# Geology Unit 11

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1. How often do earthquakes occur in the US?
They occur randomly.
2. In what year was an earthquake felt in Corpus Christi and where was the epicenter?
On March 24, 1997-a 3.8 earthquake with its epicenter at Alice TX was felt in Corpus Christi. Another on April 24, 2010 with 4.0
3. How fast does a tsunami wave travel over the ocean?
Tsunami waves can move at speeds of 500 mph in the deep oceans.
4. Who derived the "elastic rebound theory"?
H.F. Reid
5. Define the "elastic rebound theory" that is used to explain earthquakes.
The sudden release of "stored elastic energy" will create earthquake "waves of energy".
6. Define an earthquake focus on a fault.
Point within the Earth where the initial fault slippage generates earthquake energy. The focus represents the area of released elastic energy
7. Define an earthquake epicenter.
A point on the Earth's surface directly above the focus.
8. Identify a fault, epicenter, and focus from a sketch of an earthquake.
9. What is a seismogram?
Recording of a seismic event or "graph" of an earthquake made by a seismograph.
10. Which travels faster: body waves or seismic waves (body and surface)?
Body seismic waves travel faster within the Earth (which provides body pathways) than surface seismic waves which travel slower along the Earth's surface (which provides surface pathways).
11. What are three types of seismic waves (body and surface)?
• Seismic Body Waves
• Primary Seismic Waves (P-Waves)
• Secondary Seismic Waves (S-waves)

Seismic Surface Waves

Surface Seismic Wave (Surface waves)
12. Describe P-wave (seismic) relative speed (as compared to other seismic waves).
Primary body waves arrive first because they are the fastest waves.
13. Describe S-wave (seismic movements).
Secondary body waves arrive second, later than P-waves.
14. Describe Surface-wave (seismic) movements.
This wave is slower than P-waves and S-waves.
15. Describe P-wave (seismic) movements.
P-waves are formed by alternating pulses of compression and dilation ( a rapid push-pull). P-waves pass through solids, liquids and gasses.
16. Describe S-wave (seismic) movements.
S-waves vibrate perpendicular to the direction of travel (a shearing motion). S-waves do not travel through liquids and gasses-only solids. Near earthquakes, S-waves are larger and more dangerous than P-waves.
17. Describe Surface-wave (seismic) movements.
Surface Seismic Waves are restricted to traveling along Earth's surface. They have an orbital motion, similar to ocean waves that would be traveling through rocks instead of water.
18. How is an earthquake focus depth determined?
Can be calculated by comparing the arrival times of the three seismic waves (first P-wave, first S-wave and first surface wave).
19. Which "depth" earthquake is the most common (i.e shallow, intermediate, deep)?
Shallow focus earthquakes.
20. How is an earthquakes epicenter located?
By calculating a distance by comparing P-wave and S-wave arrival times at a seismograph.
21. The Western US earthquake zones are associated with ___.
Present-day tectonic features.
22. The Eastern US earthquake zones are associated with ___.
"Intra-plate" earthquakes: those that occur along ancient or fail plate boundaries.
23. How can magma cause an earthquake?
As the magma rises toward the Earth's surface, the molten rock fractures rock masses and causes continuous tremors that can last to several hours or days.
24. What earth "location" accounts for 80% of our planet's earthquakes?
The Pacific Ocean rim accounts for about 80% of our planet's earthquakes.
25. What are earth tremors?
Minor earthquakes.
26. What defines the main shock of an earthquake?
Foreshocks.
27. Define aftershocks of an earthquake. (How can you determine which is main shock or aftershock?)
Aftershocks follow main shocks. They are smaller than the main shocks of energy.
28. How long may aftershocks last after a major earthquake?
They may last over a period of weeks, months, or years.
29. How strong can aftershocks be? (Hint: depends on main shock)
The larger the main shock, the larger and more numerous will be the aftershocks. and the longer  the aftershocks will continue.
30. Compare structural earthquake damage to houses, bridges, etc. built on solid rock as to those built on sand and clay (like Corpus Christi area).
Structures built on bedrock usually suffer considerably less damage than structures built on sand or clay.
31. Describe liquefaction and its effects on buildings.
When wet sand can become liquid-like when strongly shaken. The liquefied sand may flow to the surface like a volcano. Structures can fall over "intact" under the influence of liquefaction.
32. What is the name of the earthquake intensity scale?
Mercalli.
33. What is the name of the earthquake magnitude scale?
Richter.
34. Explain the differences between earthquake intensities and earthquake magnitudes.
Magnitude measures the maximum energy released by and earthquake and compare earthquakes to exploding quantities of TNT. Intensity  is based on total energy released, distance from the epicenter, and rock type.
35. Which scale is used by insurance companies to set insurance rates?
Mercalli Intensity Scale.
36. Name and explain three common types of earthquake myths.
• The Swallowing Earth: No one has fallen into an earthquake chasm and died.
• Earthquake Immunity: Small earthquakes will not prevent large earthquakes.
• Astrological Considerations: Aligned planets do not create.
37. What might explain why we do not have many earthquakes in Corpus Christi area (Clarkwood Fault)?
Because there is no shallow bedrock that is hard enough to store strong elastic energy. The local Clarkwood Fault produces only very weak seismic signatures because it involves only relatively soft sediment.
38. Where was the location of the largest continental USA earthquake?
Located in Missouri along the Mississippi River.
39. Where did the largest TX earthquake occur?
Far West-Texas of Valentine experienced its most severe earthquake in 1931. It had a magnitude of 5.80 and an intensity of VIII.
40. What should you do if you move into earthquake prone areas?