Transcript PowerPoint-Prдsentation

First Steps Towards 3D Global Density and
Dynamic Model of the Crust and Mantle
M. Kaban, A. Baranov and M. Rothacher GFZ Potsdam and
H. Schmeling J. W. Goethe University, Frankfurt/M
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Main Goals of the Project
1. Integrative density model of the crust and upper mantle.
a. Improvement of the existing global crustal compilation (Central & South Asia).
b. Global determination of the lithosphere thickness (Sodoudi and Kind).
c. Modelling of the lithosphere and upper mantle density structure and
computation of the non-isostatic geoid anomalies and dynamic topography.
2. Construction of a new “snap-shot” dynamic model of the mantle.
Key issues:
a. Modelling of effects of the transition zone boundaries on the geoid and
dynamic topography.
b. Considering strong lateral viscosity variations in the mantle.
3. Modelling temporal geoid variations and effects of sublithospheric
convection.
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Integrative Model of the Mantle and the Lithosphere
(existing background and main problems)
Some of the Key Problems:
1. Crust is the most heterogeneous layer in the Earth. It is principal to determine its
effect beforehand using available information.
2. Impact of compositional and temperature variations in the upper mantle is unclear.
3. Gravity effect of the transition zone (potentially very strong) has not identified in
the observed gravity field/geoid.
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Improvement of the Global Crustal Model
Main focus
of this study
70
60
50
40
30
20
10
-130
-120
10
-110
15
-100
20
25
-90
30
-80
35
40
-70
45
-60
50
-50
-40
km
North America (Kaban
and Mooney in prep.)
1.
2.
EuCRUST-07 (Tesauro, Kaban
and Cloetingh, 2007 subm.)
Quality of the existing global crustal models do not meet present-day requirements.
The new global crustal model is principally improved based on high resolution regional
data.
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Collection of new data for Central & South Asia
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Moho depth - China
Based on the data from (Li, Mooney and Fan ; Sodoudi et al., 2006, 2006; Huanga &
Zhaob, 2004; Chunju et al. 2005; Mangino et al., 1999) and more …
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Moho depth – Middle East
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Moho depth - India
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Modelling of the effect of the transition zone on the
geoid and dynamic topography
1. How significant is the impact of the transition zone on the
dynamic geoid?
2. Up to now, most of the combined gravity-seismic models are
based on the tomography data, in which the effects of
velocity variations and phase boundaries are mixed. This can
lead to strong artificial seismic velocity anomalies and,
consequently, to false inferences on the mantle structure.
3. Artificial “dynamic” reconstructions of the transition
boundaries give the topography, which is remarkably different
from observations (e.g. Cadek and Fleitout, 1999;
Steinberger, 2007).
4. We use the new tomography model of Gu et al. (2003), in
which mantle velocities have been estimated in a joint
inversion with the transition zone discontinuities.
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
“Effective” velocity and density variations in the TZ
based on traditional tomography models
Z
In fact, the observed Vs variations
could be either negative or positive in
the vicinity of the 660 discontinuity
depending on many variable factors!
Parametrization, Gu et al., 2003
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
“Effective” velocity-to-density scaling factor
“Effective” velocity-density scaling factor in the TZ
for traditional tomography models
Vertical resolution of the model, km
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
New global seismic model based on a simultaneous
inversion (660 km)
Gu et al., 2003
SPP 1257
Ekström and
Dziewonski, 1998
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Inversion Scheme
To calculate the effect of density variations on the geoid we use a direct method for solution of
the differential equation system, which provides a possibility to model arbitrary distributions of
density and viscosity with depth (Kaban et al., 2007).
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Results of the Simultaneous Inversion
(scaling factor)
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Variations of the Model Parameters
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Variations of the Model Parameters
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Observed and Calculated Geoid
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Impact of the transition zone boundaries
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Summary and Perspectives
1. The global model of the crust is principally improved in several
key regions. This model provides a basis for construction of a
global integrative density model of the crust and upper mantle.
2. Considering the transition zone provides much better similarity of
the calculated and observed geoid relative to the previous
tomography models.
a. The calculated scaling factor and density jump for the 400-km
discontinuity are very close to the mineral physics prediction.
b. The effective density contrast for the 660, which characterizes its
depth variations, is 4 times less than the PREM value. We analyze
possible mineral physics applications of this result.
c. In agreement with previous GIA studies, viscosity of the layer right
above 660 is remarkably less than of the neighboring layers.
3. More results coming soon!
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data
Thank you!
SPP 1257
Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data