Widespread land subsidence in Metro Manila, Philippines and surrounding areas detected by InSAR time-series analysis

Extensive land subsidence in and around Metro Manila has been recognized and quantified since the 1990s from field observations of wells rising out of the ground, the frequency with which roads have had to be raised, and social surveys of historical flooding and tide heights. To define more precisely the subsiding areas and their rates, 2003-2010 Envisat and 2007-2011 ALOS PALSAR-1 imagery were processed using the PSInSAR method. During these periods, Manila, CAMANAVA, Rosario, San Pedro, Las Piñas and Dasmariñas subsided by at least 2-4 cm/yr, due mainly to over-extraction of groundwater. InSAR data also reveal subsidence in highly urbanized areas that also rely heavily on groundwater along southern segments of the West Marikina Valley Fault, but none on the northern segment. Land subsidence along the coast exposes its residents to worsening floods, tidal incursions and storm surges. Additionally, differential movements at pre-existing faults caused considerable damage to overlying properties.