28 



Symposium on Microseisms 



of storms and a recording seismograph. Nev- 

 ertheless it has been accomplished. Figure 8 

 shows an example of early storm detection. 

 The left side of the picture shows a portion of 

 the Caribbean just south of the west end of 

 Cuba, where the synoptic situation was not 

 conclusive as to the existence of a hurricane. 

 On the basis of an abrupt increase in micro- 

 seismic amplitude at Swan Island, a weather 

 plane was sent to investigate the area and the 

 situation shown in the right side of the pic- 

 ture was found to exist. This storm developed 

 rapidly and the intensification was immediate- 

 ly registered by the Swan Island seismograph 

 before any other sort of warning, such as in- 

 creasing swells or winds, reached Cuba, Swan 

 Island, or Yucatan. Property located seismo- 

 graphs would always give similar advance 

 warnings. In other words, it would be im- 

 possible for a storm to develop into a danger- 

 ous hurricane or for a fully developed hurri- 

 cane to approach a seismograph station with- 

 out giving sufficient warning to permit the 

 carrying out of all necessary precautions. The 

 seismograph at Guam often detects typhoons 



long before they are otherwise known. More- 

 over, a microseismic station in an area which 

 is homogeneous with that over which the 

 storms are traveling, can observe immediately, 

 from an increase or decrease in the amplitude 

 of the microseisms, any changes in the inten- 

 sity of the storms being tracked. Tropical 

 storm How in October 1951 was first deter- 

 mined to be a hurricane by the rapid increase 

 of microseisms during the night at Miami and 

 Jacksonville. Even when the synoptic reports 

 indicated that the storm was apparently filling, 

 the seismographs at Jacksonville and Cherry 

 Point showed that it continued to be attended 

 by 90 knot winds. This feature of storm de- 

 tection, that of giving a good estimate of storm 

 intensity, is an especially valuable aid in the 

 forecasting of hurricanes, especially at night 

 and at other times when there are no direct 

 observation by planes and when no ship re- 

 ports are available. 



The Micro-Ratio Charts — The microseismic am- 

 plitude charts are primarily used for detection 

 of storms, and after the storms are located, to 



Figure 8. Early detection of hurricane by microseismic amplitude increase at Swan 



Is 1 and 



