P. Schmoldt, PhD - MTNet - DIAS
P. Schmoldt, PhD - MTNet - DIAS P. Schmoldt, PhD - MTNet - DIAS
296 3D-mantle profile Inversion results for the 3D-mantle profile using stations synE02 – synL09 (decomposed for a geoelectric strike direction N45E, see Figure A.4 for inversion results and station names) are similar to the results for the 3D-mantle profile using stations syn001 – syn020 (cf. Sec. 8.3.1). Resemblance of characteristics originates from similar locations of the stations belonging to the two datasets (cf. Fig. 8.4). For stations synE02 – synL09, a model with an overall low RMS misfit (1.51, with a 5% error floor for phases and 10% error floor for apparent resistivities) is obtained. Therein, apparent resistivity responses for TE and TM mode data at stations to the south are generally slightly lower than for the true model, whereas responses for the stations to the north are generally slightly higher. The misfit is likely to originate from smoothing constraints inherent in the inversion process (cf. Sec. 6.3.3). An increased misfit, for both modes, is observable in the impedance phase data at periods 10 – 100 s. For this model, periods in that range are related to a depth of 30 km, i.e. the depth of the crust–mantle boundary (cf. Sec. 3.3). It is therefore reasonable to attribute these misfits to the fact that the synthetic model features an abrupt change from crustal to mantle region values, which is not permitted in the inversion model due to smoothness constraints. The circumstance that the misfit of the TE mode is generally higher than for the TM mode is in agreement with the finding that the TE mode is usually more affected by 3D structures [e.g. Ledo, 2005]. Profile: 3D-mantle Depth (km) TE Log 10(periods) Log 10(periods) RMS TM -2 -1 0 1 2 3 4 -2 -1 0 1 2 3 4 S N 0 50 100 150 200 250 synL09 synK08 Apparent resistivity synJ07 synI06 300 0 16 32 48 64 80 96 112 128 144 Distance (km) (Wm) 50 2000 synL09 synK08 synJ07 synI06 synH05 synG04 synF03 synE02 Misfit (Total = 1.51) synH05 synG04 Phase Log 10(Wm) degrees Log 10(Wm) degrees synL09 synK08 synJ07 synI06 synH05 synG04 synF03 synE02 Fig. A.4.: Isotropic 2D inversion results for the ‘3D-mantle’ profile on top of the synthetic 3D model (see Figure 8.5 for profile location). Electric resistivity interfaces at crustal and mantle depths are located between stations synI06 and synH05. Periods between 10 s and 100 s are related to the crust–mantle boundary; see Section 8.2.1 for a description of the model. During the inversion the crust is kept fixed at an electric resistivity value of 100 Ωm. The misfit of the uppermost region originates from the problematic of meeting the cell size requirements for the highest frequencies. synF03 synE02 A. Appendix
297 04-centre profile The profile 04-centre runs parallel to the crustal strike direction and is located on top of the more conductive crustal region (50 Ωm). The profile contains stations synD04 – synM04 (see Fig. 8.4), which are decomposed according to a geoelectric strike direction N45E. The inversion result for the 04-centre profile features two regions of increased electric conductivity located just below the crust mantle boundary (see Fig. A.5). Hence, the erroneous features are likely to originate from the fixing of the crust at 100 Ωm in combination with the effect of different electric strike direction at crust and mantle depth. The inversion model does not exhibit a continuous sharp lateral change in resistivity that can be associated with the interface. Instead, the model contains a highly resistive region in the northwestern to central area at a depth between approximately 50 km and 200 km. Given the relatively low RMS misfit of the model (2.42 with a 5% error floor for phases and 10% error floor for apparent resistivities), an investigator might erroneously infer a feature at one of these depth regions, e.g. an electric asthenosphere at the bottom of the resistor. Like for the 3D-mantle profile (Fig. A.4), the misfit of the impedance phase is mostly constrained to the periods range related to the crust mantle boundary (10 – 100 s), and the misfit for the TE mode, is higher than for the TM mode. The TM mode apparent resistivity misfit exhibits a noticeable striping for periods related to the crust, which is most likely associated with incorrect decomposition of the modes at this depth range. For the case of the 3D model used in this study, with the 90 degree difference between strike directions at crust and mantle depths, the two modes are swapped. TE and TM modes are sensitive to current flow parallel to and charge build up on the face of vertical interfaces with a direction orthogonal to the profile, respectively. Thus, swapping of the modes introduces additional vertical interfaces, which are prohibited here due to the fixing of the crust; however the conductive features at the crust mantle boundary could be indicators of effects due to the mode swapping. Depth (km) Profile: 04-centre TE Log 10(periods) Log 10(periods) RMS TM NW SE 0 50 100 150 200 250 synD04 synE04 Apparent resistivity synF04 synG04 synH04 300 0 16 32 48 64 80 96 112 128 144 Distance (km) log10 (Wm) 1 2 3 4 5 -2 -1 0 1 2 3 4 -2 -1 0 1 2 3 4 synD04 synE04 synF04 synG04 synH04 synI04 synJ04 synK04 synL04 synM04 Misfit (Total = 2.42) Log 10(Wm) Log 10(Wm) synI04 synJ04 synK04 Phase synD04 synE04 synF04 synG04 synH04 synI04 synJ04 synK04 synL04 synM04 Fig. A.5.: Isotropic 2D inversion results for the ‘04-centre’ profile on top of the synthetic 3D model (see Figure 8.4 for station locations). An electric resistivity interface at mantle depth is located between stations synI04 and synH04. Periods between 10 s and 100 s are related to the crust–mantle boundary; see Section 8.2.1 for a description of the model. During the inversion the crust is kept fixed at an electric resistivity value of 100 Ωm. The misfit of the uppermost region originates from the problematic of meeting the cell size requirements for the highest frequencies. synL04 synM04 degrees degrees A.3. Auxiliary inversion results for the synthetic 3D subsurface model
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- Page 371 and 372: Bibliography Egbert, G. D., and J.
