Chapter 5 Critical Reading Quiz

If we know the S-P arrival time, we can refer to published charts to determine the distance to the earthquake's epicenter. Use your answer from the previous question to determine the distance from the seismic station to the epicenter. (Careful - the #2 and #3 are only from the example in the book. You are looking for the distance at which the difference between the P- and S- curves equals the time interval you found above. Be sure to use the bottom scale for miles or Figure 5.14 in your book)

2900 miles

Which type of seismic waves cause the greatest degree of ground shaking? (Hint: examine the amplitude of the seismic waves)

Surface waves The extent of ground shaking is indicated by the amplitude or height of the seismic waves. From the seismogram you can see that the highest amplitude waves are associated with the surface seismic waves. These typically cause the greatest damage.

Long term earthquake prediction is based on ________.

the assumption that large faults break in a cyclical manner

Using the nomogram (graph) below, determine the Richter scale magnitude for an earthquake 400 kilometers away, with a maximum seismic wave amplitude of 0.5 mm. (simply enter the number you determine. For example "5.5 or 2.0") Hint: When you type your answer do not go beyond one decimal)

4

The time interval between P- and S- waves can help determine the distance from your location to an earthquake's epicenter. If the vertical lines represent 1-minute, what is the time interval between the arrival of the first P-wave and the arrival of the first S-wave? (enter your answer as X minutes. For example "10 minutes")

6 minutes

Earthquakes can be described by their intensity or their magnitude or both. Match the definitions with the correct term. A). a measure of ground shaking at a location caused by an earthquake: B). a measure of energy released during an earthquake

A): intensity B): magnitude Be certain that you understand the difference between these terms. Intensity is influenced by many factors and a single earthquake can generate many local intensity values. There will be only one magnitude for a single earthquake and that magnitude can be determined from data collected at multiple locations.

The largest earthquake ever recorded was a Magnitude 9.5 event that occurred in _______________ in 1960

Chile

All earthquakes occur at plate boundaries.

False Intraplate earthquakes occur as well. The famous 1811-1812 New Madrid, Missouri earthquakes occurred in the center of the North American plate in a seismic zone associated with the buried fault system known as the Reelfoot Rift. The Reelfoot rift is identified today as a subsurface system of fractures and faults in the earth's crust. New Madrid seismicity is spatially associated with the Reelfoot rift and may be produced by movement on old faults in response to compressive stress related to plate motions.

Map Reading - Paleoseismology studies have found that the section of the San Andreas Fault that failed during the Fort Tejon quake (segment 3) produces a major earthquake every 135 years, on average. Based on this information, how would you rate the chances of a major earthquake occurring along this section in the next 30 years? Explain your answer by noting when that segment last triggered an earthquake.

My Answer: A major earthquake may occur in the next 30 years due to the evidence of seismic gaps accumulating seismic strain. A seismic gap can last for century and since a we're approaching the next cycle after 105 year , and earthquake could be triggered anytime once the years have been reached. Teacher's Answer: Chances are good that a major earthquake will occur. Based on long-term earthquake predictions, this segment is statistically likely to experience another earthquake of similar magnitude to the 1857 quake after 135 years or in 1992 (which has passed so this could happen soon)

What are seismic gaps and how do scientists use them to help predict earthquake events?

My Answer: A seismic gap is a segment that does not experience earthquakes but they accumulate seismic strain, which is used to help predict future earthquakes. Teacher's Answer Seismic gaps are places where scientists think that faults are storing elastic strain. Scientists can identify segments of faults that may represent seismic gaps. These are considered the segments that are most likely to shift and release energy in response to strain - thereby generating earthquakes

Faults, hypocenters, and epicenters are closely related. But provide a brief definition for each that shows they are not the same.

My Answer: Faults are the fractures of cracks in the ground that occur from an earthquake. Hypocenter is the source of the earthquake. The epicenter is the point on the Earth's surface directly above the hypocenter. Teacher's Answer: Slippage of rocks that generate earthquakes occur along faults. The hypocenter is the place slippage occurs between the rocks and the epicenter is the location on Earth's surface directly above the hypocenter.

In addition to the destruction created directly by seismic vibrations, define these other types of hazards associated with earthquakes and briefly state how they occur - liquefaction, subsidence, landslides, and tsunamis.

My Answer: Liquefaction is associated with earthquakes where the intensity of the shaking from earthquakes loosen water-logged material like sand deposits into liquid-like behaving substances. This hazard can cause cars or buildings to sink. Subsidences are triggered by earthquakes, where violent shaking caused coastal sediments to slump. When this hazard occurs, dock areas can collapse into the sea, Landslides are where a layer of clay losses its strength due to an earthquake's shaking and can cause portions of land to slide from its original position. Tsunamis are caused due to underwater earthquakes creating a high velocity ripple effect in oceans, that can travel to land as a wave. Teacher's Answer: Liquifaction is where normally solid material behaves more like a fluid during an earthquake and occurs because pore spaces between particles in unconsolidated sediments close and displace fluids during shaking. Ground shaking can also cause large sections of ground to collapse vertically (subsidence) or slide down slope (landslides) during earthquakes. Tsunamis are large ocean waves that can be highly devastating when they approach the coast. Most are generated by megathrust faults that suddenly shift large sections of sea floor.

