Natural Disasters- Test 1- Unit 3

What can be done to a building, either during construction, or after, to reduce the shaking of a building during an earthquake, and therefore reduce the possibility of severe damage? How does this work?

* Use base isolation pads between the building and its foundation. * The base isolation pads act as shock absorbers to minimize transfer of ground shaking to the building.

Where in the Rocky Mountains are the largest and most-frequent earthquakes?

* Utah to eastern Idaho to western Montana

In some buildings, often a single floor will collapse. What characteristics of a building will lead to such a single-floor collapse?

* Weak floors; too many windows on a certain floor; garages or storefronts on the ground floor

Sometimes a single floor of a building (above the ground floor) collapses in an earthquake, even though the rest of the building is relatively undamaged. What aspect of the design of the building often leads to that collapse?

* a floor with too many windows lacks lateral (or diagonal) support

How much greater energy is released by a magnitude 6 earthquake than a magnitude 5 earthquake?

* about 32 times

How much more energy is released in a magnitude 7 earthquake than in a magnitude 6 earthquake?

* about 32 times

What is the largest earthquake ever recorded since modern seismographs were invented - or in the last 100 years?

* about 9.5

What is the largest possible earthquake magnitude? Why?

* about magnitude 10 because the longest fault length that could be broken is the circumference of the Earth, about 40,000 km.

Having dug a trench across an active fault, what kinds of information should be collected to determine when the fault last moved, how much it moved, and how frequently?

* amount of offset of layers * age of soil layers from organic material in the layers - ± sand blows - ± compaction zones

What type of feature is commonly used to prevent a building from shaking so much during an earthquake?

* base isolation, for example, rubber pads between the building and its foundation

What kinds of structural materials make dangerously weak walls during an earthquake?

* bricks, concrete blocks, stone, or adobe (mud)

Why do so many people in certain regions get sick and often die from sickness after an earthquake?

* broken sewer lines contaminate water supplies

Why are building fires so hard to fight after an earthquake?

* broken water mains

Since most deaths in earthquakes are caused by buildings and other structures, what sometimes causes collapse of a mid-floor of a building (e.g., 3rd floor of a 7-story building) when the other floors remain standing?

* building oscillates at same frequency as the ground during an earthquake

What is the motion of P-waves?

* compressional; compressing and stretching particles in the direction of wave travel

Why are strong concrete structures sometimes destroyed in a large earthquake, whereas nearby homes built with frame construction (wood lumber) are little damaged?

* concrete is rigid so it will crack and break rather than bending or flexing during earthquake shaking * wood is flexible and will bend or flex but not break during earthquake

What aspect of building design can help keep an intermediate floor of a building from falling over or collapsing in a strong earthquake?

* concrete tightly wrapped with steel

What type of wall strengthening is commonly used to prevent a building from being pushed over laterally during an earthquake?

* diagonal beams

What aspect of building design can help keep an intermediate floor of a building from falling over or collapsing in a strong earthquake?

* diagonal braces or shear walls

In addition to the amount of damage, increases in what factors go along with an increase in earthquake magnitude? List several.

* fault offset * length of fault ruptured * acceleration of the ground * time of shaking * velocity of motion of the ground

Consider a magnitude 7 earthquake, near its source. What is the approximate rate of acceleration during the earthquake, in terms of percentage of the acceleration of gravity or as a multiple of the acceleration of gravity?

* generally > 80 percent of g

What does the Mercalli Intensity Scale depend on?

* how much damage occurred and how strongly people feel the earthquake

Where and when was the largest earthquake ever recorded?

* in Chile, 1960

Where, in the United States and southern Canada, are the largest and most frequent earthquakes and on what fault?

* in western California along the San Andreas Fault

Why are surface waves the most destructive type of earthquake waves (two different reasons)?

* larger amplitude of shaking (greatest ground motion) * closer to surface of earth and thus closer to building

Since most deaths in earthquakes are caused by buildings and other structures falling on people, what building materials are most susceptible to collapse?

* masonry (brick, stone), adobe

If you find a well exposed fault that moved before seismographs were available, how can you infer the approximate magnitude of earthquakes generated by the movement? (two different ways)

* measure the offset distance (distance moved) during the event * measure the total length of fault break during the event

Consider a magnitude 7 earthquake, near its source. What is the likely amount of damage? Provide examples.

* most masonry structures destroyed.

