com/id/7807001/ns/technology_and_science/#. Ul 9 Z 9 Civm 5 c