Seismic Refraction Studies — FURUMOTO and Woollard 
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m). The estimated depth to the mantle is 9 
zb 0.4 km. This location corresponds roughly 
with Shor and Pollard’s Station 29, where they 
obtained what appeared to be anomalous crustal 
structure. Here their measurements indicate 
that the basal crustal layer has a velocity of 
6.97 km/sec, which is somewhat high for this 
layer, and that the layer’s thickness is only about 
half its normal value. However, the reanalysis 
of their data by the National Science Founda- 
tion, as shown in Figure 2, indicates much less 
abnormality in crustal thickness and much less 
variation in adjacent depths to the mantle. As 
seen in Figure 2 the average mantle depth is 
10 km. 
THE HAWAIIAN DEEP 
Shor and Pollard ( 1964) established one pro- 
file over the Hawaiian Deep (Station 22, Fig. 
1 ) and found that the mantle there was deeper 
than normal, 13 km. The overlying crust is 
composed of four layers having velocity values 
similar to those observed on the Arch. Although 
layer c is relatively thin, layer d is significantly 
thicker than elsewhere. An earlier measurement 
on the flank of the trench off the east coast of 
Hawaii by Raitt (1936) showed a crust com- 
posed of three layers with a depth to the man- 
tle of 12.4 km. 
THE HAWAIIAN RIDGE 
Shor and Pollard ( 1964) established one pro- 
file (Station 26, Fig. 1) on the shallow water 
shelf just north of the island of Maui that is of 
considerable interest. The Moho discontinuity, 
Fig. 2. A: NSF reworked crustal section across proposed mohole site. Stations 28, 29, 30 after Shor and 
Pollard (1964); stations Bl, FI, E2 from unpublished data of Western Geophysical Co. B: Published section 
(after Shor and Pollard, 1964) along northwest-southeast section on flank of Hawaiian Arch. 