Name the three main types of earthquake waves.

* primary, secondary, surface (or) P, S, surface

What is the motion of surface waves?

* rolling like water particles in a water wave

Why did the double-deck freeway at the east edge of San Francisco Bay, collapse in the 1989 Loma Prieta earthquake, while nearby structures in low hills to the east suffered little damage?

* sediment shakes more violently (larger amplitudes) during an earthquake than bedrock

What are the three main factors that affect moment magnitude?

* shear strength of the rocks displaced * total surface area of rocks ruptured by the fault movement * average slip distance on the fault

List two characteristics of the ground that would increase or amplify the ground shaking and destruction of a building during an earthquake.

* soft mud amplifies shaking relative to bedrock * loose sand filled with water causing liquefaction

What is the type of motion shown by the San Andreas Fault, and why is it there?

* strike slip (or lateral) motion; It is a plate boundary between the Pacific and North American plates.

What are the main types of fault motion? Provide the name and type of motion.

* strike-slip, normal, reverse, thrust

How is the Richter Magnitude Scale measured?

* the logarithm (to the base 10) of the amplitude of a set of earthquake waves on a seismograph

What does earthquake wave frequency mean?

* the number of wave crests (or cycles) to pass a location per second

Since most deaths in earthquakes are caused by buildings and other structures, what types of construction or design are most likely to cause building collapse?

* unbraced (weak) ground-floor garages

Since most deaths in earthquakes are caused by buildings and other structures what types of construction or design are most likely to cause building collapse?

* unbraced (weak) ground-floor garages (or store-fronts) * too many windows on any floor * walls not well secured to floors

What is the motion of S-waves?

* up and down shear motion of particles / wiggling

In some buildings, often a single floor will collapse. What characteristics of a building will lead to a single-floor collapse?

* weak floors, such as garages or storefronts on the ground floor

Where, in the United States and Canada, is the most seismically active zone? Be specific.

* western fringe of California (onshore), Oregon, Washington, and southwestern Canada (just offshore).

How much greater amplitude of earthquake waves is a magnitude 6 earthquake than a magnitude 5 earthquake?

*10 times

Consider a magnitude 7 earthquake, near its source. What is the approximate length of fault broken during the earthquake?

*50-80 km

thrust

*gently-sloping fault with the block above the fault moving up

Strike-slip

*lateral slip of one block past the other

Extension of the Earth's crust generally causes what type of fault or faults? What type of plate boundary would produce such a fault or faults?

*normal faults *rift (or spreading)

Where is the safest place to be in an earthquake?

*outside

Compression of the Earth's crust generally causes what type of fault or faults? What type of plate boundary would produce such a fault or faults?

*reverse or thrust faults * ocean-continent or continent-continent collision

Buildings of different heights shake back and forth at different frequencies. Which shake at higher frequencies, short buildings or tall buildings?

*short buildings

normal

*steep fault with the block above the fault moving down

reverse

*steep fault with the block above the fault moving up

Which waves are used to determine earthquake magnitude?

Any of them

Where are two other significant and active earthquake zones in the continental United States and southern Canada?

* "Intermountain Seismic Belt" (or east edge of the Basin and Range of Utah, southeastern Idaho, to southern Montana) [p. 69] * New Madrid fault zone (or NE Arkansas, SE Missouri, western Tennessee and western Kentucky.

What is the approximate frequency of shaking, or back and forth sway, of a typical 20-story building?

* 0.2 back and forth motions per second (= 0.2 Hz) or 5 seconds per back and forth motion.

Consider a magnitude 7 earthquake, near its source. What is the approximate distance of offset?

* 2-3 meters

Consider a magnitude 7 earthquake, near its source. What is the approximate time of shaking?

* 20-30 seconds (almost a half minute)

How much greater energy is released by a magnitude 7 earthquake than a magnitude 5 earthquake?

* 32 x 32 = 1024 times (more than 1000 times)

What is the approximate frequency of shaking, or back and forth sway, of a typical 2-story building?

* 5-10 back and forth motions per second (= 5-10 Hz) or 1/5 -1/10 second per back and forth motion.

What is the approximate P-wave velocity through the Earth? Indicate whether your answer refers to the earth's crust or mantle.

* 5-6 km/sec in continental crust; 8 km/sec in mantle

Provide an example of the amount of fault offset and the magnitude of earthquake generated.

