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Ground Movement
Associated with the Magnitude 7.2 Earthquake on November 29, 1975
When the ground stopped shaking from the magnitude 7.2 earthquake located
beneath the south flank of Kilauea, people began noticing dramatic changes
to familiar landmarks along the volcano's shoreline. At Halape (see photos
below), 30 km southwest of the epicenter, the ground subsided
by as much as 3.5 m, which left a grove of coconut palms standing
in water about 1.2 m deep and the new shoreline about 100 to 150 m
inland from the presubsidence shoreline (see
photo
from ground).
Pre-earthquake view of Halape SE toward coconut grove
Photograph by Don Reeser, National Park Service
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Post-earthquake view of Halape NE toward submerged coconut grove
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Inland of Halape, a nearly continuous zone of ground cracking and faulting
occurred for about 25 km along the large Hilina fault system, which consists
of a series of normal faults with scarps as high as 500 m on Kilauea's south
flank. Scientists measured vertical offsets along some faults as much
as 1.5 m (note brown scarp in photo, right).
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The magnitude of the horizontal displacements became apparent
only when the large HVO survey network on Kilauea was measured
after the earthquake. Coastal areas between Kalu`e and Keauhou
Landing moved seaward between 4 and 8 m, among the largest
observed displacements caused by any earthquake (photo left).
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Subsidence Associated with Earthquake
![](https://webarchive.library.unt.edu/eot2008/20090825005944im_/http://hvo.wr.usgs.gov/earthquakes/destruct/1975Nov29/75eqVert.gif)
Subsidence of the ground shown by contours (m) on Kilauea Volcano
associated with the magnitude 7.2 earthquake on November 29, 1975 (epicenter
shown by star).
Horizontal Ground Movement
Associated with Earthquake
![](https://webarchive.library.unt.edu/eot2008/20090825005944im_/http://hvo.wr.usgs.gov/earthquakes/destruct/1975Nov29/75eqHoriz.gif)
Horizontal displacments of benchmarks surveyed before and
after the magnitude 7.2 earthquake on November 29, 1975 (epicenter shown by star).
Use the vector scale (displacement, above) to determine the horizontal movement.
For example, Kilauea's caldera moved southeast about 1 m and its south
flank moved southeast between 4 and 8 m.
Disappearing Evidence of 1975 Earthquake
The physical evidence that such large movements occurred on Kilauea
Volcano during the 1975 earthquake is becoming increasingly difficult
to recognize. The famous submerged coconut grove at Halape is now barely
recognizable.
![Coconut grove at Halape, Hawai`i](https://webarchive.library.unt.edu/eot2008/20090825005944im_/http://hvo.wr.usgs.gov/earthquakes/destruct/1975Nov29/30424303_012_S.jpg)
Halape coconut grove in 1975
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![Coconut grove at Halape, Hawai`i](https://webarchive.library.unt.edu/eot2008/20090825005944im_/http://hvo.wr.usgs.gov/earthquakes/destruct/1975Nov29/30424303_016_S.jpg)
Halape coconut grove in 1987
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Similar earthquakes and associated ground movements
and tsunamis can be expected to occur on Hawai`i as long as Kilauea
and Mauna Loa volcanoes remain active. Because the number of residents
of the Big Island has greatly increased since 1975, with most
having no memory of the earthquake or tsunami, people need to
periodically remind themselves of the safety steps to take before,
during, and immediately after the next large earthquake.
Reference
Lipman, P.W., Lockwood, J.P., Okamura, R.T., Swanson, D.A., and
Yamashita, K.M., 1985, Ground deformation associated with the
1975 magnitude-7.2 earthquake and resulting changes in activity
of Kilauea Volcano, Hawaii: U.S. Geological Survey Professional
Paper 1276, 45 p.
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The URL of this page is:
http://hvo.wr.usgs.gov/earthquakes/destruct/1975Nov29/deformation.html
Contact:
hvowebmaster@usgs.gov
Updated:
17 December 1998
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