9714882 Mackie This is a proposal to continue research begun under a one-year pilot project for investigating upper mantle electrical conductivity structure under the North American continent and urrounding oceans using very long period magnetotelluric (MT) data. A reanalysis of existing long period data sets collected primarily near oceans and on islands will be complemented with the acquisition of new MT data sets in continental areas, for which there is currently a paucity of data. The PIs propose to use telephone lines connected to buried electrodes near magnetic observatories for recording the electric field data, which will be combined with the magnetic data from the observatory to compute MT response functions. Under the pilot project, they have successfully instrumented the Tulsa, Oklahoma magnetic observatory, and they plan to instrument the Boulder, Colorado observatory in early 1997. This continuation grant will provide funding to instrument two additional observatories, and to continue the recording over a period of three years in order to obtain stable estimates of the long period MT response functions. ***
