. Compendium of meteorology. Meteorology. APPLICATION OF MICROSEISMS TO FORECASTING 1313 this type of microseisms to vibrations caused by the beating of surf on a rocky coast. The fourth theory held that group microseisms are produced in some manner by storm centers at sea and are propagated through the earth's crust to the continents. This theory was espoused by Klotz, Shaw, Lee, Banerji, and especially by Gherzi who suggested as the mechanism a "pumping" or vertical oscillation of the air vortex in a typhoon, hurricane, or other closed circulation over deep water, thus explaining w
. Compendium of meteorology. Meteorology. APPLICATION OF MICROSEISMS TO FORECASTING 1313 this type of microseisms to vibrations caused by the beating of surf on a rocky coast. The fourth theory held that group microseisms are produced in some manner by storm centers at sea and are propagated through the earth's crust to the continents. This theory was espoused by Klotz, Shaw, Lee, Banerji, and especially by Gherzi who suggested as the mechanism a "pumping" or vertical oscillation of the air vortex in a typhoon, hurricane, or other closed circulation over deep water, thus explaining why microseisms cease to be produced when the stonn center reaches land. Many investigators have attempted to decide be- tween these various theories by correlating large amplitudes chronologically •ndth other phenomena, but without any decisive results. Several, for example, Linke, Lee, Archer, Neumann, and Leet, have attempted to determine the direction of arrival of the waves, on the assumption that they are true Rayleigh waves, by determining the relative amphtudes of the three components on the records of a single station. This method also proved inadequate. A direct attack on the problem of direction of the propagation of the microseisms without any assumption was made independently by Ramirez at Saint Louis and by Trommsdorf at Gottingen in 1938 by means of the observations of the time intervals between the successive arrivals of the same wave at the three corners of a tripartite station, using these time intervals be- tween successive arrivals to calculate both the direction of propagation and the speed of travel. Suitable equations for this purpose were developed by Krug, Gilmore, Macelwane, and Schuyler who also devised a nomogram. The following equations are valid for any tripartite station. Let A, B, and C (Fig. 2) be the known angles of the triangle named counterclockwise; and let a, b, and c represent the respective opposite sides of kno^vn length. Assume that a
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