Explain how the different seismic waves were used to reconstruct the physical properties of rocks in Earth's interior and to ultimately establish that Earth's outer core is liquid while the inner core is solid.

My Answer: Seismic waves are used to reconstruct the physical properties of rocks in the Earth's interior through the way P waves and S waves travel through it. S waves travel can't travel through liquid masses while P waves can. Though both P waves and S waves can travel through solid masses of rock. In the Core, the S wave is nonexistent in the outer layer, which shows that layer is liquid in mass. Though on the other hand, the inner core is solid because the S wav can once again travel through it. Teacher's Answer: Waves change velocities depending upon the material they encounter. For example, waves travel more slowly through hotter material. Velocity also increases with depth and through stiffer rock. Seismic waves are reflected, refracted, and diffracted as they pass through Earth and encounter different layers or boundaries between layers. A major discovery from the use of seismic waves was that the outer core is liquid. We know this because the S-waves cannot pass through that layer of the inner earth

Measuring earthquakes is no easy task. Explain the difference between the Modified Mercalli Intensity scale, the Richter scale, and the Moment Magnitude scale.

My Answer: The Modified Mercalli Intensity scale was initially based off California buildings as a reference which is based on a 12 point intensity scale of observations civilians may have had during an earthquake. The Richter scale is calculated based on a scales measuring the amplitude of an earthquakes largest seismic wave that is recorded on a seismogram. The Moment Magnitude scale is newer and its used or medium or large earthquake, where an estimation of energy released is recorded. The moment magnitude is calculated by determining the average amount of slip on the fault, the area of the fault surface that slipped, and the strength of the faulted rock. Teacher's Answer:

The world's TWO major earthquake belts are the circum-Pacific earthquake belt and the Alpine-Himalayan belt. Explain why these two belts exist in terms of your knowledge of plate tectonics. (Be sure to address the types of plate boundaries occurring at each location. A complete answer may also include some names of the major lithospheric plates involved.)

My Answer: These two major earthquake belts exist because they are either located on a plate boundary. The circum-Pacific earthquake belt lies on the convergent Pacific plate boundary. While the Alpine-Himalayan earthquake belt is caused due to being on a convergent boundary between the convergent Eurasian and Indian plates. Teacher's Answer:

Even though the lithospheric plates are in constant motion, most faults are "locked" because high confining pressure increases friction on the fault. When movement occurs, the rocks often demonstrate elastic rebound. Explain what is meant by elastic rebound.

My Answer: Elastic rebound is how energy is stored in rocks and then released by earthquakes. When that energy is released, the surface in that area will deform and return to its original state. Teacher's Answer: Rocks can deform when stressed as with build up to an earthquake; when rocks snap back to their original shape after slippage, this is termed elastic rebound.

The different types of seismic waves cause rocks to behave with different types of motion. Match each type of seismic wave with the appropriate impact it might have as it passes through rocks. P waves: S waves: Surface waves:

P waves: As these waves pass through, they cause rocks to compress and stretch much like an accordion. S waves: As these waves pass through, they cause rocks to exhibit a shaking motion. Surface waves: They waves cause complex motions in rocks that cause rolling or shearing.

The fastest type of seismic waves and the ones that will reach your location (and seismogram) first are ____________

Primary waves (p-waves)

The accompanying image shows a doubledecked section of Interstate 880 (the Nimitz Freeway) that collapsed during the 1989 Loma Prieta earthquake and caused 42 deaths. About 1.4 kilometers (0.9 mile) of this freeway section, commonly called the Cypress Viaduct, collapsed, while a similar section survived the vibration. Both sections were subsequently demolished and rebuilt as a single level structure, at a cost of $1.2 billion. Examine the map and seismograms from an aftershock that shows the intensity of shaking observed at three nearby locations after the 1989 Loma Prieta earthquake in California. What type of ground material experienced the greatest amount of ground shaking?

Soft mud The amount of ground shaking is measured by the amplitude (height) of the seismic waves in a seismogram. The seismograms show the highest amplitude waves occurred in the locations with the soft mud.

Earthquake depth reflects HOW an earthquake is triggered and it can also be important in impacting the damage of an earthquake. At which of the following plate boundaries are you most likely to find a deep earthquake (as opposed to one triggered by movement at shallow depths in the Earth)?

a convergent boundary such as the Peru-Chile trench Earthquake depths actually helped scientists learn a lot about plate tectonics. Scientists confirmed their hypotheses about subduction zones at convergent boundaries by noting that the depth of earthquakes increased moving away from trenches.

The map below shows the locations of the largest earthquakes since 1900. Which type of plate boundary is associated with these events.

convergent The most destructive earthquakes are caused by movement along megathrust faults that are associated with convergent plate boundaries. If you think back to our plate tectonics lesson, recall that convergent plate boundaries surround the Pacific Ocean.

As the distance from an earthquake epicenter increases, the difference or "gap" between the arrival of the P-wave and S-wave on a seismogram will

increase Because P-waves travel so much faster than S-waves, the farther away you get from an earthquake, the bigger the time gap between the P- and S-waves on a seismogram. Just look at this picture below. Nome, Alaska must be farthest from the earthquake epicenter.

Investigate the image below. What conclusions can you draw about the relationship between the frequency and strength of earthquakes? For example, we hear a LOT about big earthquakes. But are these the most common types of earthquake events?

millions of earthquakes occur each year but have magnitudes that are less than what humans can feel