I have recently moved to Gated community apartments in OMR Road with my as a tenant in a flat in eighth floor.Here I want to write my experience on 11th April 2012 when a powerful earthquake struck.
First let us know about how earth quakes strike the earth and its effects:
An earthquake (also known as a quake, tremor or temblor) is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Theseismicity, seismism 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 cause 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 2011 (as of 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.
In its most general sense, the word earthquake is used to describe any seismic event — whether natural or caused by humans — that generates seismic waves.
Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests. An earthquake's point of initial rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter.
Effects of earthquakes
The effects of earthquakes include, but are not limited to, the following:
Shaking and ground rupture
Specific local geological, geomorphological, and geostructural features can induce high levels of shaking on the ground surface even from low-intensity earthquakes. This effect is called site or local amplification. It is principally due to the transfer of the seismic motion from hard deep soils to soft superficial soils and to effects of seismic energy focalization owing to typical geometrical setting of the deposits.
Shaking and ground rupture are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings and other rigid structures.
Ground rupture is a visible breaking and displacement of the Earth's surface along the trace of the fault, which may be of the order of several metres in the case of major earthquakes.
Landslides and avalanches
Earthquakes, along with severe storms, volcanic activity, coastal wave attack, and wildfires, can produce slope instability leading to landslides, a major geological hazard. Landslide danger may persist while emergency personnel are attempting rescue.
Earthquakes can cause fires by damaging electrical power or gas lines. In the event of water mains rupturing and a loss of pressure, it may also become difficult to stop the spread of a fire once it has started. For example, more deaths in the 1906 San Francisco earth quake were caused by fire than by the earthquake itself.
Soil liquefaction occurs when, because of the shaking, water-saturated granular material (such as sand) temporarily loses its strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, like buildings and bridges, to tilt or sink into the liquefied deposits. This can be a devastating effect of earthquakes. For example, in the 1964 Alaska earthquake, soil liquefaction caused many buildings to sink into the ground, eventually collapsing upon themselves.
Tsunamis are long-wavelength, long-period sea waves produced by the sudden or abrupt movement of large volumes of water. In the open ocean the distance between wave crests can surpass 100 kilometers (62 mi), and the wave periods can vary from five minutes to one hour.
Such tsunamis travel 600-800 kilometers per hour (373–497 miles per hour), depending on water depth. Large waves produced by an earthquake or a submarine landslide can overrun nearby coastal areas in a matter of minutes.
Tsunamis can also travel thousands of kilometers across open ocean and wreak destruction on far shores hours after the earthquake that generated them.
Ordinarily, subduction earthquakes under magnitude 7.5 on the Richter scale do not cause tsunamis, although some instances of this have been recorded. Most destructive tsunamis are caused by earthquakes of magnitude 7.5 or more.
A flood is an overflow of any amount of water that reaches land. Floods occur usually when the volume of water within a body of water, such as a river or lake, exceeds the total capacity of the formation, and as a result some of the water flows or sits outside of the normal perimeter of the body. However, floods may be secondary effects of earthquakes, if dams are damaged. Earthquakes may cause landslips to dam rivers, which collapse and cause floods.
An earthquake may cause injury and loss of life, road and bridge damage, general property damage (which may or may not be covered by earthquake insurance), and collapse or destabilization (potentially leading to future collapse) of buildings. The aftermath may bring disease, lack of basic necessities, and higher insurance premiums.
The 2012 Indian Ocean earthquake was a magnitude 8.6 Mw undersea earthquake that struck near the Indonesian province of Aceh on Wednesday, 11 April 2012 at 15:38 local time. Initially, authorities feared that the earthquake would cause a tsunami and warnings were issued across the Indian Ocean; however, these were subsequently cancelled.The earthquake was the 11th strongest earthquake since 1900.(Source : http://en.wikipedia.org/wiki/2012_Indian_Ocean_earthquake ).
My experience of Earthquake on 11 April 2012:
The tremors due to the earth quake were felt in many places in India including Chennai. When the tremors were felt in Chennai, my wife and myself were watching a TV programme and both of us felt a little shaking of the sofa. We thought that it was due to a tremor and went out of our flat and noticed that our neighbours with their children also came out telling that they also felt the tremor and advised that it is better go down the steps rather than going by the lift.
After some minutes about 5 persons came down from different blocks and they informed that got the news about the tremor through their relatives/friends and TV news. We could see many persons standing outside their flats in different floors of different blocks without the knowledge of the tremors and with out understanding the danger to their life if the earthquake is strong enough to affect the building.
I could not understand why there was no alarms raised/public announcement made advising all the residents to evacuate the building immediately.Such a system must be there as followed in many high raised residential buildings/offices
It is advisable that mock drills are periodically conducted by the Security Department in such high raised buildings to create awareness among the residents about the steps to be taken at the time of disasters like fire,earth quake etc.utilising the services of government agencies like Fire Department etc.
I have consolidated some useful tips given below on the steps to be taken during and after such earth quakes;
What to do during an earthquake:
PETS: During and after
AFTER THE QUAKE
SOURCE: American Red Cross, FEMA, SF Fire Department, SF Chronicle
Read more: http://www.sfgate.com/cgi-bin/article.cgi?f=/earthquakes/archive/quakedrill.dtl#ixzz1vnmP2NQp