8 



Symposium on Microseisms 



Banerji might be cases in point. I do not pass 

 judgment on these theories here, but merely 

 wish to indicate that there is a proximity fac- 

 tor in their historical development. 



As Father Macelwane has pointed out, 

 there are three general theories for the origin 

 of microseisms (1) local meterological or geo- 

 logical conditions, (2) meterological gradients 

 over continental areas, and (3) meterological 

 conditions at sea. There seems to be almost 

 universal agreement that the source is meteor- 

 ological. 



Two problems have been considered at 

 length in this connection ; first, what meteor- 

 ological conditions supply the energy to the 

 ground, and secondly, how is the energy trans- 

 ferred. The source of the energy is usually 

 sought in "active" meteorological situations 

 such as fronts or low pressure areas. Water 

 bodies are frequently considered as a coupling 

 medium to pass the energy into the ground. As 

 mentioned by Father Macelwane, a long list 

 of seismologists and meteorologists have for- 

 mulated theories or portions of theories, but 

 no one of them seems to explain all of the mi- 

 croseisms all of the time. Some of them fool 

 some of the microseisms some of the time, and 

 one might even say that some of them fool 

 some of the microseisms all of the time. 



I think a fact that is sometimes forgotten 

 in trying to assess the various theories is that 

 all of them must, of mathematical necessity, 

 deal with rather idealized cases that may fit a 

 given piece of geography fairly well, but will 

 fail rather badly to match in other parts of 

 the world. In this connection, I think it is an 

 historical fact, and so worth mentioning in this 

 historical discussion, that after any seismolo- 

 gist has tended the same station for a few 



decades he begins to know his own microseisms 

 fairly well and, if he has become interested in 

 them, he is likely to be able to relate his mi- 

 croseisms rather consistently to certain weath- 

 er conditions, but he still may not be able to 

 formulate a theory that will stand up for all 

 the other stations in the world. 



In studying both the nature and origin of 

 microseisms, seismologists have made consider- 

 able use of large masses of data. Some of this 

 has been done out of necessity in an attempt to 

 extract useful microseism data from seismo- 

 grams run for the routine recording of earth- 

 quakes. In other cases it has been in an at- 

 tempt to obtain correlations between microseis- 

 mic activity and weather conditions. To me, a 

 very interesting transition has taken place in 

 the past ten or fifteen years with more empha- 

 sis now on the study of individual microseismic 

 storms and, in many cases, with the aid of 

 seismographs specifically designed and oper- 

 ated for recording them. To some this might 

 seem like a tree-to-tree examination before we 

 have seen the forest, but having been unable 

 for so long to get a clear picture of the forest, 

 it may well be the proper method. 



Discussion from the Floor 



Bath. Dr. Gutenberg emphasized the parallel 

 behavior of microseisms in northern Europe. 

 In a comparison of microseisms at Uppsala, 

 Bergen, and Copenhagen, this result was con- 

 firmed as far as the broad outlines are con- 

 cerned, but there were significant deviations 

 in detail. These could be explained by the 

 hypothesis of an origin along a line source, but 

 were not in accord with the hypothesis of a 

 point source. 



