Kona Earthquake — MACDONALD AND WENTWORTH 
283 
the long dimension of their base oriented 
north-south. Therefore, the stones rock in an 
east-west direction much more easily than in 
any other, and, consequently, the most likely 
azimuth of fall is east-west. Furthermore, un- 
der sustained shaking, there is a tendency for 
all loose objects, including the soil cover, to 
work downslope to the west under the in- 
fluence of gravity. 
Rotation of Columns 
Imamura (1937: 96) has shown that the 
direction of rotation of short rectangular 
columns, such as many headstones are, can 
be useful in determining the direction of 
motion during an earthquake and, conse- 
quently, the approximate azimuth of the line 
toward the epicenter. If the earthquake mo- 
tion is parallel to the sides or to the diagonal 
(A — B, inset. Fig. 12) of the column, rotation 
probably will not occur. However, if the 
earthquake motion is in some intermediate 
direction, such as E — E' in Figure 12, a 
rocking of the column will be accompanied 
by a rotational tendency. A ground motion 
in the direction E' will cause the column to 
rock on the corner B. At the same time, the 
resultant of the force E' in the direction CD 
will tend to rotate the column about the 
corner B in a counterclockwise direction. 
Similarly, a motion in the direction E will 
tend to cause a counterclockwise rotation 
about corner A. Directions of earthquake 
motion lying in the unshaded octants of the 
diagram tend to cause counterclockwise ro- 
tation of the column, and directions of motion 
in the shaded octants tend to cause clockwise 
rotation. 
However, this law of rotation can be, and 
commonly is, upset by other conditions. In- 
homogeneity of the terrane may cause the 
principal motion to be, locally, in a direction 
other than the azimuth pointing directly to 
the epicenter. Also, excentric irregularities in 
the bottom of the monument or its under- 
lying base, or in the adhesion between the 
monument and its base, may result in rotation 
Fig. 12. Map of the central Kona area, showing the 
prevalent direction of rotation of monuments in ceme- 
teries. The cemeteries are; 1, Daifukuji, Honalo; 
2, Hongwanji Mission, Kealakekua; 3, Hongwanji 
Mission, Keei; 4, Kalahiki Japanese. At each cemetery 
the arrow indicates the prevalent direction of rotation. 
The boundaries of the octants containing the direction 
toward the epicenter are prolonged. The stippled area 
west of Captain Cook is that in which three or more 
of the octants overlap. The inset in the lower left is 
a diagram (after Imamura, 1937) of a horizontal 
cross section of a rectangular column, indicating the 
manner in which horizontal earthquake motion E — E' 
causes rotation of the column. 
around those irregularities independent of the 
rotation described above. 
During this study it soon became evident 
that, to be of value, the direction of rotation 
must be considered on a statistical basis. 
Thus, two columns only 10 feet apart in the 
Christ Church cemetery at Kealakekua were 
rotated approximately equal amounts in op- 
posite directions. However, by using the pre- 
vailing direction of rotation of a number of 
columns in a single area, more useful results 
were obtained. The average direction of ro- 
tation of monuments in each of six cemetery 
areas from 5 miles north to 10 miles south of 
Napoopoo were all consistent with an origin 
of the earthquake on or near the Kealakekua 
fault from 2.5 to 5 miles west of Napoopoo. 
