Monitoring Earthquakes
Chapter 2, Section 3
Did you Know? The problem of
predicting Earthquakes is one of the
many scientific questions that remains
unsolved!
It is important for scientists to develop
ways to predict earthquakes because:
• A warning allows people who live in the area
to protect themselves by:
– Reinforcing buildings and other structures
– Getting emergency supplies
– Evacuating
• Earthquakes are dangerous, so scientists are
trying to monitor them (monitor =watch
closely)
What do scientists use to monitor and measure
Earthquakes now?
SeismoGRAPH
• The machine that measures earthquake
seismic waves
The Seismograph
The Seismograph
The Seismograph
Seismic Waves cause the
seismograph’s drum to vibrate
• The suspended weight with the pen attached
to it moves very little
• Pen stays in place and records the drum’s
vibrations
Review: Which part of the
Seismograph is moving?
The part of the Seismograph that is
moving is the rotating drum
http://www.youtube.com/watch?v=G
bd1FcuLJLQ
Modern-day Seismographs are digital
and these are called “SeismoMETERS”
Seismogram
• The pattern of lines that show a record of an
earthquake’s seismic waves
• Seismograms are produced by the
Seismograph machine
SeismoGRAM –the written record of
the seismic waves
Look for the P waves, S waves, and
Surface waves
Seismic Waves on the Seismogram
• P waves –fastest and arrive first
• S waves –arrive shortly after p waves
• Surface waves –move the most slowly and
produce the LARGEST disturbance on the
seismogram
In order to predict WHEN earthquakes
are going to happen, where do you
think is the first place that Geologists
look?
Geologists monitor FAULT LINES
• WHY?
Geologists hypothesize that along a
fault, they can monitor the stress
buildup in the crust to predict when an
earthquake might occur
Geologists measure the STRESS in the
Earth’s crust on either side of faults,
looking for:
• a slight rise or fall in the elevation (height) of
the crust
• the tilt of the crust
• and the distance of horizontal ground
movement
Instruments for Monitoring Faults
• Tiltmeters
• Creep Meters
• Laser-Ranging Devices
• GPS Satellite
1) Tiltmeter
Tiltmeters
• Measures the “tilting” or lift of the crust on
either side of the fault
• Consist of two contraptions that are filled with
liquid and connected by a hollow stem
• If the land rises or falls slightly, the liquid will
flow from one contraption to the other
What type of faults are Tiltmeters used
for?
Used on NORMAL and REVERSE Faults
2) Creep Meter
Creep Meter
• Uses a wire stretched across a fault to
measure horizontal movement of the ground
• One side of the fault, the wire is anchored to a
post
• On the other side, the wire is attached to a
weight that can slide if the fault moves
Creep Meters
• Used on Strike-Slip Faults
3) Laser-Ranging Devices
Laser-Ranging Device
Laser-Ranging Device
• Used on Strike-Slip faults
• Uses a laser beam to detect horizontal fault
movements
• The device times a laser beam as it travels to a
reflector and back
• The device can detect any change in distance to
the reflector
4) GPS Satellite
GPS (Global Positioning System)
• Scientists can monitor changes in elevation
AND horizontal movement along faults
• Scientists can see changes in elevation and
horizontal movement
• Used for Normal, Reverse, and Strike-Slip
Faults
The movement along faults depends
on how much friction there is between
the sides of the fault
• Friction: the force that opposes the motion of
one surface as it moves across another
• Low Friction = no Earthquake
• Moderate Friction = small Earthquake
• High Friction = big Earthquake
Did You Know?
• Even with data from many sources, geologists
cannot predict when and where an
Earthquake will strike
• Reasons:
– Sometimes stress builds up along a fault, but an
Earthquake does NOT occur
– Sometimes an earthquake relieves stress in an
unexpected part of a fault
The problem of predicting Earthquakes
is one of many scientific questions that
remains unsolved!