COMPARISON OF TWO-DIMENSIONAL MODELS -- BC87 BC87 data set information, Vers. 2.0 1994/Jan/12. This dataset of MT (RXX, RXY, RYX & RYY) & GDS (TZX & TZY) responses is for distribution to scientists wishing to test out their full interpretation procedures. The data are very complex and require some form of distortion correction prior to modelling/inversion. The data are stored in two different formats: SEG/EDI (Society of Exploration Geophysics/Electronic Data Interchange standard) J-format (J format; same as the COPROD2 and BC87 datasets were distributed) For a description of the J-format, see the file /ftp/pub/mtnet/docs/jformat.doc The data are compressed in two different forms: Unix compression (compress/uncompress - for Unix) ZIP (PKZIP/PKUNZIP - for PC) A shareware version of PKUNZIP is available in /ftp/pub/mtnet/misc/pkunzip.exe. Remember to set for BINARY conversion when downloading any of the data files. This directory contains the following 5 files:- README this information bc87.edi.Z BC87 data in EDI format in UNIX compression bc87.zip BC87 data in EDI format in ZIP compression bc87j.tar.Z BC87 data in J format in UNIX compression bc87j.zip BC87 data in J format in ZIP compression These MT data are "raw" in the sense that they are as we received them from the contractor (Phoenix Geophysics of Toronto). All four elements of the MT impedance tensor are given, both in terms of apparent resistivities and phases, and as impedances (in S.I.). The full dataset consists of twenty-seven (27) sites over a 150 km traverse with forty (40) responses in the range 384 Hz to 1820 s. The data are oriented in geographic coordinates, with 'X' denoting north and 'Y' denoting east, thus the RXY component is the ExHy resistivities (and phases). The profile is from the Valhalla Gneiss Complex to the Rocky Mountain Trench in southeastern British Columbia. Background information is given in Jones (1993). See previous interpretations in Eisel and Bahr (1993) and Jones et al. (1993; see also Jones et al., 1988). The .prf file gives the eastings and northings of the stations. The centre of the coordinate system is at 50 North, 120 West. Some comments on the data: a) If a value is set to -999, then no value exists for that response at that period. b) If a resistivity is set to a negative value, then I have judged it to be too scattered (i.e., too biased) from its neighbours for the error level associated with it. You can ignore this value or reset it to positive to include it in your inversions. c) Note: the XY responses are the E-polarization or TE mode, with phases in the range 0 - 90 degrees (first quadrant). The YX responses are the B-polarization or TM mode, with phases in the range -180 - -90 degrees (third quadrant). You may work with these data provided that you observe the following caveats. 1) In the acknowledgements in any publication, you acknowledge LITHOPROBE (Doug Oldenburg, UBC) and the GSC (Alan Jones) for making the data available. Also, you must obtain a "Lithoprobe Publication Number" from the Lithoprobe Secretariate (604-822-4138) and add this to any published paper. Please obtain this number once your paper has been accepted for publication. 2) Please do not give these data on to anyone. I would prefer that all participants of BC87 get the data from me so that everybody has the same data - I know how easy it is to "edit" data then forget you have done so, then pass it on to somebody else as the kosher BC87 dataset (this occurred frequently with the COPROD1 dataset). 3) Keep me informed of your results - I hope to write a comparative paper in a few years time (something I kept meaning to do for COPROD1) with every participant as a co-author. Especially I would like preprints/reprints/reports etc. of any manuscript that uses these data. Alan G. Jones Geological Survey of Canada 1 Observatory Crescent OTTAWA, Ontario Canada, K1A 0Y3 tel: (613) 992-4968 FAX: (613) 992-8836 email: ajones@nrcan.gc.ca References ========== Jones, A.G., 1993. The BC87 dataset: tectonic setting, previous EM results, and recorded MT data. J. Geomagn. Geoelectr., vol. 45, pp. 1089-1105. Eisel, M. and Bahr, K., 1993. Electrical anisotropy in the lower crust of British Columbia: an interpretation of a magnetotelluric profile after tensor decomposition. J. Geomagn. Geoelectr., vol. 45, pp. 1115-1126. Jones, A.G., Groom, R.W. and Kurtz, R.D., 1993. Decomposition and modelling of the BC87 dataset. J. Geomagn. Geoelectr., vol. 45, pp. 1127-1150. Jones, A.G., Kurtz, R.D., Oldenburg, D.W., Boerner, D.E. and Ellis, R., 1988. Magnetotelluric observations along the LITHOPROBE southeastern Canadian Cordilleran transect. Geophys. Res. Lett., vol. 15, pp. 677-680.