Homework Chapter 3

The reduction of ______ waves at the core-mantle boundary indicates that the outer core is mostly liquid.

S

__________ waves travel only through solids; on reaching liquid or gas, the wave energy is reflected back into rock or is converted to another form.

S

The point on Earth's surface directly above the point where the fault first ruptures is called the ____________.

epicenter

Earth's interior is homogeneous.

false

Earthquake magnitude scales such as the Richter scale assess the effects on people and buildings.

false

The _________ waves' motion is similar to S waves, except it is from side-to-side in a horizontal plane roughly parallel to Earth's surface.

Love

Seismic waves that travel only near Earth's surface are of two main types: _________ waves.

Love and Rayleigh

_________ waves are transverse waves that propagate by shearing or shaking particles in their path at right angles to the direction of advance.

Love and S

The _____ wave travels fastest and moves in a push-pull fashion of alternating pulses of compression (push) and extension (pull).

P

Velocities for __________ waves in granite are about 5.5 to 6 km/sec, but in water they slow to 1.4 km/sec.

P

The ________ waves advance in a backward-rotating, elliptical motion.

Rayleigh

The Richter scale is set up so that for every _______ increase in the amplitude of the recorded seismic wave, the Richter magnitude increases one number, e.g., from 4 to 5.

Ten-fold

Using the S-P timing method, epicenters can be located using seismograms from a minimum of ______ recording stations.

Three

In seismology, wave __________ is the height of the wave above a starting point.

amplitude

A tall office building built on a foundation designed to slide or roll with an earthquake is an example of using __________ to reduce earthquake-induced damage.

base isolation

The __________ is measured in cross-sectional view as the angle of inclination from horizontal of a tilted rock layer, and _______ is viewed in map view as the compass bearing of the rock layer where it intersects a horizontal plane.

dip; strike

A normal fault occurs when the hanging wall moves ________ relative to the footwall.

down

Following the paths of P and S waves from Earth's surface inward, there is an initial increase in wave speed but then a marked slowing occurs at a depth of about 100 meters; this defines the top of the lithosphere.

false

In Figure 3.22, a seismogram with a P-wave and S-wave separation is 11 minutes, the seismic station is located about 9200 km from the epicenter.

false

In igneous rocks such as granite, S waves travel about 1.7 times faster than P waves.

false

Large earthquakes do not generate body waves energetic enough to be recorded on seismographs all around the world.

false

Normal faulting occurs when the hanging wall moves upward relative to the footwall.

false

Seismograms are the actual machines that record the earthquake, and the record of the event is recorded on a seismograph.

false

The acceleration due to gravity is 9.8 meters per second squared (32 feet per second squared), which is referred to as 1.0 g and is used as a comparative unit of measure. Earthquake accelerations have never been measured in excess of 1.0 g.

false

The duration of the shaking is not a significant factor in damages suffered and lives lost.

false

The point where a fault first ruptures underground is known as the epicenter.

false

The time of day an earthquake strikes is not a critical factor affecting loss of life from the event.

false

Transform faults have mostly vertical displacement rather than horizontal displacement.

false

P waves can travel through ____

gases, liquids, solids

Earthquake-induced ground motions cause buildings to sway at certain periods. In general, the taller the structure, the _______ the period.

longer

Flexible buildings (made of wood or steel) have a ________ resonant period than a stiffer building (one of brick or concrete).

longer

Which of the following is not a way to improve a building's resistance to earthquakes?

match its period to seismic waves at that location

Despite the profound effects that earthquakes have had on civilizations for so many centuries, systematic scientific observations were not made until the early _________ century, when good descriptions were made of earthquake effects on the land.

nineteenth

Faults on which the dominant forces are extensional are recognized by the separation of the pulled-apart rock layers in a zone of omission; these are __________.

normal faults

Steno's law of __________ states that sediment layers are continuous, ending only by butting up against a topographic high, such as a hill or a cliff, by pinching out due to lack of sediment, or by gradational change from one sediment type to another.

original continuity

The law of __________ explains that sediments (such as sand, gravel, and mud) are originally deposited or settled out of water in horizontal layers.

original horizontality

__________ occurs when a building's period matches period of passing seismic waves.

resonance

The process of reinforcing existing buildings to increase their resistance to seismic shaking is known as __________.

retrofitting

With compressional forces, the hanging wall moves upward relative to the footwall; this type of fault is referred to as a __________ fault.

reverse

________ faults are commonly found at areas of plate convergence where subduction or continental collision occurs.

reverse

The strike-slip San Andreas Fault in California is a _______ fault more than 1,300 km long.

right-lateral

Usually, the biggest concern in designing buildings to withstand large earthquakes is the ____________ components of movement.

sideways push from the horizontal

When most of the movement along a fault is horizontal, the fault is referred to as a __________ fault.

strike-slip

Earthquakes are most commonly caused by ______________.

