• Leaving Cert. Geography (Higher) 2008: Part Two Q3
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How destructive an earthquake is depends on a number of factors including the time of year and the time of day that it occurs, the population density, the economic wealth of the country, the type of construction of the buildings, the geology of the area and the magnitude and duration of the earthquake.

The most destructive earthquakes occur in areas with high population densities. Ground vibrations cause more damage and loss of life than any other earthquake hazard, particularly if the ground is unconsolidated (silt, sediment) and buildings poorly constructed. Liquefaction can occur, destroying structures.

The Izmit earthquake, 1999, in Turkey had a more hazardous effect than the Los Angeles one in 1994. The Izmit earthquake measured 7.4 on the Richter scale, lasted 45 seconds and killed 20,000 people. Most died when poorly constructed buildings collapsed and a tsunami followed the earthquake. Bodies were left decaying causing diseases, e.g. cholera and typhoid. Emergency services were unable to deal the scale of the disaster. The Los Angeles earthquake measured 6.7 on the Richter scale and lasted 40 seconds. Just over 60 people were killed. The number of deaths would have been higher had the earth quake not occurred early in the morning of a public holiday and also if the buildings had not been reinforced with steel. Most of the deaths and destruction occurred in older, poorly constructed buildings. Emergency measures had been well planned and rescue operations went well. Rescuers had up-to-date equipment, e.g. fibre-optic cameras.

Seismologists detect seismic activity using seismometers, instruments for detecting seismic waves, and seismographs which record data about waves. Tilt meters are also used in the prediction of earthquake activity. Here, changes in the shape of the earth’s crust can be measured prior to a tectonic event; however, earthquakes occur at such a fast rate it is often too late to take remedial action against the earthquakes. In some instances animal activity has been noted to be abnormal prior to an imminent quake. This occurred in Thailand prior to the tsunami in 2004. Animals left the coastal villages and headed for the higher land behind the villages.

Another example of an earthquake occurred on November 1, 1755 in Lisbon, Portugal. This was one of the worst earthquakes in European history. The devastating results caused a tsunami, or tidal wave. This flooded the Tagus River. At the same time, the earthquake caused a fire which destroyed large parts of the city. Estimates of the number of deaths vary from 10,000 to 60,000. The quake was the result of Portugal lying near the edge of the Eurasian and African plates.

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Leaving Cert Notes

Wednesday, 16 march 2016, physical geography- prediction and effects of earthquakes, no comments:, post a comment.

Explain how earthquakes and volcanic eruptions can be monitored and predicted

The study of plate tectonics has meant that seismologists can now very accurately predict where earthquakes will occur – it’s when they will occur that’s difficult to pinpoint. It is well known that major earthquakes occur at plate boundaries, especially convergent boundaries where two plates collide, or transform boundaries where two plates slide past each other. Japan, for example, is a major earthquake zone because it is on the boundary of three major plates. The San Andreas Fault in California is another boundary where earthquakes regularly occur, albeit a transverse one. Seismologists have mapped the recent earthquakes along the fault and can accurately predict where the next earthquake will occur, they just don’t know when. The bigger the time gap since the last earthquake, the more convergent the next one will be.

Seismologists use modern technology to monitor earthquake activity along fault lines. Lasers and tiltmeters are used to monitor changes along the fault. Scientists use seismometers to study the tremors along the fault lines. Water and oil levels in wells are also closely monitored for sudden changes that might mean that the ground is under pressure. Radon gas levels are measured because any sudden increase in radon gas levels means rocks are fracturing underground. In China, changes in animal behaviour have been observed in the past and claim to be early warnings for earthquakes.

Like earthquakes, volcanoes also occur most often at plate boundaries. The more convergent volcanoes tend to occur at convergent boundaries. It is a lot easier to predict where volcanoes will occur as they are very active in the days preceding an eruption. Even dormant volcanoes are kept under strict observation and any changes are monitored using modern technology.

Before volcanoes erupt there are many obvious signs. A gradual or sudden swelling of the magma chamber in the volcano is a sign of the magma moving upwards through the vent into the cone. This was very clear to see before Mt St Helens erupted in 1980. Lasers can very accurately monitor these changes in the shape of volcanoes. In addition, there is also a significant increase in the emissions of sulphur dioxide before an eruption. This is a sure sign of major volcanic activity as it shows that more magma is rising near to the surface. Finally, the use of seismometers is key to monitoring volcanoes as tremors before an eruption are giveaway signs of magma moving up through the crust.


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