Download Earthquakes

EARTHQUAKES
• Natural, rapid shaking of the ground that
results from displaced rocks within the crust.
• Breaks in the rock release energy that travel
through the Earth as seismic waves.
• When the waves reach the surface, the
ground moves.
EARTHQUAKES
• When seismic waves reach the ocean floor,
tidal waves (tsunamis) are formed.
• Earthquakes tend to occur along plate
boundaries, however, an earthquake can
occur along ANY fault in the rock anywhere!
SEISMIC WAVES
• Seismic waves are detected using a
seismograph, which uses a series of springs
and weights to record vibration.
• 3 types of seismic wave:
• Primary (P) waves: compressional or
longitudinal, like sound waves. Travel fastest
and so are detected first – hence the name.
Can travel through solids, liquids, and gases.
SEISMIC WAVES
• 3 types of seismic wave:
• Secondary (S) waves: transverse, like ocean
waves or light. Particles move perpendicular
(at right angles) to the direction of the wave
and can only travel through solids.
SEISMIC WAVES
• 3 types of seismic wave:
• Surface waves: produced by interaction of P
and S waves, resulting in a rolling motion of
the ground.
EPICENTER AND FOCUS
• The break in the rock which is the source of
the waves is called the focus.
• Area directly above focus is called the
epicenter.
EPICENTER AND FOCUS
• The location of the epicenter is determined by
the arrival of P- and S-waves:
• Using a seismograph to record the waves,
distance to epicenter can be calculated if you
know when waves arrived and how fast each
wave type moves. Which we do.
• You need three seismograph stations to find
an epicenter (triangulation).
EPICENTER AND FOCUS
• Why three? What if you only had one
seismograph station?
• What if you had two?
• Triangles. Is there anything they can’t do?
EARTHQUAKE MEASUREMENT
• There are two scales I expect you to know:
• Richter scale
• Measures energy of earthquakes.
• Scale goes from 0-9. Each increase in number
means a tenfold increase in magnitude (a
logarithmic scale).
• So a 6.0 is 10x as large as a 5.0. A 7.0 is
100x as large as a 5.0.
EARTHQUAKE MEASUREMENT
• Modified Mercalli Intensity scale (MMI)
• Measures destruction level at a given
location.
• Scale goes from I to XII.
EARTHQUAKE MEASUREMENT
• Image – Richter and MMI scales