Md. Arafat Rahman
The sudden release of the energy stored in the rock causes the earth’s surface to tremble for a moment and some parts of the earth’s crust to move. This form of sudden and transient vibration is called earthquake. The energy generated from vibrational waves is expressed through earthquakes. These waves are generated in a specific area of the earth’s crust and spread around the source. Earthquakes usually last from a few seconds to a minute or two. Sometimes the vibration is so weak that it cannot be felt. But strong and devastating earthquakes caused extensive damage to homes and property and resulted in numerous casualties.
The term earthquake refers to any type of seismic event – whether natural or man-made. Most earthquakes are caused by underground cracks and sediments, but they can also be caused by other causes, such as volcanoes, landslides, mine explosions, or nuclear tests conducted underground nuclear research. The initial rupture of an earthquake is called focus or hypocenter. The epicenter is the surface of the soil along the hypocenter.
The main source place of an earthquake is called the center. From this center the vibrations spread all over through different waves. When the compressive strength of the rock goes beyond tolerance, cracks appear in the rock and energy is released. So often the epicenter of an earthquake is located in the fault line. The center is usually located within 16 km of the earth’s surface. However, earthquakes can also arise from 700 km deep mantles.
Earthquakes usually have some causes. Our surface is made up of many plates. These plates are separated from each other by faults or cracks. Beneath these plates is all the molten material in the interior of the earth. Displacement of these molten substances due to any natural cause also causes some displacement of the plates. Any part of one plate when penetrate to the bottom of the other plate, causing the ground to vibrate. And this vibration appears to us in the form of an earthquake. Earthquakes can sometimes be caused by volcanic eruptions and molten lava eruptions.
Earthquakes can sometimes be caused by large-scale avalanches from mountains or elevations. For some reason, a large boulder from the mountains collapsed on the crust and caused an earthquake. Usually there are more earthquakes near the folded mountains.When the crust is compressed by radiating heat, cracks and folds are formed, causing earthquakes. There are many reasons for the formation of underground steam. As this vapor continues to rise, it pushes the lower part of the crust that result a strong earthquake. Sometimes huge glaciers suddenly fall down from the foothills. This causes an earthquake.
Bangladesh is in fact affected by two fault lines between India and Myanmar. Bangladesh is located in the tectonic plate of India, Eurasian and Myanmar. The two Indian and Eurasian plates since 1934 have been stuck in the foothills of the Himalayas for a long time, waiting for a major earthquake. There are 8 fault zones in Bangladesh, namely: Bogra Fault Area, Tanore Fault Area, Tripura Fault Area, Sitakunda Teknaf Fault Area, Halwaghat Fault Area, Dubri Fault Area, Chittagong Fault Area, and Rangamati Fault Area.
Although there are no guarantees of safety during an earthquake, identifying potential hazards ahead of time and advance planning can save lives and significantly reduce injuries and property damage. Repairing deep plaster cracks in ceilings and foundations, anchoring overhead lighting fixtures to the ceiling, and following local seismic building standards, will help reduce the impact of earthquakes. Trere are six type tof works to do beforew an earthquake.
1. Checking for Hazards in the Home:
a) Placing shelves securely to walls, b) Placing large or heavy objects on lower shelves, c) Storing breakable items such as bottled foods, and glass in low, closed cabinets with latches, d) Hanging heavy items such as pictures and mirrors away from beds, couches, and anywhere people sit, e) Bracing overhead light fixtures, f) Repairing defective electrical wiring and leaky gas connections, g) Securing a water heater by strapping it to the wall studs and bolting it to the floor, h) Repairing any deep cracks in ceilings or foundations i) Getting expert advice if there are signs of structural defects, j) Storing weed killers, pesticides, and flammable products securely in closed cabinets with latches and on bottom shelves.
2. Identifying Safe Places Indoors and Outdoors:
a) Under sturdy furniture such as a heavy desk or table, b) Against an inside wall, c) Away from where glass could shatter around windows, mirrors, pictures, or where heavy bookcases or other heavy furniture could fall ove, d) In the open, away from buildings, trees, telephone and electrical lines, overpasses, or elevated expressways, e) Interior columns and beams, which can serve as safe zones.
3. Educating Family Members:
a) Contacting local emergency management and also reading how to protect property from earthquakes, b) Teaching children how and when to call police, or fire department and which radio station to tune to for emergency information, c) Teaching all family members how and when to turn off gas, electricity, and water, d) Identifying escape routes within the building.
4. Having Disaster Supplies on Hand:
a) Flashlight and extra batteries, b) Portable battery-operated radio and extra batteries, c) First aid kit and manual, d) Emergency food and water e) Nonelectric can opener, f) Essential medicines, g) Cash and credit cards, h) Sturdy shoes, i) Blankets.
5. Developing an Emergency Communication Plan:
a) In case family members are separated from one another during an earthquake (a real possibility during the day when adults are at work and children are at school), b) developing a plan for reuniting after the disaster, c) Asking an out-of-state relative or friend to serve as the “family contact,” so that after a disaster, it’s often easier to call long distance, d) Making sure everyone in the family knows the name, address, and phone number of the contact person, e) Finding a well-known meeting place in the case that during the earthquake family members become separated.
