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Background seismicity before and after the MS7.8 Tangshan earthquake in 1976: Is its aftershock sequence still continuing?
  • Yue Liu,
  • Jiancang Zhuang,
  • Changsheng Jiang
Yue Liu
Institute of Earthquake Forecasting, CEA

Corresponding Author:[email protected]

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Jiancang Zhuang
Institute of Statistical Mathematics
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Changsheng Jiang
China Earthquake Administration
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Abstract

The aftershock zone of the 1976 7.8 Tangshan earthquake, China, remains seismically active, experiencing moderate events such as the December 5, 2019,4.5 Fengnan event. It is still debated whether aftershock sequences following large earthquakes in low seismicity continental regions can persist for several centuries. To understand the current stage of the Tangshan aftershock sequence, we analyse the sequence record and separate background seismicity from the triggering effect using a finite-source epidemic-type aftershock sequence (FS-ETAS) model. Our results show that the background rate notably decreases after the mainshock. The estimated probability that the most recent 4.5 earthquake (December 5, 2019, Fengnan District, Tangshan) is a background event is 63.8%. This indicates that the contemporary seismicity in the Tangshan aftershock zone can be characterised as a transition from aftershock activity to background seismicity. Although the aftershock sequence is still active in the Tangshan region, it is largely overridden by background seismicity.