gluglulglugluglgug midterm 1

which of the following measures contraction and expansion?

... A strainmeter measures volume changes whereas a tiltmeter measures slope changes. GPS measures elevation of the land surface. Through repeated surveys, changes in elevation can be observed. Although GPS doesn't directly measure volume changes or slope changes, it indirectly provides indications of whether there is expansion or contraction and about slope.

in california, the city of los angeles does not sit on the same tectonic plate as san francisco. if current rates of plate motion continues, how long will it take for los angeles to move to a position further north than san francisco?

10 million years

the lithosphere, which is the outermost layer of the earth, averages out to be roughly _ kilometers thick

100

To locate the epicenter of an earthquake, at least _______ locations with seismometers is needed.

3

Which of the following is part of the elastic rebound theory?

In between earthquakes, strain is stored by elastic strain of rocks.

If all else is the same, shaking will be greater if __________________________ is larger.

earthquake magnitude Earthquake shaking is larger close to the focus, when magnitude is larger, and it is larger in sediments (particularly saturated sediments) than rock.

if a rock returns to its original size and shape after stress is removed, its behavior is

elastic if the rock returns to its original shape after stress is removed, the behavior is elastic. if the rock breaks, it is brittle. if it deforms (changes size or shape) permanently but does not break, its behavior is plastic or ductile.

The ______________________ is the location on the surface directly above the ________________________ of an earthquake.

epicenter; focus

true or false: all types of plate boundaries produce volcanoes

false

A tsunami can only be generated by an earthquake.

false: Correct! Any disruption of the seafloor can generate a tsunami - volcanic eruptions, meteor impacts, underwater landslides, etc.

The 2011 Tohoku Japan earthquake was unprecedented in it's magnitude.

false: Historic records indicate an earthquake of similar magnitude happened in the year 896, but was not considered in risk assessment because it predated the invention of seismic recording technology.

which of the following has the highest viscosity?

felsic magma felsic magma has the highest viscosity and mafic the lowest.

The ______________________ is the location on the fault plane where rupture begins. It lies directly below the ________________________.

focus; epicenter Hypocenter and focus are the same, and are both the location on the fault plane where the earthquake rupture begins. The epicenter is the location on the surface.

violent volcanic eruptions can produce eruption columns which can send ash 40+ kilometers (25 miles) into the atmosphere! which magma type is most likely to create these types of eruptions?

high viscosity rhyolitic magmas.

sulfur dioxide can:

irritate respiratory systems

at mid-ocean ridges, magma is generally

mafic

which of the following has the lowest viscosity?

mafic felsic magma has the highest viscosity and mafic the lowest.

Damage due to surface rupture along faults could be reduced by:

making pipelines flexible where they cross fault zones: Buildings or infrastructure that cross faults needs to be able to surface sudden movement (displacement). So flexibility would be needed, the building should be isolated from ground movement, and/or new construction should be prevented.

fractional crystallization of magma is a process by which:

mineral that crystallize at higher temperatures form first and remove iron and magnesium from the magma

When the period of earthquake seismic waves matches the resonance of a building, ______________________________ occurs.

more swaying and increased damage When the natural timing of the building sway matches that of the earthquake waves, the movements add together. This results in greater sway and more damage.

which of the following statements is true about the location of earthquakes and volcanoes worldwide?

most earthquakes and volcanoes are located along plate boundaries

shield volcanoes erupt:

mostly lava

Compared to wind-generated waves, tsunami waves in the open ocean (away from shore) are:

much faster

paleomagnetic data from the seafloor was a key piece if evidence supporting the idea of "seafloor spreading." the symmetrical patterns of paleomagnetic stripes on either side of the mid-ocean ridge indicated:

new ocean crust is formed at ridges and spreads out in both directions from the ridge.

If the hanging wall moves downward relative to the footwall, the fault is _________________________.

normal

this fault is a:

normal fault

The "shadow" zone occurs because S waves won't pass through the __________________________.

outer core S-waves or shear waves cannot pass through liquid.

decompression melting occurs when:

pressure decreases decompression melting occurs when pressure is reduced, so when rock is rising. flux melting occurs when water is added. partial melting occurs because different minerals have different melting points. silica rich minerals melt first, producing a melt that is more silica-rich than the remaining minerals.

