Datapages, Inc.Print this page

Abstract: Preservation of Surface Waves Formed as a Result of the October 16,1999 Hector Mine 7.1 M Earthquake, Ludlow, CA

FIFE, DONALD, Consulting Geologist, Tustin, CA; JOHN ROSSI, Consulting Geologist, Pahrump, NV

Near the north end of the surface rupture of the Lavic Lake and Bullion Fault system the effects of the surface waves generated by this seismic event 12-15km from the epicenter were responsible for the derailment of an Amtrack passenger train that was traveling westward between Ludlow and Pisgah Volcanic Center. The soil surface at the derailment was highly fractured by surface waves (Love Waves?). Preserved "oscillatory" surface waves at the nearby cinder mining operation at Pisgah Cinder Cone may shed light on the derailment. The cinder mining, crushing and screening operation has left several acres of stock piled and flat layers of light weight scoriaceous andesitic basalt on the surface. This material is highly angular, and ranges from fine to coarse- grained sand size. A composite sample gave a field density of 73 lb/cu ft. (1166.9 kg/M3). The stockpiles show evidence of lateral spreading. Both cinder stockpiles and the flat layers show spectacular cyclic (?) wave forms preserved within the stockpile surface. Wavelengths averaged I m (peak to peak), with amplitudes averaging 6 to 10 cm (crest to trough). The direction of the wave front trends about N 55 W or roughly 45 degrees westward from a projection of the north end of the last known surface rupture of the northwest trending Lavic Lake fault. If similar waves intersected the rails beneath the speeding Amtrack train, it is quite understandable that the train was derailed. To our knowledge no surface fault ruptures have been found displacing the tracks at the site of the train wreck.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California