The Test on Building Earth's Surface consists of 18 questions. Correct answers are found through links located at the end of each question.
The answer section is formatted for on-screen use, not printing, and will waste a lot of paper if printed directly.
Have a fun learning experience!
Question #1: The basic concept needed to understand the principle of uniformity is
(A). immense spans of geologic time.
The basic concept in understanding the principle of uniformity is the concept of immense spans of geologic time. Immense spans of time with slow, incomprehensible change taking place is difficult to comprehend since it cannot be observed or experienced in a lifetime. Thus, understanding the principle of uniformity requires a mental model. This model is based on the observable events that build up the surface and wear it down and on an understanding of geologic time.
Question #2: Rocks that are stressed by compressional forces, then return to their original shape have undergone
(C). elastic strain.
The adjustment to stress is called strain and there are three types: elastic, plastic, and fracture. In elastic strain, rock units recover their original shape after the stress is released. In plastic strain, rock units are molded or bent under stress and do not return to their original shape after the stress is released. In fracture strain rock units crack or break as the name suggests.
Question #3: Rocks that are stressed by pulling forces, then bending in a way that they do not return to their original shape have undergone
(B). plastic strain.
The adjustment to stress is called strain and there are three types: elastic, plastic, and fracture. In elastic strain, rock units recover their original shape after the stress is released. In plastic strain, rock units are molded or bent under stress and do not return to their original shape after the stress is released. In fracture strain rock units crack or break as the name suggests.
Question #4: Anticlines, synclines, and domes are evidence of
(C). plastic strain.
Anticlines, synclines, and domes are regional structures that were created from plastic deformation of flat, horizontal layers of sedimentary rocks. When the folding occurred the rock layers were in a ductile condition, probably under considerable confining pressure from deep burial. The anticlines, synclines, or domes are under very different conditions when they can be seen at the surface.
Question #5: Normal faulting is associated with
(C). pulling-apart stress.
A normal fault is one in which an upper block of rock (the hanging wall) has moved downward relative to a block of rock below (the footwall). This is normal in the sense that you would expect an upper block to slide down a lower block along a slope. Click here to see the hanging and footwall relationship. Normal faulting results from a pulling-apart stress that might be associated with diverging plates.
Question #6: Reverse or thrust faulting is probably the result of
(B). compressional stress.
In a reverse fault the hanging wall block has moved upward relative to the footwall block. Click here to see the hanging and footwall relationship in reverse and thrust faults and how this probably resulted from compressive stress.
Question #7: About 15% of all the earthquakes that occur in the world do not have a shallow focus and occur
(C). in a narrow zone around the Pacific Ocean.
About 85 percent of all earthquakes are of a shallow focus, occurring in the top 70 km (about 45 miles) of the surface, 12 percent are intermediate-focus earthquakes -- 70 to 350 km deep (45 and 220 mi) -- that occur in the upper part of the mantle, and 3 percent are deep-focus earthquakes that occur in the lower part of the upper mantle. There is a worldwide pattern to the distribution of earthquakes, as most occur in long narrow belts, although they do occasionally occur elsewhere. Of all the intermediate-depth earthquakes in the world, 9 out of 10 occur in a narrow zone, or belt, which encircles the rim of the Pacific Ocean. Essentially all the earth's deep-depth earthquakes also occur within this particular belt.
Question #8: Most earthquakes that occur worldwide are
(A). near the surface along a fault.
About 85 percent of all earthquakes are of a shallow focus, occurring in the top 70 km (about 45 miles) of the surface, and along a fault plane. You might expect more earthquakes near the earth's surface since the rocks here are brittle, and those deeper are more ductile from increased temperature and pressure.
Question #9: In California the boundary between the North American Plate and the Pacific Plate is known as
(B). San Andreas fault.
Shallow-focus earthquakes are typical of those that occur at the boundary of the North American Plate, which is moving against the Pacific Plate. In California, the boundary between these two plates is known as the San Andreas fault. The San Andreas fault runs north-south for some 1,300 km (800 miles) through California, with the Pacific Plate moving on one side and the North American Plate moving on the other. The two plates are tightly pressed against each other, and friction between the rocks along the fault prevents them from moving easily. Stress continues to build along the entire fault as one plate attempts to move along the other. Some elastic deformation does occur from the stress, but eventually the rupture strength of the rock (or the friction) is overcome. The stressed rock, now released of the strain, snaps suddenly into new positions in the phenomenon known as elastic rebound. The rocks are displaced to new positions on either side of the fault, and the vibrations from the sudden movement are felt as an earthquake. The elastic rebound and movement tend to occur along short segments of the fault at different times rather than along long lengths. Thus, the resulting earthquake tends to be a localized phenomenon rather than a regional one.
Question #10: Most earthquakes are explained by
(B). the movement of rock blocks along faults.
