Australia Cretaceous Climate and Tectonics: International Ocean Discovery Program Expedition 369

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The seismic reflection method is the primary tool for investigating the buried structure of the Earth. The method is the same as used to image a fetus in the womb by ultra-sound, but on a much larger scale. A sound pulse is generated at the surface and the time is recorded for this pulse to be echoed from some buried change in geology back to a receiver at the surface. By repeating the experiment along a profile, an image of the subsurface can be generated that maps the layers of rock. However, there is a problem. The image is recorded as a function of time for the echoes to return to the surface whereas geologists require to know the depths. The key is to obtain a map of the sound-speed so time can be converted to depth. By using multiple receivers it is possible to obtain an estimate of this sound-speed map but the information is incomplete and prone to errors and uncertainty. By careful analysis of the seismic data, we have obtained quantified estimates of these uncertainties for profiles that cross the sites that are to be drilled by the International Ocean Discovery Program during leg 369. So once these sites are drilled we will have ground truth at a point on the seismic image so we can see how good our estimates are and whether the expected geological layers are at the depth and time that we have predicted. We can then use the well information to label the each layer and extrapolate this labeling away from the well using the seismic data and compare this with a manual interpretation of the seismic image. What we hope to learn is what level of confidence can we place in our predictions of the structure of the subsurface based on seismic data. This has major implications in Earth Sciences as the seismic reflection method is the primary tool used by the hydrocarbons industry to locate oil and gas, equally it is used by the carbon sequestration industry to bury and monitor CO2 to try to mitigate global warming. Further, the understanding developed here can be used across a wide-range of non-destructive imaging methods in the medical, construction and engineering industries.