Primer on the 18 November 2019 Magnitude 5.9 Southern Bukidnon Earthquake
What is happening in Bukidnon and vicinity?
At 09:22 PM Philippine Standard Time (PST) of 18 November 2019 (Monday), a moderate earthquake of Magnitude (M) 5.9 shook the province of Bukidnon and vicinity. This earthquake has an epicenter located 8 kilometers northwest of Kadingilan, Bukidnon, and a depth of 5 kilometers. This was preceded by five earthquakes with magnitudes ranging from 2.4 to 4.3 on 16 November 2019. Smaller magnitude earthquakes (M1.4 to 3.8) followed the M5.9 event, and as of 01:00 PM PST of 19 November 2019, 193 earthquakes have been recorded by the DOST-PHIVOLCS.
Using the PHIVOLCS Earthquake Intensity Scale (PEIS), the ground shaking based on preliminary intensity reports are summarized below.
The maximum intensity felt for this event is PEIS VI (very strong). At this intensity level, it is expected that many people are frightened. Many run outdoors; some people lose their balance. Motorists feel like driving with flat tires. Heavy objects or furniture move or may be shifted. Small church bells may ring. Wall plaster may crack. Very old or poorly built houses and structures are slightly damaged though well-built structures may not have noticeable damage. Limited rockfalls and rolling boulders occur in hilly to mountainous areas and escarpments. Trees are noticeably shaken.
Have moderate to major magnitude earthquakes affected Bukidnon in the past?
Yes. The most recent earthquake events that affected Bukidnon are the 05 August 2017 M5.0 Valencia, Bukidnon and the 12 April 2017 M6.0 Wao, Lanao del Sur earthquakes. The maximum intensity of the M5.0 event was felt at PEIS V in Valencia City, Bukidnon, while the maximum intensity of the M6.0 event was felt at PEIS VII in Kalilangan, Bukidnon and Wao, Lanao del Sur.
At areas where PEIS VII was felt, most people are frightened and run outdoors. People find it difficult to stand in upper floors. Heavy objects and furniture overturn or topple. Big church bells may ring. Old or poorly-built structures suffer considerably damage. Some well-built structures are slightly damaged. Some cracks may appear on dikes, fish ponds, road surface, or concrete hollow block walls. Limited liquefaction, lateral spreading and landslides are observed. Trees are shaken strongly.
At least seven onshore earthquakes ranging from M5.0 to M7.6 occurred in Bukidnon and vicinity from 1924 to present based on the PHIVOLCS Earthquake Catalog, the Southeast Asia Association of Seismology and Earthquake Engineering (SEASEE) Report, and the 1983-1995 compilation of Manahan and Lasala (1998).
Why do earthquakes occur in Bukidnon?
Bukidnon is part of the seismically active region of Northern Mindanao (Region X) because of the presence of several active faults in the area which include the Central Mindanao Fault, Linugos River Fault, Cabanglasan Fault, Tagoloan River Fault, Lanao Fault System and segments of the Mindanao Fault. Furthermore, there are other nearby local faults, some of which may be covered by recent deposits, and could be sources of minor to strong magnitude earthquakes.
Can this earthquake indicate volcanic activity?
No. Although the nearest active volcanoes from the epicenter are Musuan, Ragang and Makaturing Volcanoes, the M5.9 event is tectonic in origin. Nonetheless, DOST-PHIVOLCS closely monitors earthquake events that may be related to any activity of the abovementioned active volcanoes.
What can we expect from the current earthquake activity?
Minor to moderate earthquakes are expected to occur in the epicentral area but occurrences of strong earthquakes cannot be discounted. These may continue for several days to weeks, some of which may be felt.
Aside from strong ground shaking, what other seismic hazards are life-threatening?
In Bukidnon, areas near mountains or hills may be affected by landslides, rockfalls and other types of mass movements. Debris from mass movements that temporarily dam rivers may subsequently breach and could cause flash floods. Liquefaction effects such as subsidence, sand boils or lateral spreads may affect low-lying, water-saturated and sandy areas often near banks and shorelines.
Can this recent earthquake event trigger a destructive tsunami?
No. The epicenter of the earthquake is inland. Bukidnon is also landlocked, hence it is safe from tsunami.
What should be done by the affected communities?
People are reminded to be cautious of structures visibly weakened or with signs of damage caused by the 18 November 2019 M5.9 earthquake, as these may be further damaged by succeeding earthquakes. In case of houses and other buildings with noticeable damage, it is best to contact the Municipal/City Engineering Office for advice. Civil engineers from the local government, other agencies and organizations are strongly advised to inspect buildings and infrastructures to determine their integrity, and recommend appropriate actions to the affected groups or individuals. Affected buildings should not be reoccupied unless certified safe by these engineers.
Slopes should be checked for tension/incipient cracks that may have resulted from the strong ground shaking. Tension cracks may render slopes more susceptible to landslides. Areas that may be potentially affected should be avoided.
The best course of action is preparedness. In case of another strongly felt earthquake, it is recommended that people protect themselves by doing the “drop, cover and hold” if inside a structurally sound building. In homes and offices, heavy furniture should be strapped to the walls, hanging objects be securely fastened, and appliances be secured to prevent them from toppling and causing injuries to persons.
During these events, rumors are easily spread that may cause panic. Please avoid sharing messages from unconfirmed and unreliable sources.
What is the role of DOST-PHIVOLCS?
DOST-PHIVOLCS operates and maintains a network of 104 seismic stations spread across the Philippines. Twenty-six of these seismic stations are located in Mindanao, nine of which are staffed-controlled and are located in Cagayan De Oro City, Kidapawan City, Cotabato City, Davao City, Bislig City, Surigao City, Dipolog City, Zamboanga City, and General Santos City. DOST-PHIVOLCS also has 17 remote-telemetered seismic stations located in Valencia City in Bukidnon, Pikit in Cotabato, Bacolod in Lanao del Norte, Marawi City, Bagumbayan in Sultan Kudarat, Talacogon in Agusan del Sur, Butuan City, General Luna in Surigao del Norte, Tandag in Surigao del Sur, Loreto in Dinagat, Don Marcelino in Davao del Sur, Mati City and Cateel in Davao Oriental, Laak in Compostela Valley, Pagadian City and Ipil in Zamboanga Peninsula, and Bongao in Tawi-Tawi. Data from the seismic stations are used to determine the location, magnitude and other characteristics of earthquakes. The closest seismic stations to Bukidnon are the Cagayan de Oro City Seismic Station (staff-controlled), and remote-telemetered seismic station in Valencia City (Bukidnon).
Aside from monitoring the occurrences of earthquakes, DOST-PHIVOLCS also provides information and services such as hazards analyses and assessments. DOST-PHIVOLCS works hand-in-hand with other government agencies in mitigating the damaging effects of earthquakes. Furthermore, DOST-PHIVOLCS immediately deploys Quick Response Teams in areas affected by strong and damaging earthquakes to assess geologic impacts and structural damage, and conduct information dissemination campaigns to allay the fears of the public.
Please visit our website at www.phivolcs.dost.gov.ph, and our Facebook (/PHIVOLCS) and Twitter (@phivolcs_dost) accounts for earthquake information, volcano updates, hazard maps, and other information on earthquakes and volcanoes. Observed effects of the earthquake may also be reported to DOST-PHIVOLCS at telephone numbers (02) 8929-9254 and (02) 8426-1468 to 79, local 307 and 308.