Characteristics of coseismic water level changes at Tangshan well for the Wenchuan MS_8.0 earthquake and its larger aftershocks

摘要

Coseismic water level changes which may have been induced by the Wenchuan MS8.0 earthquake and its 15 larger aftershocks(MS≥5.4) have been observed at Tangshan well.We analyze the correlation between coseismic parameters(maximum amplitude, duration, coseismic step and the time when the coseismic reach its maximum amplitude) and earth-quake parameters(magnitude, well-epicenter distance and depth), and then compare the time when the coseismic oscillation reaches its maximum amplitude with the seismogram from Douhe seismic station which is about 16.3 km away from Tangshan well.The analysis indicates that magnitude is the main factor influencing the induced coseismic water level changes, and that the well-epicenter distance and depth have less influence.MS magnitude has the strongest correlation with the co-seismic water level changes comparing to MW and ML magnitudes.There exists strong correlation between the maximum amplitude, step size and the oscillation duration.The water level oscillation and step are both caused by dynamic strain sourcing from seismic waves.Most of the times when the oscillations reach their maximum amplitudes are between S and Rayleigh waves.The coseismic water level changes are due to the co-effect of seismic waves and hydro-geological environments.