What is happening in Davao de Oro and vicinity?
At 06:44 PM Philippine Standard Time (PST) on 01 February 2023 (Tuesday), a strong Magnitude (Mw) 6.0 Earthquake shook the provinces of Eastern Mindanao. The earthquake has an epicenter located 2 kilometers southwest of Compostela, Davao de Oro and an estimated depth of 17 kilometers (Figure 1). As of 3:00 PM PST on 02 February 2023, the DOST-PHIVOLCS Philippine Seismic Network (PSN) has recorded a total of 390 aftershocks ranging from M 1.3 to M 3.6. Using the PHIVOLCS Earthquake Intensity Scale (PEIS), the highest reported intensity is PEIS VI (Very Strong) based on the DOST-PHIVOLCS Earthquake Information 4 (Annex 1). At PEIS VI, many people are frightened and many run outdoors. Heavy objects and furniture move. Wall plaster may crack. Very old or poorly built houses and structures are slightly damaged though well-built structures are not affected. Limited rockfalls and rolling boulders occur in hilly to mountainous areas.
Have strong to great earthquakes affected Davao de Oro and vicinity in the past?
Yes, at least nine strong to great earthquakes ranging from M6.0 to M8.3 occurred in Davao de Oro and vicinity from 1891 to present based on the SEASEE Report and PHIVOLCS Earthquake Catalog. The most damaging earthquake that affected Davao de Oro was the 21 June 1893 M7.3 Monkayo earthquake (Bautista and Oike, 1999) along the Philippine Fault which produced numerous landslides, liquefaction impacts, and structural damages. This earthquake generated long and wide cracks that may be attributed to a surface rupture along the Central Compostela Valley segment of the Philippine Fault (Perez et al., 2015). Based on historical accounts, the earthquake was felt at a maximum intensity of VII (Destructive) in Monkayo (SEASEE, 1985).
Why do earthquakes occur in Davao de Oro and vicinity?
Davao de Oro in Eastern Mindanao is one of the seismically active regions in the country because of the presence of several active faults that include the East Compostela Valley, West Compostela Valley, Central Compostela Valley, Nabunturan, Caraga River, and Mati Segments of the Philippine Fault (Perez et al., 2015), and the Central Mindanao Fault (Figure 1). There are other nearby local faults, some of which may be covered by recent deposits, that could be sources of small- to strong-magnitude earthquakes.
What can we expect from the current earthquake activity?
Due to the magnitude of the recent earthquake, minor to light aftershocks are expected to occur in the epicentral area, but occurrences of moderate aftershocks are not discounted. These may continue for several days to weeks, some of which may be felt.
Figure 1. Preliminary plot of the 01 February 2023 Magnitude 6.0 Davao de Oro Earthquake and aftershocks as of 02 February 2023, 3:00 PM.
Minor earthquakes: M3 to 3.9; Light earthquakes: M4 to 4.9; Moderate earthquakes: M5 to 5.9; Strong earthquakes: M6 to 6.9; Major earthquakes: M7 to 7.9; Great earthquakes: M8.0 and above.
Aside from strong ground shaking, what other seismic hazards may be expected?
Landslides, rock falls, and other types of mass movement may occur in mountainous or hilly areas. Liquefaction, manifested by subsidence, ground fissures, sand boils, and/or lateral spreads may affect low-lying, water-saturated, and sandy areas near water bodies. In particular, areas adjacent to active river channels and coasts may be vulnerable to inundation of seawater due to the combination of liquefaction-induced subsidence, and changes in sea level.
Can this recent earthquake event trigger a destructive tsunami?
No. The epicenter of the earthquake is inland, and tsunamis are often produced by earthquakes generated by active trenches and offshore faults or faults with significant vertical movements or mass movement related to earthquake-induced landslides near bodies of water. However, localized sea-level disturbances may be observed as a result of extreme ground shaking resonating along bays. At present, DOST-PHIVOLCS operates a sea-level monitoring station at Mati, Davao Oriental as part of the local tsunami early warning system.
What should be done by the affected communities?
Communities should prepare for aftershocks. In case of another strongly felt earthquake, it is recommended that people protect themselves by doing the “drop, cover, and hold.” In homes and offices, heavy furniture and appliances should be strapped to the walls, and hanging objects securely fastened to prevent these from causing injuries. People should be cautious of structures visibly weakened or having signs of damage caused by the Mw 6.0 earthquake event, as these may further be damaged by succeeding earthquakes and injure building occupants. It is best to contact the concerned Municipal/City Engineering Office for inspection and advice. Civil engineers from the local government, and other organizations are strongly enjoined to inspect buildings and infrastructure to determine their structural integrity and recommend appropriate actions. Structurally compromised buildings should not be reoccupied unless certified safe by structural 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, especially during heavy rainfall or aftershocks. Areas that may be affected by impending landslides should be avoided. During earthquake events, rumors that may cause panic are easily spread. Please avoid sharing messages from unconfirmed and unreliable sources, and only rely on information from DOST-PHIVOLCS and pertinent Disaster Risk Reduction and Management Offices (DRRMOs).
What is the role of DOST-PHIVOLCS?
DOST-PHIVOLCS operates and maintains a network of 116 seismic stations spread across the Philippines. The closest seismic stations to Davao de Oro are the staff-controlled seismic stations in Davao City, Bislig City, and Kidapawan City; and satellite-telemetered seismic stations located in Laak in Davao de Oro, Cateel in Davao Oriental, Talacogon in Agusan del Sur, Valencia in Bukidnon, and Mati City. Data from the seismic network will be used for monitoring earthquakes. The PHIVOLCS Mindanao Cluster Monitoring Center for Earthquake and Tsunami in Davao City, serves as one of the redundant monitoring centers, in case of any failure among the essential monitoring and information dissemination functions at the Data Receiving Center in Quezon City.
DOST-PHIVOLCS will deploy a Quick Response Team (QRT) to Davao de Oro and vicinity whose main tasks are to assess impacts and hazards, and conduct information dissemination campaigns to allay the fears of the public. Furthermore, DOST-PHIVOLCS works hand-in-hand with other government agencies in mitigating the damaging effects of earthquakes.
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. Earthquake observations may also be reported to DOST-PHIVOLCS at telephone numbers (02) 8929-9254 and (02) 8426-1468 to 79, local 307 and 308 or through our official Facebook account.
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