Salt Lake Community College - Geography 1700
Quiz #2 - February, 2013
A. J. Allred, Adjunct
Student Name: ____________________
Score: _____
1. In an earthquake, the epicenter will be the most dangerous location in terms of shaking, ground displacement and
damage to buildings and facilities.
True ___
False _X__
Comment: The epicenter is nothing more than the point on the Earth’s surface that is directly above the hypocenter.
The hypocenter is the place where the rupture occurred. The epicenter is a handy location for news media to describe
where on Earth a quake occurred. In reality, the rupture or release of energy was somewhere below the epicenter,
sometimes many miles below.
Energy waves dissipate or attenuate in all directions away from the hypocenter. Conditions surrounding the
hypocenter vary widely in how they react to quaking, thus energy waves may affect the epicenter very differently
from places elsewhere. Moreover, surface conditions vary hugely: hard rock, water, mud, sand, steep slopes, urban
areas, tall buildings or structures made of wood, or places where no one lives. All of these conditions greatly affect
how much damage or injury a quake may cause. A place on the surface where the most shaking occurs may cause no
damage at all, because nothing was there to be damaged. Meanwhile, a place that experiences little shaking could
experience substantial damage due to the fragility of structures.
Overall, it is common for the epicenter to experience substantial quake effects, but the worst effects are often in places
with either “more to lose” or less readiness to withstand the shock.
2. Earthquake energy is released in various waves, the fastest of which are:
a. Primary
b. Secondary
c. Surface
d. Tsunami
e. Sound (speed of sound)
Comment: The “P” was is compressional – a forward shove or push. As such it goes straight forward with no
wasting energy going side to side. A “P” wave can go through any substance, reaching speeds of about 13,000 mph,
MUCH faster than the speed of sound that travels at about 750 mph.
3. Human populations are growing in many of the world’s most earthquake-prone regions. To compensate for that
trend, buildings have been made safer through comprehensive adoption of uniform building codes and the use of
consistent practices for emergency management and alert systems.
True ___
False _X__
Comment: The first statement is true: however, buildings and emergency management practices are fully ready in
only a few places. Consider how much readiness is lost at EACH of the successive steps below:
Research: How good is our scientific research and knowledge? Well . . . we are getting better but we still don’t know
how to predict, or even forecast very well.
Policy: Our polices always lag behind our research. It takes time for scientists to get the attention of people and it
takes time for policy makers to decide to take action.
Law:
Elected officials struggle with how much policy a community can afford. There is always opposition to
new government rules, especially when they cost money.
Enforcement: Government officials struggle to keep track of new laws and how to make people comply. Enforcing
the law is expensive, time-consuming and politically frustrating. Lawsuits often result when people disagree.
Non-conformance: There will always be conditions that are out-of-date or illegal. It takes time and money to keep up
with the latest things. Some communities simply do not have the money to be ready. In other situations, people have
a ‘vested interest’ in not complying.
When you add up ALL of the disconnects, we can confidently say that the answer to Question #3 is FALSE.
4. An earthquake of M = 6.4 releases about how much more energy than a quake of M = 5.9?
a. 2.3 times more
b. 4.3 times more
c. 230.0 times more
d. 320.0 times more
e. 33,000.0 percent more
Comment: The USGS (earthquake.usgs.gov) and other sources provide similar, but still different ways of calculating
Magnitude, amplitude and shaking. The USGS Web site may appear to complicate the issue by comparing “bigger”
to “stronger”.
To keep things simple and consistent with the textbook, let us just refer to energy released as M=magnitude, and
shaking as a more subjective factor relating to how much motion the quake produces.
For energy (M=magnitude) we multiply by 32 for whole number increases. A change of 0.2 = 100 percent increase,
or double the Magnitude. A Magnitude increase of 0.1 represents a 30 percent increase in energy released.
Based on all that, here are two different paths to calculating the difference in energy release:
5.9  6.0 = 30% more
6.0  6.2 = double or 100 % more
6.2  6.4 = double again
-----1.3 x 2.0 x 2.0 = 4.3 times more
5.9  6.1 = double
6.1  6.3 = double again
6.1  6.4 = 30% more
----2.0 x 2.0 x 1.3 = 4.3 times more
The biggest reason why the USGS or other sources of information may yield a different result is due to differences in
rounding that magnify quickly when using exponents with a base of 32.
So, let’s keep this issue as simple as we can and stay in general agreement with the textbook.
5. A tsunami wave originating from a quake 3,500 miles away will probably arrive in about how many hours:
a. Five hours
b. Eight hours
c. Four hours
d. Fourteen hours
e. There is no way to make an accurate estimate without knowing the run-up zone
Comment: Class discussion was based on an open-ocean wave speed of about 450 mph for a typical tsunami wave.
At the beach zone, the wave energy is attenuated and modified to result in much higher amplitude, much shorter wave
length and speed of closer to 40 mph.
Based on that, a wave originating 3,500 miles away should take about 3,500/450 = 7.777 hours. With the slow-down
that occurs when waves reach the shoreline, the total transit time should be close to eight hours. Additional time will
be involved when waves refract against off-shore islands and collide with long-shore currents that are already in
place.
6. Inland urban centers like Salt Lake County are far enough away from the ocean to be safe from water waves
caused by earth movement.
