11:40 AM - 11:55 AM
[SEM14-10] Understanding the spatial distribution characteristics of the MT response using Variogram
Keywords:Magnetotelluric, Variogram, Static shift correction method
In the magnetotelluric method (MT method), the subsurface resistivity structure can be estimated based on the apparent resistivity and phase (MT response) for each frequency. Recently, in order to reduce the influence due to the small-scale heterogeneous structure near the surface (static distortion), the analysis of resistivity structure is done based on Zssq, a rotational invariant of impedance tensor. However, the spatial characteristics of Zssq, especially the horizontal distribution feature s, have not been discussed.
In this study, the spatial distribution and the characteristics of the MT response (Zssq) obtained from various two-dimensional resistivity structures are discussed qualitatively. We investigated the spatial correlation of MT response using Variogram often used in geostatistical researches. We prepared seven different types of subsurface resistivity models, and compared the spatial wavelength of the distributions of Zssq apparent resistivity and phase values for three different frequencies. Prior to that discussion, we also investigated the relationship between the range in Variogram and the wavelength of spatial changes, whose wave shape follows the normal distribution function.
As a result, it was found that there is no simple correlation in spatial wavelength between Zssq apparent resistivity and phase, and also found that the range of Zssq apparent resistivity is greater than the range of Zssq phase. Furthermore, it was clarified that the range is up to about 3.6 times the spatial wavelength (standard deviation of normal distribution function), and that the range also depends on the spacing of the resistivity anomalies. From the spatial relationship between apparent resistivity and phase, it was suggested that the degree of static shift, often seen in actual MT exploration, is discussed based on the geostatistical analysis.
In this study, the spatial distribution and the characteristics of the MT response (Zssq) obtained from various two-dimensional resistivity structures are discussed qualitatively. We investigated the spatial correlation of MT response using Variogram often used in geostatistical researches. We prepared seven different types of subsurface resistivity models, and compared the spatial wavelength of the distributions of Zssq apparent resistivity and phase values for three different frequencies. Prior to that discussion, we also investigated the relationship between the range in Variogram and the wavelength of spatial changes, whose wave shape follows the normal distribution function.
As a result, it was found that there is no simple correlation in spatial wavelength between Zssq apparent resistivity and phase, and also found that the range of Zssq apparent resistivity is greater than the range of Zssq phase. Furthermore, it was clarified that the range is up to about 3.6 times the spatial wavelength (standard deviation of normal distribution function), and that the range also depends on the spacing of the resistivity anomalies. From the spatial relationship between apparent resistivity and phase, it was suggested that the degree of static shift, often seen in actual MT exploration, is discussed based on the geostatistical analysis.