ABSTRACT
Rock-avalanche seismograms, uncontaminated by tectonic earthquakes, give accurate data on landslide onset and duration, often unattainable from other sources. They may show pulsing from retrogressive source collapse. Teleseisms filtered to between 0.1 and 0.02 Hz at 450 to 500 km from source are very simple waveforms that appear to vary in direct proportion to potential energy loss as if they were from reactive acceleration of the landslide substrate. By comparing wave amplitudes, and using the known 12 × 106 m3 volume of the Mount Cook rock avalanche of December 1991, the collapse of Mount Fletcher in May 1992 was 13 × 106 m3 and in September 1992, 5 × 106 m3. Landslide tremor may be the first warning of submarine-landslide-generated tsunami, giving reason to automate recognition of landslide seismograms even though the tremor is far smaller than a tectonic earthquake with sufficient fault rupture to initiate a tsunami.
