Downdip tensional earthquakes beneath the Tonga arc: a double seismic zone ?

Kawakatsu, H.
J. Geophys. Res., 91, 6432-6440, 1986.

Abstract

Seismicity at intermediate depth beneath the Tonga-Kermadec arc is studied to determine the possible existence of a double seismic zone. Newly available focal mechanism solutions show that there are several down-dip tensional events beneath the Tonga arc, where the dominance of down-dip compression has been known. Furthermore, these down-dip tensional events are consistently located below and seaward of down-dip compressional events and appear to constitute a double seismic zone. The result of a relative relocation technique applied to these earthquakes also supports this observation. The existence of a double seismic zone in Tonga would suggest that double seismic zones, located at intermediate depth in subducting slabs, are more common than previously thought.