The history of timing, size and rupture geometry of past earthquakes provide the most direct basis on which to determine past seismic periodicity and to predict future activity. However, seismographically recorded earthquake histories are too short for this approach. Some coasts in Vanuatu, Southwest Pacific, uplift during each interplate thrust zone earthquake, and the uplift raises shallow-living coral colonies above sea level and kills them. The characteristic coral morphology of these events, combined with recently refined thermal ionization mass spectrometric 230th dating makes it possible to date these events precisely and thereby determine the coseismic uplift history. This project, collaborative with EAR89-04987, will collect a suite of corals showing uplift-kill morphology along several segments of central Vanuatu and conduct 230th age dating. Results will allow calculation of coseismic uplift periodicity and since Vanuatu is considered a weakly coupled subduction zone, results will also help in calculating the proportion of aseismic vs. seismic slip and determine at what point in the earthquake cycle the aseismic slip occurs.
