Seismicity characteristics before the 2003 Chengkung, Taiwan, earthquake

We investigate the variations in seismicity pattern in the Taiwan region before the 2003 Chengkung, Taiwan, earthquake (Mw = 6.8) by calculating the standard normal deviate of the Z-values and b-values from the Gutenberg–Richter relation. The Mogi donut-shaped variations in the seismicity can be identified in the Z-value map surrounding the Chengkung earthquake source region. Noticeable decreases in the b-values have also been found around the mainshock region before the Chengkung event. The relatively low-seismicity rate and the decrease in the b-values may be the precursory phenomena associated with the quiescence in overall seismicity and the activation of moderate-sized events occurred around the mainshock region before the Chengkung event.