Moonquake
Until 1969,scientists wondered if quakes happen on the Moon, and if so, if they resemble quakes on Earth. Answers were provided by the lunar space program of the United States. Beginning in November 1969， seismographic stations were set up on the Moon during the landings of Apollo spacecraft 12,14,15,16,and 17. Special seismographs placed at the five landing sites were operated continuously, sending back a steady stream of geophysical data on the Moon’s interior. Study of the location and mechanisms of earthquakes has revealed a great deal about the way Earth is deforming; it was expected that seismographs on the Moon would provide similar information about its interior and deformation.
But quakes on Earth are a consequence of the planet’s massive dynamic processes. In stark contrast to Earth, the Moon has, for millions of years, been an unchanging planetary body with no visible active volcanoes and no regions where the crust has split apart. It was therefore somewhat startling that each of the lunar seismographic stations detected between 600 and 3,000 moonquakes every year, on the average. Most of the moonquakes were tiny, with magnitudes of less than about 2 on the Richter scale. The fact that the Moon has no atmosphere or oceans means that it has an extremely quiet background, so that the seismographs can be operated with very high magnifications, at least 100 to 1,000 times those that are normally possible on Earth.
Three different kinds of quake events are indicated. First are the deep moonquakes, which have their centers at depths of 600 to 900 kilometers in the Moon. These deep events are surprising. They seem localized at a specific number of places in the Moon’s interior, of which more than 40 have been identified. At these active deep centers, moonquakes commonly occur within an interval of a few days during perigee, the point at which the Moon’s orbit is closest to Earth. About equal numbers of deep moonquakes occur at these centers at opposite phases of this tidal pull, so that the most active periods are fourteen days apart. These periodic properties at least suggest that Earth’s tidal pull on the Moon triggers the occurrence of the deep seismic energy releases. On Earth, similar conditions of the occurrence of earthquakes with perigee have been sought for many years, but generally without success.
The second type of moonquake occurs nearer the surface. These moonquakes are not as common as the deeper events, and their locations do not exhibit any particularly regular pattern over the surface of the Moon. It is thought that, like most earthquakes, moonquakes are caused by the release of tectonic strain in the rocks of the Moon’s crust. If so, then either groundwater is present in the Moon or some dry fracturing is occurring in the unusual thermal conditions of the lunar surface, with its extreme range of cold and heat.
The third type of seismic event results from the impact of objects, both natural and artificial. The lunar seismographic stations were efficient detectors of meteorites hitting the surface, even at a range of 1,000 kilometers. In order to help with the determination of seismic-wave velocities of lunar rocks, parts of the lunar spacecraft were programmed to crash back on the lunar surface. These high- speed impacts generated seismic waves strong enough to produce clear recordings at lunar seismographic stations, and because the time and position of impact were known precisely, the travel times of the seismic waves could be calculated easily. This calculation was the first step in discovering the general architecture and properties of the Moon’s interior.
The waves recorded by lunar impacts and moonquakes indicated that most of the Moon is solid rock. The layered crustal shell on the surface is about 60 kilometers thick, and below lies a denser solid mantle about 1,000 kilometers thick. This overlies a central core that may be somewhat softer than the mantle but is most probably not liquid. The picture of Earth’s interior is markedly different. Moonquakes themselves differ sharply from earthquakes. A small earthquake may shake a remote seismograph for a minute or so, but on the Moon, the recorded shaking of the lunar surface in a moonquake continues for as much as an hour.
1
Until 1969,scientists wondered if quakes happen on the Moon, and if so, if they resemble quakes on Earth. Answers were provided by the lunar space program of the United States. Beginning in November 1969， seismographic stations were set up on the Moon during the landings of Apollo spacecraft 12,14,15,16,and 17. Special seismographs placed at the five landing sites were operated continuously, sending back a steady stream of geophysical data on the Moon’s interior. Study of the location and mechanisms of earthquakes has revealed a great deal about the way Earth is deforming; it was expected that seismographs on the Moon would provide similar information about its interior and deformation.
According to paragraph 1, which of the following was brought about by the Apollo landings?
AScientists began to use information about how the Moon is deforming to understand how Earth is deforming.
