Long-period Seismometers Research Articles

Report on some experimental long-period seismographs

ABSTRACT The unexpected usefulness in research of the Press-Ewing seismograph system (Press, Ewing and Lehner, 1958) has stimulated further efforts to obtain even higher seismograph sensitivity in the period range beyond 100 see. A major difficulty has been in maintaining pendulum stability at long periods. This paper describes a stable long-period seismometer and gives results from several seismograph systems incorporating long-period pendulums and galvanometers.

Crustal structure and surface-wave dispersion in Africa*

In 1953, through cooperation of the Bernard Price Geophysical Institute of the University of the Witwatersrand and the University of Natal, a Columbia University-type long-period seismometer (To = 15 sec., Tg = 75 sec.) was installed in the seismological observatory of the University of Natal at Pietermaritzburg, Union of South Africa. This instrument was well situated for receiving surface waves from the shock in northern Algeria of September 9, 1954, and the aftershock next day, which was of such intensity that its seismogram supplemented that of the original shock for the larger phases. The dispersion of the Rayleigh waves from these seismograms can be measured with greater precision than has been practicable heretofore for continents, because the path is longer (7,890 km.) than any which has been available for a long-period vertical instrument, and is remarkably free from obvious anomalies such as major mountain ranges. The scarcity of suitable seismograms for the study of Raleigh-wave dispersion along continental paths is due to the fact that suitably placed long-period vertical seismographs have not been available until recently.