26 



Symposium on Microseisms 



report of 6 November. At that time the storm 

 quickly developed into a typhoon with winds in- 

 creasing from 55 to 100 knots in the next 24 

 hours. A simultaneous sharp increase in mi- 

 croseisms occurred at all three stations but 

 was greater at Okinawa because the storm was 

 nearer that station. This increase occurred 

 at all stations long before storm swells from 

 the intensified winds around the storm could 

 possibly build up and travel the great distances 

 to the three stations. 



Typhoon Patricia in October 1949 was a 

 small tropical storm with only 35 knots of wind 

 when it passed Guam on the 20th. This storm 

 also rapidly developed into a typhoon with 90 

 knot winds, starting about 2400 GCT on 23 

 October. The microseisms increased rapidly 

 at all three stations when the storm was about 

 740 miles from each station. The maximum 

 increase was greater and a day later at Okin- 

 awa because the storm was approaching that 

 station and crossing increasingly larger lines 

 of equal microseismic amplitude. Here again it 

 was physically impossible for the intensified 

 swells to reach the three land masses and ac- 

 count for the rapid increase of microseisms on 

 24 October. 



Almost one month later typhoon Allyn 

 passed south of Guam on 17 November and the 

 seismograph registered microseisms of 240 

 mm in double trace amplitude. The micro- 

 seisms fell rapidly to 83 mm as the storm moved 

 westward and the winds decreased to 80 knots 

 by 1200 GCT on 20 November. This typhoon 

 suddenly intensified when it was located by 

 aircraft at a midway point about 740 miles 

 from Guam, Okinawa, and Manila. The si- 

 multaneous sharp increase in microseismic am- 

 plitude at the three stations, lower right of 

 Figure 7, again occurred before storm gener- 

 ated swells could build up after the storm in- 

 tensified and travel the necessary 740 miles. 



The rapid intensification of the three ty- 

 phoons was identical with the sharp increase 

 of microseismic amplitude at each station. It 

 may be pointed out here that these three ty- 

 phoons generated very large microseisms at 

 three stations 740 miles away in three different 

 directions ; yet a very similar storm was with- 

 in 600 miles of Cherry Point for three days 

 without causing the slightest increase in am- 

 plitude. Each storm was moving away from 

 Guam when the microseisms suddenly in- 

 creased in amplitude; i.e. the storms were 



US. NAVY MICRO SEI SMIC RESEARCH PROJECT 



Figure 6. Forecasting movement of storm by microseismic amplitude at Bermuda 



