Marine Geophysics - Modeling and Full Waveform Inversion of Marine Seismic Data

Note: This project is designed for up to two students. 

Project description

Motivation (background):
Acquisition and processing of marine seismic data (both towed marine and ocean bottom data) makes it possible to delineate subsurface crustal and upper mantle structure in great detail. This is important for a variety of reasons. The first successful application of this technique was to offshore hydrocarbon exploration. Later on, since the 1990s, this type of data has also been important in other areas of geoscience, including the determination of the subsurface structure near mid-ocean ridges and subduction zones. This has led to a much better understanding of geodynamics, and in particular, to the detection of magma chambers of submarine volcanoes and an improved understanding of the dynamics of megathrust events in subduction zones, the world’s largest earthquakes. Another, more recent, application of these methods is the monitoring of CO2 injected into the subsurface.

Hypothesis (scientific problem):
The processing of marine seismic data consists roughly of four main steps. The complexity of these steps increases significantly with each step, with the fourth step, imaging or full waveform inversion (FWI), being the most complicated and time consuming and arguably also the most important. In order to improve the quality and resolution of the computed subsurface images it is therefore useful to improve this last processing step. This can be done in various ways by focusing on the modeling method underlying the imaging or FWI and/or by focusing on the inversion algorithm itself. The goal of these proposed master projects is to develop and test improved modeling/inversion techniques and apply to them an area of interest (such as mentioned above: exploration, mid-ocean ridge structure, shallow subduction zone structure, CO2 storage).

Test (work):
The two main components, modeling and inversion, of the final processing step, can be improved by focusing on theoretical aspects, the numerical implementation or both. Improvements can, for example, be made by incorporating attenuation and anisotropy in the starting model in the inversion. This is important because in practice the subsurface is anelastic, whereas many modeling algorithms assume an acoustic or elastic isotropic subsurface. Doing this makes the computations more challenging and a sub-goal would be to make sure that the corresponding increase in computational requirements is minimized. The inversion typically is formulated in terms of a linear least square problem which involves inverting large matrices, which is challenging. Various inversion algorithms exist to do this inversion. In the case of imaging the inversion is quite straightforward but the results not optimal. In the case of FWI there are various inversion algorithms which are more complicated but give better results. If the focus of the project is on inversion then the goal would be to develop and test an improved inversion algorithm and apply this to a synthetic data set generated for a specific geodynamic application.

Proposed course plan during the master's degree (60 ECTS):
GEOV274 (10 sp) or AG335 (10sp, geophysics field course in UNIS Svalbard)
GEOV276 (10 sp)
GEOV277 (10 sp)
GEO-DEEP course on mantle dynamics in UiO (5 sp) (depending on topic)
GEOV300 (5 sp)
Geophysics field course (5 sp)
GEOV302 (5 sp)

Prerequisites
Bachelor in Geophysics