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| Titel |
The lithosphere-asthenosphere boundary observed with USArray receiver functions |
| VerfasserIn |
P. Kumar, X. Yuan, R. Kind, J. Mechie |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1869-9510
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| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 3, no. 1 ; Nr. 3, no. 1 (2012-05-24), S.149-159 |
| Datensatznummer |
250000843
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| Publikation (Nr.) |
 copernicus.org/se-3-149-2012.pdf |
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| Zusammenfassung |
| The dense deployment of seismic stations so far in the western half of the
United States within the USArray project provides the opportunity to study in
greater detail the structure of the lithosphere-asthenosphere system. We use
the S receiver function technique for this purpose, which has higher
resolution than surface wave tomography, is sensitive to seismic
discontinuities, and is free from multiples, unlike P receiver functions. Only
two major discontinuities are observed in the entire area down to about 300 km
depth. These are the crust-mantle boundary (Moho) and a negative boundary,
which we correlate with the lithosphere-asthenosphere boundary (LAB), since a
low velocity zone is the classical definition of the seismic observation of
the asthenosphere by Gutenberg (1926). Our S receiver function LAB is at a
depth of 70–80 km in large parts of westernmost North America. East of the
Rocky Mountains, its depth is generally between 90 and 110 km. Regions with
LAB depths down to about 140 km occur in a stretch from northern Texas, over
the Colorado Plateau to the Columbia basalts. These observations agree well
with tomography results in the westernmost USA and on the east coast.
However, in the central cratonic part of the USA, the tomography LAB is near
200 km depth. At this depth no discontinuity is seen in the S receiver
functions. The negative signal near 100 km depth in the central part of the
USA is interpreted by Yuan and Romanowicz (2010) and Lekic and Romanowicz
(2011) as a recently discovered mid-lithospheric discontinuity (MLD). A
solution for the discrepancy between receiver function imaging and surface
wave tomography is not yet obvious and requires more high resolution studies
at other cratons before a general solution may be found. Our results agree
well with petrophysical models of increased water content in the
asthenosphere, which predict a sharp and shallow LAB also in continents
(Mierdel et al., 2007). |
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