A special project by the Bureau of Mines and Geosciences of creating geohazard maps of major cities was initiated in commitment to public service and a desire to be more relevant to the times. Metro Manila, being the nation’s capital, is the first to be prepared.

Severalsuccessive procedures have been used in producing the different data types for each of the four geohazard maps. These include collection of available data, digitization, and analyses and generation of new information all in a Geological Information System (GIS) platform. GIS platforms utilized include MapInfo and the Integrated Land and Water Informations System (Ilwis).

Four hazards were identified to be relevant to Metro Manila: flood, landslide, earthquake and liquefaction. Flood Prone areas are classified according to the 2-10 years flood cycle period by Miranda (1994), 50-100 years cycle period by Balce (Marikina area, 1994), and sea level rise within 100 years by Punongbayan (1987). The Earthquake Risk map was adapted from Saldivar-Sali (1995) which was based on drilling data. Liquefaction was adapted from Torres (1994) and is located mainly along the Manila bay coast and in the Marikina River basin. They roughly correspond to High to Very High Earthquake Risk zones, which are mostly underlain by dense to loose sand and/or firm to soft clay. Landslide prone areas map was based only on slope factors. Areas with slopes equal to or greater than 18% were inferred to have high risk for landslides or mass movement incidents. Reports of unstable slopes after the Cherry Hills incident were found to occur mainly near the periphery of slope breaks. Thus, a 500-meter buffer distance along slope class boundaries merited serious attention in land development.