Earthquakes are one the world’s most deadly natural hazards. Large earthquakes often strike without warning in areas of high population density, which can lead to Catastrophic events.
What is an earthquake?
An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.
Sometimes an earthquake has foreshocks. These are smaller earthquakes that happen in the same place as the larger earthquake that follows. Scientists can’t tell that an earthquake is a foreshock until the larger earthquake happens. The largest, main earthquake is called the mainshock. Mainshocks always have aftershocks that follow. These are smaller earthquakes that occur afterwards in the same place as the mainshock. Depending on the size of the mainshock, aftershocks can continue for weeks, months, and even years after the mainshock!
How earthquake recorded?
Seismic waves are the vibrations from earthquakes that travel through the Earth; they are recorded on instruments called seismographs. Seismographs record a zig-zag trace that shows the varying amplitude of ground oscillations beneath the instrument. Sensitive seismographs, which greatly magnify these ground motions, can detect strong earthquakes from sources anywhere in the world. The time, locations, and magnitude of an earthquake can be determined from the data recorded by seismograph stations. These are the seismographic devices:
How Earthquakes Cause Damage
The severe shaking produced by seismic waves can damage or destroy buildings and bridges, topple utility poles, and fracture gas and water mains.
S waves can put stress on buildings to tear them apart. Also trigger landslides or avalanches.
Effects Of Earthquakes
Earthquakes are less advantageous and more harmful to man.Damage done is chiefly in following respects:
Loss of Property:Severe earthquakes reduce to rubble human structures ranging from huts to palaces and single storey to multi storey buildings.Even pipelines laid under the ground and railway lines are damaged or displaced.The best example of this type of damage is Koyana earthquake in 1970.
Loss of Life:Earthquake tremors of a few seconds takes the lives of thousands of people.Many people have been rendered homeless or suffered injuries in various ways.
Changes in the course of rivers:On account of the impact of earthquakes,sometimes rivers also change their course.Consequently ,when floods come they play havoc with people’s lives.
Tsunamis:The earthquakes in the sea generate massive waves called Tsunami in Japanese language.It sometimes rises to the height of 20-25 metres.It causes great damage to life and property of people living in coastal areas as well as to tourists.Tsunami caused by an earthquake in the sea near Sumatra on 26th Dec,2004 hit southeast Asian countries including India and Sri Lanka.There was heavy damage in these countries.More than 3 lakh people died.
Mud Fountains:On account of earthquakes of high intensity,warm water and mud fountains also burst.
Cracks in Earth Crust:Earthquake cause cracks in earth’s crust anywhere in fields,roads,parks and even hills.They are thus rendered useless.
Top 10 Strongest Earthquake in Philippines:
The following are top 10 strongest earthquakes in the Philippines that caused major destruction’s and casualties:
1. Magnitude 8.0 earthquake in Mindanao (August 17, 1976)
A magnitude 8.0 earthquake took place near Mindanao and Sulu a little past midnight of August 17, 1976 that was felt as far as Visayas. It was then followed by a massive 4 to 5 meters high tsunami covering 700 kilometers of coastline bordering the island
. Because it was dark, the people were caught by the raging water which claimed 8,000 lives, injuring 10,000, and leaving 90,000 more, homeless.
2. Magnitude 7.8 earthquake in Northern and Central Luzon (July 16, 1990)
A total of 2,412 people died and at least ₱10-billion worth of damages to public and private properties was reported after a magnitude 7.8 earthquake struck Northern and Central Luzon at around 4:00 p.m. of July 16, 1990.
Hyatt Terraces Plaza, Nevada Hotel, Baguio Hilltop Hotel, Baguio Park Hotel, and FRB Hotel, all in Baguio collapsed trapping and burying people alive.
Although the epicenter was recorded in Nueva Ecija, it caused more damage in the City of Pines. And the quake that just lasted for about a minute was one of the tragedies in the country that would never be forgotten.
3. Magnitude 7.5 earthquake in Luzon (November 30, 1645)
The magnitude 7.5 earthquake that crushed Luzon on November 30, 1645 at about 8:00 pm was called the “most terrible earthquake” in Philippines history. The Epicenter of the said quake was in Nueva Ecija caused by the San Manuel and Gabaldon Faults.
The extent of the tremor was felt as far as Cagayan Valley. It has caused many landslides which buried many people alive and destroyed many buildings and churches including Manila Cathedral.
