A magnetotelluric traverse across the Yellowstone Region

Abstract

Five magnetotelluric stations were taken in the Yellowstone region. Sufficient coherent signal was obtained in the frequency band 10−4 to 10−1 hz to yield useful apparent resistivity (ρa) spectrums. At stations near Yellowstone the resistivity was linearly proportional to ω at long periods; this is due to the existence of a high conductivity substrate at some depth. The effective thickness of the low conductivity surface zone as inferred from the intercept of the response curve is consonant with the geological setting; it is thin (<5 km) in the Yellowstone thermal area, and thicker on the Snake River Plain (≈ 15 km). Stations well away from Yellowstone show ρa ∼ ω0.7, suggesting a lower, gradient of conductivity in the substrate. Precise inversion of the data is not practical: however, the comparison of ρa at neighboring stations shows distinct differences in electrical response of the crust which may be discussed in a geological context.