what makes an earthquake deadly
Population density. The magnitude 9.2 Great Alaska Earthquake, near Anchorage, of 1964 resulted in only 131 deaths. At the time few people lived in the area (Figure 1.1). Not size. Only about 2,000 people died in the 1960 Great Chilean earthquake, the largest earthquake ever recorded. The Indian Ocean earthquake of 2004 was one of the largest ever, but most of the 230,000 fatalities were caused by the tsunami, not the earthquake itself. Ground type. Solid bedrock vibrates less than soft sediments, so there is less damage on bedrock. Sediments that are saturated with water undergo liquefaction and become like quicksand (Figure 1.2). Soil on a hillside may become a landslide. Liquefaction of sediments in Mexico City caused the collapse of many buildings in the 1985 earthquake.
In earthquake-prone areas, city planners try to reduce hazards. For example, in the San Francisco Bay Area, maps show how much shaking is expected for different ground types (Figure 1.3). This allows planners to locate new hospitals and schools more safely. The expected Modified Mercalli Intensity Scale for an earthquake of magnitude 7.1 on the northern portion of the Hayward Fault. Click image to the left or use the URL below. URL:
damage from earthquakes
We know that earthquakes kill lots of people. However, the ground shaking almost never kills people, and the ground does not swallow someone up. Fatalities depend somewhat on an earthquakes size and the type of ground people inhabit. But much of what determines the number of fatalities depends on the quality of structures. People are killed when structures fall on them. More damage is done and more people are killed by the fires that follow an earthquake than the earthquake itself.
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what can make an earthquake deadly?
a) intensity b) ground type c) construction --> d) all of the above
most fatalities in an earthquake are caused by
a) tsunamis b) liquefaction c) building damage --> d) none of the above
very few people died in the magnitude 9.2 great alaska earthquake in 1964 because the population density was very low.
--> a) true b) false
solid rock vibrates more than soft sediments in an earthquake.
a) true --> b) false
the quality of construction greatly affects the number of fatalities in a quake.
--> a) true b) false
what was the main reason for the increase of damage and fatalities of the 1960 chilean earthquake?
a) size of the population --> b) the tsunami c) poorly built buildings d) all of the above
mexico city is built in an old lakebed so the large quake there in 1985 caused
--> a) buildings to collapse. b) water to flood the streets. c) fire. d) all of the above
what about ground shaking kills people in an earthquake?
a) when the ground opens up and swallows people and buildings. --> b) when buildings fall on people. c) when people fall and hit their heads on the ground. d) when people become upset and stampede to get out of a location.
a modified mercalli intensity scale is best for city planners because, before choosing the site of a new hospital, they need to know
a) how much energy will be released in an earthquake. b) how the people will respond in an earthquake. --> c) how the ground will behave in an earthquake. d) all of the above
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