What Is An Earthquake
Earthquakes refer to shaking of earth. There is continuous activity going on below the surface of the earth. There are several large plates (size of continents) below the surface of the earth, which move (at a very slow speed). As a part of this movement, sometimes, they collide against each other. And, after the collision, they might still continue to push each other. As they continually keep pushing each other, there is a pressure building up – across these plates below the surface. And, then, at a certain time, one of the plates might slide over another. This causes an earthquake.
Some earthquakes might be caused by activity above the surface. For example in a mountainous region, there might be a heavy landslide. Due to a huge mass of land falling, at the point of the fall, there could be a minor shaking of earth, due the impact of fall. However, usually, such earthquakes are not very major.
Classifying An Earthquake
The impact of an earthquake (at any location) is characterized by two primary characteristics:
Intensity This measures the magnitude of the event. Higher is the value, the bigger is the magnitude. The most common scale used for measuring an earthquake is Richter Scale. It should be understood that Richter scale is a logarithmic scale. What this means is an earthquake measuring 6.0 is 10 times more powerful than an earthquake measuring 5.0
Epicenter This denotes the exact location, where the earthquake originated. The deeper it is inside the earth, the lower will be the impact on the surface – where human beings reside.
There are 100s of earthquakes taking place on a daily basis all around the world. However, most of these earthquakes are really low-intensity, too-low to be noticed. However, sometimes there are some earthquakes which are significantly intense.
Some Recent Earthquakes
Some of the earthquakes in recent times have been (not in any particular order):
- El Salvador; In 2001; Magnitude: 7.7
- S. Peru; In 2001; Magnitude 7.9
- Algeria; In 2003; Magnitude 6.8
- Indonesia: In 2004; Magnitude 9.0
- India; In 2001; Magnitude 8.1
- China - Sichuan Province; In May 2008; Magnitued 8.1; More than 68,000 dead, and, 3,50,000 injured
Fault Lines And Earthquakes
Usually, areas around fault-lines are more prone to earthquakes.
Some of the major fault lines are around:
- Italy (hit in 1980; magnitude: 7.2)
- Hayward, San Francisco in California (hit in 1906 at San Francisco; magnitude: 7.8 and again in 1989 at Loma Preita; magnitude: 6.9)
- Himalayan region (hit several times since 1999, at various places spanning across Afghanistan, Pakistan, India etc.)
Nature of Losses And Damages
The most common kinds of loss that are caused by an earthquake (depending on the severity) are:
- Damage to structures
- Causing partial or total collapse, damage to road and rail network, damage to utility carriers etc.
- Sea activity
- Water level in the sea could rise suddenly, causing very high waves, several meters in height, which could then flood the coastal areas. These could give rise to tsunamis, causing damage to coastal areas.
- As earth shakes, in mountainous regions, huge chunks of land could fall/slide onto lower regions of the mountains. This could have several impacts, including: changed topography, blocked roadways, damage to anything that comes in the way of the landslide, massive damage to the structure which sits on the piece of sliding land – and massing damage to the houses and roads where the piece of land finally lands. The landslide could also trigger another set of minor earthquakes.
Quake Lakes: In the earthquake in China (May 2008), landslides blocked Jiangjiang river, resulting in creations of (about 35) lakes. These lakes in turn posed severe threat of flooding downstreams - due to possible bursting. More than 1,50,000 people had to be evacuated - due to this threat of flooding.
Earthquakes typically impact a huge area, spanning whole city, and many times, several cities. The impact due to this is that besides the instantaneous damage to life and property at the time of the event, there is a long-drawn suffering.
Earthquakes are also characterized by aftershocks. After any major seismic activity below the earth, the new order might take a while to finally settle down. During this time, there might be some more activity below the earth (sort of “adjusting” of the new positions for the various plates, layers etc.) These activities result in several more earthquakes. These are called, “aftershocks”. Typically, “aftershocks” are much smaller in magnitude, however, some times, one of the “aftershocks” could be more severe than the main earthquake. Also, “aftershocks” could strike up to several days after the main event.
For example the earthquake in Northern Chile (Nov. 2007) has had aftershocks till 3 days after the main earthquake.
Similarly, in China (May, 2008) an aftershock of the magnitude of 6.4 on the Ritcher scale hit 13 days after the main earthquake on May 12. This aftershock destroyed 70,000 houses and damaged many more. Each of these aftershocks were increasing the anxiety about the capacity of the quake-created lakes to hold their water.
Implications of Aftershocks
The implications of “aftershocks” are the following:
- Structures which are not severely damaged during the main earthquake could now get damaged during one of the “aftershocks” – as they are getting continuously weakened by the earthquake and the “aftershocks”.
- While rescue teams are trying to search through the debris of fallen buildings/bridges etc for trapped people, an aftershock could destabilize the debris further, causing these rescue teams themselves to become a victim. Besides, increasing the list of victims, it has two other major impacts:
- Loss of trained people and specialized equipments; which in turn means significant impediment to the speed of further rescue
- Fear among rescue teams for their own lives – due to the possibility of an “aftershock” causes them to proceed with extreme caution; thus, they are not able to work to their fullest capability
In the May 2008 earthquake of Sichuan, about 200 relief workers died in mudslides triggered by aftershocks.
- People who have suffered during an earthquake are in psychological trauma. Each “aftershock” causes immense panic amongst them.
Recognizing an Earthquake
The most common ways to identify the onset of an earthquake would be:
- A feeling of shaking of the ground below you, if you are sitting/standing. The most common feeling is – as if the person is feeling giddy.
