The Alaska Earthquake of 1964: Radiation of long-period surface waves and source mechanism

Abstract

The records of multiple Love and Rayleigh waves of the Alaska earthquake of 1964 were recovered from the 30-100 seismograph records at the WWSSN stations. The seismograms were equalized to a propagation distance of 9rr/2 (equivalent to G5 and R5 at --r/2). These seismograms were compared with synthetic seismograms for radiation pattern and amplitude to estimate various source parameters. The synthetic seismograms were computed from the normal mode solutions. One simple, yet plausible, source model was found. The nature of the fault is essentially that of a low-angle thrust faulting. The direction of rupture propagation does not coincide with the strike of the fault. This enables one to distinguish between the fault plane and the auxiliary plane. The source parameters determined are as follows: force system. double couple, reverse dip slip; fault plane, dip angle 20 , dip direction N 24W; rupture length. 600 km; rupture velocity, 3.5 km/sec towards S25W; moment, 7.5 X 10 dyne-em; average slip dislocation, 7 meters in N24W direction; stress drop, 28 bars: strain drop, 0.4 X 10-; released strain energy. 1.5 X 10 = eras. The moment and the width of the fault plane of this earthquake are mucL larger than those of any other earthquakes reported. The Prince William Sound, Alaska, earthquake of March 28, 1964, is one of the largest earthquakes in history. Despite its tectonic importance, however, considerable ambiguity still exists concerning the nature of the faulting. This is elearlv due to the lack of reliable seis-,, mologieal data, 1)artieularly S-wave and surfacewave data. The debate about the source meehanisn of this earthquake is well-known. Algerrnissen [1966] who used P-wave data, suggested that it is a predominantly normal fault along a steeply dipping plane. Press and Jackson [1965], and Press [1965], showed that the surface deformation can be explained in terms of a nearly vertical fault extending to a depth of 100-200 km. On the other hand, Plafker [1965] proposed on the basis of the tectonic deformalions associated with this earthquake that the source of this earthquake is a low-angle thrust fault. Savage ad Hastie [1966] advocated Plafker's interpretation. Stauder and Bottinger [1966]