Earthquake Philippines: 5 Deadliest Tremors in HistoryMore often than not, natural phenomena such as earthquake in the Philippines almost always caught us off guard. The 7.2-magnitude quake that recently hit Central Visayas is no exception.

With over 150 casualties and astonishing number of damaged historical churches, the earthquake that hit Visayan provinces on Tuesday is one of history’s strongest. In fact, Philippine Institute of Volcanology and Seismology (Phivolcs) Director Renato Solidum said that its impact is almost equivalent to “32 Hiroshima bombs.”

What causes earthquakes?

Earthquake is formed when plates underneath the Earth’s surface move in different directions. These plates often form a friction between each other in areas called faults. Once the impact of the collision becomes significant, it sends a signal on an outward direction commonly known as seismic waves.

Depending on the intensity, earthquakes may cause minor disruption or significant damage in properties. Here are history’s top 5 strongest earthquakes that caused major destruction in the Philippines:

5. Bohol earthquake (2013) A 7.2-magnitude tremor that killed more than 150 people, destroyed century-old churches and affected more than 3 million families in Central Visayas.

4. Mindoro earthquake (1994) A total of 1530 houses in the coastal areas of Baco and Calapan, Oriental Mindoro were swept away by a tsunami generated by a 7.1-magnitude earthquake. The tragedy also killed 78 people.

3. Casiguran earthquake (1968) This 7.3-magnitude earthquake killed a total of 270 people and also caused massive landslides and tsunami in Casiguran, Aurora. Almost 300 people were also killed when the Ruby Tower in Binondo collapsed as a result of the tremor.

2. Luzon earthquake (1990) On July 16, 1990, one of the strongest earthquakes to ever struck the country occurred in several areas of Central Luzon and Cordillera region. This 7.8-magnitude tremor resulted to a total of 1,621 deaths and serious damage in properties.

1. Moro Gulf earthquake (1976) With a 7.9 magnitude and almost 3,000 casualties, this Mindanao earthquake is officially the strongest and deadliest earthquake in Philippine history. Almost 40, 000 people in Regions 9 and 12 were also left homeless by this tragedy.

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. The seismicity, 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 or weak and magnitude 7 and over potentially cause serious damage over larger 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 2014), 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. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity.

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.

Aftershocks

An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. An aftershock is in the same region of the main shock but always of a smaller magnitude. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock. Aftershocks are formed as the crust around the displaced fault plane adjusts to the effects of the main shock.

WHAT TO DO IMMEDIATELY WHEN SHAKING BEGINS

Your past experience in earthquakes may give you a false sense of safety; you didn't do anything, or you ran outside, yet you survived with no injuries. Or perhaps you got under your desk and others thought you overreacted. However, you likely have never experienced the kind of strong earthquake shaking that is possible in much large earthquakes: sudden and intense back and forth motions of several feet per second will cause the floor or the ground to jerk sideways out from under you, and every unsecured object around you could topple, fall, or become airborne, potentially causing serious injury. This is why you must learn to immediately protect yourself after the first jolt... don't wait to see if the earthquake shaking will be strong!

In MOST situations, you will reduce your chance of injury if you:

DROP down onto your hands and knees (before the earthquakes knocks you down). This position protects you from falling but allows you to still move if necessary.

COVER your head and neck (and your entire body if possible) under a sturdy table or desk. If there is no shelter nearby, only then should you get down near an interior wall (or next to low-lying furniture that won't fall on you), and cover your head and neck with your arms and hands.

HOLD ON to your shelter (or to your head and neck) until the shaking stops. Be prepared to move with your shelter if the shaking shifts it around.

Wherever you are, protect yourself! You may be in situation where you cannot find shelter beneath furniture (or low against a wall, with your arms covering your head and neck). It is important to think about what you will do to protect yourself wherever you are.

Trying to moving during shaking puts you at risk: Earthquakes occur without any warning and may be so violent that you cannot run or crawl; you therefore will most likely be knocked to the ground where you happen to be. So it is best to drop before the earthquake drops you, and find nearby shelter or use your arms and hands to protect your head and neck. "Drop, Cover, and Hold On" gives you the best overall chance of quickly protecting yourself during an earthquake... even during quakes that cause furniture to move about rooms, and even in buildings that might ultimately collapse.

DO NOT run outside or to other rooms during shaking: The area near the exterior walls of a building is the most dangerous place to be. Windows, facades and architectural details are often the first parts of the building to collapse. To stay away from this danger zone, stay inside if you are inside and outside if you are outside. Also, shaking can be so strong that you will not be able to move far without falling down, and objects may fall or be thrown at you that you do not expect. Injuries can be avoided if you drop to the ground before the earthquake drops you.

O NOT stand in a doorway: An enduring earthquake image of California is a collapsed adobe home with the door frame as the only standing part. From this came our belief that a doorway is the safest place to be during an earthquake. True- if you live in an old, unreinforced adobe house or some older woodframe houses. In modern houses, doorways are no stronger than any other part of the house, and the doorway does not protect you from the most likely source of injury- falling or flying objects. You also may not be able to brace yourself in the door during strong shaking. You are safer under a table.