Earthquakes

Earthquakes

• Earthquakes – series of shock waves traveling through the earth

• Elastic rebound – a movement (slippage) caused by rocks shifting to an unstressed position, when this movement occurs waves of motion in the earth radiate from the point of slippage

Earthquakes

• Aftershock – secondary earthquakes produces when slippage occurs in one location of the fault it increases strain in another location causing more slippage

• Seismologists – earthquake scientists• Seismographs – instruments that detect

and measure earthquake waves

Earthquakes

• Richter Scale – named after Charles Richter. The scale indicates the magnitude of the earthquake. (Ranges from 0 – 9+. Anything over 3 you can feel.)

• Magnitude – amount of energy released• Each step up the Richter Scale indicates

31.6 times more energy. (Ex. Magnitude 3 on the Richter Scale has 31.6 times more energy than a magnitude 2).

Earthquakes

• Intensity – earthquake’s destructiveness– Factors of intensity include:

• Location underground• Distance• Duration• Structures and population nearby

• Focus – center of the earthquake’s activity• Epicenter – the location on the surface

that is directly above the focus

Earthquake Hazards• Hazard – it’s the source of danger, can’t do anything

about a hazard• Risk – possibility of injury or property damage, you

can reduce the risk• Hazards of earthquakes– Buildings falling– Fire – electrical problems– Tsunamis – waves caused by earthquakes– Landslides– Mudslides

Earthquake Waves

Earthquake Waves

• P Waves – first waves to hit a seismic station, body waves (called P for primus, which means first)– Body waves – waves that can pass through the

interior of the earth– Can travel through solid and liquid material– Travel through the earth (mantle, crust, inner

and outer core)– Short wavelengths and short amplitude

• Wavelength – distance between crests• Amplitude – amount of the earth that is displaced

from its resting position

Earthquake Waves

• S Waves – second waves to hit a seismic station, body waves (called S for secundus which means secondary)– Body waves– Large amplitude– Slower and stronger waves– Travel only through solid material– Do not penetrate core just lithosphere and

mantle

Earthquake Waves

• L Waves – last waves to hit a seismic station, travel along the surface– Slowest of the earthquake waves– Most destructiveof the earthquake waves

Earthquake Waves

• How do we know where the epicenter of an earthquake is?– Length of time between the P and S waves

indicates distance from the epicenter. Three seismic stations record the time between the P and S waves. Each station then draws a circle using the station as the center of the circle, and the radius the distance from the epicenter. Where the three circles meet is the epicenter.

Predicting Earthquakes

• Some earthquakes follow volcanoes• Some volcanoes follow earthquakes• Historical data• Bottom line we cannot predict

earthquakes so work on making man made structures more earthquake friendly

10 Things You Didn’t Know About Earthquakes

• http://www.youtube.com/watch?v=ftZVk0CUWxA