80 



distances. A minimum installation on an island should include a short period, 

 vertical component seismograph with peak response between l/5 and 1 second 

 and three matched, long period component seismographs. A particularly useful 

 instrument consists of a 10-20 second pendulum operating into a 90 second gal- 

 vanometer; the resulting period response minimizes the effect of microseisms 

 which occur with particularly large amplitudes on islands. Consideration should 

 be given to installation of such seismograph stations on key islands, the cost of 

 a single station being no more than that of maintaining an oceanographic vessel 

 for a few days. 



Existing Sofar installations have been used to monitor tectonic activity of 

 the sea floor as manifest by the occurrence of T-Phases (sounds originating in 

 earthquakes and propagated through the Sofar channel). Occasionally the com- 

 pressional and shear wave phases have been recorded. Much additional infor- 

 mation on sound propagation in the ocean and crustal structure of the ocean floor 

 could be obtained by Sofar detectors having frequency response down to 1 cycle 

 per second. Even with present Sofar installations, seismicity of the ocean floor 

 can be deternnined with a degree of precision previously not possible. Topo- 

 graphic reflections of T-Phases have been used to delineate unknown features 

 of sea floor topography. 



The processes of interaction between the atmosphere and the oceans which 

 produce microseisms, air-coupled tidal waves, tidal waves associated with 

 severe storms is a fertile field for investigation. Necessary instrumentation 

 includes seismographs described previously, a sensitive microbarovariograph 

 such as developed at Columbia University, tsunami recorders as developed at 

 Scripps Oceanographic Institution and standard tide gauges. A deep sea pres- 

 sure recorder sensitive to fluctuations with microseism periods is particularly 

 desirable. 



DISCUSSION: J. Lamar Worzel 



Since Dr. Raitt has described the methods and equipment for making 

 seismic measurements at sea, which are similar to those we have evolved on the 

 Atlantic side during the past 16 years, and Dr. Press has described the earth- 

 quake seismology studies and equipment in use at the Lamont Geological Obser- 

 vatory, my comments will be restricted to some of the other phases of geophys- 

 ics that bear on oceanography. 



Soundings are of importance in themselves for topographic studies, but 

 they are of great significance in conjunction with nearly every other geophysical 

 observation. For almost all purposes a recording of the soundings is vastly 

 superior to a visual or audible presentation. Until recently sounders available 

 in this country could only record on the to 2000 fathom scale. Fortunately, 

 many of us have learned to make a simple modification to these recorders so 

 that they will also record on the 2000 to 4000 fathom scale, so that they can now 

 be used over about 80% more of the oceanic areas. These modified sounders 

 have proved useful but a number of additions or changes are needed to make 

 them really adequate for taking proper sounding data for research purposes. 

 First of all, a controlled frequency for driving the timing motor is essential. 

 The sounding measurement is only as good as the timing measurement. Second- 

 ly, the pit log readings and time should be automatically put on the record at in- 

 tervals of about one-half hour. Many sounding records have been useless be- 

 cause they could not be related to the ships track. At present a 24 hour watch 

 must be employed for this purpose, and man hours at sea are especially expens- 

 ive. Thirdly, the resolution is not adequate for many problems. It should be 

 'possible to expand the scale so that full scale covers at least 200 fathoms at any 



