Earthquake swarm in Long Valley caldera, California, January 1983: Evidence for dike inflation

Journal of Geophysical Research B: Solid Earth
By:  and 



The 1982–1983 deformation observed by trilateration and leveling surveys across the Long Valley caldera is apparently related to the 8.5‐km‐long by 8‐km‐deep vertical rupture surface defined by the January 1983 earthquake swarm that occurred in the south moat of the caldera. The observed deformation can be explained as follows. In late 1982, 0.03 km3 of magma was injected into a dike that dips 30° northward from the bottom of the rupture surface. The downdip dimension of this dike is 8 km. The dike inflation accounts for the uplift observed across the caldera as well as some of the horizontal deformation. Inflation of the dike generated a tension of about 3 bars across the vertical plane that was to become the rupture surface of the January swarm. This reduced the frictional stress on the rupture plane and perhaps triggered the slip that caused the January swarm. Right‐lateral slip (0.22 m) on the uppermost 2 km of the rupture plane during and after the January swarm accounts for the additional horizontal deformation observed. The model can be improved marginally if strike slip is admitted over the entire rupture surface and 0.006 km3 of magma is injected along that surface in the depth interval 3–8 km. The improvement in the model fit, however, is not sufficient to require shallow injection of magma. Thus we conclude that inflation of a dike at depth (8–12 km) dipping northward beneath the resurgent dome plus shallow right‐lateral slip on the rupture surface is a simple, but not unique, explanation of the observed deformation and seismicity.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Earthquake swarm in Long Valley caldera, California, January 1983: Evidence for dike inflation
Series title Journal of Geophysical Research B: Solid Earth
DOI 10.1029/JB089iB10p08315
Volume 89
Issue B10
Year Published 1984
Language English
Publisher Wiley
Contributing office(s) Earthquake Science Center
Description 10 p.
First page 8315
Last page 8324
Country United States
State California
Other Geospatial Long Valley Caldera
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