6. Helping the Community Get Ready:
a) Publishing a special section in local newspaper with emergency information on earthquakes, b) Localizing the information by printing the phone numbers of local emergency services offices and hospitals, c) Conducting a week-long series on locating hazards in the home, d) Working with local emergency services to prepare special reports for people with mobility impairments on what to do during an earthquake, e) Providing tips on conducting earthquake drills in the home, f) Interviewing representatives of the gas, electric, and water companies about shutting off utilities, g) Working together in the community to apply knowledge to building codes, retrofitting programs, hazard hunts, and neighborhood and family emergency plan.
Staying as safe as possible during an earthquake is the first step. Some earthquakes are actually foreshocks and a larger earthquake might occur. Minimizing movements to a few steps to a nearby safe place and staying indoors until the shaking has stopped and ensuring exiting is safe is the second step.
a) Dropping to the ground, taking cover by getting under a sturdy table or other piece of furniture and holding on until the shaking stops, b) If there isn’t a table or desk near, covering face and head with arms and crouch in an inside corner of the building, c) Staying away from glass, windows, outside doors and walls, and anything that could fall, such as lighting fixtures or furniture, d) Staying in bed if anyone is there when the earthquake strikes, e) Holding on and protecting head with a pillow, unless anyone under a heavy light fixture that could fall and in that case, moving to the nearest safe place, f) Using a doorway for shelter only if it is in close proximity and if it is a strongly supported, load bearing doorway, g) Staying inside until shaking stops and it is safe to go outside because research has shown that most injuries occur when people inside buildings at tempt to move to a different location inside the building or try to leave, h) Be awaring that the electricity may go out or the sprinkler systems or fire alarms may turn on, i) not using the elevators.
a) Staying there, b) Moving away from buildings, streetlights, and utility wires c) Once in the open, staying there until the shaking stops beacuse the greatest danger exists directly outside buildings, at exits, and alongside exterior walls. Ground movement during an earthquake is seldom the direct cause of death or injury. Most earthquake-related casualties result from collapsing walls, flying glass, and falling objects.
If in a moving vehicle:
a) Stopping as quickly as safety permits and staying in the vehicle, b) Avoiding to stop near or under buildings, trees, overpasses, and utility wires, c) Proceeding cautiously once the earthquake has stopped, d) Avoiding roads, bridges, or ramps that might have been damaged by the earthquake.
If trapped under debris:
a) Not lighting a match, b) Not moving about or kicking up dust, c) Covering mouth with a handkerchief or clothing, d) Tapping on a pipe or wall so rescuers can locate, e) Using a whistle if one is available and f) Shouting only as a last resort because shouting can cause to inhale dangerous amounts of dust.
What to Do After an Earthquake?
a) Checking self for injuries. Often people tend to others without checking their own injuries. Anyone will be better able to care for others if he is not injured or if received first aid for injuries, b) Protecting from further danger by putting on long pants, a long-sleeved shirt, sturdy shoes, and work gloves. This will protect from further injury by broken objects, c) After have taken care of self, helping injured or trapped persons. If having it in own area, giving first aid when appropriate, d) not trying to move seriously injured people unless they are in immediate danger of further injury.
e) Looking for and extinguish small fires and eliminating fire hazards. Putting out small fires quickly, using available resources will prevent them from spreading. Fire is the most common hazard following earthquakes, f) Leaving the gas on at the main valve, unless smelling gas or think its leaking. It may be weeks or months before professionals can turn gas back on using the correct procedures. Explosions have caused injury and death when homeowners have improperly turned their gas back on by themselves, g) Cleaning up spilled medicines, bleaches, gasoline, or other flammable liquids immediately and avoid the hazard of a chemical emergency.
h) Opening closet and cabinet doors cautiously. Contents may have shifted during the shaking of an earthquake and could fall, creating further damage or injury and inspecting home for damage. Getting everyone out if your home is unsafe. Aftershocks following earthquakes can cause further damage to unstable buildings. If the home has experienced damage, get out before aftershocks happen, i) Helping neighbors who may require special assistance. Elderly people and people with disabilities may require additional assistance. People who care for them or who have large families may need additional assistance in emergency situations.
j) Listening to a portable, battery-operated radio or television for updated emergency information and instructions. If the electricity is out, this may be the main source of information. Local radio and local officials provide the most appropriate advice for particular situation. k) Expecting aftershocks and each time feel one, drop, cover, and hold on! Aftershocks frequently occur minutes, days, weeks, and even months following an earthquake, l) Watching out for fallen power lines or broken gas lines, and staying out of damaged areas. Hazards caused by earthquakes are often difficult to see, and anyone could be easily injured.
m) Staying out of damaged buildings and if are away from home, returning only when authorities say it is safe. Damaged buildings may be destroyed by aftershocks following the main quake, n) Using battery-powered lanterns or flashlights to inspect home. Kerosene lanterns, torches, candles, and matches may tip over or ignite flammables inside, o) Taking pictures of the damage, both to the house and its contents, for insurance claims, p) Avoiding smoking inside buildings and q) when entering buildings, using extreme caution. Building damage may have occurred where least expect it and carefully watching every step.
Author is a Columnist & Asst. Officer, Career & Professional Development Services Department, Southeast University