New equipment and processing for magnetotelluric remote reference observations

Abstract

Robust estimates of magnetotelluric and geomagnetic response functions are determined using the coherency and expected uniformity of the magnetic source field as quality criteria. The method is applied on data sets of three simultaneously recording sites. For the data acquisition we used a new generation of geophysical equipment (S.P.A.M. MkIII), which comprises novel concepts of parallel computing and networked, digital data transmission. The data‐processing results show that the amount of noise on the horizontal components of the magnetic field varies considerably in time, between sites and over the frequency range. The removal of such contaminated data beforehand is essential for most data‐processing schemes, as the magnetic channels are usually assumed to be free of noise. The standard remote reference method is aimed at reducing bias in response function estimates. However, this does not necessarily improve their precision as our results clearly show. With our method, on the other hand, we can filter out source field irregularities, thereby providing suitable working conditions for the robust algorithm, and eventually obtain considerably improved results. Contrary to previous concepts, we suggest rejecting as much data as feasible in order to concentrate on the remaining parts of high‐quality observations.

Correlation between deep fluids, tremor and creep along the central San Andreas fault

“…Standard robust processing techniques in frequency domain [33][34][35] produced high-quality transfer functions for periods longer than 5 s, but often failed to separate the shorter-period MT signal from strong periodic noise with a fundamental period of ~5.1 s that was correlated over all channels and over wide areas. Noise levels were particularly high near buried gas pipelines suggesting cathodic protection currents commonly imposed on pipelines as the source of this noise.…”

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

“…Short-period automatic magnetotelluric systems (S.P.A.M. MKIII; Ritter et al 1998) and Earth data loggers were used to record data in the frequency range from 1 kHz to 1 mHz. Induction coil magnetometers (Metronix MFS05/6) were used to record three orthogonal magnetic field components; the horizontal electric fields were measured with non-polarisable Ag/AgCl electrodes of the Geophysical Instrument Pool Potsdam.…”

“…Data acquisition was accomplished with two independent teams, working at the same time in Jordan and Israel which allowed us to record with up to 30 instruments simultaneously. This provided great flexibility for remote reference processing with many possible station combinations which improved data quality considerably, particularly in the period band 1-10 s. All data were processed with the EMERALD package (Ritter et al 1998;Weckmann et al 2005;Krings 2007) to calculate MT impedance tensors and vertical magnetic transfer functions (VTFs). Remote reference data processing (Egbert 1997) is also used to improve the data quality at few noisy sites.…”

Comparison of electrical conductivity structures and 2D magnetic modelling along two profiles crossing the Beattie Magnetic Anomaly, South Africa

“…Along the eastern profile MT4, centred around Jansenville, (Figure 2b) we acquired 5-component MT data at 31 broad band stations in a period range from 0.001 s to 1000 s using GPS synchronized S.P.A.M. MkIII (Ritter et al, 1998) and CASTLE broadband instruments. Metronix MFS05/06 induction coil magnetometers and non-polarizable Ag/AgCl telluric electrodes were used to record natural electric and magnetic field variations.…”

“…Metronix MFS05/06 induction coil magnetometers and non-polarizable Ag/AgCl telluric electrodes were used to record natural electric and magnetic field variations. The data were processed according to Ritter et al (1998) and Weckmann et al (2005). In Figure 3, we show apparent resistivities and phase diagrams, which are derived from the MT impedance tensor, and induction vector plots.…”