Single-site magnetotelluric response functions using b-robust w-estimators, with an application to earthquake prediction research


Published: Jan 1, 2001
Keywords:
Earthquake Prediction Magnetotellurics Impedance Tensor Robust Estimation W-estimator
A. TZANIS
Abstract

The accumulation of stress and strain is known to induce changes in the electrical properties of rocks, which can be monitored for signs of earthquake preparation processes. To this effect, the Magnetotelluric sounding method presents some unique advantages. However, single-site MT data are notoriously susceptible to natural or anthropogenic time-varying coherent noise, which may severely bias the response function estimators and degrade their repeatability, unless treated with dedicated processing techniques. Such a technique is presented herein, involving the W-estimator with random error weighting, followed by an iterative robustification scheme based on an influence function approach. The algorithm is demonstrated on a set of severely distorted data exhibiting a marginal distribution of outliers, and is shown to effectively reduce the bias errors and the variance. It is also applied to the long-term monitoring of crustal resistivity with MT response functions at a noisy site located near Aerino village, SE Thessaly, Greece, achieving a sustainable repeatability threshold of 10-20% and faring very well with respect to the data quoted from the international literature.

Article Details
  • Section
  • Seismology
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References
ARVIDSSON, R. AND KULHANEK, O., 1993. Enhancement of seismic electric signals using magnetotellurics, Tectonophysics, 224, 131-139.
BEAMISH, D., 1982. The time dependence of electromagnetic response functions. Geophysical Surveys, 4, 405-434.
BEAMISH, D., 1986. Deep geoelectric structure beneath the Northumberland Basin, Geophys. J. R. astr. Soc, 84, 619-640.
CHAVE, A.D., THOMSON, D.J. AND ANDER, M.E., 1987. On the robust estimation of power spectra, coherences and transfer functions, J. Geophys. Res., 92, 633-648.
CRATCHLEY, CR., 1983. Volos Project, PA 85F. Progress report, IGS component for the period 1st April-30 September 1983, British Geological Survey.
EGBERT, G.D. AND BOOKER, J.R., 1986. Robust Estimation of Geomagnetic Transfer Function Data, Geophys. J. R. astr. Soc, 87, 173-194.
EGBERT, G.D. AND LIVELYBROOKS, D.W., 1996. Single station magnetotelluric impedance estimation: Coherence weighting and the regression M-estimate, Geophysics, 61, 964-970.
ERNST, T, JANKOWSKI, J., ROZLUSKI, C. AND TESSEYRE, R., 1993. Analysis of the electromagnetic field recorded in the Friuli seismic zone, NE Italy, Tectonophysics, 224, 141-148.
HAMPEL, F.R., RONCHETTI, E.M., ROUSSEEUW, P.J. AND STAHEL, W.A., 1986. Robust Statistics: An Approach Based on Influence Functions, Wiley.
HUBER, P.J., 1981. Robust Statistics, Wiley.
JOHNSTON, M.J.S., 1997, Review of electrical and magnetic fields accompanying seismic and volcanic activity, Surv. Geophys., 18, 441-475.
JONES, A.G., OLAFSDOTTIR, B. AND TIIKKAINEN, J., 1983. Geomagnetic induction studies in Scandinavia III. Magnetotelluric observations, J. Geophys., 54, 35-50.
KHARIN, E.P, 1982. Changes in the transfer functions with time, Geophysical Surveys, 4, 467-500.
LARSEN, J.C., 1989. Transfer functions: Smooth robust estimates by least squares and remote reference methods, Geophys. J. Int., 99, 655-663.
MYACHKIN, V., BRACE, W., SOBOLEV, G. AND DIETERICH, J., 1975. Two models of earthquake forerunners, Pure Appi. Geophys., 113, 169-181.
KOUSKOUNA, V., 1991. Factors which modify the attenuation of seismic intensities in central Greece and contribution to the mapping of earthquake hazard, Doctorate Thesis, Univ. of Athens (in Greek, w. extended abstract in English).
PARK, S.K., JOHNSTON, M.J.S., MADDEN, T.R., MORGAN, F.D. AND MORISSON, H.F., 1993. Electromagnetic precursors to earthquakes in the ULF band: a review of observations and mechanisms, Rev. Geophys., 31, 117-132.
PEDERSEN, L.B., 1982. The magnetotelluric impedance tensor - its random bias and errors, Geophysical Prospecting, 30, 188-210.
ROZLUSKI, C.P., AND YUKUTAKE, T, (1993). Preliminary analysis of magnetotelluric and seismic activity in the Cxubu district, Japan, Acta Geophys. Polonica, 41, 17-26.
SCHOLZ, C.H., 1990. The Mechanics of Earthquakes and Faulting, Cambridge University Press, 439pp.
SIMS, W.S., BOSTICK, EX., JR. AND SMITH, H.W., 1971. The estimation of magnetotelluric impedance tensor elements from measured datai, Geophysics, 36, 938-942.
SUTARNO, D. AND VOZOFF, K., 1991. Phase-smoothed robust M-estimation of magnetotelluric impedance functions, Geophysics, 56, 1999-2007.
SVETOV, B.S., KARINSKIJ, S.D., KUSKA, Y.I. AND ODINTSOV, V.l., 1997. Magnetotelluric monitoring of geodynamic processes, Annali di Geofìsica, 40, 435-444.
TZANIS, Α., 1988. Investigations on the properties and estimation of the Earth response operators from EM sounding data, PhD Thesis, Univ. of Edinburgh.
TZANIS, A. AND BEAMISH, D., 1989. A high resolution spectral study of audiomagnetotelluric data and noise interactions, Geophys. J., 97, 557-572.
TZANIS, Α., 1994. MAGNET: A magnetotelluric data editing system, suitable for earthquake prediction research. Proceedings, XXIV ESC Gen. Assembly, Athens, Greece, 1994, Vol. I, 129-141.
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