5:15 PM - 6:30 PM
[MIS08-P05] Numerical estimation of source current intensity causing ULF emission associated with earthquakes and correlation with the earthquake magnitude
Keywords:Ultra Low Frequency electromagnetic wave, Weighted Laguerre Polynomial FDTD, Seismo-electromagnetics
For decades, many papers reported that the Ultra Low Frequency (ULF) emission associated with earthquakes were observed by magnetometers installed at the Earth's surface. In this study, we have developed the numerical simulation of the ULF wave propagation in the lithosphere, by using the the weighted Laguerre polynomial finite-difference time-domain (WLP-FDTD) method. The numerical simulation allows us to estimate the source current intensity from observed electromagnetic fields in the ULF band. The correlation between magnitude of earthquakes and the estimated source current intensity is deduced from the numerical simulation.
The observed ULF anomaly depends on the time before the main shock of earthquakes, which are classified as follows: (1) Preseismic anomaly occurs several days before the main shock and (2) Near-seismic ULF bursts are observed around several hours around the main shock.
We adopt Loma Prieta earthquake as a standard because both the preseismic and the near-seismic effects are observed for this event, and because the observation was performed over wide range of frequency bands. The different current intensity spectra are deduced from the observed magnetic fields.
The source current intensity of other earthquakes, such as Spitak(1988), Guam(1993), Biak(1996), and so on, are analyzed, considering their observed time preceding the main shock, and the relative intensity of their source currents are identified.
From the above analyses, it is found that the relative intensity of source currents shows good correlation with the magnitude of EQs.
The observed ULF anomaly depends on the time before the main shock of earthquakes, which are classified as follows: (1) Preseismic anomaly occurs several days before the main shock and (2) Near-seismic ULF bursts are observed around several hours around the main shock.
We adopt Loma Prieta earthquake as a standard because both the preseismic and the near-seismic effects are observed for this event, and because the observation was performed over wide range of frequency bands. The different current intensity spectra are deduced from the observed magnetic fields.
The source current intensity of other earthquakes, such as Spitak(1988), Guam(1993), Biak(1996), and so on, are analyzed, considering their observed time preceding the main shock, and the relative intensity of their source currents are identified.
From the above analyses, it is found that the relative intensity of source currents shows good correlation with the magnitude of EQs.