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Earth Hazards quiz 5

Terms in this set (18)

How does bedrock differ in the central U.S. vs. that of California?
The bedrock is a hard cold slab. In California the bedrock is more shattered and hot.
How could damming water affect seismicity?
Damming water could affect seismicity by causing earthquakes if the water is dammed up too quickly. It causes a greater loading on the earth and if there are some faults there a large earthquake could occur
How is an 'enhanced' geothermal field different from a traditional geothermal system?
an 'enhanced' geothermal field has water pumped into a hot area where micro-fracturing of the hot, dry rock occurs to produced steam. A traditional field uses only existing steam in the area.
In your opinion, is this human activity worth the additional seismic hazard? Just a few sentences is sufficient, if some critical reasoning is clearly included.
I think that if the proper precautions are taken this human activity could be worth the additional seismic hazard. I believe this because this could be better than some of the other energy sources humans use.
What activities can result in induced earthquakes? How do those activities change the crust enough to cause quakes?
The collapsing of mines caused induced earthquakes. Some of the others are oil production related (the extraction) and the filling of Lake Mead. They changed the mass inside the earth which caused different pressures to occur on the faults below which resulted in earthquakes.
How has the numberof induced earthquakes changed over the past 40 years? Hint: This is a cumulative plot, meaning the number shown at 2005 is the total from year 1975 to year 2005. No change in the rate of quakes would produce a constant, linear slope like in the first three decades shown here.
rate is increasing
How has the distribution of quakes in the central U.S. changed in the last six years vs. the previous 30?
The distribution of quakes in the central U.S. is not as scattered any more. In recent years most of the earthquakes are concentrated in southern Oklahoma and Kansas, as well as some of Texas.
Which well type is associated with greater seismic activity?
wastewater disposal wells
Why might induced earthquakes in the central U.S. be potentially more dangerous than many of those that occur in the western U.S.?
Construction standards are not the same as they have in California. This means that weaker shaking in central U.S. could be more dangerous and life threatening.
How big was the rupture (amount of displacement) associated with the 1964 megathrust earthquake?
500 miles
The epicenter and hypocenter of an earthquake are not the same - which statement is true?
The hypocenter is the actual origin of the quake, possibly located at great depth
Where does displacement typically occur in the case of convergent margin quakes? Describe how these happen (brief text description is fine, simple convergent margin diagram provided below for reference).
as the oceanic crust subducts below the continental crust, it drags the continental edge back to the left a bit. Whenever that edge springs back, a quake occurs.
How high (in feet) is half a meter?
1.64 feet
When you first notice the ocean doing something unusual, either drawing back or creeping forward farther than is normal, how much time do you have before you need to evacuate the area?
You need to evacuate immediately. That water is moving faster than someone can run so getting out immediately is very important.
What should people immediately do if they feel an earthquake?

And what should they not do?
Drop, cover, and hold on is the recommended action to take when you feel an earthquake. So you get on the floor, get under a table, hold onto the table with one hand and the back of your neck with the other, and count until the earthquake is over.

You should not run to a doorway, run outside, or go near the ocean.
What do sedimentary drill cores collected off the coast tell us about earthquakes along the Cascadia fault?
cores tell us when quakes occurred because the seafloor sediments contain landslide sand layers deposited due to the quakes.
Without precise earthquake prediction, what options do we have to minimize casualties from quakes? What limitation does this method have?
Earthquakes generate their own warning system. They generate the p waves first which rarely cause more than a jolt. This warning time between the p waves and the s waves is crucial. Once the p wave is felt, a warning can be issued.

Some limitations are that the closer the earthquake, the less warning one will have. Some now believe that engineering not geology is the answer.
Describe the structure that Cannon Beach, OR is building to be both earthquake and tsunami resistant - focus on features that offer protection and resilience not typically found in conventional buildings.
A survival platform over 30 ft high that can hold a 1,000 people on top of city hall. It can take very large forces, not just the waves, but parts of building and cars hitting it. Tension steel cables hold it together and recenter it after the earthquake. Reinforced concrete pillars allow water and debris to go through. Extra deep foundations allow it to continue standing.
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