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Titill

Crustal conductivity and distribution of melt beneath the Krafla caldera, N-Iceland inferred from magnetotelluric data

Útdráttur

Subsurface resistivity structure across the divergent plate boundary of Iceland is
characterized by thin, intermittent near-surface high conductivity layers associated with
geothermal alteration and a thick, mid-crustal conductor deepening away from the plate
boundary. In addition, one-dimensional magnetotelluric (MT) models of the Krafla central
volcano have revealed two anomalous, updoming zones of high conductivity beneath the
Krafla caldera overlapping partly shear wave shadow zones interpreted as areas of melt
accumulation during the 1974-1989 rifting episode. To further constrain the extent of the
updoming conductors and elucidate their relationship with the lower crustal conductor as
well as near surface anomalies two-dimensional magnetotelluric inversions were
conducted along two east-west profiles across the Krafla caldera. The northern profile
which crosses both shear-wave shadow zones reveals a single updoming conductor within
the western zone suggesting that the northern boundary of the eastern zone is located just
south of the profile. Sensitivity tests indicate that the dimensions of the updoming
conductor (0.5 – 2 km wide and 4 – 5 km high) are in a good agreement with seismic and
geodetic data. The conductive dome connects with a near-surface conductive layer, at less
than 500 m, which correlates with surface geothermal manifestations and the mid crustal
connector, at 6-16 km depth. The top of the deeper conductor correlates fairly well with the
brittle-ductile crustal boundary. Although joint interpretation of magnetotelluric data with
other geophysical data further illuminates the geometrics of the shallow magma system of
Krafla the percentage of partial melt within the mid-crustal conductor remains unknown.

Birting
8.6.2010


Skrár
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