Earthquakes
Chapter 19
San Francisco

https://www.youtube.com/watch?v=Z7eABGp
OHv8
Focus vs. Epicenter


Focus
_________–
where the
rock breaks and
seismic waves begin;
can be at deep or
shallow depths
_________
Epicenter – point on
the surface directly
above the focus;
usually what is used to
locate the position of an
earthquake
Seismic Waves

Primary
_______ (P) Wave –
fastest, able to travel
through liquids, energy
travels in the same direction
wave is traveling
 Secondary
________ (S) Wave –
slower, not able to travel
through liquids, energy
travels at right angles to
direction wave is traveling
Surface (L) Wave –
 ________
travels along the surface,
knocks down and
destabilized structures.
The interior
structure of
the earth is
determined by
the pattern of
seismic
waves. The
outer core
__________
is liquid so
s-waves can
not pass
through.
The difference in
arrival times between
p-waves and s-waves
lag time
is called __________.
The greater the lag
time (shown here as
the distance between
the two curves) the
greater
_________
the
distance away from
the earthquake.
To locate the
epicenter of an
earthquake, a
minimum of ____
three
seismograph
stations is
needed. The
location is where
all circles
intersect
_______.
How do we measure earthquakes
Earthquakes are measured on 2
scales
• Richter Scale measures
_magnitudes
• Modified Mercalli Scale
measures damage