none 10.1190/1.2194513 Society of Exploration Geophysicists Society of Exploration Geophysicists 186 21815793 5981 2025121113393642000 10.1190 2025-12-11T18:39:46Z 2006-06-09T19:13:16Z 0 Geophysics 1942-2156 0016-8033 2006 01 01 2006 71 3 Jiuping Chen 1Formerly University of British Columbia, Vancouver, Canada: presently Schlumberger-EMI Technology Center, 1301 South 46 Street, Building 300, Richmond, California 94804. E-mail: jchen16@slb.com. Douglas W. Oldenburg 2University of British Columbia, Department of Earth and Ocean Sciences, 6339 Stores Road, Vancouver, British Columbia, Canada. E-mail: doug@eos.ubc.ca. Abstract Magnetometric resistivity (MMR) is an electromagnetic (EM) exploration method that has been used successfully to investigate electrical-resistivity structures below the sea-floor. Apparent resistivity, derived from the observed azimuthal component of the magnetic field, often is used as an approximation to the resistivity of a layered earth. Two commonly used formulas to compute the apparent resistivity have their own limitations and are invalid for a deep-sea experiment. In this paper, we derive an apparent-resistivity formula based upon the magnetic field resulting from a semi-infinite electrode buried in a 1D layered earth. This new formula can be applied to both shallow and deep marine MMR surveys. In addition, we address the effects that arise from the transmitter-receiver (Tx-Rx) depth difference and the choice of the normalized range (the radial distance between transmitter and receiver, divided by the thickness of seawater) on data interpretation and survey design. The performance of the new formula is shown by processing synthetic and field data. 2006 01 01 2006 05 19 2006 G73 G81 10.1190/1.2194513 https://pubs.geoscienceworld.org/geophysics/article/71/3/G73/274048/A-new-formula-to-compute-apparent-resistivities https://pubs.geoscienceworld.org/seg/geophysics/article-pdf/71/3/G73/3209129/gsgpy_71_3_G73.pdf https://pubs.geoscienceworld.org/seg/geophysics/article-pdf/71/3/G73/3209129/gsgpy_71_3_G73.pdf http://geophysics.geoscienceworld.org/cgi/doi/10.1190/1.2194513 Chave 931 1991 Electrical exploration methods for the seafloor Geophysical Journal International Chen 149 679 2002 10.1046/j.1365-246X.2002.01688.x Three-dimensional numerical modeling and inversion of magnetometric resistivity data Exploration Geophysics Chen 35 157 2004 10.1071/EG04157 Magnetic and electric fields of direct currents in a layered earth Geophysics Edwards 50 153 1985 10.1190/1.1441825 First results of the MOSES experiment: Sea sediment conductivity and thickness determination, Bute Inlet, British Columbia, by magnetometric offshore electrical sounding Edwards 47 1991 The magnetometric resistivity method Geophysical Research Letters Evans 29 10.1029/2001-GL014106 2002 10.1029/2001GL014106 Crustal resistivity structure at 9° 50′N on the East Pacific Rise: Results of an electromagnetic survey Journal of Geophysical Research Evans 103 12321 1998 10.1029/98JB00599 Hydrothermal circulation at the cleft-vance overlapping spreading center: Results of a magnetometric resistivity survey Geophysics Wolfgram 51 1808 1986 10.1190/1.1442227 Polymetallic sulfide exploration on the deep sea floor: The feasibility of the MINI-MOSES technique