Kuang Jung Chen

Phase correction in separating P‐ and S‐waves in elastic data

Two‐dimensional elastic data containing reflected P‐waves and converted S‐wave generated by a P‐source may be separated using dilatation and rotation calculation (Sun, 1999). The algorithm is a combination of elastic full wavefield extrapolation (Sun and McMechan, 1986; Chang and McMechan, 1987, 1994) and wave‐type separation using dilatation (divergence) and rotation (curl) calculations (Dellinger and Etgen, 1990). It includes (1) downward extrapolating the (multicomponent) elastic data in an elastic velocity model using the elastic wave equation, (2) calculating the dilatation to represent pure P‐waves and calculating the rotation to represent pure S‐waves at some depth, and (3) upward extrapolating the dilatation in a P‐velocity model and upward extrapolating the rotation in an S‐velocity model, using the acoustic wave equation for each.

A search for a correlation between time change in transfer functions and seismic energy release in northern Taiwan

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 ML 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 Au and Bu (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.