GEO 3100 Natural Disasters - Exam 2

What is a fault?

a fracture or belt of fractures where the two sides move past each other

Describe a normal fault.

a dip-slip fault in which the upper fault block has moved downward in response to tensional stresses

Describe a reverse fault.

a dip-slip fault where the upper fault block has moved upward in response to compressional stresses

How do dip-slip faults differ from strike-slip faults?

A dip-slip fault is a fault where most of the movement is either up or down in response to pushing or pulling. A strike-slip fault is a fault where most of the movement is horizontal or slide-past in character.

Define stress.

external forces acting on mass or along surfaces; forces include shear, tension, and compression.

Define strain.

Strain is a change in the form or size of a body due to external forces.

At which plate tectonic boundary do normal faults occur?

divergent plate boundaries

Explain how a seismograph is constructed so that it accurately records seismic waves.

a seismometer must have a part that remains as stationary as possible while the whole Earth beneath it vibrates.

What is inertia?

the property of matter by which it will remain at rest unless it is acted on by an external force

What are the two types of body waves?

P-waves (primary) and S-waves (secondary)

What does the speed of P-waves depend on?

density of material - greater density = greater speed

Which type of body wave will only travel through solids?

S-waves

List the two types of surface waves and discuss their motion.

Love waves are a shearing motion - they don't travel through liquid or gas and travel faster than Rayleigh waves. Rayleigh waves are backward rotating and cause vertical and horizontal movement. Shallow focus creates stronger Rayleigh waves - they move through solid and liquid and can travel long distances.

List all the information needed to locate an epicenter.

An epicenter is located by using information from three seismograph stations. You need to know the arrival times of P and S waves, and be able to plot them on a travel time graph. This allows you to determine the distance from recorder to epicenter. You need information from three stations - where all three cross is the epicenter.

What is the difference between an epicenter and a hypocenter?

An epicenter is the point on the surface of the Earth directly above a fault movement (i.e. earthquake location). A hypocenter is the initial portion of a fault that moved to generate an earthquake. Hypocenters are below the ground surface; epicenters are above them on the surface.

Is the Richter magnitude scale used to measure all earthquakes? Why or why not?

No - it does not work well for distant or truly large earthquakes

Explain resonance.

the act of resounding, ringing. A vibrating body moves with maximum amplitude with the frequency of seismic waves is the same as the natural frequency of the body. In other words buildings sway with a preferred frequency - if that matches the ground motion, the affects are amplified.

List all of the variables that can affect the Mercalli Intensity Scale.

earthquake magnitude; distance from hypocenter/epicenter; foundation materials; building style; duration of the shaking

List five ways a building can be retrofit to make it quake resistant.

bolt it; bracket it; brace it; block it; panel it

List all the principal geologic hazards that could occur in Utah as a result of large to moderate magnitude earthquakes.

ground shaking; surface fault rupture and tectonic subsidence; soil liquefaction and related ground failure; landslides; various types of flooding

List all of the states within the Intermountain Seismic Belt.

Nevada, Arizona, Utah, Wyoming, Idaho, Montana

When and where did the two largest historical earthquakes occur in Utah?

Richfield area 1901 (6.5 mag); Hansel Valley 1934 (6.6 mag)

How long is the Wasatch fault? How many segments make up the fault?

240 miles long; ten segments averaging 25 miles long

Surface fault rupture can occur in earthquakes with magnitudes of _____ or greater.

6.5

Liquefaction can occur in earthquakes of _____ magnitude or greater.

5.0

A magnitude 7.5 earthquake can generate rockfalls along mountain fronts as much as _____ miles in any direction from the epicenter.

175

What are two general mitigation strategies for earthquake hazards?

building codes and land-use planning

Which type of building is most vulnerable to ground shaking along the Wasatch Front?

un-reinforced masonry buildings, such as brick homes built before the mid-1970s

Be able to recognize the different faults and know the plate tectonic boundary they are associated with

Normal fault - figures 3.8 and 3.9 (pg. 55)

Reverse/Thrust fault - figure 3.10 (pg. 56)

Strike Slip fault - figures 3.11, 3.13, 3.14 (pg. 56-58)

Know all the various seismic waves and their characteristics.

