Neotectonics, Paleoseismology, Paleoclimatology
Research Interests
Neotectonics deals with crustal deformation, earthquakes, and their underlying causes. In the 19th century, Charles Darwin recognized that the morphology of coral reefs records vertical crustal movements: barrier reefs form on subsiding coasts and marine terraces on uplifting coasts (Fig. 5). Those original principles can be applied on the scale of entire coral reefs that have uplifted or subsided hundreds of meters over millennia. Or, those same principles can be applied on the scale of individual coral colonies that have moved up or down only a few centimeters over decades. On time scales of thousands of years and longer, rates of vertical deformation are determined by isotopic dating of coral samples from measured heights above or below sea level. For the smaller motions of recent decades, the timing and amounts of vertical tectonism are determined by counting annual density growth bands in coral skeletons that were affected by vertical movements relative to sea level. By using both approaches, we can document the long-term accumulation as well as the increments of vertical deformation that integrate to produce the longer-term tectonic deformation.
In related studies, we use the Global Positioning System (GPS) to measure the horizontal plate motions that drive earthquakes and both horizontal and vertical deformation at the edges of SW Pacific tectonic plates (Figs. 6,7). Some of our results are startling: 24 cm/yr convergence rates of the Pacific plate at the northern Tonga arc and fragmentation of the New Hebrides arc where a large segment of the arc is being shoved eastward at rates of 4 - 8 cm/yr due to impingement of the subducting d'Entrecasteaux ridge against the forearc (See figures). In December 1997, we made the initial GPS measurements on marks emplaced in the South Shetland Islands of Antarctica and South America to study plate motions and deformation related to motion of the Scotia tectonic plate and adjacent platelets (Figs. 8, 9). We will return to remeasure the sites in order to determine any tectonic motion.
Fortunately for paleoclimate studies, chemical variations in the annual density bands in corals (similar to tree rings) precisely record sea surface temperatures(Figs. 2, 3, 4). The ratios of two isotopes of oxygen (18O/16O), Sr/Ca, Mg/Ca, and U/Ca are analyzed in a series of tiny samples taken along the growth direction in a coral skeleton (Fig. 4). Variations in these ratios reflect how temperatures have changed over time so precisely that the seasonal cycle is clear even where the seasonal variation is only 2° C. These records allow us to compare temperature records of various times in the past with the present.
Two paleoclimate programs conducted in parallel in the Western Pacific Warm Pool region (Figs. 1-5) aim to determine the temperature history of an area that is critical to the earth's climate and weather: One project is analyzing cores drilled from living corals to obtain a record of climate extending back several hundred years (Figs. 1, 2, 3). The second project is analyzing cores of fossil corals from deep drilling of uplifted reefs to obtain climate records for times back through the last glacial maximum about 22,000 years ago (Figs. 1, 5). We have collected live coral samples from New Caledonia, Vanuatu, and the Solomon Islands, and will drill live corals in Papua New Guinea in mid-1998. Our deep drilling has recovered glacial maximum corals and younger in Vanuatu and Papua New Guinea. The results from this research will help us to better understand past climate changes and their causes and how climate may change in the future.
Selected Publications Calmant, S., Pelletier, B., Pillet, R., RŽgnier, M., Lebellegard, P., Maillard, D., Taylor, F.W., Bevis, M., and Recy, J., 1997, Aseismic and co-seismic motions in GPS series related to the Ms 7.3 July 13, 1994, Malekula earthquake, central New Hebrides subduction zone, Geophys. Res. Letts., 24, 3077-3080. Crowley, T.J., Quinn, T.M., and Taylor, F.W., Henin, C., and Joannot, P., 1997, Evidence for a volcanic cooling signal in a 335 year coral record from New Caledonia, Paleoceanography 12, 633-639. Quinn, T.M., Taylor, F. W., Crowley, T.J., and Link, S.M., 1996, Evaluation of sampling resolution in coral stable isotope records: A case study using monthly stable isotope records from New Caledonia and Tarawa, Paleoceanography 11, 529-542. Taylor, F.W. et al. 1995, Geodetic measurements of convergence at the New Hebrides island arc indicate arc fragmentation due to an impinging aseismic ridge: Geology, 23, 1011-1014. Mann, P., Taylor, F.W., Edwards, R.L., and Ku, T.L., 1995, Actively evolving microplate formation by oblique collision and sideways motion along strike-slip faults: an example from the northeastern Caribbean plate margin: Tectonophysics, 246, 1-69. Chen, J.K., Taylor, F.W., Edwards, R.L., Cheng, H., and Burr, G.S., 1995, Recent emerged reef terraces of the Yenkahe resurgent block, Tanna, Vanuatu: Implications for volcanic, landslide, and tsunami hazards: J. Geology, 103, 577-590. Taylor, F. W., Quinn, T. M., Gallup, C. G., and Edwards, R. L., 1994, Quaternary plate convergence rates at the New Hebrides arc from the chronostratigraphy of Bougainville Guyot (Site 831), Proc. ODP, Sci. Results, 134, College Station, TX (Ocean Drilling Program) 47-57. Bevis, M., Taylor, F.W., Schutz, B.E., Recy, J., Isacks, B.L., Helu, S., Singh, R., Kendrick, E., Stowell, J., Taylor, B., and Calmant, S., 1995, Geodetic observations of convergence and back-arc spreading at the Tonga island arc, Nature, 374, 249-251. Taylor, F. W. 1992, Quaternary vertical tectonics of the central New Hebrides Arc, In Proc. Ocean Drilling Prog., Init. Repts, 134:, 33-42.
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