VELOCITY OF ELASTIC WAVES IN GRANITE 
By L. Don LrEEet anp W. Maurice Ewina 
HARVARD SEISMOGRAPH STATION AND LEHIGH UNIVERSITY 
(Received January 14, 1932) 
«ABSTRACT 
The velocity of elastic waves in granite was determined at Quincy and Rockport, 
Massachusetts, and Westerly, Rhode Island. The waves measured were generated by 
dynamite explosions. They were recorded by portable seismographs at distances rang- 
ing from fifty feet to four thousand six hundred feet. The observed velocities for longi- 
tudinal waves were: 
Quincy...... 16,260+ 70 ft./sec. or 4.96+0.02 km/sec.* 
Westerly. ...16,400+120 ft./sec. or 5.00 +0.04 km/sec. 
Rockport....16,670+ 40 ft./sec. or 5.08 +0.01 km/sec. 
Average..... 16,530+ 90 ft./sec. or 5.04+0.03 km/sec. 
A three-component seismograph, used only at Quincy, recorded transverse waves, 
the velocity of which was 8150+90 ft/sec., or 2.48+0.03 km/sec: From the two 
velocities determined at Quincy and the density of specimens taken from the shooting 
location, 2.65 grams/cm!, values for the bulk modulus, k, compressibility, 8, rigidity,u, 
Poisson's Ratio, s and Young’s Modulus E, were obtained as follows: k=44+1 X10" 
dynes/cm?; 6=2.28+0.05X10-2 cm?/dynes; »=16.3+0.4X10!° dynes/cm?; 
o =0.333 40.005; E=43 +1 X10! dynes/cm?. The form of the time-distance curves, 
straight lines through the origin, indicated that the waves did not penetrate deeply. 
Accordingly, the values obtained are for pressures of only a few atmospheres. The 
bearings of these results upon earlier investigations of the elastic constants of granite 
are discussed. Although direct comparisons between laboratory and field results 
are not conclusive, they indicate that the Adams and Williamson curve is incorrect 
for pressures below 2,000 megabars, and that there is no marked difference between 
dynamically and statically determined compressibilities of granite. 
I. Location 
ETERMINATIONS of the velocity of elastic waves in granite were 
made in three well-known granite quarrying areas, Quincy and Rock- 
port, Massachusetts, and Westerly, Rhode Island. Within each area a zone 
of practically no topographic irregularity was selected. The continuity of the 
granite in each zone was proven by numerous quarries and outcrops. Maps 
of these zones appear in Fig. 1. The observing stations and shot locations 
shown there were mapped by plane table on a scale of 300 feet to the inch. 
II. MetHop 
The elastic waves were produced by the explosion of charges of dynamite 
which were always placed in contact with the granite. Sixty percent quarry 
gelatine was used. Their arrival at a point on the granite at any desired dis- 
tance from the explosion was recorded by a seismograph placed at that point. 
* The + values given in this paper are probable errors. 
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