Groundwater level data minute value

Missing values in the dataset were denoted as 999999.0. After replacing 999999.0 with NAN, it was found that the Zhaogezhuang well had 4522 missing values, and the Yutian Ji 03 well had 2076 missing values. Linear interpolation was used to fill these missing values. The datasets after filling are shown in Figures. The red dashed line in the figure indicates the dates that separate the seismically Active (SA) and seismically inactive (non-SA) periods. The period on the left of the red dotted line represents the SA period, and the right part to before the earthquake represents the non-SA period. The black dashed line represents the moment when the earthquake occurred.