Errors in travel times measured on paper seismograms |
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| Authors: | C Wright S J Harris |
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| Institution: | Division of seismology and Geothermal Studies, Earth Physics Branch, Department of Energy, Mines and Resources, Ottawa, Ontario K1A 0Y3, Canada |
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| Abstract: | Summary. The investigation of temporal variations in seismic velocities sometimes requires the use of paper seismograms. For this reason, an investigation of all of the sources of random error in measuring travel times on seismograms has been undertaken using a mathematical model devised by Jeffreys and some additional results derived using elementary statistics. The most important contribution to the total error is often the error due to linear interpolation between minute markers or other time marks on the seismogram, which can be as high as 0.13 s on smoked paper seismograms recorded at 120 mm min?1, and as high as 0.076 s on short-period seismograms of the Canadian network recorded at 60 mm min?1. For 32 explosions at short distances (< 50 km) recorded on smoked paper, however, the median value of the total error in the travel times was 0.016 s. Interpolation errors are generally insignificant for travel-time studies of teleseisms, but may be important in some special studies of local earthquakes and explosions. The theoretical results are useful, not only in seismology, but wherever the accurate timing of an event relative to two reference time markers on a chart recorder is required. |
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