11:00 AM - 1:00 PM
[MIS10-P03] Signal Identification of ULF electromagnetic time series data observed in Boso Peninsula using MSSA (Multi-channel Singular Spectrum Analysis) : Characteristics of global signal and residuals
Keywords:MT method, Multi-channel Singular Spectrum Analysis, Signal discrimination, Boso peninsula, ULF band
In 2014 ~ 2016, the MT (magnetotelluric) survey was conducted to estimate the subsurface electrical structure of Boso Peninsula, Japan. The MT method, which uses natural electromagnetic waves, estimates the electrical properties (resistivity structure) of the Earth's interior using the principle of electromagnetic induction generated in the Earth's interior in response to variations in the Earth's magnetic field of solar origin. Therefore, it is necessary to obtain the external magnetic field as a source with high accuracy. In places were greatly affected by artificial noise, such as the Boso Peninsula, it is necessary to reduce the effect of the noise in the source magnetic field by using the reference magnetic field of a quiet place. On the other hand, in short-term earthquake prediction studies, the ULF electromagnetic field variations have been shown to have precursor-like variations and statistically significant correlations with earthquakes of a certain magnitude or larger. Therefore, the ULF electromagnetic field variation is a promising parameter for short-term earthquake prediction. In general, there are strong solar-origin variations in the observed ULF electromagnetic field, and it is desirable to develop a method to remove them effectively. Thus, Multi-channel Singular Spectrum Analysis (MSSA) is introduced. MSSA can decompose C channels time series into (C×window length (WL)) principal components (PCs) by performing singular value decomposition of the trajectory matrix, which is created by shifting the C-channel time series data by one data which column is window length L. Therefore, MSSA is unique because it does not require basis functions and is helpful for natural electromagnetic field signals, which are non-stationary processes.
The following is an overview of this method for short-period signals (period of about 40 to 300 seconds).
1. Decompose 7ch data (Hx, Hy, Hz, Ex, Ey, Rx, and Ry, H, E, and R are measured magnetic field, electric fields, and reference magnetic field, respectively, and x, y, and z are south to north, west to east, and vertical downward component, respectively) with application MSSA to the raw data into (7 × WL) PCs.
2. Create the detrended time series by summing PCs that have short-period signals.
3. Decompose7ch detrended time series with application MSSA into (7 × WL) PCs.
4. Create MT signal by summation selecting high correlation PCs that have large amplitude.
The method can decompose the signal into the solar-origin global signal and other (residual) signals resulting from applying it to real Boso MT data and confirming its effectiveness. Specifically, for the magnetic field data, signals other than the global signal of about 1 nT could be extracted, and for the electric field data, the effect of induced currents could be reduced to some extent. As a result of checking the MT response function of the global signal estimated by this method using the Robust Remote Reference, a stable apparent resistivity is obtained, indicating that the estimated global signal is a plausible global signal among the signals discriminated by this method. Therefore, the present method is effective as a signal discrimination method to remove the global signal included in the ULF electromagnetic field fluctuation. In this presentation, we will present the properties of the global signal and the residual signal.
The following is an overview of this method for short-period signals (period of about 40 to 300 seconds).
1. Decompose 7ch data (Hx, Hy, Hz, Ex, Ey, Rx, and Ry, H, E, and R are measured magnetic field, electric fields, and reference magnetic field, respectively, and x, y, and z are south to north, west to east, and vertical downward component, respectively) with application MSSA to the raw data into (7 × WL) PCs.
2. Create the detrended time series by summing PCs that have short-period signals.
3. Decompose7ch detrended time series with application MSSA into (7 × WL) PCs.
4. Create MT signal by summation selecting high correlation PCs that have large amplitude.
The method can decompose the signal into the solar-origin global signal and other (residual) signals resulting from applying it to real Boso MT data and confirming its effectiveness. Specifically, for the magnetic field data, signals other than the global signal of about 1 nT could be extracted, and for the electric field data, the effect of induced currents could be reduced to some extent. As a result of checking the MT response function of the global signal estimated by this method using the Robust Remote Reference, a stable apparent resistivity is obtained, indicating that the estimated global signal is a plausible global signal among the signals discriminated by this method. Therefore, the present method is effective as a signal discrimination method to remove the global signal included in the ULF electromagnetic field fluctuation. In this presentation, we will present the properties of the global signal and the residual signal.