GEOL 106 Lecture Notes - Seismogram, Seismometer, Epicenter
DepartmentGeological Sciences and Geological Engineering
Course CodeGEOL 106
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To locate the quake focus:
• Need a minimum of 3 seismometer stations
Where do earthquakes occur?
• At what depth?
o Less than 700 km
o 90% are less than 100 km deep
o Note: radius of earth is 6370 km
Why do earthquakes only occur in the outer 10% of the earth?
• Only the outer part of the earth is rigid enough (ie.
Sufficiently ELASTIC) to experience BRITTLE FAILURE (fault
• Deeper on the earth it is to PLASTIC (or liquid?)
How do we estimate energy released from a Quake?
• 1. “Measure” the Intensity
o based on observed damage (eg. The Mercalli Scale)
o Varies with distance from epicenter
• 2. Measure the Richter Magnitude
o a quantitative measure of energy released
determined from the maximum s-wave amplitude
on a seismogram (corrected for distance)
The lines on a skwigale is an open ended scale. (
we don’t know how high it could go)
o The largest earthquakes ever recorder are 9 on the
Quakes <2.5 magnitude are not felt by humans
Each magnitude integer step corresponds to
approx. a 30-fold difference in energy release
How much more energy is released in a magnitude 7 earthquake
than in a magnitude 5 earthquake ? 30x30 = 900
How about a magnitude 8 earthquake? 30x30x30 = 27000
How about magnitude 9?
What do the Richter numbers mean in terms of ACTUAL ENERGY
• How would you figure that out?
• Compare to known explosions (eg nuclear blasts)
<3 OVER 1000000 /YEAR
>3 OVER 30000 / YEAR
>6 100 / YEAR
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