- Swinging of overhead hanging stuff, e.g. fans, chandeliers etc. However, in this situation, you should distinguish between swaying of overhead hanging stuff – due to wind
- A feeling as if both the rear tires of your car are flat (if you are driving)
During an earthquake, there are many ways by which one can get hurt (many times, fatally)
- People inside buildings could get hurt (even critically) by fall of objects/walls/ceilings
- People outside the buildings could get hurt by falling debris from damaged buildings, glasses etc.
- People traveling could get hurt by their vehicles falling off the tracks, bridges, material falling from overhead bridges etc.
- People could get electrocuted by snapped electrical wires
- People could get washed away by floods – caused due to tsunamis, breaches in dams etc.
Hence, in case of an earthquake, the safest place to be would be in an open ground – away from all kinds of buildings and tall structures.
If you can not rush out of your building, you can duck under some sturdy desk etc. which might provide protection against heavy objects falling on your body.
If even that is not possible, sit against a wall, with your back pushing the wall firmly, and, lean forward – to take your head in between both your knees, and, put your hands at the back of your head – to provide protection to your head and spine.
Or, you could stand directly below one of the door-frame in your house. This one appears a bit strange to many people. In fact, there are jokes that after an earthquake – you don’t see all those door-frames standing. So, whats the reasoning behind advising people to stand below door-frames? In most styles of construction, doorframes are made very strong, or, would have a “RCC beam” running right above these frames. Either way, this “strong” structure would take the impact of objects falling from above, and, would break the impact of the heavy objects falling on the person. If you use this posture, remember to save your arms and fingers from swaying doors etc. If not careful, they could cause damage by chopping off fingers etc. due to the banging of the doors against the frame.
Predicting An Earthquake
Earthquakes have very low predictability in short term, i.e. in most cases, there is no warning – even a few minutes before an earthquake. However, in most cases, a much higher degree of predictability exists in long term – in the sense that if a certain area is sitting on a fault line, it can be said that over a long period of time, there is a high risk of earthquake. However, whether the earthquake occurs within the next few minutes, few years, few decades – or, maybe a few centuries might not be predicted.
In April 2008, USGS reported that the state has a 46% chance of a 7.5 or larger earthquake in California state during the next 30 years. So, relatively high predictability over the next 30 years, but, absolutely zero predictability in the immediate short term!!
There are certain schools of thoughts that believe that there are certain animal instincts which provide certain degree of indication of an impending earthquake. While the beliefs in this matter are varied, the closest scientific successful attempt to predict an earthquake is known to be the incident of earthquake at Haicheng, Liaoning Province of China in Feb. 1975. An alert local community and the earthquake administration noticed a change in water level in ground-wells as well as behaviour patterns of certain animals. Taking this to be an indication of an impending earthquake, many people were evacuated out of their houses. Even though, many people had to stay outdoors in the cold, it is believed that timely evacuation helped in saving thousands of lives.
Still, the scientific community is divided about the possibility of accurately predicting earthquakes. Even if the above example is considered as an example of ability to predict earthquakes, its a matter of fact – that since 1975 many more earthquakes have jolted our earth, without anybody being forewarned. Some of these have been in China itself.
Many countries monitor the seismic activity below the earth. Since there are a lot of seismic activities below the earth on a continuous basis, these countries are not necessarily interested in these low-intensity activities. However, their interest is to see if there is a sudden increase in seismic activities. An increase in seismic activity could imply an impending earthquake in the near-future. However, how close (in “time”) might still not be predictable.
Constructing Your House
People who stay in an earthquake prone area might do well to make investments in earthquake-proofing of their houses.
The process starts with the construction of the house.
Traditionally, people in earthquake prone areas used to build homes using lighter materials, and, also materials which could be reused, e.g. wood. The advantage with wood is: being lighter – it does not cause heavy damage – when it falls on the residents, and, secondly, most of the wood can be salvaged from the debris, and, reused. This reduces the cost of rebuilding.
However, during the last several decades, due to change in construction technology, people are going in for concrete structures – specially designed to withstand earthquakes or other seismic activities. The choice of concrete over wood is gaining ground, because: if the structure is well-designed to withstand earthquakes, it would not get damaged. So, there is “no” cost of rebuilding, and, there is no damage due to falling material. However, the cost of construction would be high. Since people build houses for long-term, and, earthquakes have a certain degree of predictability in long period, there is an increasing acceptance to the idea of this investment.
Some simple thumb rules to follow for constructing a house in an area prone to earthquake:
- The entire construction should be a single monolithic structure, so that the whole structure can move as a whole
- To the extent possible, material used should be something that has been available locally. This would allow very little differential in the movement of your building vis-à-vis the material over which the house sits – thus reducing the chances of sinking
- Minimum use of glass in building facades. These decorative pieces could be deadly, during an earthquake. Glass being very brittle, even a minor twist in the structure could cause breakage. And, glass being very heavy and injurious could cause severe damage.
- Doors and windows should have fasteners, so that they can be fastened. If the doors and windows are not fastened, they might cause any of the following situations:
- Swaying/banging of doors and windows against the frame could damage your limbs/fingers/toes etc.
- The doors might get “stuck” due to damaged/misaligned frame – making it difficult for you to run out, or, for the rescue teams to reach you.
- Consult a good structural engineer to ensure that the structure is strong enough to withstand seismic activities
Earthquake-Proof Your Home
When staying in the house, simple precautions should be used:
- Large/heavy items should be fastened, so that they don’t fall-off, during earthquakes.
- Hanging items (like: fan, chandeliers, decorations etc.) should be fastened, rather than just left hanging through a hook
- You should be adequately prepared to live without utilities for several days. As earthquake causes severe damages over large areas, most of the utilities that we might take for granted, might not be available for several days. These are anyways generic precautions against disasters of any kind.