The Koolau Volcanic Plug — Adams and Furumoto 
299 
inches/sec Some of these records will be re- 
ferred to later, under the section on interpre- 
tation, as they are critical to the analysis. 
Important travel-time picks taken from the 
seismograms are listed in Table 2. Although 
the values are given to a millisecond, the data 
are not necessarily reliable to better than 10 
milliseconds. Because of the short spread-length 
(250 ft) necessary, apparent velocities are not 
given as they are not regarded as having any 
real significance. 
INTERPRETATION OF DATA 
The writers’ interpretation of the data is pre- 
sented in Figure 5 as a standard travel-time 
graph. The sample record locations are noted, 
and the reader should refer to them as needed 
while reading the remainder of this section on 
interpretation. The present interpretation is not 
the first derived, nor the one presented by 
Furumoto at the Eastern Section of the Seismo- 
logical Society of America (Furumoto, 1964). 
The change in interpretation resulted from sub- 
sequent additional shooting. 
The most prominent feature on the records 
and on the travel-time plot of the data is the 
strong, frequent occurrence of a second arrival 
about 0.450 sec after the initial motion. This 
has been interpreted as being a bubble pulse. 
The theoretical time-delay value that should bt 
obtained for a shot in a 50-ft depth of water, 
neglecting the bottom effects, can be obtained 
from the equation 
W 1 / 8 
T — 4 19 
“ ^ (ft 4 - 33 ) 5 / 6 
where FI is the depth in feet of the shot point, 
and W is the weight of explosive in pounds. 
From this calculation, we obtain 0.368 sec, 
which is considered to be in satisfactory agree- 
ment with the observed interval of 0.45 sec 
since bottom effects have been ignored. From 
the sample record corresponding to a distance 
of 379 km (Fig. 4), the similarity of the bub- 
ble pulse to the initial motion in both ampli- 
TABLE 1 
Time and Location of Shots for the Seismic Refraction Study* 
SHOT NO. * * 
DATE 
TIME 
WHITE TRUCK 
GREEN TRUCK 
Distance 
(km) 
Elevation 
(ft, ± 5 ft) 
Distance 
(km) 
Elevation 
(ft, ± 5 ft) 
4T601 
10/1/64 
0929 
7.99 
190 
not recorded 
4T602 
“ 
0932 
not recorded 
8.78 
280 
4T603 
“ 
1021 
5.94 
140 
9.62 
260 
4T604 
“ 
1103 
5.35 
0 
10.43 
40 
4T605 
“ 
1145 
4.55 
40 
11.70 
140 
4T606 
“ 
1230 
3.79 
20 
not recorded 
4T607 
“ 
1330 
7.27 
100 
13.51 
95 
4T901 
11/15/64 
1330 
12.70 
100 
not recorded 
4T902 
1 
1400 
not recorded 
18.10 
40 
4T903 
“ 
1450 
14.80 
200 
19.50 
90 
4T904 
“ 
1540 
15.20 
400 
18.90 
70 
* All charges were 50 lb at 50 ft deep in 50-ft depth of water (on bottom). 
** T = 1 for white truck, 2 for green truck. 
