Joint Inversion Of Magnetotelluric And Teleseismic Data

Joint inversion is a concept of inverting multiple disparate geophysical datatogether and finding the simultaneous objective estimation of similar or integratedmodels by petrophysical approach or structural approach. Different geophysicalmethod presents different petrophysical properties of subsurface structure. Eachmethod examines geologic body from one point of view on physical parameters, thusit only images one-side. However, it is evident that joint inversion possesses severalkey advantages: (1) it can stabilize inversion and achieve convergent solutions, (2) itcan reduce the number of acceptable models, (3) it can reduce the contamination byenvironmental noise, (4) it can get better geological interpretation.Upon tracing and studying the most popular geophysical joint inversion methodsin the world in recent years, we centered on magnetotelluric and teleseismic data andperformed joint inversion of the both methods.First of all, basic research work was performed on teleseismic data processingmethod and magnetotelluric 3-D inversion. About teleseismic data processing, weillustrated time-domain iterative deconvolution technique of receiver function andstacking methods of stacking similar epicentral distance and back azimuth andcalculating average a receiver function, which can be used in joint inversion.Futhermore, we also discussed the methods of 3-D teleseismic tomography, especiallyon FMTOMO and its subspace inversion algorithm. About magnetotelluric 3-Dinversion, we studied dataspace methods. Besides, we respectively inverted generateddata of a theoretical model by 3-D teleseismic tomography and 3-D MT inversion andanalyzed the results.Secondly, we applied joint inversion of receiver functions and magnetotelluricsto datasets from the Namche Barwa, eastern Himalayan syntaxis in Tibet, based on agenetic algorithm proposed by Moorkamp. Receiver functions are calculated usingtime-domain iterative deconvolution, while apparent resistivity and phase curves areobtained by Rhoplus analysis of Berdichevskiy invariant. The average receiverfunction and apparent resistivity and phase from the same station are joint inverted forone-dimentional Earth to infer lithospheric structure. Using genetic algorithm, weanalyzed the compatibility between the magnetotelluric data and the seismic data bytrade-off plots. The comparison of predicted data and measured data manifests thatthey coincide on both data sets. The results demonstrate:(1) In the mid-upper crust, a high resistivity, high velocity layer (9～14 kmthickness) overlays a low resistivity and low velocity layer which may be related toaqueous fluids and partial melts.(2) There exists a highly conductive crust-mantle transition layer (thickness <20km) with the S wave velocity of～4 km/s in the lower crust, and also exists thelithosphere-asthenosphere boundary deeper than 130km～150km in the upper mantle.(3) A possible interpretation about the high resistivity, high velocity layer in theupper crust is the migmatitic amphibolite facies (Duoxiongla Formation), while thelow resistivity, low velocity layer beneath Zhibai station is relevant to partial meltinghigh-pressure granulite facies which may derive from petrological transformation of mafic rocks in the crust-mantle transition layer or from mantle-derived magmaunderplating.Finally, based on 3-D teleseismic tomography (FMTOMO) and 3-D MTinversion algorithm above, we studied a 3-D joint inversion algorithm withcross-gradient coupling. I wrote the codes by FORTRAN and operated on LINUX andsuccessfully achieved the 3-D joint inversion algorithm. Several generated data oftheoretical models were jointly inverted to testify the validity and reliability of thisjoint inversion algorithm. The results indicate that for MT joint inversion, the spatiallocation of anomalous body recovers better than single inversion results, not only onsingle prism model, but also on double prism model. The resistivity value in jointinversion of single prism model is much closer to the true model, while the jointinversion of double prism model can remove false anomaly of wall rock to a certaindegree. Moreover, we also obtain large improvement on seismic tomography by jointinversion, which increase the resolution of deep structure of anomalous body.Compared to single inversion, the resistivity model and velocity model of jointinversion is much closer to the true model. Joint inversion can also improve the resultsby separate inversion when resistivity and velocity is incompatible, which indicatesthat the cross-gradient is not dependent on the relationship of physical properties, thushas a wide applicability。...