Earthquakes and Tsunamis

What is an earthquake? Why does it even occur when our ground is solid? Well, an earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. It is an important area in Physics, and therefore I have decided to include in under Term 3's Physics topic in my Science E-Portfolio. The seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time. Earthquakes are measured using observations from seismometers. The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe. The more numerous earthquakes smaller than magnitude 5 reported by national seismological observatories are measured mostly on the local magnitude scale, also referred to as the Richter scale. These two scales are numerically similar over their range of validity. Magnitude 3 or lower earthquakes are mostly almost imperceptible and magnitude 7 and over potentially causes serious damage over large areas, depending on their depth. The largest earthquakes in historic times have been of magnitude slightly over 9, although there is no limit to the possible magnitude. The most recent large earthquake of magnitude 9.0 or larger was a 9.0 magnitude earthquake in Japan in March 2011, and it was the largest Japanese earthquake since records began. Intensity of shaking is measured on the modified Mercalli scale. The shallower an earthquake, the more damage to structures it causes, all else being equal. At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground. Earthquakes can also trigger landslides, and occasionally volcanic activity. Earthquakes usually occur in neighbouring countries of Singapore as well, such as the recent Sumatra earthquake in Indonesia, which happened in 2007. Singapore faced tremors from this earthquake, and vibrations could be felt from structures built on artificial reclaimed land, such as One Raffles Quay.

What is a tsunami, then, and how is it related to an earthquake? When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. It is derived from a Japanese term, which also means ‘harbour wave’.  Tsunamis are also known as tidal waves, and are extremely common in earthquake prone countries. They are caused by underwater explosions of any sort, be it volcanoes, bombs, meteorites or earthquakes.

A tsunami can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the Earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. More specifically, a tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, owing to the vertical component of movement involved. Movement on normal faults will also cause displacement of the seabed, but the size of the largest of such events is normally too small to give rise to a significant tsunami. A tsunami can be humongous, giving it its name as the ‘tidal’ wave. Tidal waves usually travel up to 700km/h and can rise as high as up to 30 metres as it approaches land, and apart from capsizing large ships, it can destroy structures on land and kills many people.

Reflections:

I feel that although earthquakes and tsunamis destroy our structures and kill many innocent lives, they are inevitable as they are part of nature, being natural disasters which come about naturally. I believe this is an interesting topic in physics, as it is amazing how an earthquake can cause a tsunami, such a large and titanic wave which causes much devastation even on land. These tidal waves can even bring down small buildings and tear down houses, as I recently saw in documentaries i=of the recent 2011 Japan earthquake and tsunami incident. Although this was extremely devastating and killed many and caused many to lose their homes in Japan, I am impressed by the Japan citizen’s calm reactions towards this shocking incident, and I feel that this is the way that everyone should react when facing such an incident, as such natural disasters are inevitable and neither can we blame nature for this happening. However, I am interested to find out more on such occurrences, as I am extremely intrigued by how earthquakes are formed, as it is an interesting part of physics, when the tectonic plates underground can shift and cause such massive destruction. Overall, I believe that earthquakes and tsunamis are extremely interesting, although deadly.