L’un des premiers sismographes a été développé par le Dr L. Don Leet de l’université de Harvard. Il fut utilisé en juillet 1945 pour étudier les oscillations de la croûte terrestre, lors du premier essai atomique.



One of the first analog seismographs was the Leet seismograph developed by Dr. L. Don Leet of Harvard University and shown This seismograph utilized a three-component geophone. A compartment held a roll of light sensitive paper. A needle for each channel vibrated from movement causing voltage changes. A mirror attached to a shaft connected to the needle reflected a bright light back to light sensitive paper. This created a displacement waveform on the advancing paper. A notable use of the Leet seismograph was during the first atomic test blast, Alamorgordo, New Mexico, 1945.

Five Leet three-component strong motion mechanical seismographs recorded the TRINITY motions at five different ranges and azimuths (Ref. 1). The seismogram from one of these stations (8.2 km north of TRINITY) was discussed in a 1946 paper (Ref. 2) and has been the subject of some controversy since the name Hydrodynamic wave was given to one unusual appearing section of the seismogram because the particle motion was prograde and elliptical, resembling that of a water wave (Fig. 2). In a 1962 paper (Ref. 3), it was suggested that the Hydrodynamic or H wave emanated only from explosions and might be useful in discriminating between the seismic waves produced by nuclear explosions and those resulting from naturally occurring earthquakes.



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