Earthquakes Flashcards
Definition
Earthquakes are vibrations caused by earth movements at plate boundaries and at major fault lines. They can occur at all four major plate boundaries, but the most severe earthquakes are normally found at conservative and destructive plate boundaries. They occur when two plate boundaries are unable to move past each other easily. These plates become locked together, and friction causes pressure to build up. Suddenly the pressure is released and the plates jolt into a new position, causing seismic waves.
Seismographs record the extent of the shaking by a pen identifying the trace of the movement on a rotating drum. The line graph produced is called a seismogram.
Richter
The Richter scale measures the magnitude of a tremor presenting whole numbers and decimal fractions. Although the Richter scale has no real limit, the largest earthquake ever recorded was in 1960 in Childe, which measure a 9.5. It is a logarithmic scale, which means that 6 on the scale is 10 times bigger than 5 and 100 times bigger than 4. This scale is useful as it is mathematic and can be used to compare earthquakes around the world.
Mercalli
The Mercalli scale measures the effects of an earthquake using a scale from 1 (barely felt) to 12 (total destruction, waves seen on ground surface). It is a finite scale and stops at 12. It is very subjective and depends on personal opinions, and the descriptions are quite vague. Factors that need to be taken into account are location, quality of buildings etc. A 4.5 on the Richter scale in London would be a huge devastation as our buildings are not built to withstand earthquakes, and the measure on the Mercalli scale could be of a similar one to an 8.5 in japan.
Factors affecting damage caused
Emergency services: in places like Afghanistan, the services are poor with hospitals of bad quality and hygiene issues, which could cause problems in the event of an earthquake
Building design and construction: buildings need to be built to a standard to withhold earthquakes, and if they are poorly constructed, even a small earthquake will cause great devastation.
Time of day: if an earthquake is at night and people are asleep, there is a higher chance of death as people would not be awake and able to evacuate the area fast enough. Another problem would be if it is in the middle of the day and a lot of people may be in large office buildings.
Education : if people are given the right education, they will be able to construct better buildings to ensure safety, and more people will be taught about earthquake safety so they know what to do if one ever happens.
Physical landscape: Mexico City is built on a dried up lake bed, so liquefaction occurs, meaning the rocks are moving, causing more buildings to collapse.
MDC Kobe
In Kobe, japan, an earthquake occurred on the 17th January 1995. Japan lies on the Eurasian plate where the Philippines plate and pacific plate subduct underneath it. The earthquake measured a 7.5 on the Richter scale. Over 6000 people were killed, 40,000 were seriously injured and 300,000 were left homeless. Roads, railways, water mains were all damaged with gas mains catching fire. Only 30% of trains from Osake to Kobe were able to run. 2 million homes were without electricity, 1 million homes were without water for 10 days. Emergency serves, families and friends searched through the rubble to find any survivors. Motorola maintained telephone connections for free, and railways were 80% operational within a month. After a year, the port was 80% operational, but much of the container shipping business had been lost. New buildings were built further apart to avoid the domino effect.
LDC Haiti
In Haiti an earthquake occurred on the 12th january 2010. It occurred at a fault that runs right through Haiti and is situated along the boundary between the Caribbean and North American plates. The earthquake measured a 7.0 on the Richter scale, with at least 52 aftershocks of up to 4.5 on the scale for two weeks after. 316,000 people were killed and 1 million people were left homeless. 250,000 home and 30,000 other buildings (including the president’s palace) were either destroyed or badly damages, as were hospitals and schools. The main prison was destroyed allowing 4000 inmates to escape. 1 in 5 people lost their jobs. The large number of deaths meant that hospitals and morgues were full, so bodies were piled up in the streets leading to the spread of diseases such as cholera. $100 million in aid was given by the USA and $330 million by the European Union. 810,000 people were placed in aid camps, 115,000 tents and 1 million tarpaulin shelters were provided. 4.3 million people were provided with food rations in the weeks following the earthquake. Temporary schools were created and new teachers trained.
Monitor and Prevention
Geologists, university departments etc monitor earthquakes around the glove. On the 26th December 2003 an earthquake occurred in Iran which was a 6.6 on the Richter scale, causing over 26,000 deaths, and geologists have been monitoring the fault line it occurred on since. There were no emergency services as it is a rural area, and the buildings were not built to withstand anything. the best thing to do in an earthquake zone is to prepare people for them, such as mdc like japan and California where they are taught that under tables are a good place to hide during an earthquake so the rubble cannot get to you. Some people would be told to store food or medication in case of an earthquake. San Francisco is on the San Andreas fault line, so there is a skyscraper which has been built to be earthquake proof with a wider base. These pyramid shaped buildings are good as the wide base lowers the centre of gravity of the building.