* A 2-3 meter offset would generate a magnitude 7 earthquake.

What is the relationship between the magnitude of an earthquake and the displacement or offset on the fault causing the earthquake?

* A larger magnitude earthquake is generated by a larger fault offset.

If a building is to be built on soft sediment, is a short or tall building safer? Why?

* A short building. Soft sediment shakes at a low frequency, and a short building shakes at a high frequency so they do not shake in resonance during an earthquake.

What are some inexpensive ways to minimize earthquake damage to a single-story frame (wood construction) house?

* Anchor the floor to the foundation. * Install diagonal braces or sheets of plywood along walls. * Anchor loose, heavy objects to the floor and walls - for example, water heaters, refrigerators, book cabinets, TV sets.

Why are structures on soft sand or mud often destroyed in an earthquake, when nearby structures on bedrock remain essentially undamaged?

* Bedrock shakes with small amplitude vibrations. * Soft sediment shakes with stronger (large amplitude) vibrations, meaning greater back and forth distances.

Western Washington State sees damaging earthquakes every few years. These earthquakes are 100-200 km inland from the oceanic trench. What types of faults are causing these earthquakes and why are they there?

* Blind thrust faults over the descending subduction zone

List the characteristics of brick walls in buildings 100 to 200 years old that make them vulnerable to collapse during an earthquake. Assume the bricks and the mortar between them are still of good quality.

* Brick walls are rigid and will crack and break rather than flex during an earthquake. * Old brick walls are structural brick with no internal reinforcing (e.g.: rebar) and no internal frame structure

What hazard does liquefaction pose, and for who or what?

* Differential settling of the ground can collapse or topple buildings on people.

What is liquefaction?

* Earthquake shaking of loose water-bearing sand causes settling and compaction of the sand and expulsion of the water.

What is unsafe about old brick or stone construction in an earthquake?

* Flexing of the walls can permit the beams to pull out and the floors to fall.

If a building is to be built on bedrock, it that good or bad? Why?

* Good. Bedrock shakes at a high frequency, and a tall building flexes at a low frequency so they do not shake in resonance during an earthquake.

Apartment buildings with ground-floor garages are often heavily damaged during a strong earthquake. What is the main damage and why?

* Ground-floor garages lack much lateral support because of their wide openings for car entry so that floor falls over laterally.

There has been at least one highly successful prediction of a major earthquake that saved a very large number of lives. Where and when was that earthquake? What information led to the prediction?

* Haicheng, China, in 1975 * numerous foreshocks and very strange animal behavior

If you were sitting in a parked car next to an old brick building in Boston, St. Louis, or Seattle, what would you do if an earthquake begins shaking violently - and why? Assume that you cannot merely drive away.

* Immediately get out of the car and away from the building because brick walls or parapets can fall and crush the car and any occupants.

For years before the 1989 Loma Prieta earthquake south of San Francisco, earthquake seismologists had been concerned about the possibility of a significant earthquake on the San Andreas Fault in that particular area. Other than the fact that it was on the San Andreas Fault, an area that has seen earthquakes in historic time, what lead them to that conclusion?

* It was a seismic gap, an area of fault that has not seen a major earthquake in a long time, even though areas on either side of the gap have had earthquakes.

What causes formation of a sand boil? Be specific.

* Liquefaction and compaction of sand at depth expels the excess water to the surface, carrying sand with it.

Why is it advisable to keep well away from an old brick building during an earthquake, even if the walls do not collapse or crumble and the windows do not break?

* Many have overhanging brick parapets (brick roof overhangs) that break off and fall, crushing anything below.

Between magnitude 7 and magnitude 8, about how much harder is the shaking during an earthquake? Or, how much increase is there in the acceleration of the ground?

* NOT MUCH!!!!

Some major faults show migration with time (e.g. over the past few hundred or a thousand years), of earthquakes along the fault. Name one such fault - or indicate exactly where it is. When was the last major earthquake on that fault?

* North San Anatolian fault in Turkey * 1999

Which is more likely to be damaged during an earthquake, a building down on low, flat ground next to a bay or on top of a hill nearby (ignore the possibility of any landsliding) and why?

* On low, flat ground next to a bay, soft sediment would shake more violently (larger amplitudes) during an earthquake than harder rock on a hilltop nearby.

Which type or types of earthquake waves arrive at a distant seismograph most quickly by traveling through the mantle of the earth?

