Coseismic and Quaternary vertical tectonic movements, Santo and Malekula Islands, New Hebrides Island Arc

Abstract

Emerged late Quaternary coral reefs show that on the lo3 to IO5 years time scale the western part of the central New Hebrides arc is divided into several semi-independent uplifted blocks. The blocks are separated by tectonic discontinuities, oriented approximately normal to the arc trend, across which tilt directions or uplift change suddenly. However, none of the blocks is tilted in a direction normal to the arc trend of N20"W. Two of the discontinuities, across Santo and Malekula Islands, occur near the places where ridges on the north and south flanks of the d'Entrecasteaux fracture zone, a major bathymetric feature on the underthrusting plate, intersect the arc. Each of these tectonic discontinuities approximately coincides with one end of the rupture zone inferred .for a shallow thrust-type earthquake sequence in 1965. The discontinuity across Santo also nearly coincides with the south end of the rupture zone inferred for another earthquake sequence in [1973][1974]

Seismic recurrence intervals and timing of aseismic subduction inferred from emerged corals and reefs of the Central Vanuatu (New Hebrides) Frontal Arc

“…When earthquake sequence includes more than one event, the moment values in the [Minster and Jordan, 1978] does not include the expected contribution from back arc spreading on the Fiji plateau [e.g., Falvey, 1975]. Boundaries between frontal arc segments are taken from Taylor et al [1980Taylor et al [ , 1987 and are supported by independent studies including Ebel [1980]. Chatelain et al [1986] proposed the additional boundary limiting the southern side of the SM (south Malekula) block.…”

“…Previous work, including more than 70 isotopic ages for Holocene samples, documents emergence of Holocene fringing reefs and uplift rates on Santo and Malekula during the past 6000-7000 years [Launay and Recy, 1972 ;Neef and Veeh, 1977;Taylor et al, 1980;Jouannic et al, 1980Jouannic et al, , 1982Gilpin, 1982;Bloom, 1980;Bloom and Yonekura, 1985;Urmos, 1985]. By determining the maximum height of the Holocene terrace, we estimate the average rate R at which emergence occurred.…”

“…The hierarch~ of precision from most to least precise is (1) coral growth bands, (2) 230 Th by mass spectrometry, (3) 14 C, and (4) 0 Th by alpba spectrometry. Age data are from Taylor et al [1980Taylor et al [ , 1981Taylor et al [ , 1987, Jouannic et al [1980], Bloom and Yonekura [1985], Edwardr et al [1986,1988], and several unpublished 14 C ages. Mean late Holocene uplift rates for each area are represeented by the sloping lines.…”

Coastal staircase sequences reflecting sea-level oscillations and tectonic uplift during the Quaternary and Neogene

“…There, the mechanisms are less clear as they result from the combination of co-seismic uplift (e.g. as in Vanuatu, see Taylor et al, 1980), tectonic shortening of the upper plate, crustal underplating, and magmatic addition. Overall, these mechanisms all combine to promote uplift on the various plate margins.…”

“…Yet, identifications of MIS 3 paleocoasts often remain ambiguous. Out of all purported MIS 3 sites, highstands remain only from fast uplifting coastlines, as found on the Mahia Peninsula in New Zealand (Berryman, 1992(Berryman, , 1993a, or islands of the Vanuatu archipelago such as Santo Taylor et al, 1980;Jouannic et al, 1982;Taylor et al, 1982Taylor et al, , 1987Galipaud and Pineda, 1998), Malekula (Cabioch and Ayliffe, 2001) and Torres (Taylor et al, 1985), and Kikai island in the Ryukyus archipelago (Konishi et al, 1970;Ikeya and Ohmura, 1983;Ikeda et al, 1991;Ota and Omura, 1992;Sasaki et al, 2004;Maejima et al, 2005;Inagaki and Omura, 2006).…”