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| Titel |
2.5D complex resistivity modeling and inversion using unstructured grids |
| VerfasserIn |
Kaijun Xu, Jie Sun |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250125906
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| Publikation (Nr.) |
 EGU/EGU2016-5559.pdf |
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| Zusammenfassung |
| The characteristic of complex resistivity on rock and ore has been recognized by people for a
long time. Generally we have used the Cole-Cole Model(CCM) to describe complex
resistivity. It has been proved that the electrical anomaly of geologic body can be quantitative
estimated by CCM parameters such as direct resistivity(ρ0), chargeability(m), time
constant(τ) and frequency dependence(c). Thus it is very important to obtain the
complex parameters of geologic body. It is difficult to approximate complex structures
and terrain using traditional rectangular grid. In order to enhance the numerical
accuracy and rationality of modeling and inversion, we use an adaptive finite-element
algorithm for forward modeling of the frequency-domain 2.5D complex resistivity
and implement the conjugate gradient algorithm in the inversion of 2.5D complex
resistivity.
An adaptive finite element method is applied for solving the 2.5D complex resistivity
forward modeling of horizontal electric dipole source. First of all, the CCM is introduced into
the Maxwell’s equations to calculate the complex resistivity electromagnetic fields. Next, the
pseudo delta function is used to distribute electric dipole source. Then the electromagnetic
fields can be expressed in terms of the primary fields caused by layered structure and the
secondary fields caused by inhomogeneities anomalous conductivity. At last, we calculated
the electromagnetic fields response of complex geoelectric structures such as anticline,
syncline, fault. The modeling results show that adaptive finite-element methods can
automatically improve mesh generation and simulate complex geoelectric models using
unstructured grids.
The 2.5D complex resistivity invertion is implemented based the conjugate gradient
algorithm.The conjugate gradient algorithm doesn’t need to compute the sensitivity
matrix but directly computes the sensitivity matrix or its transpose multiplying
vector. In addition, the inversion target zones are segmented with fine grids and the
background zones are segmented with big grid, the method can reduce the grid
amounts of inversion, it is very helpful to improve the computational efficiency. The
inversion results verify the validity and stability of conjugate gradient inversion
algorithm.
The results of theoretical calculation indicate that the modeling and inversion of 2.5D
complex resistivity using unstructured grids are feasible. Using unstructured grids can
improve the accuracy of modeling, but the large number of grids inversion is extremely
time-consuming, so the parallel computation for the inversion is necessary.
Acknowledgments:
We thank to the support of the National Natural Science Foundation of China(41304094). |
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