Body waves (P & S); Surface (Love & Rayleigh)

List the characteristics of P waves:

travel fastest, reach recorder first; travel through any medium - liquid, solid and gas; compress and expand the material; vibrate particles in the rock in a direction parallel to the direction of wave propagation; speed depends on density of material; commonly known as sound waves

List the characteristics of S waves:

travel slower (2/3 as fast as the P-wave); travel through only solids; rock particles vibrate perpendicular to the direction of wave propagation;

Which body wave will not move through liquid or gas

S-waves

Which magnitude scale is used today?

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What is the difference between a magnitude scale and an intensity scale?

magnitude estimates amount of energy released; intensity scale records what people feel during an earthquake

Know all the types of possible destruction from earthquakes.

shaking due to ground motion; rupture of ground surface; liquefaction; quick clays; tsunami; landslide; fire

What does the actual amount of structural damage depend on?

magnitude and duration of ground motion; nature of material; design of structure;

Which is better to build on - unconsolidated material or bedrock? Why?

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What kind of material does liquefaction occur in?

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What are base isolators?

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Explain the Elastic Rebound Theory

stress is applied to rock; rock is deformed as a result of stress (strain); strain exceeds rock's strength, rock beaks and releases stored energy; returns to original shape

How long did ground motion last during the Alaska 1964 earthquake? What caused the death of most of the 131 lost during that earthquake?

up to 7 minutes; tsunami

In the Mexico City 1985 earthquake, how far was the city from the actual epicenter? List the 4 design flaws in the buildings that failed

220 miles away; amplitude of shaking increases up the building, buildings with long axes perpendicular to ground motion suffer more shaking, buildings with different heights sway at different frequencies and bang into each other, buildings with different heights tend to break apart

What are the two lines of evidence for a large earthquake in the Pacific Northwest in about 1700?

tsunami records from Japan; tree rings of drowned dead trees

What caused most of the damage in the 1906 earthquake that destroyed San Francisco?

fire

Discuss at least 3 reasons why building collapse was extensive in the Marina District.

Seismic waves were amplified in the artificial fill that the Marina District was built on. Some fill underwent permanent deformation and setting, and some formed slurries and underground water and loose sediment flowed as fluids in the process of liquefaction. The central cause of building failure was flawed design. People needed places to park their cars, so obstructions were cleared from the first stories of buildings to make space for parking lots. This creates a "soft" first story, so that in an earthquake, buildings simply pancake and become one story shorter.

What is a seismic gap? Is San Francisco on a seismic gap?

A seismic gap is a segment of an active fault that has not slipped in an unusually long time, and is therefore considered to be the fault segment most likely to suffer future earthquakes. Today, San Francisco is a seismic gap, that is, it is on a locked segment of the fault.

List the 3 patterns that are identified for large earthquakes in the Bay Area of California.

6-7 magnitude earthquake common every 10 years or one 8+ magnitude earthquake every 100 years; E-W pairings on splays of fault; northward progression of earthquakes

The Puget Sound earthquake in 2001 was 6.8 magnitude and lasted for 45 seconds yet not much damage and no loss of life occurred. List and explain two reasons for this.

Since the 1970s Seattle has had an earthquake code for buildings. The space needle is 600' high built in 1962 to withstand a 9.1 magnitude earthquake.

Is Puget Sound on a divergent, convergent, or transform plate boundary?

divergent

List and explain the two techniques geologists use to read the ancient earthquake record.

