A brief tilt and strain survey was conducted in the Krafla-Namafjall area in the North of Iceland during August of 1979 in order
to study the feasibility of applying solid earth tidal observations
in the exploration of volcanic geothermal systems. The rationale
of the survey was based on the expectation that various types of
geological structures such as rift zones and magma chambers can lead
to observable distortions of the local solid earth tidal amplitude
field. The field procedure consisted in measuring the local tidal
amplitudes and comparing them with normal theoretical amplitudes at
the same location.
The Krafla volcanic complex is a central volcano traversed by
a N-S trending fissure swarm, that has been tectonically and volcanically
active since December 1975. Accompanying this activity have been
periodic inflations of the Krafla caldera, presumably caused by a flow
of magma into a local magma chamber and resulting in long term tilts
of the order 0.5 ��rad/day that have been observed at two sites south
and southeast of the caldera.
In computing theoretical amplitudes the effects of the ocean tides
need to be estimated. In the case of north Iceland they are found
to be of the same magnitude as the solid earth tides. The amplitudes
of the M��� ocean loading tilt at Krafla are estimated to be 0.066 ��rad
and 0.032 ��rad for the NS and EW components respectively.
The most noteworthy result was obtained at a site in the
Namafjall geothermal area inside the active Krafla fissure swarm. The
ratios of the observed to the theoretical M��� tidal tilt amplitudes at
this site as estimated by a least squares spectral analysis method are
found to be 0.9 �� 0.3 and 3.2 �� 1.5 for the NS and EW components
respectively. On the basis of some simple order-of-magnitude estimates
we can exclude one of the numerous nearby fractures as a possible cause
for the EW tilt anomaly and conclude that it is most likely to be
generated by a large body of magma below the Krafla fissure swarm.
Due to thermoelastic noise other tilt data obtained during this survey
turned out to be less reliable. However, our work at a site east of
the fissure swarm and southeast of the caldera indicated a possible
anomaly. The strain data are highly contaminated by thermal noise and
could not be successfully analyzed.
These results tend to confirm that tidal tilt observations can
be of use in explorations of volcanic and geothermal systems. Our work
indicates that a few improvements of the simple field techniques
adapted may enhance the quality of data. These include (1) increasing
the instrument resolution, (2) selecting sites with surface layers
that are incapable of transmitting thermal stresses and (3) obtaining
more extensive higher quality temperature recordings, that should
enable the thermal noise to be largely removed. / Graduation date: 1981
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29419 |
| Date | 04 December 1980 |
| Creators | Axelsson, Gudni |
| Contributors | Bodvarsson, Gunnar |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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