Create schema electronic gps to monitor earthquakes.
Many records of earthquakes exist now for which the instrument response is unknown. Calibration is essential for accurate measurement of earthquake magnitude, in particular, for measurements used for statistical studies and statistical comparisons of earthquakes in different areas. Even if the seismometer constants are known, the lack of computers in Richter’s time would have made corrections to ground motion a difficult computational process. The Richter magnitude scale eliminated the uncertainty in instrument response by limiting magnitude computations to earthquakes observed on one particular instrument, the Wood-Anderson torsion seismometer, and by specifying it s gain, free period and damping. With digital data and today’s desktop computers, calibration is not so difficult a task. This objective of this chapter is to explain how a home made seismometer may be calibrated.
An important component in sharing data from a seismic station is maintaining a calibrated system. Calibration is essential if data from a seismometer are to be used for research, such as for computing magnitudes and for comparing the signals generated by the earthquake source. If everyone used identical instruments and did not change any of the settings or constants, records could be compared directly, but computation of the ground motion would still require calibration. Standard calibration signals consisting of a known acceleration function and the relevant constants were marked on each record. This calibration pulse and the associated constants contain all the information needed to define the seismometer s response. Today, digital recording and the advent of low-cost seismometers that can record directly on personal computers has started another revolution in seismology, making possible more detailed images of the Earth’s structure. Such instruments could take seismic recording out of the research laboratory and make seismic data widely available through open exchange over the Internet. For home-based systems to contribute to research, they will also need to be calibrated.
The format of the header data files is usually transparent to the user. In practice, the format depends on the recording system and the analysis system built for the seismometer. Problems can develop when attempting to convert data from one system to another, because the calibration information may be incomplete or expressed in different formats. However, when the calibration facts are complete, techniques borrowed from signal processing theory can be used to generate seismograms that look like seismograms recorded on any system. Only the noise and sampling rate for data recorded on the originating system limit the conversion of the appearance of a seismogram in one recording system to another.
The techniques used to calibrate new digital systems are the same as those used to calibrate simple systems of any age and design. A known force is applied to the seismometer mass and the response is measured. The simplest force is the gravitational attraction of a small test weight that is lifted off the seismometer mass. This is referred to as a weight lift test. The same effect occurs when the test weight is placed on the mass, but this is unreliable because variations in momentum of the test weight when it hits the seismometer mass cause variations in the signal amplitude. Alternatively, a force may be applied by an electromagnetic force, that is by a motor. The motor typically consists of a calibration coil placed near a magnetic portion of the seismometer and the force applied to the seismometer is proportional to the current sent through the coil. The signal generated when the small test weight is removed, or when a current is sent through the calibration coil, is the calibration pulse. The calibration pulse contains the information needed to compute the frequency response of the seismometer. The rest of the information, the gain, can be obtained either from a careful measurement of the mass and mechanical behavior of the seismometer, or by a comparison of two seismometers sensing the same signal. In this chapter the technique for computing the instrument response using a weight lift is given first, and the simpler comparison technique is given second.
create an electronic gps to monitor earthquakes