* P- and S-waves

Which earthquake waves arrive first?

* P-waves

Which waves travel fastest and how fast do they move through the Earth's mantle?

* P-waves. They travel at about 8 km/sec.

What is the difference between elastic deformation and plastic deformation?

* Rocks subjected to stress involving elastic deformation return to their original form after the stress is relieved; the deformation is reversible. * Rocks subjected to plastic deformation do not return to their original shape but remain deformed after the stress is relieved.

Which seismic waves do not travel through liquids?

* S-waves

Which waves travel next fastest and how fast?

* S-waves. They travel at about 5 or 6 km/sec.

Are wood-frame houses safe or unsafe for the occupants in a moderately strong earthquake? Why?

* Safe for the occupants though the house may be severely damaged. * Wood structures are flexible and will not generally collapse.

What is the nature of the major fault boundary or boundaries in the westernmost United States?

* San Andreas Fault, a strike-slip fault in most of California * Cascadia subduction zone just offshore of Oregon, Washington, and southwestern Canada

For a very long fault such as the San Andreas in California and the subduction zone fault off the west coast of Mexico, what can be used to identify the specific areas that are most likely to generate a large earthquake in the next few decades? Explain briefly how this works.

* Seismic gaps, the gaps in recent earthquake activity, are most likely to be areas of new fault slip and therefore earthquakes. Motion between the two tectonic plates continues; other areas along the boundary have slipped so those that have not slipped recently are most likely to go next.

Freeway overpasses often collapse in a strong earthquake, even though their supports are concrete and heavy duty steel reinforcing bars. Why?

* Shaking in the earthquake cracks and crumbles the concrete. That leaves the rebar without lateral support so it bends and the freeway collapses.

Which earthquake waves arrive last?

* Surface waves

Which of the three main types of earthquake waves tend to be most destructive to buildings?

* Surface waves

Which types of earthquake waves do the most damage?

* Surface waves

Which waves have the lowest frequencies?

* Surface waves

Which waves come next and how fast do they travel?

* Surface waves. They travel at about 2 or 3 km/sec.

Where in North America, east of the Rocky Mountains, is the area that has seen earthquakes as large as the largest recorded on the San Andreas Fault in historic time?

* The New Madrid area of southeastern Missouri and adjacent Tennessee

What is the difference between the epicenter and the focus of an earthquake?

* The focus is the point of origination of the earthquake (generally below the Earth's surface). The epicenter is the point on the Earth's surface directly above the focus.

Sometimes a single floor of a tall building (above ground floor) collapses in an earthquake even though the floors have identical construction. Why?

* The frequency of shaking of the ground matches the frequency of shaking of the building.

Why do the floor or deck beams of parking garages and bridges sometimes fail and fall during an earthquake?

* The horizontal beams, resting on a surface designed to permit thermal expansion and contraction, shake completely off their ledges.

Why do the wood floors in old brick buildings sometimes collapse in a strong earthquake, even though the brick walls do not?

* The joists (horizontal wood floor beams) often rest loosely in slots in the brick walls. Lateral shaking of the walls can shake the floor beams out of the slots and permit them to fall.

In many old brick or stone buildings how are the floors held up?

* The wood floor beams rest loosely in notches in brick or stone wall.

What can you conclude from the Gutenberg-Richter Frequency-Magnitude relationship?

* There are frequent small earthquakes, fewer moderate-size, and only rarely large earthquakes.

If the electricity goes out at night during an earthquake, why should matches or candles not be used to provide light?

* They can ignite gas in the air.

How do seismologists determine the location of an earthquake?

* They determine the distance of the earthquake from at least three seismographs of quite different locations and draw circles of distance from each seismograph. The earthquake was at the intersection of the three distance circles.

How do seismologists determine how far away an earthquake was from their seismograph?

* They determine the time lag between the P- and S-wave arrival and knowing the different velocities of those waves, calculate the distance. The time lag increases the farther they are from the earthquake.

Although single-story frame (wood construction) houses don't often collapse in an earthquake, they are sometimes severely damaged. What is the most common cause of such damage, and how could it have been prevented?

* They shake off their foundations. * The house should be well bolted to the foundation.

Where a tall building is right next to a short building, why is the tall building often damaged? Why does the damage occur and where in the building?

Tall buildings sway at a lower frequency than short buildings so the buildings bang into one another. The tall building breaks at the top of the short building.