Alan R. Nelson, Stephen F. Personius, Rolly E. Rimando, Raymundo S. Punongbayan, Norman Tungol, Hannah Mirabueno, and Ariel Rasdas
Multiple large earthquakes in the past 1500 years on a fault in metropolitan Manila, the Philippines
Bulletin of the Seismological Society of America (February 2000), 90(1):73-85

Abstract:
The first ¹⁴ C-based paleoseismic study of an active fault in the Philippines shows that a right-lateral fault on the northeast edge of metropolitan Manila poses a greater seismic hazard than previously thought. Faulted hillslope colluvium, stream-channel alluvium, and debris-flow deposits exposed in trenches across the northern part of the west Marikina Valley fault record two or three surface-faulting events. Three eroded, clay-rich soil B horizons suggest thousands of years between surface faulting events, whereas ¹⁴ C ages on detrital charcoal constrain the entire stratigraphic sequence to the past 1300-1700 years. We rely on the ¹⁴ C ages to infer faulting recurrence of hundreds rather than thousands of years. Minimal soil development and modern ¹⁴ C ages from colluvium overlying a faulted debris-flow deposit in a nearby stream exposure point to a historic age for a probable third or fourth (most recent) faulting event.