activation of splay faults rupturing in sedimentary prisms (Sanriku, Japan; Kurils),5 or rupture propagating in a jagged mode along poorly coupled interfaces in sediment-starved environments (Nicaragua, Peru).6 In turn, this raises the questions whether any subduction zone can be the site of a tsunami earthquake, and conversely whether the documented occurrence of such events (most often comparatively small in the magnitude 7.5 range) precludes the occurrence of mega-earthquakes as would be suggested by the available historical record in Nicaragua or Java. Despite active research efforts in this domain, we presently have no firm answers in this respect.

REFERENCES

1. Abe, K., K. Abe, Y. Tsuji, F. Imamura, H. Katao, I. Yohihisa, K. Satake, J. Bourgeois, E. Noguera, and F. Estrada. 1993. Field survey of the Nicaragua earthquake and tsunami of September 2, 1992. Bulletin of the Earthquake Research Institute University of Tokyo 68(1):23-70.

2. Polet, J. and H. Kanamori. 2000. Shallow subduction zone earthquakes and their tsunamigenic potential. Geophysical Journal International 142(3):684-702.

3. Newman, A.V. and E.A. Okal. 1998. Teleseismic estimates of radiated seismic energy: The E/M0 discriminant for tsunami earthquakes. Journal of Geophysical Research 103(B11):26885-26898.

4. Weinstein, S.A. and E.A. Okal. 2005. The mantle wave magnitude Mm and the slowness parameter THETA: Five years of real-time use in the context of tsunami warning. Bulletin of the Seismological Society of America 95(3):779-799.

5. Tanioka, Y., L.J. Ruff, and K. Satake. 1997. What controls the lateral variation of large earthquake occurrence along the Japan trench?Island Arc 6(3):261-266.

6. Fukao, Y. 1979. Tsunami earthquakes and subduction processes near deep-sea trenches. Journal of Geophysical Research 84(B5):2303-2314.



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