Anisotropic and Viscoelastic Full Waveform Inversion

Project description

Motivation (background):

Determination of the Earth’s subsurface, especially the upper part of the crust is important for various reasons. It can, for example, be used for to optimize energy and resource exploitation. It is also very relevant for a better understanding of various aspects related to the environment, climate and natural disasters, including volcanic eruptions and earthquakes. The most important method to determine the upper crustal structure is seismics and over the past two decades a lot of progress has been made to improve seismic images/subsurface characterization.
However, a lot of work still remains. In particular, accurate determination of the crust’s elastic (anisotropic) as well as its viscoelastic properties is challenging. The goal of the two master projects described here are to develop and test new (1) anisotropic and (2) viscoelastic full waveform inversion methods.

Hypothesis (scientific problem):

Processing of active source seismic data consists of a number of steps. The most important, most challenging and most expensive of these steps is full waveform inversion (FWI). Various types exist but they all require a seismic forward modeling method. Therefore, a first step in this project is the development of such a forward modeling method for anisotropic and a forward modeling method for viscoelastic media. Besides being accurate it would also be very beneficial if these modeling methods are fast. The first goal of these projects are to come up with such fast modeling methods. A second goal would then be do use the modeling methods to perform FWI for both simple and more realistic test models.

Test (work):
Seismic modeling is already challenging in (3D) acoustic medium.Therefore, the modeling in these projects will be confined to 2D media. This is a not a big restriction as the extension to 3D media, which is more realistic, often does not pose great technical difficulties. A second way to speed up the modeling is to use scattering methods rather than the more commonly used finite difference modeling. Scattering methods, especially the ray-Born approximation, have turned out to be very useful in practice as they are relatively easy to implement and test. Moreover, they are much faster than finite differences codes and a number of programs both for the modeling and FWI already exist. In particular, both the anisotropic FWI method and viscoelastic ray-Born modeling and FWI build on simpler codes that already exist. Therefore, in practice much of the work of these projects consists of using and expanding these codes.

Proposed course plan during the master's degree (60 ECTS)

Geov276 (10 sp)
Geov274 (10 sp)
Inf264 (10 sp)
Geov300 (5 sp)/spesial pensum (5 sp)
Geov375 (10 sp)
AG335 (10 sp)
Geov352 (5 sp)

Prerequisites

Bachelor in geophysics

Field-, lab- and analysis work

NA