Topographic effects on long offset transient electromagnetic response
Tóm tắt
The forward modeling procedure used in this article is formulated with the volume integral equation based on the tensor Green’s function. The electromagnetic components responses are first calculated in the frequency domain and then transformed to the time domain by digital filtering. The valley and hill topography with a layered earth is stimulated by a horizontal electric dipole (HED) transmitter, which is common in field surveys, and the TEM responses are calculated at the transmitter and receivers. The topography effects on the long offset electromagnetic transient (LOTEM) responses are discussed in detail. The results show that both valley and hill topography has significant effect on the LOTEM measurement. If the HED is located in the bottom of a valley, the distortion of the observed anomalous field at distance is severe. A valley at the receiver locations show a strong effect but are localized in space and time. In general, hill-shaped topography shows smaller effects no matter where its located. When the topography is located between source and receivers, the influence is negligible. We conclude that the location of the source is much more important than the receivers and it is critical to put the transmitter in an open flat area in the field survey.
Tài liệu tham khảo
Adhidjaja, J. I., Hohmann, G. W., and Oristaglio, M. L., 1985, Two-dimensional transient electromagnetic responses: Geophysics, 50, 2849–2861.
Anderson, W. L., 1984, Computation of Green’ tensor integrals for three-dimensional electromagnetic problems using fast Hankel transforms: Geophysics, 49, 1754–1759.
Commer, M., Helwig, S. L., Hördt, A., and Tezkan, B., 2005, An interpretation of long-offset transient electromagnetic data from Mount Merapi, Indonesia, using a threedimensional optimization Approach: J. Geophys. Res., 110, B03207. doi:10.1029 /2004JB003206.
Goldman, M., Tabarovsky, L., and Rabinovich, M., 1994, On the influence of 3-D structures in the interpretation of transient electromagnetic sounding data: Geophysics, 59, 889–901
Hohmann, G. W., 1975, Three-dimensional induced polarization and electromagnetic modeling: Geophysics, 40, 309–324.
Hohmann, G. W., 1983, Three-dimensional EM modeling: Geophysical Surveys, 6, 27–53.
Hördt, A., and Müller, M., 2000, Understanding LOTEM data from mountainous terrain: Geophysics, 65(4), 1113–1123.
Nabigian, M. N., 1979, Quasi-static transient response of a conducting half-space: An approximate representation: Geophysics, 44(10), 1700–1705.
Nabighian, M. N., 1992, Electromagnetic methods in applied geophysics, Volume 1, Theory: Society of Exploration Geophysicists, 120–296.
Newman, G., A., Hohmann, G. W., and Anderson, W. L., 1986, Transient electromagnetic response of a threedimensional body in a layered earth: Geophysics, 51, 1608–1627.
SanFilipo, W. A., and Hohmann, G. W., 1985, Integral equation solution for the transient electromagnetic response of a three-dimensional body in a conductive halfspace: Geophysics, 50, 798–809.
Strack, K. M., 1992, Exploration with deep transient electromagnetic method: Elsevier.
Tang, X. G., Hu, W. B., and Yan, L. J., 2005, The detectability of transient electromagnetic method to multiple 3D bodies with the valley topography: Seismology and Geology, 27(2), 316–323.
Wannamaker, P. E., Hohmann, G. W., and SanFilipo, W. A., 1984, Electromagnetic modeling of three-dimensional body in layered earth using integral equations: Geophysics, 49, 60–74.
Yan, L. J., Hu, W. B., and Yang, S. F., et al., 2001, The trail researches of electromagnetic exploration methods in carbonate areas in South: China Petroleum Industry Press, Beijing.