Transcript Slide 1 - Cloudfront.net

Magnitude: measuring the
amplitude of seismic waves
Measured by seismograph
 Scaled on the Richter scale

– Logarithmic scale: for each increase of 1
point, the earthquake is 10 times stronger
 A 5.0 earthquake is 10x stronger than a 4.0
 A 8.0 earthquake is 100x stronger than a 6.0
Seismograph: Records the motion of
the earth, and thus the seismic waves
Seismograph Reading

P-waves arrive first, then S waves, the
Surface waves (love and rayleigh)

Seismograph recording stations will record
the time between the arrival of P waves and
S waves to determine how far away the
epicenter is
– Longer time between the waves means the
earthquake is further away
3 seismograph readings are used to
find the epicenter



Each site
determines its
distance from
the EQ and
maps it as a
radius around
the site
The place where
all circles
intersect is the
epicenter
Distance is
different at each
of these sites,
but magnitude
reading is the
same.
Intensity: Measure of damage or
shaking an earthquake causes
Scaled on the Mercalli Scale
 Given based on observation of damage, so
values are different in different locations

– Closer to the epicenter = higher intensity
rating
Mercalli Scale rates EQs 1-12
Northridge
Earthquake
Intensity
Haiti
Earthquake
Intensity
Volcanoes
Hills or mountains that erupt lava
 Formed at divergent and convergent plate
boundaries
 Divided into two categories:

– Steep slope
– Gentle Slope
Steep Slope Volcanoes
Composite volcanoes are also known as
stratovolcanoes
Steep Slope Volcanoes

Viscous (thick) lava
– Does not flow easily (think of syrup or tar), so
builds up on the sides of volcanoes. This is
what creates the steep slope
– What happens when you blow bubbles in
syrup?
 Gas gets trapped in the viscous lava
– Causes VIOLENT eruptions!
Steep Slope Volcanoes

Form at
convergent
boundaries
– Pressure
built up
under
subduction
zones
causes
violent
eruptions
Ring of Fire:
active volcanoes surrounding the convergent boundaries
that border the Pacific Ocean
Gently-sloped Volcanoes
Gently-Sloped Volcano

Lava is not viscous (Not thick; runny)
– Flows easily down the volcano, so gentleslope is formed
– Gas not trapped in lava (think of blowing
bubbles in water)
 Eruptions are calm (no pressure built up from gas)

Lots of Lava when it erupts!
Gently-sloped Volcanoes:
Form at divergent boundaries or Hot Spots
(This is what formed Hawaii!)
Hot Spots: Very hot regions in earth’s
interior
•Hot spots stay
in the same
place, but plates
move over them
•This forms
volcanic island
chains, such as
Hawaii