Calibration Of The Seismometer At The Seismic Station

Seismometers are important equipments for seismological observation. Their performance parameters can affect the accuracy of the data recorded. And these parameters also play an important role in seismic waveform inversion and calculation of the earthquake's magnitude. But these parameters may vary as time elapses for lots of reasons. So a seismometer should be calibrated before and after being set on the seismic station time after time.This article is about the research work on seismometer calibration. It contains three parts: step calibration, sine calibration and compared method of measuring seismometer sensitivity. These three methods are used to get the transfer function of the seismometer.Step calibration is used to get the characteristic of the seismometer's transfer function in the low frequency part. The former algorithm for processing step calibration data can not work without people operating the computer. And the results have a large deviation when we calibrate the same seismometer time after time. Therefore, the new algorithm improves the automatism of data processing. Computer can deal with everything and no people have to be involved in. It also improves the stability of the calibration results. The deviation of the results is very small. We calibrate a seismometer with a type of BBVS-60 time after time. And the largest relative deviation is 0.03%.Sine calibration is used to get the characteristic of the seismometer's transfer function through the whole band. The former algorithm for processing sine calibration data can not work without people operating the computer, either. The new algorithm also improves the automatism of data processing. It can automatically pick up the waveform to be measured. So no people have to do this boring job again. It can also recover the waveform that is distorted. So the results become more accurate.This article also introduces a compared method of measuring seismometer sensitivity. It analyzes the relation between the stability of the results and the signal-to-noise ratio. So it can tell us how the noise affects the stability of the results. The first chapter introduces the background and the meaning of this research work. The second chapter introduces the current methods to calibrate the seismometers, the problems with these methods and some new ideas to solve these problems. The third chapter introduces how to implement these ideas with C codes to make software. The forth chapter introduces the results of experiments with these new methods. The fifth chapter is the summery and the discussion.The algorithms of step calibration and sine calibration are used in the calibration software which is part of the seismic observatory network project of China. The compared method of measuring seismometer sensitivity is used in the seismic observatory lab now.