[...NW Mindanao, in Butuan City.]
you mean NE Mindanao?
That had me confused also. Actually Butuan City is due north from Davao and the earthquakes seems to be due east from there.
My error.
Yes, NE section of Mindanao, but NW area of Caraga region, facing the Sea of Bohol, not the Pacific Ocean.
I don’t even think of the Zamboanga peninsula as part of Mindanao anymore.