Unlike typhoons, there is no way earthquakes can be predicted or where it will happen. They are caused by nature and largely unpredictable.
In a recent tweet, the Philippine Institute of Volcanology and Seismology (Philvolcs) has reiterated this fact. “We cannot predict when or where an earthquake… will happen,” the country’s lead agency tasked to record and monitor seismic movements, pointed out.
“What we do is prepare earthquake scenarios of hazards and impacts to be used as a guide tor mitigation, preparedness, and response,” added Philvolcs, an agency of the Department of Science and Technology.
This reminder came after three powerful earthquakes hit Mindanao region in a span of two weeks. The Philvolcs also recorded hundreds of aftershocks from these three huge quakes. Over an interview with CNN Philippines, Erlinton Olavere clarified that the earthquakes that took place on October 29 with magnitude 6.6 and on October 31 with magnitude 6.5 were not mere aftershocks but interrelated tremors.
“Siguro hindi natin masasabi na aftershock ito (magnitude 6.5) almost same, e,” explained Olavere, Philvolcs science research specialist. The series of earthquakes started on October 16, with magnitude 6.3.
Magnitude, according to United States Geological Survey (USGS), is “a number that characterizes the relative size of an earthquake.” It is based on measurement of the maximum motion recorded by seismograph.
In all those three earthquakes, the epicenter – the central point where an earthquake originates – were all recorded in North Cotabato.
In an October 29 earthquake primer, Philvolcs explained why earthquakes happen in Cotabato. “Central Mindanao, which includes Cotabato, is one of the seismically active regions in the country because of the presence of several active faults in the area which include the M’lang Fault, Makilala-Malungon Fault, North Columbio Fault, South Columbio Fault, and the western extension of the Mindanao Fault (Cotabato-Sindangan Fault),” it said.
Scientists say earthquakes occur on fault, a thin zone of crushed rock separating blocks of the earth’s crust. “When an earthquake occurs on one of these faults, the rock on one side of the fault slips with respect to the other,” scecinfo.us.edu said.
Earthquakes also occur in trenches, those steep depressions in the deepest parts of the ocean. “With depths exceeding 6,000 meters (nearly 20,000 feet), trenches… account for the deepest 45% of global ocean,” the Woods Hole Oceanographic Institution said.
“Cotabato Trench is also a major source of earthquakes which can affect the (Central Mindanao) region,” Philvolcs added. “In addition, there are other nearby local faults, some of which may be covered by recent deposits, and could be sources of small to strong magnitude earthquakes.”
Most of those affected by the three successive earthquakes from Davao del Sur are very much worried as the tremors were near the country’s highest peak, Mount Apo, which is touted to be an active volcano whose most recent eruption had not been recorded. In fact, there were some apprehensions that the recent earthquakes may indicate volcanic activity.
Contrary to what most people think, the nearest active volcanoes from the epicenter are Matutum Volcano and Parker Volcano. As part of its monitoring procedures for moderate to large earthquakes occurring near active volcanos, Philvolcs “will closely monitor earthquake events in relation to any activity that may be associated with Matutum and Parker volcanoes.”
People have already building tents outside their homes or in open areas because of the successive earthquakes and aftershocks. When will these tremors end? “We expect small- to moderate-magnitude earthquakes to occur in the epicentral area which may continue for several days to weeks, of which may be felt,” the Philvolcs primer stated.
Philvolcs, however, made a caution: “Although the occurrence of another earthquake higher than magnitude 6.6 cannot be discounted, the possibility of it coming from the same source area is low.”
Those living in the upland areas are asked to take necessary precautions. “Landslides, rock falls, and other types of mass movements may occur on mountainous or hilly areas,” the Philvolcs warned. “Liquefaction, manifested by subsidence, sand boils or lateral spreads may affect low-lying, water-saturated and sandy areas often near banks and shorelines.”
Philvolcs said offshore large shallow earthquakes may generate tsunami waves that may inundate nearby shorelines. However, the recent earthquakes don’t trigger tsunami as the epicenter is inland.
“(North) Cotabato is landlocked, hence it is safe from tsunami,” Philvolcs said. “Based on the current Active Faults and Trenches Map of Philvolcs, the tsunami threat for Sultan Kudarat, Sarangani and adjacent coastal areas in Central Mindanao region would come from the movement of Cotabato Trench, located west of this region.”
