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Multiple Large Earthquakes in the Past 1500 Years on a Fault in Metropolitan Manila, the Philippines

2000; Seismological Society of America; Volume: 90; Issue: 1 Linguagem: Inglês

10.1785/0119990002

1943-3573

Alan R. Nelson,

Geological and Geochemical Analysis

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.