APPLICATION OF MICROSEISMS TO FORECASTING 
underneath the wind system would challenge the re- 
sources of any but a governmental organization. 
Another type of microseisms is found in a band 
whose dominant period les in the neighborhood of two 
seconds (Fig. 6). Much less is known about these 
microseisms than about those of longer period. For 
some time the U. 8. Navy maintained a tripartite 
station near Corpus Christi, Texas (Fig. 7). A prelimi- 
nary study of the records was made by Jennemann. 
There were times when this type of microseisms dom- 
inated the records sufficiently to permit a determination 
of the direction of arrival at the station. They appeared 
to come from west of north. This means that these 
microseisms were coming not from the Gulf of Mexico 
Fig. 8.—Short-period microseisms. Wood-Anderson record, 
Florissant station. Time marks every half-minute. 
but from the continent. It was possible to correlate 
these microseisms tentatively with disturbed weather 
conditions existing to the northward of the station. At 
Fordham University a tripartite station has been set 
Fig. 9.—Three-tenth-second microseisms as recorded by a 
Sprengnether-Volk seismograph. 
up for the express purpose of studying these two-second 
microseisms on contract with the Office of Naval Re- 
search. Other preliminary studies have been made by 
Leet and Gutenberg. While it is too early to form a 
positive judgment, the results so far seem to hold 
promise for forecasting of conditions related to frontal 
disturbances. 
Preliminary studies are in progress on quite another 
type of microseisms of frequency of two to three cycles 
per second on a contract between Saint Louis Univer- 
sity and the Office of Naval Research (Fig. 8). They 
are being studied with a tripartite station equipped 
1315 
with three components at each corner of the triangle 
and separated by distances considerably less than a 
wave length with a view to determining how, if at all, 
they are related to weather conditions and whether 
they have forecasting value (Fig. 9). 
There are other bands of frequencies in the spectrum 
of microseisms but their possibilities for weather fore- 
casting have not been tested. 
Conclusions. There is a limit to what can be done with 
statistical studies of microseisms. The record of more 
than three quarters of a century of such studies shows 
what great care must be taken in their planning and 
in the interpretation of results. Quite contradictory 
conclusions have been drawn from parallel correlations. 
Much the same may be said of vectorial analysis of 
microseismic records. A very fruitful line of research 
has been opened up by the use of tripartite stations 
whose dimensions are less than one wave length. This 
method is independent of all assumptions except the 
successive arrival of an identical wave front at the 
three corners of the tripartite station. It gives a com- 
pletely independent determination of the direction and 
speed of wave travel. Cross bearings between two or 
more tripartite stations locate the source of the micro- 
seisms and thus furnish a clue for the investigation of 
the point of origin within the storm provided there 
are a sufficient number of tripartite stations available 
for the observation of one storm. Research on the 
origin of the microseisms or the mechanism by which 
they are produced is difficult but very necessary. The 
possibility of air oscillations acting as a hammer may 
be investigated by means of microbarographs disposed 
on small islands in the path of typhoons and hurri- 
canes. A similar system for the investigation of standing 
waves, or of the oscillations of a water vortex, would 
be much more difficult and costly. One might think of 
pressure gauges on a submarine cable laid in a path 
frequently followed by tropical storms and terminating 
at a recording station somewhere on land. 
REFERENCES 
I. The following papers contain extensive surveys of the 
literature on microseisms and their relation to the weather: 
1. GurensereG, B., ‘Untersuchungen iiber die Bodenunruhe 
mit Perioden von 4 bis 10 Secunden in Europa.” Veréff. 
ZentBur. int. seism. Ass., 106 SS., Strasbourg (1921). 
2. Macenwane, J. B., ‘‘Storms and the Origin of Microseisms.”’ 
Ann. Géophys., 2:281-289 (1946). 
3. Ramirez, J. E., ‘An Experimental Investigation of the 
Nature and Origin of Microseisms at St. Louis, Missouri.” 
Bull. seism. Soc. Amer., 30:35-84, 139-178 (1940). 
II. Important papers on hurricane and typhoon forecasting 
by means of microseisms are: 
4. Gitmore, M. H., ‘‘Microseisms and Ocean Storms.’’ Bull. 
seism. Soc. Amer., 36:89-119 (1946). 
5. —— and Husert, W. E., ‘“‘Microseisms and Pacifie Ty- 
phoons.”? Bull. seism. Soc. Amer., 38:195-228 (1948). 