True ___
False _X__
Comment: All bodies of water can be shaken, resulting in wave action. A ‘seiche’ wave on a fresh water lake may
have the same effect as a ‘tsunami’ wave on the ocean. True, salt water is heavier than fresh water, but the motions
are essentially the same. The Salt Lake region has many lakes, reservoirs and other bodies of water, above or below
ground. Earthquakes in our region have produced water waves large enough to inundate sensitive areas and cause
damage and injury. Elsewhere in the world, spectacular effects have been caused by fresh water bodies being moved
by quaking and associated landslides.
7. The details of a local coastline, at a scale of just a few feet or yards, may be just as important for safety planning
as the size and activity of a nearby undersea continental subduction zone that produces ‘megathrust quakes.’
True _X__
False ___
Comment: Shorelines may have steep banks or shallow banks, sand bars, coastal dunes, tall buildings and the widest
imaginable variety of features that affect how a large wave runs-up. Off-shore islands may deflect, refract or even
concentrate a wave. Local off-shore currents and weather conditions can move water in ways that affect how the
shoreline lifts or falls, and how tsunami waves are generated and delivered.
Often, small waves can be devastating to unprepared people. In contrast, a very large wave may be completely
avoided based on a person’s location and actions. The readiness of people to receive information and respond is vital
to safety. The choices people make about where to locate structures and how to use other resources are also vital to
safety.
8. Compared to the outdated Richter scale, the modern Modified Mercalli method ensures a quick and accurate
measure of earthquake magnitude and damage assessment.
True ___
False _X__
Comment: Modified Mercalli methods result in a relatively accurate picture of an earthquake and its effects. Such
accuracy takes a great deal of time and effort, and may include studying a wide variety of information including
newspaper reports, interviews and the study of rocks, buildings and other factors. There is nothing quick or easy
about getting the full picture.
9. What level of change would a GPS or laser device show for a full year of seismic “creep” or continental drift at
many of the world’s great tectonic plate boundaries?
a. 0.4 inch
b. 0.004 inch
c. 40 feet
d. 400 feet
e. 4000 feet
Comment: In class discussion, the statement “almost one half inch” has been used to describe “finger nail growth”
and a variety of slow tectonic forces: the creation of new crust at the Atlantic mid-ocean ridge, the rebound of
continental crust after the ice age abated, and the movement of some significant fault lines.
10. Volcanic rocks and magma that are high in silicon content are more likely to be involved in explosive, dangerous
eruptions such as with massive “shield” volcanoes.
True _X__
False ____
Comment: Felsic rocks contain large amounts of silica (the element Silicon) and are therefore more likely to be
involved in volcanic explosions than are heavier mafic rocks: in melted state, silicates are relatively lighter in weight
and demonstrate more ‘stickiness’ or viscosity. When large amounts of volcanic gases are also present, felsic rocks
can hold together until an explosive pressure is built, and then vault into the sky due to their lighter weight.
So, the first statement in Question #10 is true; however, the second state is not true: “shield” volcanoes typically
exhibit relatively less explosive gas pressure and melted rocks that are less viscous (less sticky) due to lower silicate
content.
11. Among the following options, the relatively best earthquake warning system would rely on:
a. The magnitude of “S” waves
b. Electronic messaging based on the arrival of “P” waves
c. The time difference between the hypocenter and the epicenter
d. Surface waves
e. An alarm that is based on sound waves (at the speed of sound) traveling through the air.
Comment: Secondary waves travel more slowly than do primary waves. The size of secondary waves does not help
develop a quake warning system. Primary waves arrive more quickly and when combined with an electronic message
system may actually be able to arrive in time to allow people to take evasive action.
In contrast, there is nothing to be gained by studying the difference between the epicenter and the hypocenter. The
arrival of surface waves is obviously too late to do any good. Alarms based on slow sound waves is equally
unhelpful.
12. An event forecast will not usually include a date and time.
True _X__
False ___
Comment: Forecasts are general in nature, such as a weather report that provides a percent chance of something
occurring over a general area and during a general period of time. In contrast, a prediction usually includes a specific
date and a specific time for a specific event at a specific location.
13. If a tsunami warning is issued for your location, which of the following practices is probably best:
a. Avoid panic and confusion by waiting for local officials to advise what action to take.
b. Invoke your own personal action plan for evacuation based on your own planning and personal fitness
c. Choose your action based on keeping a good view of the beach to verify tsunami behavior
d. Take time to stock up on bottled water and secure your personal possessions until the alert is lifted
e. Maintain good public order by following the general flow of other people as they react to the news.
Comment: The first line of defense for every person is a willingness to be prepared. Preparation includes continual
awareness of nearby conditions and active interest in understanding hazards that exist anywhere people go.
A personal action plan will include being responsive to information provided by public safety personnel and others in
authority, but will also include the ability to act reasonably when no one is in charge. In many natural disasters,
public safety personnel may not be available or may not be fully informed. If you believe a wave is coming, then
move to higher ground in an orderly manner.
14. The modern Modified Mercalli system for earthquake reporting is a good predictor of the size, number and timing
of tsunami waves.
True ____
False _X___
Comment: The Modified Mercalli system is about creating a comprehensive, accurate picture of an earthquake and its
effects. That system is not about predicting a quake, but about reporting on it.
15. Western Utah has shares a vast region of intense geothermal resources that goes all the way into California. The
key resource needed for successful geothermal energy development is Utah’s dry, sunny climate.
True ___
False _X__
Comment: The key resource for geothermal development is WATER. There is no other practical way to transfer heat
from a magma body to the location of use. The same is true for power plants and a host of other human activities:
WATER is the medium for transferring heat.