Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006geoji.165..835l&link_type=abstract
Geophysical Journal International, Volume 165, Issue 46, pp. 835-849.
Astronomy and Astrophysics
Astronomy
8
1946 Aleutian Earthquake, Slow Earthquakes, Tsunami Earthquakes
Scientific paper
We present a re-evaluation of the seismological properties of the Aleutian `tsunami earthquake' of 1946 April 1, characterized by a deceptively low conventional magnitude (7.4) in view of its catastrophic tsunami, both in the near and far fields. Relocation of 40 aftershocks show that the fault zone extends a minimum of 181 km along the Aleutian trench, in a geometry requiring a bilateral rupture from the original nucleation at the epicentre. Their spatial and temporal distribution are typical of the aftershock patterns of a large earthquake, and rule out the model of a landslide source exclusive of a dislocation. The analysis of the spectra of mantle waves favours the model of a large seismic source, with a static moment of 8.5 × 1028 dyn-cm, making the event one of the ten largest earthquakes ever recorded (hence the destructive tsunami in the far field), and of a slow bilateral rupture, at an average velocity of only 1.12 km s-1, hence the destructive interference in all azimuths for all but the longest mantle waves. The exceptionally slow character of the earthquake is confirmed by a deficiency in radiated seismic energy expressed by the lowest value measured to date of the energy-to-moment ratio. The earthquake appears as an end member in the family of `tsunami earthquakes', resulting from the combination of anomalous, but not unprecedented, parameters, such as low stress drop and rupture velocity.
López Alberto M.
Okal Emile A.
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