Update on the October 2019 Cotabato fault system earthquake series
What is happening in Cotabato and vicinity?
As of 07:00 AM Philippine Standard Time (PST) of 08 November 2019 (Friday), the total number of earthquakes recorded since the 29 October 2019 Magnitude 6.6 earthquake event is now 2226, with 917 plotted and 161 felt at various intensities. Figure 1 shows earthquake plots as of 07 November 2019 (6PM).
Another DOST-PHIVOLCS Quick Response Team (QRT), consisting of geologists, civil engineers, seismologists and information officers, was immediately deployed on 30 October 2019. The team will investigate geologic impacts, assess structural damages, establish additional portable seismic stations in the vicinity of the earthquake epicenters to augment existing DOST-PHIVOLCS seismic monitoring network (Figure 2) to monitor and study ongoing occurrence of earthquake events, and conduct intensity surveys and information education campaigns and briefings with local DRRMOs and residents of affected communities. A day after the QRT was deployed, the area experienced another Magnitude 6.5 earthquake on 31 October 2019.
Preliminary assessments of the DOST-PHIVOLCS QRT for the cumulative hazards and impacts of the strong earthquakes (Greater than Magnitude 6) are summarized below.
What can we expect from the current earthquake activity?
Minor to moderate-magnitude earthquakes may be expected to occur in the vicinity of the epicentral area and may persist for several days to weeks, with the possibility of some being felt at various intensities. Although the occurrence of another earthquake greater than M6.6 cannot be discounted, the possibility of it coming from the same source is low.
What other hazards should be considered?
The continuing ground shaking due to the aftershock events could still put slightly- to moderately-damaged structures to further damages. Other seismic hazard considerations include remobilization of landslide deposits, possible flashfloods resulting from damming of rivers and potential breaching, and road cut-off. Liquefaction effects such as presence of fissures, sandboils and lateral spreading may affect foundations of buildings, as well as the quality and depth of the water table.
What should be done by the affected communities?
As previously advised, people are reminded to be cautious of structures that are visibly weakened by ground shaking during the 16 October 2019 M6.3, the 29 October 2019 M6.6 and the 31 October 2019 M6.5 earthquakes. Stringent inspection of damaged structures after these earthquakes should be done by local building officials to determine if these are still safe for long-term occupancy.
Considering the magnitude of the structural damages, civil engineers from other government agencies and professional organizations are strongly urged to assist the affected communities in inspecting buildings, monuments and infrastructures to determine their integrity, and to provide recommendations and appropriate actions to the affected groups or individuals.
Areas with visible evidence of tension/incipient cracks that resulted from the strong ground shaking should be closely monitored and avoided, if possible, as these may be aggravated by ongoing earthquake activity. Rains may also render slopes more susceptible to landslides.
Preparedness of communities is highly encouraged and people are enjoined to protect themselves by doing the “drop, cover and hold” procedure during a strongly felt earthquake.
Individuals are likewise advised not to forward or pass on rumors and messages from unconfirmed and unreliable sources related to earthquakes, tsunami or volcanic eruptions as these may only cause undue panic to the populace.
What is the role of DOST-PHIVOLCS?
As previously mentioned, DOST-PHIVOLCS operates and maintains a network of 104 seismic stations spread across the Philippines, 26 of which are located in Mindanao. Of the 26, nine are staffed-controlled and are located in the cities of Kidapawan, Cotabato, Davao, Cagayan De Oro, Bislig, Surigao, Dipolog, Zamboanga, and General Santos. The remaining 17 are remote-telemetered seismic stations located in Pikit in Cotabato, Bacolod in Lanao del Norte, Marawi City, Valencia in Bukidnon, 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, 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 Cotabato are the Kidapawan City Seismic Station (staff-controlled) in Kidapawan City (Cotabato), and remote-telemetered seismic station in Pikit (Cotabato). This is further augmented by the initial five temporary stations shown in Figure 2.
DOST-PHIVOLCS QRTs deployed in the affected areas are continually assessing impacts and conducting other earthquake and volcanic hazard assessments, as well as conducting information dissemination campaigns to allay the fears of the public. 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 bulletins, 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.