Source mechanism of the May 18, 1980, Mount St Helens eruption from regional surface waves ( USA).


A reference source equalization method using regional surface waves from the Mount St Helens eruption of May 18, 1980, and the Elk Lake event of February 14, 1981, was used to determine the St. Helens eruption source time history. The initial S force corresponds to the acceleration of the landslide in a N direction approx 5-10s after the triggering earthquake. Lateral forces were isolated 70-140s later, consistent with the occurrence of the larger lateral blast and the slide changing its direction down the Toutle River Valley. There also appears to be significant source activity between 140-250s after the initial pulse. This later activity may correspond to the final deceleration of the landslide. Several vertical pulses were located between 10-60 and 100-120s after the eruption began. Much of the vertical force represents the 2 sets of explosions which occurred during the eruption.-after Authors

Publication Title

Journal of Geophysical Research