As for Davao region, the tsunami threat would come from the movement of the Philippine Trench or other offshore active faults, located east of the region.
“Other sources of tsunamis which may affect the coastal communities of southern Mindanao would come from movement of Sangihe, Halmahera and North Sulawesi Trenches located farther south offshore of Mindanao,” Philvolcs stated.
Being part of the Ring of Fire, earthquakes are here to stay. “For the last 35 years, the Philippines had been affected by 10 earthquakes with magnitude greater than 7.0,” said a fact sheet circulated by Philvolcs. “Hence, the likelihood of these destructive earthquakes occurring again in the future is indeed very strong.”
Several studies pointed out the Philippines archipelago lies between two major tectonic plates, the Philippine Sea Plate and the Eurasian Plate. Philvolcs says the Philippine Sea Plate is moving towards the Philippine Archipelago at the rate of about 7 centimeters per year. The Eurasian Plate is being subducted along western side of Luzon and Mindoro at the rate of 3 centimeters per year except on Mindoro and northwest of Zamboanga where collision is taking place.
“At the intersection of these two plates is found the Philippine Fault Zone which decouples the northwestward motion of the Pacific with the southwestward motion of the Eurasian Plate,” Philvolcs explains. “Movements along other active faults are responsible for the present-day high seismicity of the Philippine Archipelago.”
Every day, at least 5 earthquakes occur in the country. “Based on the distribution of earthquake epicenters, the most seismically active part of the county is its eastern section containing eastern Mindanao, Samar and Leyte with an average of 16 perceptible earthquakes per year.”
The Philvolcs believe the key to saving lives and properties in times of natural calamities like typhoons, floods or earthquakes is preparedness. So it urges Filipinos to take a proactive role in making their communities safer and more resilient.
To do this, Philvolcs recommends every Filipinos to evaluate the structural soundness of home, office and buildings they frequent. “Determine the safest areas both inside and outside,” said a Philvolcs primer.
The primer also recommends that every home must be prepared for the eventuality. “Secure heavy furniture to prevent sliding or toppling over by affixing them to walls or floors with brackets or tying to grillwork. Keep heavy objects on lowest shelves. Check hanging objects (like ceiling fans, mirrors, heavy picture frames). Affix bolts or hooks on cabinet doors especially those in the kitchen to prevent them from flying open and allowing breakable items to spill out. Keep only very necessary chemicals and flammable liquids in unbreakable containers. Store them on low shelves.”
The Philvolcs primer also suggests setting up an earthquake readiness plan at home. “Make sure your children, elderly members and house helpers are properly instructed on what to do. Practice drills with them. Familiarize yourself with First Aid procedures. Keep a manual handy in case you forget. Make sure everyone knows the locations of and how to switch off the electrical and water mains. At home (and at work), master the quickest, safest way out,” it says.
The primer also recommends preparing a small bag – no more than 5-6 kilograms – for each member of the family. Among those that should be packed inside the bag are two changes of clothes, a blanket, a towel, basic toiletries, sturdy shoes, flashlight, batteries, a bottle of water, biscuits candy, a small radio, any medications for chronic ailment suffers, first aid kit, contact phone numbers and addresses. Important papers (passport, recent medical records, bank books, insurance papers, etc.) must also be included.
What should a family do during an earthquake? The primer says: “Stay calm. Call out instructions to children or others who seem to be in panic.”
If you happen to be inside a building that is structurally sound during an earthquake, you must stay there. However, if you have doubts about the building, leave immediately by the safest, quickest route.
Once you are outside the building, look for an open area where you can stay. But you must stay away from power lines, telephone poles, and trees. If objects are falling, brace yourself in the doorway of a building.
If driving, pull over and stop. You should not cross bridges, over or underpasses. If on a mountain road, pull over and stay clear of ridges. If by the sea, move inland to higher ground.
After an earthquake, check yourself and other members of the family. In addition, check for fire, chemical spills and act on them right away. In case of doubt about leaks or damage, switch off all electric main fuse and turn off gas tanks.
If you must evacuate, take your small bag with you and leave message with a contact person as to where you are headed. Do not go sightseeing.
Be prepared for aftershocks. Do not enter damaged buildings because aftershocks can finish them off.
It is said, and you should heed this, that natural calamities like earthquake happen when you have forgotten about them.