Interdependent quality control of collocated seismometer and accelerometer

A new method for the interdependent quality control (IQC) of a collocated seismometer and accelerometer is presented. It is useful for seismic stations, where broadband seismometer and strong-motion accelerometer are installed side by side. The number of this type of seismic stations is growing and so is the number of activities associated with the quality control. With the IQC, the collocated seismometer and accelerometer are controlled with the single procedure. It is based on the calculation of transformation matrix which numerically transforms the detection of a seismic signal of accelerometer to the space of detection of seismometer. This matrix contains a lot of information; among them were also the “orientation misalignment,” “sensitivity corrections,” and two indicators, from which the quality of data and the error of systems can be identified. The procedure uses seismic signals, detected by both systems. The self-noise of commercial accelerometers is usually higher than the average seismic noise; therefore, a moderate shaking of the ground is needed. This type of shaking can come from stronger regional earthquakes. In this article, a mathematical description of the procedure is introduced first; then, a few examples with real data are presented. A critical error was discovered with the help of this algorithm. It cannot be identified by testing signals, injected from an acquisition unit into the STS-2 seismometer. There is also an example of serious orientation misalignment between a seismometer and an accelerometer.