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Earthquake Measurement
Chapter 8 Section 2
Locating Earthquakes
Locating Earthquakes
Seismographs are instruments located at
or near the surface of the Earth that
record seismic waves
Seismogram is a tracing of earthquake
motion created by a seismograph
Scientists can find out when an earthquake
starts by comparing the arrival time of the
P&S waves
They compare the arrival time with other
seismographs in the area
Locating Earthquakes
Epicenter is the point on the Earth’s
surface directly above an earthquake’s
starting point
Focus is the point inside the Earth where
an earthquake begins
They can use seismographs to find out
where an earthquake started
Scientist use the s-p method
They measure the lag time between the SP waves
The further away it is the longer the
lapsed time between the S-P wave
Triangulation
Scientists need at least three seismograph
stations to locate the epicenter of an
earthquake
Using a compass to draw the (distance)
radius out from the seismograph
Scientist do the same thing at other
seismograph stations
When three of the circles lines intersect
they have found the epicenter