MANILA — A magnitude 7.8 earthquake struck waters off Sarangani on Monday morning, with strong shaking felt across parts of Mindanao, according to the Philippine Institute of Volcanology and Seismology (PHIVOLCS). In its Earthquake Information No. 2 bulletin, PHIVOLCS said the quake occurred at 7:37 a.m. and was located about 32 kilometers south 4 degrees…