That time, only Spanish are counted so the recorded number of casualties was only 600 while the injured was 3,000.
4. Magnitude 7.3 earthquake in Casiguran (August 2, 1968)
Most of the people in Casiguran, Aurora was still fast asleep when a magnitude 7.3 earthquake struck at 4:19 a.m. of August 2, 1968.
It was another deadly and shocking seismic activity in the country. And the City of Manila got the most severe damage. Many buildings were either damaged or destroyed totally.
The said event was also called the Ruby Tower earthquake after the said six-story building located in Binondo collapsed, and caused the death of 260 people. A total of 268 people died that day and 261 more were injured.
5. Magnitude 7.2 earthquake in Bohol (October 15, 2013)
I can still remember how people panicked in the morning of October 15, 2013. It was around 8:12 a.m. when a strong earthquake was felt here in Tacloban City. Only to find out after the lights came back that what we have experienced was nothing compared to the damage it caused in Bohol which was the epicenter of the magnitude 7.2 earthquake.
The quake affected most of Central Visayas, particularly Bohol and Cebu. It was felt in the whole area of Visayas and reached as far as Masbate Island in the north and Cotabato in Southern Mindanao.
According to the National Disaster Risk Reduction and Management Council (NDRRMC), a total of 222 people died, 8 went missing and 976 others were injured. An estimated 73,000 structures were damaged wherein more than 14,500 of which were destroyed totally.
6. Magnitude 7.1 earthquake in Mindoro (November 15, 1994)
November 15, 1994, at around 3:15 a.m., a magnitude 7.1 earthquake rocked Mindoro. A gigantic 8.5 meters (28 ft) tsunami then followed which devastated the islands of Baco and Calapan, Mindoro.
A total of 7,566 houses were washed out and some 78 people died because of that tragedy.
7. Magnitude 6.9 earthquake in Central Visayas (February 6, 2012)
A total of 51 people died, 62 still missing and 112 were injured when a 6.9 earthquake Central Visayas, particularly Negros and parts of Mindanao on February 6, 2012.
It caused a landslide which buried a barangay, damaged 15,483 houses, and a total damage of ₱383-million on infrastructures and buildings was recorded.
8. Magnitude 7.5 earthquake in Central and Southern Mindanao (March 5, 2002)
A magnitude 7.5 earthquake resulted to the death of 15 people and injuring around a hundred more in Central and Southern Mindanao on March 5, 2002.
The said quake originated near the Cotabato Trench that was followed by a tsunami. But it was the flood that was generated by landslides and falling debris that caused damage to an estimated 800 buildings.
9. Magnitude 6.5 quake in Ilocos Norte (August 17, 1983)
The magnitude 6.5 quake in Ilocos Norte on August 17, 1983 happened around 8:18 p.m. and resulted to 16 casualties and 47 people got injured.
It caused damages on various establishments such as schools, buildings, malls, residences, and etc. There were also landslides and sand boils that followed the event.
10. Magnitude 7.6 earthquake happened near Guiuan, Eastern Samar (August 31, 2012)
A very strong earthquake with a magnitude of 7.6 happened near Guiuan, Eastern Samar on August 31, 2012 that was felt as far as Mindanao.
The Philippine Institute of Volcanology and Seismology (PHIVOLCS) issued a tsunami warning Level 3, but it was lifted 5 hours later.
The quake caused damage on homes, bridges, and other infrastructures. There were also power interruptions in the affected areas. But despite the intensity only one person was reported dead and one injured because of the landslide in Cagayan de Oro City.
The bad thing about an earthquake is that we cannot prevent it and we cannot predict it. We do not know when exactly it would happen. Because of that, it would be better for us to be prepared at all times. Participate in Earthquake drills conducted by authorities, keep an emergency kit in the house, don’t panic when it happens and most importantly don’t forget to pray.
Safety Tips to survive an earthquake:
Don’t try and run. Chances are you’ll just be knocked off your feet by the shaking anyway. Instead, drop to the ground , take cover under something sturdy (like a desk or a table), and hold on until the shaking stops. If there is no convenient sturdy object to hide under, taking cover in an inside corner of a building is the next safest place to be. Drop down and cover your neck and head with your hands and arms.
In This Picture you can learn how to do during earthquake.
Before,During and After an Earthquake
Before an Earthquake:
1. Be prepared to act. Know how to act so your response is automatic. Identify safe places in your work area to ‘Drop, Cover and Hold On.’ Know at least two ways to exit the building safely after an earthquake.
