Chapter 3 Exam (Earthquake Geology And Seismology)

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.

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

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.

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

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

Transform faults have mostly vertical displacement rather than horizontal displacement.

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

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

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

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

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.

Earth's interior is homogeneous.

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.

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.

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.

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.

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

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

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

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

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.

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.

Each year, Earth is shaken by millions of earthquakes.

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.

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.

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.

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

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.

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

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.

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.

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.

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

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

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

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

Different estimates of earthquake magnitude are derived from different methods based on local shaking (Richter scale), body waves (mb), surface waves (MS), or seismic moment (MW).

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

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

Earthquakes are most commonly caused by ______________.

The Lisbon earthquakes of 1755 are historically significant because ______________.

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.

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

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.

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.

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.

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 __________.

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

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

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

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

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

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

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

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

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

P waves can travel through ________________.

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

Which of the following wave types travels slowest through rock?

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

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

The frequency of a wave is __________________.

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

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

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.

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

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

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.

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

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

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

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

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

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

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

In general, during an earthquake you should __________.

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

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.

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

Shear walls are designed to __________.

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

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

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