Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published May 1983 | Published
Journal Article Open

Lamb pulse observed in nature

Abstract

Seismograms observed at Longmire, Washington, for four eruptions of Mt. St. Helens (May 18, June 13, August 7, and August 8, 1980), can be interpreted as Lamb pulses excited by a nearly vertical single force that represents the counter force of the eruption. These data provide reliable estimates of the impulse of the force K (time integral of the force) from which the total momentum and the kinetic energy, E, of the ejecta associated with the eruption can be estimated. The values of K are estimated to be 1.4 × 10^(19), 1.4 × 10^(16), 3.7 × 10^(15), and 2.8 × 10^(15) dyne·s for the four eruptions (chronological order), respectively. The corresponding values of E are estimated to range from 0.70 to 2.6 × 10^(23), 0.70 to 2.6 × 10^(20), 1.9 to 6.9 × 10^(19), and 1.4 to 5.3 × 10^(19) ergs using values of ejecta velocity ranging from 100 to 375 m/s. The ratio of K to the amplitude of the air wave excited by the eruption is 20 to 40 times larger for the main event on May 18 than for the other events suggesting a significant difference in the eruptive mechanism. Our results demonstrate that a digital seismograph in the vicinity of volcanoes provides a simple means for quantification of the explosive power of a volcanic eruption.

Additional Information

Copyright 1983 by the American Geophysical Union. (Received November 16, 1982; revised February 16, 1983; accepted February 22, 1983.) Paper number 3L0352. We thank Robert Engdahl and John Hoffman for providing us with the LON digital seismogram tapes used in this study. Tom McEvilly gave us useful data necessary for computing the response of the DWWSSN instrument to air-waves. This research was partially supported by National Aeronautics and Space Administration grant number NSG-7610, and National Science Foundation grant EAR811-6023. Contribution No. 3843, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.

Attached Files

Published - grl2275.pdf

Files

grl2275.pdf
Files (360.9 kB)
Name Size Download all
md5:bdb310abaaa8767b16ebe26a4459e62d
360.9 kB Preview Download

Additional details

Created:
August 22, 2023
Modified:
October 18, 2023