The Central Weather Bureau's Seismological Center has found that the intensity and frequency of aftershocks are decreasing following the magnitude 6.8 earthquake that struck on Sept. 18, and believes this earthquake is approaching the end.
The Central Weather Bureau's Seismological Center has been monitoring the aftershocks of the magnitude 6.8 earthquake that struck on Sept. 18. Its chart shows that the intensity and frequency of aftershocks are both decreasing. The center also said the earthquake wasn't caused by the Chishang Fault.
Chen Kuo-chang, Director, CWB Seismological Center: “We looked at down at the surface from atop geological structures at the epicenter or the location of the main epicenters. The bigger earthquakes didn't occur on Chishang Fault.”
The center says only small local earthquakes occurred after noon on Sept. 19. It believes the criteria for "seismic sequence gradually weakening" have been reached and the period of "concentrated earthquakes" will end soon. However, geologists say that if Taiwan enters into an "active earthquake period," the most worrying of the known 36 faults is Taipei's Shanjiao Fault. An earthquake with a magnitude of 6 or above could severely affect densely populated areas.
Chen Wen-shan, Professor, Department of Geosciences, NTU: “A third of Taiwan's population reside in the greater Taipei basin. There is an active fault nearby, the Shanjiao Fault. We have already classified this fault as a second level active fault.”
The center says it may take decades or even a century for a major earthquake to occur at Shanjiao Fault. The area may collapse if such a quake occurs, and seawater will flow in. However, there are no indications showing that the fault is moving and people shouldn't worry too much.
台東6.8強震過後兩天，氣象局地震測報中心持續監控，從每小時地震發生趨勢圖看起來，地震頻率與規模都明顯下降，而目前觀察這一起地震序列，測報中心再度強調，不是池上斷層所引起。
地震測報中心主任陳國昌說：「我們在地質構造上面，往地表下來看，震央或者主要震央群的位置，尤其是規模比較大的地震，確實不是發生在池上斷層的斷層面上。」
測報中心表示，19日午後一度只剩下小區域地震，原本有點擔心，不過後來又陸續有餘震，統計後，認為目前符合地震序列逐漸衰減標準，密集地震期應該快要結束。只是台灣若進入地震活躍期，地質學者示警，全台已知36條斷層中，位在台北的山腳斷層最令人擔心，萬一發生規模6以上地震，對人口稠密區影響會很嚴重。
台大地質系教授陳文山指出：「就雙北這個區域因為這邊來講，台灣三分之一的人口是住在整個大台北盆地裡面，很重要的是它旁邊有一條活動斷層山腳斷層，這個斷層我們已經把它列為第2類的這種活動斷層。」
對此，地震測報中心認為，山腳斷層若要發生大地震，可能要醞釀幾十年到百年的時間，一旦地震，大台北地區可能陷落，海水倒灌，但是目前完全沒有跡象顯示山腳斷層有移動趨勢，民眾不用太擔心。