Abstract

The first ¹⁴C-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 ¹⁴C ages on detrital charcoal constrain the entire stratigraphic sequence to the past 1300-1700 years. We rely on the ¹⁴C ages to infer faulting recurrence of hundreds rather than thousands of years. Minimal soil development and modern ¹⁴C 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.

Addendum to Nelson et al. [Acrobat PDF File - 728k]

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