Research And Application Of Inversion Static Effect In Magnetotelluric

Magnetoelluric sounding method used natural alternating electromagnetic fieldto study the earth electrical structure, from high-impedance layer shielding， forlow-resistivity layer of high resolution. It does not need to establish artificial fieldsource, construction convenient, low-cost, large-range exploration depth. It has beenwidely used in energy, resources and deep geophysical exploration and other fields.A common problem in magnetotelluric (MT) sounding is the presence of staticshifts in the data, i.e., a vertical shifting of the log-apparent-resistivity versus periodcurves relative to regional values. These static shifts are due to the presence ofsmall-scale, shallow conductivity anomalies near the measurement site. Electriccharge builds up on near-surface anomalies that are small in comparison to the skindepth of the electromagnetic (EM) fields. The charge buildup produces a perturbationof the measured electric fields from their regional values that persists to arbitrarilylow frequencies. Incorrect removal of these local distortions leads to incorrectinterpretation of the deeper targets of investigation.The removal of parallel shifts in the log-apparent-resistivity curves and theinterpretation of the MT soundings are generally handled separately. Since differentmethods of removing the static shift from the data can lead to different sets of staticshifts for the same data set there exists a danger in removing the static shift first andthen trying to fit a model to this “corrected” data. The danger is that featuresappearing in the interpreted conductivity structure may stem only from the particularset of static shifts chosen. A method of jointly handling static shifts and modelinterpretation is desirable.In one dimension, interpretation of static shifted MT data may lead to modelshaving the same structural shape as models based on undistorted data, but resistivitiesand depths will be error. In higher dimensional surveys, the amount of static shift generally varies from station to station, and attempts to interpret uncorrected data willlead to models may be found that satisfies the data. To remove the excess roughness,two static-shift parameters are introduced at each station that serve to scale theapparent resistivities of each of the TE and TM modes but which leave the phasesunaffected. A regularized inversion is performed to solve simultaneously for theresistivities and static shifts which produce the smoothest model. By allowing thestatic shifts to be free parameters, smooth inversion ensures that structures appearingin the models are not simply due to the incorrect removal of static shift.In this paper, on the basis of collecting and understanding home and abroadrelevant information, focused on currently method commonly used in the static effectcorrection in magnetoelluric sounding data processing, and analyze the mechanism ofstatic effect. Then I use the two-dimensional finite element forward program tocalculate homogeneous half space, homogeneous layered medium and even morecomplex geoelectric model, get static effects TE, TM mode response characteristics indifferent geoelectric model. Then acting static effect as an inversion parameterdirectly involved in the inversion, correcting the static effects caused by surface localirregularities in the inversion process. The results show that the static effect of directinversion method has a good suppression effect on the static effect.Finally, I use the static effect of direct inversion to process of Benxi-Ji’an areameasured magnetoelluric sounding data. Static effects present in the data have beeneffectively suppressed, the accuracy of data interpretation has been improved.