Question 1

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.

Accepted Answer

This statement is true. The vast majority of energy released by earthquakes is due to a small number of major and great earthquakes each year.

Question 2

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.

Accepted Answer

The statement is true. The moment magnitude scale takes into account physical parameters of an earthquake such as the size of the ruptured fault and the amount of energy released, which makes it a more accurate measure than the Richter scale. Other scales may use indirect measures such as the amplitude of seismic waves recorded by a seismograph, which can be affected by the distance and type of rock between the earthquake and the instrument.

Question 3

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

Accepted Answer

Earthquake intensity scales such as the Modified Mercalli scale assess the effects on people and buildings, taking into account factors such as shaking intensity, damage to structures, and human reaction.

Question 4

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

Accepted Answer

This is because low-frequency surface waves match the natural frequency of tall buildings, leading to resonance and amplification of the vibrations.

Question 5

The two largest moment magnitudes measured to date are the 1964 Alaska earthquake (M_S of 8.3;M_W of 9.2)and the 1960 Chile earthquake (M_S of 8.5;M_W of 9.5).

Accepted Answer

The statement is true. The 1964 Alaska earthquake and the 1960 Chile earthquake are the two largest moment magnitudes measured to date, with magnitudes ranging from 8.3 to 9.5.

Question 6

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

Accepted Answer

The time of day can be a critical factor affecting loss of life from earthquakes. If an earthquake occurs during the night, people may be sleeping and less alert, making it harder for them to react quickly and evacuate if necessary. Additionally, nighttime earthquakes may cause power outages and disrupt communication systems, making it more difficult for emergency responders to reach affected areas.

Question 7

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.

Accepted Answer

This statement is true. High-frequency seismic waves, also known as primary waves or P-waves, are the fastest seismic waves and are most energetic near the epicenter of an earthquake. Low-frequency seismic waves, also known as surface waves or L-waves, carry significant amounts of energy but travel slower than P-waves, thus they can propagate for much greater distances away from the epicenter.

Question 8

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).

Accepted Answer

Different methods do indeed exist for estimating earthquake magnitude based on different aspects of the seismic waves generated by the earthquake.

Question 9

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.

Accepted Answer

The statement is true. The Richter scale is based on the amplitude of waves recorded on a seismogram, while the moment magnitude scale takes into account the size of the fault rupture, the amount of slip, and the rock stiffness. The San Francisco earthquake had a smaller fault and less slip compared to the Alaska earthquake, which is why it is assessed as a lower magnitude on the moment magnitude scale.

Question 10

Earthquakes are most commonly caused by ______________.

Accepted Answer

Earthquakes are most commonly caused by sudden earth movements along faults. These movements can occur due to tectonic activity, which is the movement of the earth's plates. When these plates move, they can cause stress and strain to build up along faults. Once the stress and strain exceed the capacity of the rocks to hold them, the rocks suddenly break, causing the release of energy in the form of seismic waves, which we feel as earthquakes. Explosions of nuclear bombs, undersea landslides, and meteorite impacts can also cause earthquakes, but these causes are relatively rare compared to tectonic activity. Volcanic activity can also cause earthquakes, but this is usually due to the movement of magma beneath the earth's surface, rather than movements along faults.

Question 11

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

Accepted Answer

Faults are geological features created by tectonic activity that can cause the displacement of rock layers over long periods of time. Some major faults can indeed offset rock layers horizontally by hundreds of kilometers, as evidenced by geological studies and observations.

Question 12

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.

Accepted Answer

The intensity of shaking is directly related to the magnitude of an earthquake. The stronger the earthquake, the more people in a larger area and for a longer time will experience the intense shaking.

Question 13

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

Accepted Answer

The duration of shaking is a very significant factor in damages suffered and lives lost. The longer an earthquake lasts, the more damage it can cause. Additionally, longer earthquakes also increase the likelihood of secondary hazards such as landslides and tsunamis, which can result in even greater destruction.

Question 14

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.

Accepted Answer

The distance from the earthquake is not always the only factor that determines the level of damage. Other factors such as the type of soil and the depth of the earthquake can also play a significant role in the amount of damage caused. Additionally, the strength and duration of the earthquake can also impact the amount of damage, regardless of the distance from the epicenter.

Question 15

Each year,the Earth is shaken by millions of earthquakes.

Accepted Answer

This is true. According to the United States Geological Survey (USGS), there are approximately 1.3 million earthquakes each year around the world, which is an average of about 3,500 earthquakes per day. However, not all of these earthquakes are felt by people or cause damage.

Question 16

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

Accepted Answer

Earthquake magnitude scales, like the Richter scale, measure the energy released by an earthquake, not the effects on people and buildings. The Modified Mercalli Intensity Scale assesses the effects on people and structures.

Question 17

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.

Accepted Answer

Earthquake accelerations have been measured in excess of 1.0 g, especially near the epicenter.

Question 18

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

Accepted Answer

This statement is true. When seismic waves match the natural vibration frequencies of buildings and geology, it can lead to resonance and amplification of the shaking, causing greater destruction. This phenomenon is known as resonance or the resonance effect.

Question 19

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.

Accepted Answer

The type of rock or sediment on which a structure's foundation sits can affect its resistance to damage from earthquake shaking. Different types of rock and sediment have different levels of strength and ability to absorb seismic energy, so it is important to consider these factors when designing or building structures in earthquake-prone areas.

Question 20

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.

Accepted Answer

This is true because rigid materials and short buildings tend to have high natural frequencies that match the frequency of high-frequency seismic waves, which results in resonance and amplification of vibrations. This can lead to increased damage during an earthquake.

Quiz 3: Earthquake Geology and Seismology