Neotectonics (the study of the youngest faults and tectonic movements) and paleoseismology (the study of prehistoric earthquakes)

How are the prehistoric earthquakes dated?

analyzing amounts of radioactive carbon in organic material in the sediment layers

What caused the Hebgen Lake landslide?

a 1959 earthquake in the Yellowstone area

Which segment of the Wasatch fault is most likely to be the next segment that will have a large magnitude earthquake? Why?

The fault segment near Brigham City has not moved in the last 2,400 years and is a likely candidate for a major event

What is the recurrence interval for 6.5 or larger earthquakes along the Wasatch fault?

once every 350 years

Is the Wasatch fault a normal, reverse, or strike-slip fault?

normal

What ist he difference between a forecast and a prediction? Is short term prediction of earthquakes possible? Why or why not?

Forecasts state where and how frequently an earthquake could occur; predictions state exactly when an earthquake will occur. There are forecasts for earthquakes but current prediction is impossible. We don't have a workable theory, and it seems quite possible that the detailed behavior of faults is too unpredictable to ever allow short-term prediction of earthquakes.

List and discuss the 4 ways humans can trigger earthquakes.

Injecting waste fluids back into the ground, fracking under high pressure to fracture rock to increase oil recovery, creating dams (when the reservoir fills the water is heavy and causes land to subside), bomb blasts, and mine collapses

What causes earthquakes in Hawaii?

movement of magma from volcanoes causes earthquakes in Hawaii

If you were terrified of earthquakes and wanted to live in a state with the lowest possible potential for an earthquake, list 5 states you could choose from

Florida, North Dakota, Minnesota, Wisconsin, Iowa

Know examples of subduction zone earthquakes.

Alaska 1964, Mexico City 1985, Cascadia Subduction Zone, Seattle 2001, Japan 2011

How long is the Cascade subduction zone?

680 miles long

What evidence is proof of a magnitude 9 earthquake in the Cascadia subduction zone?

Tsunami records from Japan; tree rings of drowned dead trees

What caused the most damage in the Japan 2011 earthquake?

Tsunami

Why are there large magnitude quakes in China and India?

India collided with Eurasia about 40 million years ago and is still moving northward

Why is there potential for a large magnitude quake in San Francisco?

San Francisco is a seismic gap - it is on a locked segment of the fault

Know the examples and information for earthquakes in the Intermountain Seismic Belt. What is the plate tectonics of this region?

Divergent boundary; Hebgen Lake, Borah Peak Idaho, Utah,

Hebgen Lake

killer landslide; 1959 earthquake in Yellowstone area; 6.3-7.5 mag; up to 26 feet of displacement; normal faults

Borah Peak, Idaho

1983; 7.3 mag (10 mi deep focus); 9 feet of displacement; normal faults

Problems with the Wasatch Fault

70% of faults in Salt Lake is built on; liquefaction problem in middle of valleys; listric faults so curve under the valley; deep valley fill so waves may be amplified

What is the earthquake model for the Wasatch Fault zone?

magnitude 7-7.5; 1 segment ruptures (average segment 25 mi); 6-15 feet of displacement; fault zone 1200 feet wide; recur every 440 years; last quake along the fault as 300-500 years ago (Nephi segment)

Why are there earthquakes in Missouri, Illinois and other midwest locations?

Old tectonic rift (Reelfoot) is a failed rift that is reactivated

Know all the methods for earthquake prediction.

Foreshocks; rise of land above a fault; water table drop; increase in radon gas

What is done along the Wasatch Fault to determine past quake patterns?

Trenching

How can human activity trigger earthquakes?

injecting waste fluids back into the ground; fracking; dams; bomb blasts; mine collapse

Over what length of coastline did the Japan 2011 tsunami inflict severe damage? What geologic event created the tsunami?

415 miles of shoreline; 9 magnitude earthquake

How much permanent land subsidence occurred in the Japan 2011 event? The region that experienced land subsidence is now subjected to coastal flooding. What two ways (or hazards) lead to increased coastal flooding due to this subsidence?

1.2 miles; high tides and storm waves

Which country has the most detailed history of tsunami? What are these waves commonly called in the U.S.?