BNew, more sensitive seismographs were developed
CScientists received important geophysical data related to the Moon’s interior
DUnexpected discoveries were made about the location and mechanisms of quakes on Earth.
2
But quakes on Earth are a consequence of the planet’s massive dynamic processes. In stark contrast to Earth, the Moon has, for millions of years, been an unchanging planetary body with no visible active volcanoes and no regions where the crust has split apart. It was therefore somewhat startling that each of the lunar seismographic stations detected between 600 and 3,000 moonquakes every year, on the average. Most of the moonquakes were tiny, with magnitudes of less than about 2 on the Richter scale. The fact that the Moon has no atmosphere or oceans means that it has an extremely quiet background, so that the seismographs can be operated with very high magnifications, at least 100 to 1,000 times those that are normally possible on Earth.
According to paragraph 2, why were scientists surprised by the information acquired by the lunar seismographic stations?
AMost of the moonquakes were much smaller than the scientists had expected.
BThey did not expect to find so many quakes, since they had no previous evidence of volcanic activity or disruptions in the Moon’s crust.
CThey did not expect the average number of quakes to vary so much from year to year.
DThey expected more background interference and were not sure the seismographs could be operated at such high magnification.
3
Three different kinds of quake events are indicated. First are the deep moonquakes, which have their centers at depths of 600 to 900 kilometers in the Moon. These deep events are surprising. They seem localized at a specific number of places in the Moon’s interior, of which more than 40 have been identified. At these active deep centers, moonquakes commonly occur within an interval of a few days during perigee, the point at which the Moon’s orbit is closest to Earth. About equal numbers of deep moonquakes occur at these centers at opposite phases of this tidal pull, so that the most active periods are fourteen days apart. These periodic properties at least suggest that Earth’s tidal pull on the Moon triggers the occurrence of the deep seismic energy releases. On Earth, similar conditions of the occurrence of earthquakes with perigee have been sought for many years, but generally without success.
Paragraph 3 indicates that scientists have tried for many years but have not generally succeeded in finding which of the following?
AThe effect of moonquakes on tidal pulls
BA link between perigee and earthquakes
CWhen deep seismic energy releases tend to occur in the Moon
DHow the occurrence of earthquakes and moonquakes have changed over time
4
The second type of moonquake occurs nearer the surface. These moonquakes are not as common as the deeper events, and their locations do not exhibit any particularly regular pattern over the surface of the Moon. It is thought that, like most earthquakes, moonquakes are caused by the release of tectonic strain in the rocks of the Moon’s crust. If so, then either groundwater is present in the Moon or some dry fracturing is occurring in the unusual thermal conditions of the lunar surface, with its extreme range of cold and heat.
Which of the following can be inferred from paragraph 4 about surface moonquakes?
AThe Moon’s surface experiences temperature changes that may create the tectonic forces possibly responsible for the surface moonquakes
BBecause surface thermal conditions on Earth vary so much from those on the Moon, moonquakes occur more frequently than earthquakes.
CScientists can predict the location of a surface moonquake with more accuracy than that of a deep seismic event.
DAlthough they are very different in nature, surface moonquakes can be as powerful as deep moonquakes.
5
The third type of seismic event results from the impact of objects, both natural and artificial. The lunar seismographic stations were efficient detectors of meteorites hitting the surface, even at a range of 1,000 kilometers. In order to help with the determination of seismic-wave velocities of lunar rocks, parts of the lunar spacecraft were programmed to crash back on the lunar surface. These high- speed impacts generated seismic waves strong enough to produce clear recordings at lunar seismographic stations, and because the time and position of impact were known precisely, the travel times of the seismic waves could be calculated easily. This calculation was the first step in discovering the general architecture and properties of the Moon’s interior.
According to paragraph 5, how were parts of the lunar spacecraft used to help discover information about the Moon?
AThey were sent deep under the Moon’s surface to try to obtain information about deep moonquakes.
BThey were programmed to hit the lunar surface and cause seismic waves at known times and distances from seismographic stations.
CThey were programmed to land 1,000 kilometers from existing seismographic stations.