"Base isolation" refers to:

preventing movement from being transmitted from the ground to the building Base isolation helps reduce the motion that is transmitted from the ground to the building.

disaster mitigation means:

proactive steps to reduce the severity or impact of natural hazards

Those living in earthquake-prone areas should consider making their houses more earthquake-resistant by:

reinforcing or replacing bricks or other masonry Houses should be secured to the foundation. First story garages or large windows could create a weak "soft story", and should be strengthened. Unless reinforced, bricks and concrete blocks do not withstand earthquake motion well. Floodplains can have problems with amplification and liquefaction.

a material with elastic properties:

returns to its original shape after stress is removed

which of the following rocks is formed by crystallization of felsic lava above ground?

rhyolite

the rapid rise in global population, mostly crowded into increasingly large population centers, sets the stage for ever more destructive disasters. world population is growing exponentially, at a rate of about 1.2% per year. using the estimator formula for doubling time found in your book, how often does world population double?

roughly every 60 years

If all are saturated, which of the following would be most likely to experience liquefaction during an earthquake?

sand Unconsolidated sediments are most likely to experience liquefaction and rocks are the least likely.

If you are in a city affected by an earthquake, shaking is likely to be greatest in which of the following settings?

saturated sand and silt As shown in the Marina District of San Francisco and in Mexico City, sediments can amplify seismic waves. This is particularly true of saturated sediments (e.g., where the water table is near the land surface).

earthquakes happen at ocean trenches (convergent boundaries) and ocean ridges (divergent boundaries). but earthquakes at ocean ridges are much more ___ than those at ocean trenches

shallow- closer to the surface

which type of volcano has the gentlest slope?

shield shield volcanoes have broad gentle slopes because the mafic magma has the lowest viscosity. they also tend to have the largest diameter because they spread out more.

which of the following is most likely to have mostly lava flows rather than explosive eruptions?

shield volcano volcanoes with more silica in the magma tend to be more explosive and more mafic magma leads to more lava flows and less explosions

Which plate boundary type is most likely to have earthquakes that generate large tsunamis?

subduction zone

the deepest earthquakes occur at:

subduction zones

past volcanic eruptions have led to short-term (one to several years) cooler temperatures globally because:

sulfate aerosols reflect radiation

According to the reading, which gas indicates that magma is near the surface?

sulfur dioxide According to the reading, sulfur dioxide indicates that magma is near the surface. Hydrogen sulfide suggests that gas is moving slowly and has time to dissolve in groundwater. That would be consistent with a relatively quiet volcano. Carbon dioxide could indicate a new magma source, but the carbon dioxide escapes from magma relatively deep.

The most damaging shaking during earthquakes generally results from:

surface waves

Which of the following is most important in determining the seismic hazard to buildings?

the acceleration caused by the earthquake at a particular location For considering the hazard to buildings, the acceleration at a location is more important than magnitude of the earthquake.

which of the following is a major factor in determining whether a volcanic eruption will be violent (explosive) or relatively quiescent (effusive)/

the amount of dissolved gas in the magma

The collapse of a freeway overpass during the 1989 Loma Prieta earthquake illustrated:

the effects of amplification of seismic waves in unconsolidated sediments

when an erupting volcano interacts with water on or near the surface, what is the typical result?

the interaction of water and magma fuels explosions

a recurrence interval, or a return period, is:

the length of time between events of the same magnitude

The epicenter of the 1895 Mexico City earthquake was actually not anywhere near Mexico city. The primary reason shaking was so much greater in Mexico city was:

the saturated lakebed sediments the city is built on.

which of the following plate boundaries is NOT commonly associated with volcanism?

transform volcanoes are common at mid-ocean ridges, rift zones, and in the arc associated with subduction zones. transform boundaries are less likely to have volcanoes. collision boundaries can have "leftover" volcanism from the past subduction zone (before the two continents collided)

Which of the following consists of continuous vibrations caused by moving magma and gas?

tremor Tremor is continuous seismic signal caused by gas/magma movement through cracks. This differs from tectonic earthquakes which fade with time.

true or false: continental crust is much thicker than oceanic crust

true

which of the following describes volcanic ash?

very small fragments of cooled magma volcanic ash consists of small fragments of magma and rock that are blasted into the air during explosive eruptions.

