Chapter 4 Flashcards

Question

Explain the effect of resonance on destruction

Answer 1

When the waves generated by an earthquake resonate (or constructively interfere) with a structure, its oscillations become increasingly larger, often resulting in ruptures. This is known to happen in bridges designed to resonate easily.

Answer 2

Instense shaking of water saturated sediments can cause them to change from solid to liquid One indicator is a sand-blow where small mounds of sand formed at the surface where water from liquified layer squirts out of the ground.

Answer 3

Divergent boundaries are caused by the separating of plates, and occurs with less energy (less stress). Therefore earthquakes produced are much smaller. Divergent boundaries in continental crust will cause earthquakes, but divergent boundaries in weak oceanic crust won't have any significant impact.

Answer 4

Convergent boundaries are the sites of the most powerful earthquakes It is much harder to compress a rock than pull it apart. These result in the shortnening of the crust

Answer 5

Shallow depths where the slab is being bent This is because shallow rock does not bend very well.

Answer 6

Deeper in the lithosphere the temperature increases to the point where stress is relieved through plastic flow. Deep quakes are believed to occur because of the spontaneous, temperature-depended conversion of materials into chemical forms that take up less space.

Answer 7

The continental part of the subducting slab and the slab above it will fuse as the slab portion below the coninent-continent suture breaks off

Answer 8

Location Time Magnitude

Answer 9

* Haicheng, china * Feb, 4, 1975 * mag = 7.3 * 2000 people killed, hundreds of thousands of lives saved * It was predicted through strange animal behaviour

Answer 10

In another region of China, at Tangshan (now called Tianjin), subject to the same stress system, those same precursors were not experienced when, without any apparent warning, on 27 July 1976, a magnitude 7.6 quake killed more than 400,000 out of a total population of 1 million This implies that although presursors sometimes indicate a future earthquake, they can be unreliable, making earthquakes difficult to predict *consistently*.

Answer 11

Foreshocks are seismic shocks caused by the first few "breaks" in rocks near a future hypocenter. They are generally the weaker rocks in the zone and form because the strength of rocks in an area is rarely homogenous.

Answer 12

They undergo more stress, potentially triggerring the earthquake immediately.

Answer 13

A section of a fault where there hasn't been much seismic activity, due to an energy buildup. These areas should be monitored.

Answer 14

When microfractures develop in a land mass, the land swells because of the extra space taken by the air. Tilt meters detect these changes. the same thing is also done in space now by satellites. These satellites build a contour map to modify elevation changes in areas of land

Answer 15

the velocity of an energy wave (let’s say we look at P-wave energy) will read steady prior to a fracture, drop dramatically as air fills the microfractures (because air is so much less conductive of energy that solid rock), then pick up somewhat as water replaces air (because water is more conductive than air but less than solid rock). These kinds of velocity changes have been measured in the range of 10-15%, so the changes are detectable. if we had a pattern of electrodes stuck into the surface, we would see similar changes in electrical conductivity as transmission efficiency changed from the high efficiency of solid rock, to the very low efficiency of air, and the moderate efficiency of water-filled fractures.

Answer 16

Radon gas, a product of Uranium decay, is present in granite and other rocks. In the event of microfractures, this will be released before the earthquake occurs

Answer 17

Parkfield, CA, the earthquake capital of the world, sits directly on top of the San Andreas fault. The USGS announced a 95% percent probability of a Magnitude 6 earthquake betwene 1987 and 1992, which did not occur. In 1992 there was a 4.5 tremor, after which it was predicted that a magnitude 6 earthquake would happen on 72 hours. This didn't happen until september 28, 2004.

Answer 18

Plate boundary movements. There is a known spreading center in the Mid-atlantic ridge, so compression has to happen somewhere. This occurs at the pacific plate. We can only guess the probability of an earthquake to occur in an area with an accuracy of ± 50 to 150 years by studying the faults that are most likely to break.

Answer 19

8.2 This is because of geology. There are only so many rocks in a straight line that might break at the *same* time.

Answer 20

by studying the history of large earthquakes in a specific area and by checking the rate at which strain accumulates in the rock.

Answer 21

Scientists study the past frequency of large earthquakes in order to determine the future likelihood of similar large shocks. For example, if a region has experienced four magnitude 7 or larger earthquakes during 200 years of recorded history, and if these shocks occurred randomly in time, then scientists would assign a 50 percent probability (that is, just as likely to happen as not to happen) to the occurrence of another magnitude 7 or larger quake in the region during the next 50 years.

Answer 22

This is because earthquake events are not independent. The occurrence of an earthquake in one area may increase or decrease the likely hood of an earthquake occuring in another area. The time since the last earthquake in the area, along with the magnitude can indicate how likely an earthquake is to occur. High magnitude earthquakes generally don't happen very often, and low magnitude earthquakes tend to happen more often.

Chapter 4 Flashcards

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