2. Stock up on emergency supplies. Keep the basics: flashlight, first-aid kit, whistle, gloves, goggles, blankets and sturdy shoes. Coordinate supplies with your work group or department. Plan as if food and water may not be available for about 24 hours and other supplies for up to 3 days.
3. Arrange your work area for safety. Make sure that bookcases, large file cabinets and artwork are anchored. Store heavy objects on low shelves. Store breakable objects in cabinets with latches. Use normal work order process to get furniture anchored.
During an Earthquake:
4. Remain calm as the quake occurs – others will respond to your actions. A cool head can prevent panic. If you are indoors when the shaking occurs, stay there. Move away from windows and unsecured tall furniture. Drop, cover and hold on under a desk, a table or along an interior wall. Protect your head, neck and face. Stay under cover until the shaking stops and debris settles.
5. If you are outdoors, move to an open area away from falling hazards such as trees, power lines, and buildings. Drop to the ground and cover your head and neck.
After an Earthquake:
6. Remain calm and reassuring. Check yourself and other for injuries. Do not move injured people unless they are in danger. Use your training to provide first aid, use fire extinguishers, and clean up spills. In laboratories, safely shut down processes when possible.
7. Expect aftershocks. After large earthquakes, tremors and aftershocks can continue for days.
8. Be ready to act without electricity or lights. Know how to move around your work area and how to exit in the dark. Know how to access and use your emergency supplies. Be aware of objects that have shifted during the quake.
9. If you must leave a building, use extreme caution. Continually assess your surroundings and be on the lookout for falling debris and other hazards. Take your keys, personal items and emergency supplies with you if safe to do so. Do not re-enter damaged buildings until an all-clear is given.
10. Use telephones only to report a life-threatening emergency. Cell and hard-line phone systems will be jammed. Text messages take less band width and may go through when voice calls can’t be made.
Have Emergency Kits
what might life be like without an emergency kit? Without one, you could be out of food, water, or supplies to help keep you warm at night with no power. First aid supplies are very useful, especially to patch up cuts, wounds, and other injuries sustained during the disaster. Once the earthquake stops, medical personnel will be focusing their time on the most critically injured, so if you’re not on that list, you’ll be fending for yourself for possibly days.
Although earthquakes strike without warning, there are many actions that can be taken to reduce their impact. It is important that precautions be taken before an earthquake occurs.
1.Before an earthquake Buildings should be inspected for:
1.cracks and weaknesses
defective electrical wiring
inflexible gas connections and leaking gas
objects that could topple, causing injury
>Bolt down water heaters and gas appliances
>Know where and how to shut off electricity, gas and water at main switches and valves
>Place large or heavy objects on lower shelves
>Securely fasten shelves and filing cabinets to walls. Computers should be attached to desks
>Strap down high or top heavy objects
Bottles, glass, china, and other breakables should be stored in low cabinets. All cabinets should be kept locked
> Overhead lighting fixtures, such as chandeliers, and fluorescent bulbs should be securely anchored and covered
> Practise earthquake drills regularly so employees know what to do in an earthquake. This would include:
the evacuation of the building
>the identification of an open space as an assembly point after the earthquake
>the formation and training of a safety committee
>developing a disaster plan
Have On Hand
>Flashlights and battery operated radios in case power is cut off
Making Buildings Safer
New buildings must be made stronger and more flexible. Older buildings must be made stronger and more flexible.
•Construction Methods –
•Base-isolated building is a building designed to reduce the amount of energy that reaches the building during an earthquake.
•Cause floods and fire when gas pipes and water mains break.
•Flexible joints and automatic shut off valves can be installed.
General recommendations during an earthquake
Find out what you should / should not do during an earthquake – inside buildings, outside, and while traveling.
Inside a building
Take cover (e. g. under a sturdy table) and keep calm
Beware of falling objects (e. g. shelves, heavy furniture, televisions, stereos and light fittings) and keep away from windows and glass walls, which may shatter
Only leave the building when the surrounding area is safe (when there are no more falling objects such as roof tiles, etc.)
Stay outside, do not seek shelter in a building
Keep away from buildings, bridges, electricity pylons, large trees, and other things that could collapse or fall
Keep away from the shores of bodies of water
In a Vehicle
Stop the vehicle and do not leave it during the quake
Do not stop on a bridge, at an underpass, or in a tunnel, and keep away from buildings at the side of the road (danger of collapse)