As magma approaches the surface, water contributes to the explosive potential of the eruption because

water dissolved in magma flashes to steam as pressure decreases, and the volume increase leads to an explosive potential

as magma approaches the surface, water contributes to the explosive potential of the eruption because

water dissolved in magma flashes to steam as pressure decreases, and the volume increase leads to an explosive potential

Liquefaction occurs:

when saturated shallow sediments are shaken Shaking of shallow, weak, unconsolidated sediments that are full of water (saturated) causes them to lose strength and act like a liquid. This can occur at accelerations >0.1 g, and magnitudes as low as 5.

Which of the following is true about volcano monitoring?

Most eruptions are preceded by seismic swarms. Prior to eruptions, the magma movement generally causes seismic swarms and results in tilt, changes of the land surface, and changes in strain. There can also be temperature changes and changes in gas emissions or temperatures. It is difficult to use these to provide warnings because the changes don't always result in an eruption.

Where would be the safest location during a subduction zone earthquake? Assume the same building height and construction in all locations.

On a flat area of bedrock that is not saturated. The beach location is vulnerable to tsunamis, and amplified seismicity, and the valley full of sediments could have amplification and liquefaction.

On a seismograph, the _____ waves will arrive first, then the _____ waves, and then _______________ waves.

P, S, surface P waves are the fastest and surface waves the slowest.

Which of the following is true of lahars?

They can occur long after an eruption. Any source of water can mix with the loose material on volcanoes (particularly composite volcanoes) to form lahars. They can occur even when there has not been a recent eruption. They move quickly and can be deadly.

Which of the following is true of tsunamis?

Wave height is tallest in shallow near shore environments

If you are in a region affected by an earthquake, shaking is likely to be greatest in which of the following settings?

a river valley full of sediments where the water table is near the surface As shown in the Marina District of San Francisco and in Mexico City, sediments can amplify seismic waves. This is particularly true of saturated sediments (e.g., where the water table is near the land surface).

chains of volcanoes, such as the hawaiian islands, suggest that plates move over a persistent magma source. if plates were not moving, what would be expected to form on the surface above a magma source?

a vey large volcano with an incredibly long period of activity

According to the reading, the most effective monitoring method for lahars is:

acoustic flow monitors The reading emphasizes that acoustic flow monitors (AFMs) are more effective than seismometers because they are designed to capture lahar movement. Tiltmeters examine changes in the slope of the land surface and strainmeters examine expansion and contraction; neither of those would be relevant.

The hazard of liquefaction can be reduced by:

all of the other answers would work (draining sediments, replacing sediments that tend to liquefy with stronger material, strengthening sediments with cement): Any of these methods can increase strength and reduce the likelihood of liquefaction.

lahars can be caused by:

all of these (a heavy rainfall, a volcanic eruption melting ice or snow, water in a volcanic lake breaks out) any source of water can mix with the loose material on volcanoes (particularly composite volcanoes) to form lahars

Which of the following is good advice after an eruption:

all of these (avoid driving on recent lahar deposits. If there has been ashfall, clean your windshield wipers to avoid damaging your windshield. avoid driving on recent lava flows.) Volcanic ash can be extremely abrasive so can damage vehicles (and be unhealthy for people). Recent lava flows and lahars might still be unstable. Don't drive on them or walk on them if it can be avoided.

why are remote sensing (airborne, including satellite-based) methods useful for monitoring temperatures, gas emissions, and land surface movement?

all of these (remote sensing methods can provide a larger viewer than measurements on the ground, volcanoes are dangerous places for scientists to take measurements, many volcanic regions are remote and difficult to access) disadvantages: they average over a large area and you cannot observe continuous changes through time.

in general, the relationship between frequency and severity of any given natural hazard is:

an inverse relationship- when one goes down, the other goes up

which size of tephra travels the farthest?

ash

which size of tephra is the smallest?

ash it also travels the farthest

which of the following rocks is formed by crystallization of mafic lava above ground?

basalt

Those living in earthquake-prone areas should consider making their houses more earthquake-resistant by:

bolting their house to the foundation The best answer here is to secure the house to the foundation. The first story garage could create a weak "soft story". Unless reinforced, bricks do not withstand earthquake motion well.

If you are hiking in a volcanic valley during an eruption, you should:

climb to higher ground if the volcano is known to have lahar or pyroclastic flow risk. In valleys, lahars or pyroclastic flows are risks. So climb to higher ground. Outrunning a lahar or pyroclastic flow is not advised. But you should know what type of volcano you are on and if lahars or pyroclastic flows are possible.

Compared to the asthenosphere, the lithosphere is

cooler and less able to flow