From August 1983 to March 1984, the RSP recorded numerous sequences of low-frequency volcanic tremor and two seismic swarms associated with submarine eruptions at Teahitia. On 20-21 December, 300 very small earthquakes were recorded. From 3 March-15 April 1984, approximately 9,000 earthquakes were recorded, accompanied by low- and high-frequency spasmodic and harmonic tremor (figure 3).

Figure 3. Seismicity near Teahitia during 3 March-17 April 1984. Number of recorded earthquakes at 12-hour intervals (solid line), duration of high-frequency tremor in minutes (bars), and cumulative seismic energy release (dashed line, log scale). Courtesy of J. Talandier.

Geological Summary. Teahitia is a submarine volcano in the Society Islands whose summit reaches to within ~1,700 m of the surface, 40 km NE of the SE tip of Tahiti Island. Several seismic swarms in the 1980s included volcanic tremor that may have resulted from submarine eruptions (Talandier and Opal, 1984). Rocks dredged in 1986 "exploded" when they reached the surface, suggesting recent lava extrusion that had not yet had time to equilibrate with pressure and temperature conditions on the submerged flanks of the edifice. Two hydrothermal fields each about 400 x 1,000 m exhibiting low-temperature hydrothermal venting were discovered on the flanks during submersible dives in 1986 and 1989.

Information Contacts: J.M. Talandier, Lab. de Géophysique, Tahiti.