The deficientTwaves of tsunami earthquakes

Abstract

SUMMARY We develop an algorithm quantifying the energy flux of T phases recorded at island stations following major teleseismic events, which we further scale by the seismic moment M0 of the earthquake, to define a T-phase efficiency, Γ. We apply this concept to a set of six recognized tsunami earthquakes, which generated tsunamis larger than expected from their conventional seismic waves. Through comparison with nearby reference events the T waves of which were recorded at the same sites, we find that the tsunami earthquakes exhibit a deficiency in Γ ranging from 1.5 to 2.5 orders of magnitude. This result settles a 50 yr old controversy on the possible correlation between T-wave generation and tsunami genesis. The deficient character of the T waves from tsunami earthquakes readily supports the proposed model of an exceedingly slow rupture velocity for this class of events, and the close examination of T wave trains supports the concept of a jerky rupture in at least two cases. The computation of Γ is straightforward in real time, and could become a valuable contribution to real-time tsunami warning in the far field.