A MAGNETOTELLURIC TRAVERSE ACROSS THE YELLOWSTONE REGION

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 (rho(a)) spectrums. At stations near Yellow-stone the resistivity was linearly proportional to omega 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 (approximate to 15 km). Stations well away from Yellowstone show rho(a) similar to omega(o,r), suggesting a lower gradient of conductivity in the substrate. Precise inversion of the data is not practical: however, the comparison of rho(a) at neighboring stations shows distinct differences in electrical response of the crust which may be discussed in a geological context.