Abstract
In this study, geomagnetic data of the Lunping observatory from 1993 to 2000 are utilized for computing the amplitude variation of short-period geomagnetic total intensity data, using the complex demodulation method (CD method). In order to compare these time changes with seismicity, earthquakes that occurred within 150 km of Lunping, with magnitude ML greater than 3.0, are located. The total sum of those earthquakes, summed month by month, is correlated with the modulus. After removing seasonal effect, our results show that the modulus of periods 24, 12, and 8 hr reveals a notable change that seems to be related to the total sum of events within the whole study period. One possible precursor is found 6 months prior to the 1999 high seismicity. The modulus for the periods 24, 12, and 8 hr increased gradually from the beginning of 1999 to August 1999. After earthquake occurrence the modulus decreased again to a normal level. We propose that this notable increase might be related to a preparation process for this strong earthquake.
Highlights
Wilson (1922) first suggested the detection of stress-induced changes in local geomag-Terr
Because the Taiwan region is an active seismic zone, the geomagnetic data from 1993 - 2000 of Lunping Observatory (121°10’E, 25°00’N, in Taiwan, see Fig. 1) were used in order to get a possible relation between the time change in modulus of short-period magnetic variations and seismic energy released to search for a possible precursor to earthquake occurrences
In order to identify the predominant frequency of short-period variation of geomagnetic total intensity, spectral analyses have previously been applied to the continuous records
Summary
Wilson (1922) first suggested the detection of stress-induced changes in local geomag-. Research on the relation between time change of conductivity and seismic activity is an important subject in earthquake prediction. Jones and Price (1970), and Bailey and Edwards (1976) developed a model to simulate geomagnetic variations on the Earth’s surface caused by underground anomalous conductivity. Hautot (2005) developed a model to simulate geomagnetic variations on the Earth’s surface caused by underground anomalous conductivity. Because the Taiwan region is an active seismic zone, the geomagnetic data from 1993 - 2000 of Lunping Observatory (121°10’E, 25°00’N, in Taiwan, see Fig. 1) were used in order to get a possible relation between the time change in modulus of short-period magnetic variations and seismic energy released to search for a possible precursor to earthquake occurrences.
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