An earthquake is a quaking, shaking, vibrating, or upheaval of the ground, a result of the sudden release of energy that comes from stress on rock beneath the earth's surface. There are limits as to how much stress rock can take before it fractures. When it does fracture, the sudden movement of blocks of rock produces vibrations that move out as waves throughout the earth. These vibrations are called seismic waves. It is strong seismic waves that people feel as a shaking, quaking, or vibrating during an earthquake. Seismic waves are generated when a huge mass of rock breaks and slides into a different position. Major earthquakes occur along existing fault planes or when a new fault is formed by the fracturing of rock. In either case, most earthquakes occur along a fault plane when there is displacement of one side relative to the other.
Question #11: The place on the earth's surface directly above the place where seismic waves originate is the
(D). epicenter.
The actual place where seismic waves originate beneath the surface is called the focus of the earthquake. The focus is considered to be the center of the earthquake and the place of initial rock movement on a fault. The point on the earth's surface directly above the focus is called the earthquake epicenter.
Question #12: All seismic waves leave the focus of an earthquake at the same time, but some distance away the _?_ arrive first.
(A). P-waves
Seismic S- and P-waves leave the focus of an earthquake at essentially the same time. As they travel away from the focus, they gradually separate because the P-waves travel faster than the S-waves.
Question #13: The time lag between the arrival of S- and P-waves is needed from a minimum of how many recording stations to locate the source of an earthquake?
(B). 3
To locate an epicenter, at least three recording stations measure the time lag between the arrival of the P-waves and the slower S-waves. The difference in the speed between the two waves is a constant. Therefore, the farther they travel, the greater the time lag between the arrival of the faster P-waves and the slower S-waves. By measuring the time lag and knowing the speed of the two waves, it is possible to calculate the distance to their source. However, the calculated distance provides no information about the direction or location of the source of the waves. The location is found by first using the calculated distance as the radius of a circle drawn on map. The place where the circles from the three recording stations intersect is the location of the source of the waves.
Question #14: A very large ocean wave generated by an earthquake, landslide, or volcanic explosion is known as a (an)
(B). tsunami.
Tsunami is a Japanese term now used to describe the very large ocean waves that can be generated by an earthquake, landslide, or volcanic explosion. Such large waves were formerly called "tidal waves." Since the large, fast waves were not associated with tides or tidal forces in any way, the term tsunami is preferred.
A tsunami, like other ocean waves, is produced by some strong disturbance in the seafloor, travels at speeds of 725 km/hr (450 mi/hr), and produces a wave height of 15 to 30 m (50 to 100 ft) when it breaks on the shore. Because of its great wavelength, a tsunami does not just break on the shore, then withdraw. Depending on the sea-floor topography, the water from a tsunami may continue to rise for 5 to 10 minutes, flooding the coastal region before the wave withdraws. A gently sloping seafloor and a funnel-shaped bay can force tsunamis to great heights as they break on the shore.
Question #15: The magnitude of an earthquake is usually reported by numbers and each higher number means
(C). 10 times more movement and 30 times more energy.
The energy of the vibrations, or motion of the land associated with an earthquake is called its magnitude. Earthquake magnitude is often reported by the media using the Richter scale. This scale assigns a number that increases with the magnitude of an earthquake. The numbers have meaning about the severity of the ground-shaking vibrations, and the energy released by the earthquake. Each higher number indicates about 10 times more ground movement and about 30 times more energy released than the preceding number.
Question #16: One of the following was not formed by complex folding resulting from compressional forces.
(A). Cascade Range
The Cascade Mountains of Washington and Oregon are a series of towering volcanic peaks. The Appalachian, Rocky, and Himalayan Mountains, on the other hand, have a great vertical relief that involves complex folding on a very large scale. The crust was thickened in these places as compressional forces produced tight, almost vertical folds. Thus, folding is a major feature of these major mountain ranges, but faulting and igneous intrusions are invariably also present. Differential weathering of different rock types produced the parallel features of the Appalachian Mountains that are so prominent in satellite photographs. The folded sedimentary rocks of the Rockies are evident in the almost upright beds along the flanks of the front range.
Question #17: The Teton Mountains of Wyoming and the Sierra Nevadas of California are classic examples of
(A). fault block mountains.
Compression and relaxation of compressional forces on a regional scale can produce large-scale faults, shifting large crustal blocks up or down relative to one another. Huge blocks of rocks can be thrust to mountainous heights, creating a series of fault block mountains. Fault block mountains rise sharply from the surrounding land along the steeply inclined fault plane. The mountains are not in the shape of blocks, however, as weathering has carved them into their familiar mountain-like shapes. The Teton Mountains of Wyoming and the Sierra Nevadas of California are classic examples of fault block mountains that rise abruptly from the surrounding land.
Question #18: The volcanoes of the Cascade Mountain Range are
(D). composite volcanoes.
A composite volcano is built up of alternating layers of cinders, ash, and lava flows, forming what many people believe is the most imposing and majestic of earthÕs mountains. The steepness of the sides is somewhere between the steepness of the low shield volcanoes and the steep cinder cone volcanoes. The Cascade volcanoes are composite volcanoes, but the mixture of lava flows and cinders seems to vary from one volcano to the next.
