Geoscience Reference
In-Depth Information
The parameters of the depth-dependent seawater density model in Eq. ( 4.10 )are
LJ D 0.00637 kg m 3 , a 1 D 0.7595 m 1 ,and a 2 D 4.3984 10 6 m 2 (cf. Tenzer
et al. 2012b ). The 5 5 arc-min continental ice-thickness data derived from Kort
and Matrikelstyrelsen (KMS) dataset for Greenland (Ekholm 1996 ) and from the
updated data for Antarctica assembled by the BEDMAP project (Lythe et al. 2001 )
were used to generate the coefficients of a global ice-thickness model. These
coefficients combined with the DTM2006.0 topographic coefficients were then used
to compute the ice (density contrast) stripping gravity correction with a spectral
resolution complete to degree 180 of spherical harmonics. For the density of the
glacial ice 917 kg m 3 (cf. Cutnell and Kenneth 1995 ), the ice density contrast
equals 1,753 kg m 3 . The sediment and consolidated crust (density contrasts)
stripping gravity corrections were computed using the 2 2 arc-deg data of the
global crustal model CRUST2.0 (Bassin et al. 2000 ) with a spectral resolution
complete to degree/order 90.
The stepwise consolidated crust-stripped gravity disturbances are shown in
Fig. 4.1 . The corresponding statistics are summarized in Table 4.1 . As seen
from a comparison of the GOCE03S gravity disturbances (in Fig. 4.1a )and
the consolidated crust-stripped gravity disturbances (in Fig. 4.1f ), the application
of the topographic and stripping gravity corrections due to the bathymetry, ice,
sediments, and consolidated crust changed the gravity map considerably. Whereas
the GOCE03S gravity disturbances are globally mostly within ˙ 250 mGal, the con-
solidated crust-stripped gravity disturbances vary between 1,416 and 473 mGal.
These gravity disturbances are mostly positive over oceans, while negative over
continents. The gravity maxima are situated along the oceanic subduction zones.
The most pronounced feature in the gravity map is the global tectonic configuration
of the boundaries between the oceanic and continental lithospheric plates, which is
distinctively marked by the absolute gravity minima. The extreme gravity minima
apply over significant orogens of the Tibetan Plateau, Himalayas, and Andes. As
mentioned before, these refined gravity disturbances have a maximum correlation
with the (a priori) Moho model.
The 2 2 arc-deg discrete data of the CRUST2.0 Moho depths were used to
calculate the compensation attraction according to Eqs. ( 4.13 ), ( 4.14 ), and ( 4.15 )
using the Moho density contrast of 485 kg m 3 (Tenzer et al. 2012b ). This correction
was further applied to the consolidated crust-stripped gravity disturbances. The
complete crust-stripped isostatic gravity disturbances are shown in Fig. 4.2 .These
gravity disturbances are everywhere positive and vary between 451 and 1,171 mGal,
with a mean of 752 mGal and a standard deviation of 67 mGal. The spatial pattern
of the isostatic gravity disturbances reveals the signature of the mantle lithosphere
density structure.
The complete crust-stripped isostatic gravity disturbances computed on a 1 1
arc-deg surface grid were used to determine the Moho depths globally using the
same grid-sampling interval. The system of observation equations was formed
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