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Analysis of seismic body waves excited by the Mount St. Helens eruption of May 18, 1980

Kanamori, Hiroo and Given, Jeffrey W. and Lay, Thorne (1984) Analysis of seismic body waves excited by the Mount St. Helens eruption of May 18, 1980. Journal of Geophysical Research B, 89 (B3). pp. 1856-1866. ISSN 0148-0227. doi:10.1029/JB089iB03p01856.

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Seismic body waves which were excited by the May 18, 1980, eruption of Mount St. Helens and recorded by the Global Digital Seismographic Network stations are analyzed to determine the nature and the time sequence of the events associated with the eruption. The polarity of teleseismic p waves (period ∼20s) is identical at six stations, which are distributed over a wide azimuthal range. This observation, together with a very small S to P amplitude ratio (at 20 s), suggests that the source is a nearly vertical single force. A simple model shows that for seismic radiation a volcanic eruption can be represented by a single force applied in the direction opposite to the blast direction. The time history of the vertical force suggests two distinct groups of events, about 2 min apart, each consisting of several subevents with a duration of about 25 s. The magnitude of the force is approximately 2.6×10^(12) N. This vertical force is in contrast with the long-period (∼150 s) southward horizontal single force which has been determined by a previous study and interpreted to be due to the massive landslide. An M_s = 5.2 earthquake initiated the eruption sequence. The direction of the P wave first motion of this event observed at two nearby stations is consistent with the radiation pattern expected for the landslide and suggests that it represents the onset of the landslide. The ground motions observed at station LON (Δ = 67 km) are dominated by Rayleigh waves (i.e., Lamb pulse) and provide tight constraints on the time sequence of the events.

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URLURL TypeDescription DOIArticle
Kanamori, Hiroo0000-0001-8219-9428
Lay, Thorne0000-0003-2360-4213
Additional Information:© 1984 by the American Geophysical Union. Paper number 3B1597. Received January 3, 1983; revised August 19, 1983; accepted September 22, 1983. We thank Robert Engdahl and John Hoffman of the U.S. Geological Survey for making available to us the digital seismograms used in this study. We thank Holly Eissler for helping us retrieve the records of the RSTN network. This research was partially supported by National Aeronautics and Space Administration grant NSG-7610 and National Science Foundation grant EAR811-6023. Contribution 3854, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.
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Caltech Division of Geological and Planetary Sciences3854
Issue or Number:B3
Record Number:CaltechAUTHORS:20141104-074343479
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Official Citation:Kanamori, H., J. W. Given, and T. Lay (1984), Analysis of seismic body waves excited by the Mount St. Helens eruption of May 18, 1980, J. Geophys. Res., 89(B3), 1856–1866, doi:10.1029/JB089iB03p01856
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51212
Deposited By: Tony Diaz
Deposited On:04 Nov 2014 17:55
Last Modified:10 Nov 2021 19:07

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