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Local Seismology: A new paradigm in Earth Imaging


Project Description

The key to accurately map seismic wave velocities in the Earth’s interior is to bring as much data as possible into an inverse problem. Classically, seismologists infer the wave velocities by measuring the seismic arrival time and the source-receiver distance. But this is limited by the seismometer station coverage and earthquakes distribution that illuminates the Earth’s interior. Likewise, techniques that employ cross-correlations to extract arrival times from seismic noise are inadequate when the inter-station azimuth misaligns with the seismic noise sources or the stations are located very close together as in dense seismic arrays.

This project will pursue wavefield gradiometry techniques to extract seismic wave velocities from ambient noise. An unprecedentedly large carpet deployment of seismometers across the United States (named USArray) provides a dense recording of the seismic wavefield which allows the application of novel analysis techniques to image the crust and upper mantle under the United States. One characteristic of data recorded by dense arrays of these seismometers has gone virtually unexploited: The constraint that the spatial and temporal gradients of a seismic wavefield pose on the seismic wave velocities locally (irrespective of the nature and origin of the seismic energy). This is what is termed here by the title “local seismology”: the overall aim of the project being to extract and interpret this information across the entire United States.

Plate tectonics has shaped the face of the planet, as plates move around due to buoyant forces subducting underneath other plates while accreting the floating continental crust. The upper mantle acts as an archive for slab fragments that subducted during the Earth’s history. These slab fragments stand out seismically with respect to the surrounding mantle material, due to their cool temperatures and resulting higher seismic velocities. This project will shed new light on (1) the subduction history and origin of various ancient slab segments spread out deeply beneath North America; (2) the recharge dynamics in the mantle and crust of the Yellowstone magmatic system; (3) the transition zone between the tectonically quiet centre of the North American plate and the deforming continental margins.

Funding Notes

NERC PANORAMA DTP prepares the next generation of environmental science leaders for industrial, governmental, NGO and academic careers and provides exceptional training across the range of environmental science in world-class research teams through an innovative, exciting and multi-disciplinary programme. PANORAMA will equip its postgraduate students with the skills necessary to understand the complex interactions within the Earth system, so they can contribute to the development of scientific, policy and industrial solutions for the national and global scale problems we face in coming decades.

References

Campillo, M., and A. Paul (2003) Long-range correlations in the diffuse seismic coda: Science, 299, 547– 549.

Curtis, A. and Robertsson, J.O.A. (2002) Volumetric wavefield recording and wave equation inversion for near-surface material properties: Geophysics, 67(5), 1602–1611.

de Ridder, S.A.L. and Biondi, B.L. (2015) Near-surface Scholte wave velocities at Ekofisk from short noise recordings by seismic noise gradiometry: Geophysical Research Letters, 42(17), 7031–7038.

de Ridder, S.A.L., and J.R. Maddison (2018). Full wavefield inversion of ambient seismic noise. Geophysical Journal International, Vol. 215(2), pp. 1215-1230.

Edme, P. and Yuan, S. (2016) Local dispersion curve estimation from seismic ambient noise using spatial gradients: Interpretation, 4(3), SJ17–SJ27.

Manduca, A., Oliphant, T., Dresner, M., Mahowald, J., Kruse, S., Amromin, E., Felmlee, J., Greenleaf, J., and Ehman, R. (2001) Magnetic resonance elastography: Non-invasive mapping of tissue elasticity: Medical Image Analysis, 5, pp. 237–254.

Sigloch, K., N McQuarrie, G Nolet (2008) Two-stage subduction history under North America inferred from multiple-frequency tomography: Nature Geoscience 1 (7), 458-462

van der Hilst, R., R. Engdahl, W. Spakman, G. Nolet (1991) Tomographic imaging of subducted lithosphere below northwest Pacific island arcs: Nature, v. 353, p. 37-42, 1991.

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