To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
This chapter addresses a range of topics that hold considerable promise for future developments. We start by considering nested-inversions that allow definition of heterogeneity across a wide range of length scales from local through regional to global. This is followed by discussion of adaptive numerical gridding, exploitation of data redundancy, the development of efficient random sampling methods for inversion, and the use of Hamiltonian Monte-Carlo techniques for efficient searching of high-dimensional spaces.
An important recent development has been the exploitation of the seismic noise field by the use of correlations between seismograms recorded at different positions. We discuss the nature of the ambient noise field, which is dominated by microseismic signals generated in the oceans. The dominant component of the correlation field comes from surface waves, and cross-correlation procedures can extract an empirical Green’s function representing propagation along the path between the stations being correlated. Such results are widely exploited in ambient noise tomography. In some circumstances body waves can also be extracted from the noise field.
The results of cross-correlation of seismic records depend on both the distribution of seismic sources and the structure in the vicinity of the path between the stations being correlated. The differences between the segments of the correlograms corresponding to opposite senses of propagation between the stations provide information on source excitation, while the properties of the dominant arrivals are mainly sensitive to structure. These properties can be exploited in inversion of the correlation wavefield, to extract both noise sources and Earth structure.
Descent methods of optimisation depend on calculating the derivatives of the composite function with respect to the large number of model parameters. Adjoint techniques allow the computation of derivatives in such complex models, with much less calculation than direct methods, and so enable practical non-linear inversion. Adjoint methods also allow effective computation of sensitivity kernels associated with the variation of critical parameters for both structure and sources. Sensitivity kernels can provide insight into the nature of Earth structure and the potential resolution of seismic tomography.
We here describe the process of waveform inversion for earthquake data, by reference to inversion for 3-D structure in seismic wavespeed and density in the eastern Mediterranean region using numerical simulation with the spectral element technique. Such waveform inversion needs to start from a good initial model, using low frequencies in the first stage. As the inversion proceeds higher frequencies and additional data can be to incorporated to achieve model refinement. We also examine the issues of practical resolution assessment, and validation of proposed models.
Current seismology depends on well-developed networks of instruments and a range of advances in both theoretical and computational developments. We provide a survey of the development of seismic recording, including the introduction of dense sets of portable instruments, so that major earthquakes are now captured by thousands of seismometers. We then discuss the way in which understanding of seismic waveforms has developed through the computation of synthetic seismograms and their exploitation in inversion. The last part of the chapter provides a description of the structure of the four Parts of the book
Email your librarian or administrator to recommend adding this to your organisation's collection.