Crustal structure in the Society and Tuamotu Islands, French Polynesia

• Published in: Geophysical Journal International
• Main Authors: Talandier, Jacques, Okal, Emile A.
• Format: Text
• Language: English
• Published: Oxford University Press 1987
• Subjects: Articles; Iceland
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/88/3/499; https://doi.org/10.1111/j.1365-246X.1987.tb01644.x

We present seismic investigations of the crustal structure of Tahiti (Society Islands), Rangiroa (Tuamotu Islands), and neighbouring areas. Records from a series of 96 explosions at the short-period stations of the Polynesian Seismic Network form a seismic refraction dataset from which we recover the crustal structures. The crust in the vicinity of Tahiti has the classic structure of 70 Myr-old ocean floor, and features an 8.8 km-thick crust (below sea floor) with 3 7.64–8.25 km s−1 jump at the Mohorovičić (Moho) discontinuity. On the other hand, the Tuamotu plateau shows a very thick crust, reaching 31 km below sea floor, with a 6.83-8.10 km s−1 jump at the Moho. In addition, Rangiroa atoll itself features a 2 km-thick layer of slow material (3.3 km s−1) which we interpret as limestone; comparable structures have been reported at Enewetak and Bikini. We further use the short-period seismic arrays on Rangiroa and Tahiti to recover the slowness vectors, and, hence, the dispersion characteristics, of Rayleigh waves in the 15–40 s period range recorded from teleseismic events. Rayleigh dispersion under the Society Islands is compatible with published oceanic models of adequate age. We also use long-period records in the 20–90 s range for the path Rangiroa-Hao orientated along the Tuamotu plateau. The Rangiroa-Hao dispersion is slower than previously determined in neighbouring oceanic areas, and compatible with a crust 22–30 km thick under the Tuamotu plateau. Dispersion under Rangiroa is even slower, and requires a thicker (∼35 km) crust. Any crust of standard thickness can be ruled out, as it leads to unacceptably low (< 3 km s−1) crustal S -velocities. These results are comparable to structures published for the Iceland-Færœ and Walvis Ridges, and confirm that the Tuamotus were formed on-ridge, in agreement with their very weak geoid signature.