318 
PACIFIC SCIENCE, Vol. XIX, July 1965 
having a velocity of 8.10 km/sec, showed irreg- 
ularities in depth which they felt appeared to be 
best explained by faulting, the upthrown side 
of the fault giving an anomalous depth to the 
mantle of 7 km. This, however, could be re- 
lated equally as well to a buried volcanic rift 
or pipe filled with mantle-like material. The 
magnetic relations (Malahoff and Woollard, in 
a forthcoming issue of Pacific Science ) strongly 
suggest this as the true explanation. The reality 
of very shallow mantle material here is sub- 
stantiated by the Western Geophysical Com- 
pany measurements which yielded a depth of 
5-8 km in the adjacent area (Station A1-A2, 
Fig. 1). 
Another shelf section off the east end of 
Maui, examined by Shor and Pollard (Station 
27, Fig. 1), showed a depth of 15.5 km to the 
mantle, with a crust having the following 
velocity structure: Layer a, 2.68 km/sec; layer 
b, 3.65 km/sec; layer c, 4.96 km/sec; layer d, 
7.15 km/sec(?); Moho, 8.10 km/sec. 
Layer d was not actually defined, but prob- 
ably is present. The results obtained along the 
north coast of Hawaii by the U.S. Geological 
Survey, recording on land and shooting at sea 
(Eaton and Ryall, personal communication), 
suggest a depth to the mantle of 13.0 km in 
this area. This agrees with the analysis made 
by Eaton ( 1962 ) of earthquake travel time data 
on Hawaii, which suggested a depth of 13-15 
km to the mantle. 
The work of the Hawaii Institute of Geo- 
physics was concentrated in and around the 
island of Oahu and was concerned with both 
crustal structure and centers of volcanic erup- 
tion. Detailed explanation and results are given 
elsewhere in this issue (Furumoto et al., p. 
306; Adams and Furumoto, p. 296). In brief, 
these studies showed Moho-like velocities at 
very shallow depths (1-2 km) over primary 
volcanic pipes and at deeper depths (6 km) 
beneath the rift zones. The volcanic pipe meas- 
urement, showing a velocity greater than 7.0 
HAWAIIAN DEEP 
HAWAIIAN RIDGE 
HAWAIIAN ARCH 
Sea Level 
Bottom 
Fig 3. Composite crustal section across the Hawaiian Archipelago. Stations A and B after Furumoto et al. 
(p. 306 in this issue); stations 27, 22, 23, 30 after Shor and Pollard (1964). Velocity in km/sec. 
