HR: 1340h
AN: S23A-0289    [Abstracts]
TI: The Pattern of Fractal Dimension Change before Large Earthquakes in Taiwan
AU: * Chen, M
EM: mcchen@utig.ig.utexas.edu
AF: Department of Geological Sciences, The University of Texas at Austin, Geol Science Dept 1 University Station C1100 , Austin,, TX 78712 United States
AU: * Chen, M
EM: mcchen@utig.ig.utexas.edu
AF: Institute for Geophysics, The University of Texas at Austin,, 4412 Spicewood Springs Rd. #600, Austin, TX 78712 United States
AU: Wu, Y
EM: drymwu@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No.1 Roosevelt Rd, Sec 4th, Taipei, 100 Taiwan
AU: Frohlich, C
EM: cliff@utig.ig.utexas.edu
AF: Institute for Geophysics, The University of Texas at Austin,, 4412 Spicewood Springs Rd. #600, Austin, TX 78712 United States
AB: We investigate the fractal dimension D, of the seven largest earthquakes (M$_{L}$ $>=$ 6.4) in the ten year period of 1994 $\sim$ 2003 located in the Taiwan area, including the 1999 M$_{L}$ = 7.3 Chi-Chi earthquake. Most showed significant increase in D before mainshocks. The D value of earthquake events without large foreshock events (M$_{L}$ $>=$ 5.2) had an obvious increase in the month preceding the mainshocks, and then fell abruptly due to clustered aftershock sequences. The pattern of D value change is slightly different for an earthquake event preceded by a large foreshock (M$_{L}$ $>=$ 5.2); here D increased earlier, about 3 or 4 months before the mainshock. The D value then declined slowly until the month with big foreshocks. Under the influence of foreshock sequences, the D value had a sharp drop before the mainshock event. This fractal analysis proved that a similar change of D value preceding large earthquakes is not due to the network processing procedure. The rise or fall of D value is not controlled by differences in efficiency of hypocenter relocation before and after large earthquake events. Even foreshocks with relatively smaller magnitudes produce an increased D value. This fact suggests that before large earthquakes, the spatial distribution of background seismicity becomes sparser then before, causing the increase of D value. Any period of steady rise in D value in the Taiwan area implies a higher potential for large earthquakes in the next few months.
DE: 7230 Seismicity and seismotectonics
DE: 3250 Fractals and multifractals
SC: Seismology [S]
MN: 2004 AGU Fall Meeting