Imperial College London
Portrait Picture

Dr Fred Richards

Faculty of Engineering, Department of Earth Science & Engineering

Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 7402f.richards19 CV

 
 
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Location

 

2.54Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Citation

BibTex format

@article{Lloyd:2024:gji/ggad455,
author = {Lloyd, AJ and Crawford, O and Al-Attar, D and Austermann, J and Hoggard, MJ and Richards, FD and Syvret, F},
doi = {gji/ggad455},
journal = {Geophysical Journal International},
pages = {1139--1171},
title = {GIA imaging of 3-D mantle viscosity based on palaeo sea level observations – part I: sensitivity kernels for an Earth with laterally varying viscosity},
url = {http://dx.doi.org/10.1093/gji/ggad455},
volume = {236},
year = {2024}
}
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RIS format (EndNote, RefMan)

TY  - JOUR
AB  - A key initial step in geophysical imaging is to devise an effective means of mapping the sensitivity of an observation to the model parameters, that is to compute its Fréchet derivatives or sensitivity kernel. In the absence of any simplifying assumptions and when faced with a large number of free parameters, the adjoint method can be an effective and efficient approach to calculating Fréchet derivatives and requires just two numerical simulations. In the Glacial Isostatic Adjustment problem, these consist of a forward simulation driven by changes in ice mass and an adjoint simulation driven by fictitious loads that are applied at the observation sites. The theoretical basis for this approach has seen considerable development over the last decade. Here, we present the final elements needed to image 3-D mantle viscosity using a dataset of palaeo sea-level observations. Developments include the calculation of viscosity Fréchet derivatives (i.e. sensitivity kernels) for relative sea-level observations, a modification to the numerical implementation of the forward and adjoint problem that permits application to 3-D viscosity structure, and a recalibration of initial sea level that ensures the forward simulation honours present-day topography. In the process of addressing these items, we build intuition concerning how absolute sea-level and relative sea-level observations sense Earth’s viscosity structure and the physical processes involved. We discuss examples for potential observations located in the near field (Andenes, Norway), far field (Seychelles), and edge of the forebulge of the Laurentide ice sheet (Barbados). Examination of these kernels: (1) reveals why 1-D estimates of mantle viscosity from far-field relative sea-level observations can be biased; (2) hints at why an appropriate differential relative sea-level observation can provide a better constraint on local mantle viscosity and (3) demonstrates that sea-level observations have
AU  - Lloyd,AJ
AU  - Crawford,O
AU  - Al-Attar,D
AU  - Austermann,J
AU  - Hoggard,MJ
AU  - Richards,FD
AU  - Syvret,F
DO  - gji/ggad455
EP  - 1171
PY  - 2024///
SN  - 0956-540X
SP  - 1139
TI  - GIA imaging of 3-D mantle viscosity based on palaeo sea level observations – part I: sensitivity kernels for an Earth with laterally varying viscosity
T2  - Geophysical Journal International
UR  - http://dx.doi.org/10.1093/gji/ggad455
UR  - http://hdl.handle.net/10044/1/110097
VL  - 236
ER  -
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