Preliminary look at the MT & CSEM data

In the first figure below, I have plotted the processed MT response functions from three sites on the southern line of receiver deployments. Site s03 was located on the incoming plate, s14 was near the trench axis, and s33 was on the Hikurangi fore-arc. The data show the apparent resistivity and phase of the transverse-magnetic (TM) and transverse-electric (TE) modes. The TM and TE modes represent the two geomagnetic field polarizations that induce electric currents parallel and perpendicular to the line of receivers, respectively. They have sensitivity to different electrical conductivity structures, which will become important when the data are modeled using geophysical inversion methods. Details aside, what is most important here is that the data look smooth, have reasonable error bars, and therefore are fairly high quality. The data shown here are generally representative of the quality of the processed MT for the southern line of sites (have yet to process the MT data from the other profiles).

Processed MT data from southern profile sites s03 (on the incoming Pacific plate far from the trench axis), s14 (on the incoming Pacific plate near the trench axis), and s33 (on the Hikurangi fore-arc slope).

In this next example, the top panel in the figure shows two repetitions of the 4-sec long waveform that is continuously transmitted by SUESI during deep-tow operations. The bottom panel shows a real snippet of the time-series from site s14, when the transmitter was within range of the receiver. There is a clear resemblance between the transmitted and recorded waveforms, but the recordings contain much more structure. This is because the transmitted waveform is being distorted by the electrical structure of the seafloor, which is what we hope to disentangle from the data with inversion modeling.

Top panel: the raw SUESI transmitted waveform. Bottom panel: waveform recordings at site s14. Channels 1&2 are the magnetic fields recorded with induction coil magnetometers. Channels 3&4 are the electric fields recorded with silver-silver chloride electrodes.