Download Chapter 2, Section 3 – Monitoring Earthquakes

Chapter 2, Section 3 – Monitoring Earthquakes
I.
The Seismograph
a. Detects and measures seismic waves created by earthquakes
b. Device with a heavy weight attached to a spring/wire
i. Pen connected to weight records vibrations
c. creates seismograms
i. record of the seismic waves
ii. shows speed and size of P, S, and Surface waves
iii. height of lines on seismogram is greater for more severe
earthquakes or those closer to the seismograph
II.
Instruments that Monitor Faults
a. Measure changes in elevation, tilting of surface, and ground
movements
b. 4 types of instruments:
i. Tiltmeter: measures tilting or raising of the ground (carpenter’s
level)
ii. Creep meter: uses a wire stretched across fault line to
determine horizontal movement on ground
iii. Laser-Ranging Device: returned reflection of laser beam is
timed to monitor difference in horizontal ground levels
iv. GPS: measures movements of ground-based receivers to
determine changes in elevation, tilt, or movement
III.
Using Seismographic Data
a. Use data provided by fault-monitors and seismographs to make
predictions about earthquake activity
b. Faults mapped/located using reflected seismic waves
c. Type of movement along a fault determines amount of friction
created
i. Low friction: earthquakes are not likely
ii. Moderate friction: sides of fault jam together creating small
earthquakes
iii. High friction: rocks lock together, building up stress – when
rocks break free, large earthquakes occur
iv. Difficult to predict earthquakes: earthquakes do not always
occur where stress is built up in large amounts.
1. cannot predict when/where an earthquake will occur
2. may happen at a different area of a fault