A Study of the Source Mechanism of the Alaska Earthquake and 
Tsunami of March 27, 1964 
Part II. Analysis of Rayleigh Wave 1 
Augustine S. Furumoto 
ABSTRACT: The source mechanism of the Alaska earthquake of March 27, 1964 
has been investigated by analyzing the Rayleigh wave recorded on the strain seis- 
mograph at Kipapa Station, Hawaii. The parameters that give the best fit to the 
observed data are: rupture length of 800 km, rupture velocity of 3 km/sec, and 
direction of rupture line of S30°W. The results of this analysis compare favorably 
with field data of elevation changes, with distribution of epicenters of aftershocks, 
and with the area of generation of the tsunami as obtained from sea-wave refraction 
diagrams. 
The United States-Japan Cooperative Field 
Survey of the Alaska Earthquake of March 27, 
1964 (Berg et al., in preparation) resulted in 
an estimate of the length and size of the rupture 
zone of the earthquake. Corroboration for these 
results was sought from seismic data. Toksoz 
et al. (1965) have published a source mecha- 
nism analysis using surface wave data. Their 
results are as follows: rupture velocity, 3.0 km/ 
sec; rupture length, 600 km; azimuth of rup- 
ture, S50°W from the epicenter. These results, 
however, are at variance with the field survey 
data. 
Shortly after the field survey, an attempt at 
source mechanism analysis by surface wave 
methods was made by using the record of the 
strain seismograph at Kipapa Station, Hawaii. 
The results of this analysis are presented here 
because they are in somewhat better accord with 
field survey data. 
This study was supported by funds from the 
National Science Foundation under Grants GP- 
2257 and GP-5111. 
METHOD OF ANALYSIS 
The analysis of source mechanism based on 
earthquake surface waves was developed by Ben- 
Menahem (1961). According to this method, 
if the Rayleigh wave is used the ratio of the 
amplitude spectrum of R 3 to the amplitude 
spectrum of R 2 can be related to directivity 
function D(f), 
D(f) = 
(v + cos 0 
( C 
\v~ cose 
( 1 ) 
where C is the phase velocity of the curve at 
frequency f, V is the velocity of rupture propa- 
gation, B is the length of the rupture, and 6 is 
the angle which the rupture line makes with 
the great circle path through the epicenter and 
observing station. A method using the Love 
1 Hawaii Institute of Geophysics Contribution No. 
185. Manuscript received June 22, 1966. 
wave has also been developed, but the present 
study utilizes the Rayleigh wave only. 
Ben-Menahem and Toksoz have applied the 
method of surface wave analysis to the study of 
the source mechanism for the Mongolian earth- 
quake of 1958 (Ben-Menahem and Toksoz, 
1962) , the Alaska earthquake of 1958 (Ben- 
Menahem and Toksoz, 1963^), and the Kam- 
chatka earthquake of 1952 (Ben-Menahem and 
311 