- Page 373 and 374: Bibliography Ganapathy, R., and E.
- Page 375 and 376: Bibliography Haak, V., and R. Hutto
- Page 377 and 378: Bibliography Hutton, R. (1972), Som
- Page 379 and 380: Bibliography Jones, A. G., and R. W
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296<br />
3D-mantle profile<br />
Inversion results for the 3D-mantle profile using stations<br />
synE02 – synL09 (decomposed for a geoelectric strike direction<br />
N45E, see Figure A.4 for inversion results and station<br />
names) are similar to the results for the 3D-mantle<br />
profile using stations syn001 – syn020 (cf. Sec. 8.3.1).<br />
Resemblance of characteristics originates from similar locations<br />
of the stations belonging to the two datasets (cf.<br />
Fig. 8.4). For stations synE02 – synL09, a model with<br />
an overall low RMS misfit (1.51, with a 5% error floor<br />
for phases and 10% error floor for apparent resistivities)<br />
is obtained. Therein, apparent resistivity responses for<br />
TE and TM mode data at stations to the south are generally<br />
slightly lower than for the true model, whereas responses<br />
for the stations to the north are generally slightly<br />
higher. The misfit is likely to originate from smoothing<br />
constraints inherent in the inversion process (cf. Sec.<br />
6.3.3). An increased misfit, for both modes, is observable<br />
in the impedance phase data at periods 10 – 100 s. For<br />
this model, periods in that range are related to a depth of<br />
30 km, i.e. the depth of the crust–mantle boundary (cf.<br />
Sec. 3.3). It is therefore reasonable to attribute these misfits<br />
to the fact that the synthetic model features an abrupt<br />
change from crustal to mantle region values, which is not<br />
permitted in the inversion model due to smoothness constraints.<br />
The circumstance that the misfit of the TE mode<br />
is generally higher than for the TM mode is in agreement<br />
with the finding that the TE mode is usually more affected<br />
by 3D structures [e.g. Ledo, 2005].<br />
Profile: 3D-mantle<br />
Depth (km)<br />
TE<br />
Log 10(periods)<br />
Log 10(periods)<br />
RMS<br />
TM<br />
-2<br />
-1<br />
0<br />
1<br />
2<br />
3<br />
4<br />
-2<br />
-1<br />
0<br />
1<br />
2<br />
3<br />
4<br />
S N<br />
0<br />
50<br />
100<br />
150<br />
200<br />
250<br />
synL09<br />
synK08<br />
Apparent resistivity<br />
synJ07<br />
synI06<br />
300<br />
0 16 32 48 64 80 96 112 128 144<br />
Distance (km)<br />
(Wm)<br />
50<br />
2000<br />
synL09<br />
synK08<br />
synJ07<br />
synI06<br />
synH05<br />
synG04<br />
synF03<br />
synE02<br />
Misfit<br />
(Total = 1.51)<br />
synH05<br />
synG04<br />
Phase<br />
Log 10(Wm) degrees<br />
Log 10(Wm) degrees<br />
synL09<br />
synK08<br />
synJ07<br />
synI06<br />
synH05<br />
synG04<br />
synF03<br />
synE02<br />
Fig. A.4.: Isotropic 2D inversion results for the ‘3D-mantle’ profile on top of the synthetic 3D<br />
model (see Figure 8.5 for profile location). Electric resistivity interfaces at crustal and mantle<br />
depths are located between stations synI06 and synH05. Periods between 10 s and 100 s are<br />
related to the crust–mantle boundary; see Section 8.2.1 for a description of the model. During<br />
the inversion the crust is kept fixed at an electric resistivity value of 100 Ωm. The misfit of the<br />
uppermost region originates from the problematic of meeting the cell size requirements for the<br />
highest frequencies.<br />
synF03<br />
synE02<br />
A. Appendix