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ABSTRACT: Mass Wasting on Pacific Convergent Margins

Roland Von Huene, Homa J. Lee

Slope failure on convergent margins is expected because the tectonic regime produces steepened slopes, high pore water pressures, and strong earthquakes. Seismic records, cores, and high-resolution swath-mapping allow failure features to be identified. Along the northern Peruvian margin, a large failure feature consists of a 20 km wide by 30 km long block that was displaced about 900 m. The front of the block formed a 1 km high scarp that subsequently failed and disintegrated to produce a 30 km long debris avalanche. If the block failure was catastrophic, it produced a local tsunami at least 50 m high. Analysis of sediment physical properties of similar sediment from nearby ODP holes shows that seismic loading likely caused both the block slide and debris avalanche and th t either could have been catastrophic.

Along the Japan Trench margin swath-mapping shows numerous morphological features that indicate slope failure. Seismic sections show local accumulations of slump debris that accrete against the margin and subduct beneath it. Observations from submersibles include faulted, disrupted slopes and abundant venting structures, formed during the escape of overpressured pore fluids.

Observations along slopes of convergent margins include considerable evidence of slope failure that commonly involves particularly large features. Landslide morphology types range from displacements of intact blocks along discrete slip planes to large-scale disintegrative failures represented by debris avalanches.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990