Abstract
Abstract The geomagnetic data of the Lunping Geomagnetic Observatory from 1988 to 2000 are utilized for computing daily geomagnetic transfer functions. The method of analysis is based on the power spectrum analysis developed by Everett and Hyndman. Monthly means are statistically obtained from these daily values of transfer functions. In order to compare these time changes with seismic activity (seismicity), the earthquakes occurring within 150 km from Lunping, with a magnitude M L greater than 4.0, are located. The related energy releases by those earthquakes, summed month by month, are correlated to the transfer functions. After removing the seasonal effect, we find that the time changes of magnitude of A u and B u (real parts of the transfer function) for frequencies of 2, 3, 4, and 6 cycles/hour seem to be strongly related to the energy release within the whole study period. Two significant precursors were found from the A and B values, 40 and 20 months before high seismicities, respectively.
Highlights
The conductivity of rocks is an important physical property which can be measured in the Earth
After removing the seasonal effect, we find that the time changes of magnitude of Au and Bu for frequencies of 2, 3, 4, and 6 cycles/hour seem to be strongly related to the energy release within the whole study period
Fujita (1990) found that the time variations in the monthly means of transfer functions are generally correlated among several observatories separately located, he concluded that the transfer functions are not adequate for shortterm earthquake prediction
Summary
The conductivity of rocks is an important physical property which can be measured in the Earth. Detecting the time change of transfer functions in short-period geomagnetic variations is an available method for monitoring the possible conductivity change in the crust or upper mantle. Some results regarding the time changes in transfer functions related to seismic activities have been reported by many authors during the last 20 years (Yanagihara, 1972; Yanagihara and Nagano, 1976; Xu et al, 1978; Rikitake, 1979; Niblett and Honkura, 1980; Shiraki, 1980; Chen, 1981; Chen and Fung, 1985, 1990, 1993; Gong, 1985; Fujita, 1990; Fujiwara and Toh, 1996). The geomagnetic data of Lunping Observatory (121◦ 10 E, 25◦ 00 N, in Taiwan, see Fig. 1) were used to search for a possible relation between the time change in transfer functions and earthquake occurrences because the Taiwan region is an active seismic zone. The raw data of the three components of geomagnetic variations were inspected and the geomagnetic short-period disturbances that have durations from 1024 to 4096 min (a)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