DThey were programmed to record meteorite activity and send it to seismographic stations.
6
The waves recorded by lunar impacts and moonquakes indicated that most of the Moon is solid rock. The layered crustal shell on the surface is about 60 kilometers thick, and below lies a denser solid mantle about 1,000 kilometers thick. This overlies a central core that may be somewhat softer than the mantle but is most probably not liquid. The picture of Earth’s interior is markedly different. Moonquakes themselves differ sharply from earthquakes. A small earthquake may shake a remote seismograph for a minute or so, but on the Moon, the recorded shaking of the lunar surface in a moonquake continues for as much as an hour.
The word “markedly” in the passage is closest in meaning to
Arelatively
Bdistinctly
Csurprisingly
Dseemingly
7
The waves recorded by lunar impacts and moonquakes indicated that most of the Moon is solid rock. The layered crustal shell on the surface is about 60 kilometers thick, and below lies a denser solid mantle about 1,000 kilometers thick. This overlies a central core that may be somewhat softer than the mantle but is most probably not liquid. The picture of Earth’s interior is markedly different. Moonquakes themselves differ sharply from earthquakes. A small earthquake may shake a remote seismograph for a minute or so, but on the Moon, the recorded shaking of the lunar surface in a moonquake continues for as much as an hour.
According to paragraph 6, all of the following are true of the Moon EXCEPT:
AThe crust of the Moon is more than 1,000 kilometers thick.
BThe central core of the Moon is probably softer than the mantle,but not liquid.
CSeismic waves from quakes on the Moon last longer than those from earthquakes.
DThe Moon is mostly solid rock.
8
The waves recorded by lunar impacts and moonquakes indicated that most of the Moon is solid rock. The layered crustal shell on the surface is about 60 kilometers thick, and below lies a denser solid mantle about 1,000 kilometers thick. This overlies a central core that may be somewhat softer than the mantle but is most probably not liquid. The picture of Earth’s interior is markedly different. Moonquakes themselves differ sharply from earthquakes. A small earthquake may shake a remote seismograph for a minute or so, but on the Moon, the recorded shaking of the lunar surface in a moonquake continues for as much as an hour.
Which of the following best describes the role of paragraph 6 in the passage?
AIt summarizes the different ways in which seismic-wave velocities can be studied both in moonquakes and in earthquakes.
BIt shows how natural and artificial lunar impacts have provided more information about the Moon’s interior than have deep and surface moonquakes
CIt illustrates how the studies on travel times of seismic waves on Earth differed from similar studies conducted on the lunar surface.
DIt explains the findings obtained through the studies of quakes and impacts on the lunar surface.
9
But quakes on Earth are a consequence of the planet’s massive dynamic processes. [■]In stark contrast to Earth, the Moon has, for millions of years, been an unchanging planetary body with no visible active volcanoes and no regions where the crust has split apart. [■]It was therefore somewhat startling that each of the lunar seismographic stations detected between 600 and 3,000 moonquakes every year, on the average. [■]Most of the moonquakes were tiny, with magnitudes of less than about 2 on the Richter scale. The fact that the Moon has no atmosphere or oceans means that it has an extremely quiet background, so that the seismographs can be operated with very high magnifications, at least 100 to 1,000 times those that are normally possible on Earth.[■]
Look at the four squaresthat indicate where the following sentence could be added to the passage
Many of Earth’s geological mechanisms, however, are absent on the Moon.
Where would the sentence best fit？Click on a square sentence to the passage.
10
Seismographic stations were set up on the Moon during the Apollo landings.
AUntil the lunar program of the United States began, people had many false beliefs about the causes of moonquakes
BDeep moonquakes occur regularly and seem to be connected to the Moon’s position relative to Earth
CMeteorite and spacecraft impacts produced information on the seismic velocities of rocks, which in turn helped determine the characteristics of the Moon’s interior
DMost moonquakes are very small, with a few larger quakes each year, probably caused by volcanic activity.
ESurface moonquakes are irregular and, like earthquakes, are thought to be caused by strain in the crust
FBecause the structure of the Moon is different from that of Earth,moonquakes are more powerful and much shorter than earthquakes
