PHIVOLCS warns Metro Manila nearby provinces vs possible 7.2 magnitude quake arge magnitude earthquake has affected Lanao del Sur in the past! On April 1, 1955, a magnitude 7.5 earthquake was experienced in Lanao area. This earthquake, which is considered to be one of the most damaging historical earthquakes in Lanao del Sur, resulted to about 400 deaths. Strong ground shaking was also felt during this event, resulting to significant damage to infrastructures including a mosque in Tugaya municipality near Lake Lanao. Several houses also collapsed and wharfs were damaged in Zamboanga City and Pagadian City. Liquefaction and landslides were also documented. Aside from this, several small to moderate earthquakes have also been recorded within the province, with intensities ranging from PEIS IV to VII. Why do earthquakes occur in Lanao del Sur? Central Mindanao, including Lanao del Sur, is one of the seismically active areas in the country because of the presence of the western...