Kona Earthquake — MACDONALD AND WENTWORTH 
273 
Altogether, from the time it was put back 
in operation until the end of August, the 
Kealakekua seismograph recorded 494 earth- 
quakes, and until the end of September 965 
earthquakes. Nearly all of these are regarded 
as aftershocks of the big earthquake of 
August 21. Most were too small and shallow- 
seated to be recorded at the other stations, 
hence their foci could not be closely located. 
It appears certain, however, that most orig- 
inated along the Kealakekua fault at the 
northern edge of the Kealakekua embayment. 
EFFECTS OF THE EARTHQUAKE 
Description ofTerrane 
The epicentral area lies on the western 
slope of Mauna Loa, a few miles south of 
the surficial boundary between Mauna Loa 
and Hualalai Volcanoes. It is transversed from 
north to south at altitudes of 1,000 to 1,300 
feet above sea level by the main highway, 
from which roads lead to the shore at Na- 
poopoo, Honaunau, Hookena, and Milolii 
(Fig. 1). In the vicinity of the highway the 
average slope of the land surface is about 
10 degrees, which is several degrees steeper 
than the average for Mauna Loa slopes in 
general. Above an altitude of 5,000 feet the 
average slope decreases to about 7 degrees. 
The steepness of the lower part of the slope 
is believed to result from an ancient fault 
scarp deeply buried by more recent lava 
flows. 
In the area within 6 miles south of Na- 
poopoo the steep zone is narrower and more 
sharply defined than farther south, and west 
of it the slope again flattens toward the sea. 
Three miles east-southeast of Napoopoo the 
steep zone turns sharply northwestward and 
becomes even steeper, taking on the unmis- 
takable characteristics of a fault scarp mantled 
by more recent lava flows. This scarp forms 
the northern boundary of Kealakekua Bay, 
and there the older lava beds in the scarp are 
not mantled by latet flows. 
The steep seaward slope results in a dis- 
tinct asymmetry of the terrane, which asym- 
metry of necessity extends to nearly all 
structures on the terrane. Buildings rest on 
foundations that are high on one side and 
low on the other. Roads in many places rest 
on a cut on one side and fill on the other, 
or on a fill which is shallow on one side and 
deep on the other. Stone walls parallel to the 
coast have one sloping side shorter than the 
other. All of this results in a lesser degree 
of stability than in structures built on level 
terranes, and in a favored direction of un- 
stability. Partly because of the higher foun- 
dations and deeper fills on the seaward side 
and partly because of the continuous effect 
of gravity, structures tended to move down- 
hill during the earthquake regardless of the 
direction of the actual shaking. This effect 
must be considered in using the direction of 
displacement of objects as a means of locating 
the epicenter. 
Rock Slides 
Many small rock slides in highway cuts 
were caused by the earthquake. Most of them 
came from cuts on the inland side of the 
highway, probably largely because the cuts 
were higher on that side. Most of the slides 
were small, bringing down blocks less than 
2 feet across. These caused little damage and 
were easily removed. A few larger slides 
brought down large blocks weighing several 
tons, the removal of which required the use 
of bulldozers or other heavy equipment. The 
large slide farthest from the epicenter oc- 
curred at a high roadcut just west of Honua- 
po, 40 miles from the epicenter. Small slides 
and rock falls in road cuts extended all the 
way to Kilauea Caldera, 44 miles from the 
epicenter. Many small rock avalanches took 
place in Halemaumau Crater during and for 
several days after the earthquake. 
A large part of the damage to road cuts 
did not, strictly speaking, result from sliding 
of the materials. Most of it was merely a 
fraying of the banks by the rolling down of 
loose or semiloose material. Few of the high- 
way cuts exceeded 5 feet in height, and few 