sudden earth movements along faults

In the law of __________, Steno stated that in an undeformed sequence of sedimentary rock layers, each sedimentary rock layer is younger than the bed beneath it, but older than the bed above it.

superposition

Which of the following wave types travels slowest through rock?

surface waves

Shear walls are designed to __________.

take horizontal forces from the floors and roofs and transmit them to the ground

The seismic moment is calculated by multiplying all but which of the following quantities together?

the Modified Mercalli Intensity at the epicenter

The intensity of an earthquake is influenced by all but which of the following?

the current air pressure

The farther away a seismic station is from an earthquake's hypocenter the __________.

the longer the delay is between the arrival of the P waves and S waves

The frequency of a wave is __________________.

the number of waves passing a given point per unit time

Which of the following buildings would likely be the safest to be located in during an earthquake?

the two-story modern wood frame house

The Lisbon earthquakes of 1755 are historically significant because ______________.

they changed the prevailing philosophies of the era, producing a more pessimistic view of the world

Human-caused and natural events can be distinguished using seismic waves because __________.

they produce different S and P wave patterns

First-order analysis of a seismogram record allows seismologists to do all but which of the following?

to develop a Modified Mercalli Intensity map

A building's period of swaying is determined, in part, by the material used to build it.

true

Aftershocks are smaller than the main shock in an earthquake sequence.

true

Both Love and Rayleigh waves are referred to as L waves (long waves) because they take longer periods of time to complete one cycle of motion and are slower moving relative to P and S waves.

true

Different estimates of earthquake magnitude are derived from different methods based on local shaking (Richter scale), body waves (m b), surface waves (M S), or seismic moment (M W).

true

Each year, Earth is shaken by millions of earthquakes.

true

Earthquake intensity scales such as the Modified Mercalli scale assess the effects on people and buildings.

true

Earthquakes can sometimes represent more than one reading on the modified Mercalli Scale.

true

For magnitudes above about 6, the bigger earthquake magnitude means that more people in a larger area and for a longer time will experience the intense shaking.

true

High-frequency P and S waves will have their vibrations amplified by 1) rigid construction materials, such as brick or stone, and 2) short buildings.

true

Low-frequency surface waves will be amplified in tall buildings with low frequencies of vibration.

true

Moving into the core, P wave velocities gradually increase until a positive jump is reached at about a 5,150-km depth, suggesting that the inner core is solid.

true

P and S waves do not follow simple paths as they pass through Earth; they speed up, slow down, and change direction, and S waves even disappear when they reach Earth's core.

true

Passing through the mantle below the asthenosphere, the seismic wave velocities vary but generally increase until about 2,900-km depth where P waves slow markedly and S waves disappear at the core-mantle boundary zone.

true

Some major faults acting for millions of years have offset rock layers horizontally by hundreds of kilometers.

true

The Richter scale assesses the 1906 San Francisco earthquake and the 1964 Alaska earthquake as both being of magnitude 8.3. However, on the moment magnitude scale, the San Francisco earthquake is probably equivalent to a Richter magnitude 7.8 and the Alaska seism is equivalent to a 9.2. The Alaska earthquake was at least 100 times bigger.

true

The biggest shaking event is called "the earthquake," the smaller ones before it are known as foreshocks, and the smaller ones after it are called aftershocks.

true

The high-frequency seismic waves are most energetic for short distances close to the epicenter, whereas low-frequency seismic waves carry significant amounts of energy for much greater distances away from the epicenter.

true

The largest moment magnitudes measured to date are from earthquakes that occurred in subduction zones.

true

The moment magnitude is more accurate than the classical Richter scale because it is tied directly to physical parameters such as fault-rupture area, fault slip, and energy release, and because other earthquake scales use indirect measures such as how much a seismograph needle moves.

true

The relation between distance and damage from an earthquake seems obvious: the closer to the hypocenter/epicenter, the greater the damage, but this is not always the case.

true

The shaking produced by Rayleigh waves causes both vertical and horizontal movement.

true

The shallower the hypocenter, the more P and S wave energy will hit the surface.

true

The types of rock or sediment on which a structure's foundation sits are of paramount importance with respect to whether the structure will be damaged by shaking from an earthquake.

true

The velocity of an S wave depends on the density and resistance to shearing of materials.

true

To describe the location in three-dimensional space of a deformed rock layer or a fault surface, geologists make measurements known as dip and strike.

true

Transform faults usually link spreading centers or connect spreading centers with subduction zones.

true

Typically fewer than 20 major and great earthquakes (magnitudes of 7 and higher) each year account for more than 90 percent of the energy released by earthquakes.

true

Where the frequencies of seismic waves match the natural vibration frequencies of local geology and buildings, destruction may be great.

true

With their up-and-down and side-to-side motions, S waves shake the ground surface and can do severe damage to buildings.

true

Can the same fault be classified as both a strike-slip and a transform fault?

yes