Mathematics – Logic
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p62a0371j&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P62A-0371
Mathematics
Logic
5430 Interiors (8147), 6207 Comparative Planetology, 6225 Mars, 7207 Core And Mantle
Scientific paper
Seismic traveltime curves are computed for several published interior structure models of Mars. The sensitivity of these curves to compositional parameters is examined as is the potential for using seismic data to constrain composition. The model of Zharkov and Gudkova (2000) produced a core shadow zone at epicentral distances of 103° to 141°. Zero-offset core reflection times for PcP and ScS were 394 s and 730 s, respectively. This model invoked a ferric number (Fe/(Fe+Mg)x100) of 20 for the mantle silicates and an Fe-FeS liquid core containing 14.5 wt.% S and 0.48 wt.% H. A thin (50 km) perovskite layer overlies the core-mantle boundary at a depth of 1642 km. The moment of inertia factor (C/MR2) and Fe/Si ratio calculated for this model agree well with the Mars Pathfinder value of 0.3662 and the chondritic Fe/Si ratio of 1.71, respectively. The strongest influences on the traveltime curves are due to those factors that control core size: the iron molar fraction (XFe) of the mantle and the sulphur content of the core. With a 1% increase in XFe, the epicentral onset of the shadow zone increased by 3° and the vertical PcP traveltime increased by 7.5 s. Increasing the sulphur content of the core enlarges it, resulting in a larger shadow zone and decreased reflection times. A 1% (wt.) increase in core sulphur decreased the epicentral onset of the shadow zone by 0.5° and decreased the PcP time by 3.2 s. At large sulphur values, the core-mantle boundary is too shallow to allow for a high-velocity perovskite lower mantle. Further work planned in this study will examine other seismic phases and the sensitivity of these results to the moment of inertia, the state of the core (liquid, solid, or both) and the strength of seismic velocity discontinuities due to mineralogical phase changes in the mantle.
Green David H.
Jadhav Manavi
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