Cotabato, Philippines: large landslides from the series of earthquakes in October 2019

In the Philippines, Cotabato in Mindanao has been hit by a series of substantial earthquakes in recent weeks, including a M=6.3 event on 16 October, an M=6.6 event on 29 October and an M=6.5 earthquake on 31 October.  These earthquakes have caused substantial levels of damage, and have triggered landslides in the hilly terrain.

DOST-PHIVOLCS has published a graphic showing two of the larger landslides triggered by the 29 and 31 October earthquakes.  This appears to show two large slope failures:-

Landslides triggered by the October 2019 earthquake sequence in Cotabato, Philippines, Image created by DOST-PHIVOLCS

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The image appears to show, on the left, a large, mostly planar landslide. In Hong Kong this would be considered to be an open hillslope failure,  It is mostly shallow, bar a deeper seated component at the crown of the slide.  There appears to be some flow structures in the deposit on the right side.  There are some buildings close to the toe of the landslide, just below the road that has been inundated.

On the other hand, the image on the right appears to be a large, channelised flow, starting from comparatively small slips high on the hillside.  There are some other, smaller landslides on the hillside as well.

Meanwhile, Sotiris Valkionitis tweeted some before and after Sentinel images of landslides triggered by the earthquake sequence  in Cotaboto:-

Before and after Sentinel images of the landslides in Cotabato, Philippines. Images from Sentinel 2, tweeted by Sotiris Valkaniotis.

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The Philippines National Disaster Risk Reduction and Management Council (NDRRMC) is publishing regular Situation Reports on the impact of these earthquakes.  SitRep12 (4 November 2019) indicates that the largest landslides were triggered by the 29 October earthquake.  To date they have recorded 22 fatalities in total, with five of these being directly attributed to landslides.  A further two people are reported to be missing as a result of landslides.  However, other fatalities are reported to be the result of “fallen debris”, which could also be the impact of mass movements.

News reports indicate that the impact of landslides could be more a little more substantial.  Inquirer reports four people missing in the landslide at Bato and three in Balawan.