[MIS04-P12] MT Survey and its preliminary result at Boso Peninsula, Japan (3)
To remove noises from MT data, we attempted remote reference method that is conventional MT method in frequency domain. Hereupon, MT impedance at southern Boso area is improved to a certain degree. In other hand, the one at northern Boso are is not very improved. Therefore, we attempted MSSA (Multi-channel Singular Spectrum Analysis) for MT data in time domain to improve MT impedance. We performed SVD (Singular Value Decomposition) of original time series in MSSA, and reconstructed time series by using the principal components that indicate relatively high correlation in horizontal geomagnetic field between observation site and remote reference site. Then, unexpected MT impedance seen after remote reference method is tend to be restrained. It supposedly indicates that preprocessing MT data in time domain is effective and promise.
We calculated underground resistivity structure from southwest to northeast by using long period sites’ data, there is low resistivity region (0.1 – 10 ohm-m) around 1 - 2 km depth. This region possibly indicates fluid in sediment layers overlying large amount of surface at Boso area. There is low resistivity region (0.1 – 10 ohm-m) under about 3 – 10 km depth at southwest site, which possibly indicates ultramafic rock or accretionary prism pushed up by subducting seamount.