22 



Symposium on Microseisms 



are generated," and throw considerable light 

 on its solution. 



Hurricane Microseisms — The first method at- 

 tempted was to determine if tropical storms 

 could be located within operational accuracy 

 by microseismic cross-bearings from two or 

 more tripartite stations. It is possible, with 

 microseisms from a tripartite station such as 

 shown in Figure 1, to calculate accurately the 

 direction they are traveling when passing over 

 a station. If microseisms from tropical storms 

 were always propagated outward in concentric 

 circles it would be very simple to determine 

 their exact origin and the location of the storm 

 by means of cross-bearing from two or more 

 tripartite stations. But accumulated data 

 show that microseisms do not always travel in 

 straight lines, often resulting in large errors 

 in tracking tropical storms, Figure 2. The 

 tripartite cross-bearings proved unsatisfactory 

 because the bearings pointed to the area of a 

 storm only when it was traversing regions 

 that lay in specific directions from a microseis- 

 mic station, such as south and west of Guan- 

 tanamo Bay, Cuba. It was therefore necessary 



to seek a new and different technique for solv- 

 ing the problem : one that would be completely 

 independent of the method of generation and 

 propagation of microseisms. Facts derived 

 from microseismic records over a period of 

 many years led the way to the development of 

 a new and important technique for detecting 

 and forecasting the movement and intensity of 

 hurricanes and typhoons. This new method 

 consists only of using observed microseismic 

 data with little or no regard to the physical 

 processes involved in their generation. The 

 amplitude and micro-ratio charts were first 

 constructed in 1950 and recent results indi- 

 cate that detection and tracking of severe trop- 

 ical disturbances is well within the necessary 

 operational accuracy. 



The tracks of six hurricanes are drawn in 

 Figure 3, and along each track are listed the 

 corresponding amplitude of recorded micro- 

 seisms in mm on top of line and the intensity 

 of the storm in knots on the bottom. The storm 

 intensities and corresponding microseismic am- 

 plitudes are very consistent throughout the 

 map, especially at points where the tracks cross 



BEARINGS CALCULATED FROM STORM MICROSEISMS 

 1800 Z 19 AUGUST 1950 



w- 



35* ERROR 



.083* 



61* ERROR 



MIAMI 



WHITING FIELD 



EACH LINE REPRESENTS THE BEARING OF AN 

 INDIVIDUAL WAVE, EACH GROUP OF LINES 

 A BUILDUP 



Figure 2. Microseismic directions obtained at Tripartite Station 



