P. Schmoldt, PhD - MTNet - DIAS

Step 1:
Isotropic 2D
inversion
Step 2:
Anisotropic 2D
inversion
Starting models for anisotropic 2D inversion
Approach 1
crust
8.3. Inversion of 3D model data
Approach 2
100 Wm mantle 1000 Wm
fixed
crust 100 Wm
1000 Wm mantle fixed
Fig. 8.16.: Starting models used for anisotropic 2D inversion; see text for details about the two inversion approaches.
Parameter Value
Period range for inversion 10 −2 − −10 5 s
Mesh resistivity value 1000 Ωm
Horizontal block width increase factor 1.2
Horizontal block target width 1.2 of a skin depth
Vertical block width increase factor 1.1
Tab. 8.5.: Parameters used to generate the mesh for the anisotropic 2D inversion
In this section, the focus is on the advances of anisotropic 2D inversion in contrast to
an isotropic approach. The effect of different inversion parameters (smoothing, static shift
correction, tear zone application) was the focus of the previous Section 8.3.1 and in the
following the therein identified optimal smoothing parameter values are used, i.e. α = 1,
β = 1, τ = 6. Because the aim of this anisotropic inversion approach is to use anisotropic
“distortion” to recover the 3D subsurface structures, no static shift corrections or tear
zones are applied and the crust is neither fixed as a homogeneous layer nor with its “true
values” (cf. Sec. 8.3.1). Instead, crustal values are determined by the inversion process.
Parameters used to generate the mesh for the anisotropic 2D inversion are summarised in
Table 8.5.
Inversion results
As for the cases of isotropic 2D and anisotropic 1D inversion (Secs. 8.3.1 and 8.3.2), evaluation
of anisotropic 2D inversion results in this Chapter is limited to stations related to
the PICASSO Phase I recording sites (stations pic001 – pic020 in Figure 8.4). Results for
other profiles are used to illustrate certain issues of the anisotropic 2D inversion approach
and are presented in more detail in the Appendix (Sec. A.3.2). In general, anisotropic 2D
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