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Mapping of
Areas Affected by Liquefaction during the 16 July 1990 Earthquake
ABSTRACT Liquefaction effects Of the 16 July l990 Earthquake were particularly pronounced in the provinces of Tarlac, Pangasinan, and La Union. These provinces are situated in recent sedimentary environments, four of which exhibited characteristics vulnerability to liquefaction: (1) backswamps in Gerona, Pura, Paniqui and Ramos, Tarlac; (2) river channels and point-bars in Dagupan City, San Carlos and Malasiqui, Pangasinan; (3) sandspits in Agoo and Sto. Tomas in La Union; and (4) deltas in Aringay, La Union and Binmaley and Lingayen, Pangasinan. The liquefaction-affected sediments are all relatively young, water-saturated, moderately-sorted, fine-grained sand deposits. The intense and prolonged ground-shaking during the earthquake caused these sediments to lose strength and subsequently exhibit sand fountaining and lateral Now of the ground. The degree by which an area is affected by liquefaction was largely controlled by intensity and duration of ground-shaking, the character Of the geologic microsettings and the densily of infrastructural development in the area. >> Introduction
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