Articles | Volume 372
Proc. IAHS, 372, 101–104, 2015
https://doi.org/10.5194/piahs-372-101-2015
Proc. IAHS, 372, 101–104, 2015
https://doi.org/10.5194/piahs-372-101-2015

  12 Nov 2015

12 Nov 2015

Frequency anomaly of groundwater level before major earthquakes in Taiwan

T.-K. Yeh1, C.-H. Chen2, C.-H. Wang3, and S. Wen2 T.-K. Yeh et al.
  • 1National Taipei University, New Taipei, Taiwan
  • 2National Chung Cheng University, Chiayi, Taiwan
  • 3Academia Sinica, Taipei, Taiwan

Abstract. Anomalous decreases on water levels were observed in 78 % of wells in central Taiwan about 250 days before the Chi-Chi earthquake whose magnitude is 7.6 on 20 September 1999. Variations in groundwater levels measured on anomalous wells from 1 August 1997 to 19 September 1999, were transferred into the frequency domain to unveil frequency characteristics. Analytical results show that amplitudes at the frequency band between 0.02 and 0.04 day−1 generally maintained at low stage and were apparently enhanced a few weeks before the Chi-Chi earthquake. Variations of amplitude at this particular frequency band were further examined along with other Taiwan earthquakes whose magnitude is larger than 6 from 1 August 1997 to 31 December 2009. Features of the enhanced amplitudes at the frequency band are consistently observed prior to the other two earthquakes during the 12.5-year study period. Result confirms that abnormal rise and fall changes in groundwater level yield an agreement with forward and backward surface displacements around epicenter prior to the Chi-Chi earthquake.