Japan; tidal waves

Give a detailed explanation of the difference between wind-formed waves and tsunami (include how they approach the shore).

Wind-blown waves rise up as they near the beach, roll forward, run up the beach for several seconds and then withdraw. Wind-blown waves not only come and go quickly, but the water run-up is confined to the beach. Tsunami arrive as the leading edge of an elevated mass of water that rapidly runs up and over the beach and then floss inland for many minutes. Tsunami are dangerous because their tremendous momentum carries water and debris far inland. A tsunami of 1 m height in the deep ocean may be moving nearly 500 mph. Wind-blown waves have a period of 5-20 seconds and a length of 130-2050 ft. Tsunami have a period of 15-60 minutes and a length of 12-485 miles.

List all the geologic events that can cause a tsunami.

Earthquakes, volcanoes, landslides/rock fall, and asteroid impact

Why did 12 people die in Crescent City, California from the tsunami generated by the 1964 earthquake in Alaska?

After 4 waves struck, people went back to the shore. A 5th wave reach 21 feet high

What are three ways that volcanic actiity can create tsunami? When did Krakatau erupt and create a deadly tsunami?

explode, collapse, send avalanches of debris into the water; 1883

What is a flank collapse and where will one most likely occur?

catastrophic event whereby the side of an oceanic volcano falls into the sea; Hawaiian Islands

What size wave would strike the east coast of North America if there is a collapse in the Canary Islands?

wave of 30 60 60 feet

What caused the tsunami in Lituya Bay, Alaska?

In 1958, a cliff fell into the sea

What is a seiche? Can seiches be caused by wind?

A seiche is a big wave in a lake or enclosed bay - the wave sloshes back and forth. Seiches can be caused by wind or earthquakes.

Explain why normal ocean waves are limited in size and speed whereas tsunami aren't.

The energy for normal ocean waves comes from wind. Because this only affects the surface, the waves are limited in size and speed. Tsunamis are caused by energy originating underwater which travels up to the surface, displaces water and raises it above the normal sea level. Then gravity pulls it back down, which makes the energy ripple outwards horizontally.

How fast can tsunami move?

over 500 miles per hour

Why are tsunami not detectable in deep ocean water?

When it's far from shore, a tsunami can be barely detectable since it moves through the entire depth of the water

List 3 ways people try to control or stop tsunami waves from destroying communities

sea walls, flood gatees, and channels to divert the water

You are hiking on a beach along the Oregon coast and receive an internet alert a tsunami is headed your way fast. List 5 things you can immediately do to survive the approaching tsunami

get as far from the shore as possible; move to higher ground; cling to something that floats; don't worry about trying to save

List all the ways tsunami can be created.

subsea fault movement (earthquakes); underwater volcanic eruption; landslides into and beneath the ocean; volcanic islands collapse; asteroid impact

Know the case histories

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Why did people in Hilo Hawaii die from the 1960 Chile tsunami?

people heard the warnings but didn't realize the danger; bay geography caused waves to build up

What were the reasons so many lives were lost in the 2004 Sumatra tsunami?

geography - many lived in coastal zones; no warning system in India Ocean area; general lack of education about tsunami; holiday - many people on beaches

How are tsunami generated in Hawaii?

volcanic islands collapse

Why is there a tsunami danger associated with the Canary Islands?

in danger of collapsing; tsunami don't occur in the Atlantic generally - not the same level of awareness as the Pacific

Why is preserving sand dunes or coastal vegetaion important for tsunami mitigation?

takes up wave energy

If you are near a coast an an earthquake occurs - how long does ground motion last before you run to high ground?

20+ seconds

Two things are very important to know in order to understand volcanic eruptions - what are they?

plate tectonics has given us great insight into earthquakes - now it will help u understnad volcanoes; magmas vary in their chemical composition, their ability to flow easily, their gas content, and their volume which determines whether eruptions are peaceful or explosive