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Multiple-frequency body-wave tomography

Sigloch, Karin (2008), Multiple-frequency body-wave tomography, Ph.D. thesis, Princeton University.

(To download the Ph.D. thesis in pdf format, scroll down to "Further Information.")

This dissertation deals with generating, exploring, and using the kind of seismic data that finite-frequency modeling was envisioned for. It represents a comprehensive inquiry into extracting frequency-dependent information from broadband waveforms of seismic body waves, and applying these data to global-scale imaging of the earth’s interior.

I develop a matched-filtering method to measure two new kinds of observables for global-scale seismology: multiple-frequency traveltimes and amplitudes. Observed waveforms are compared to predicted seismograms through cross-correlation after deconvolving the earthquake source time function from the data. The method is validated on a small data set in the Western U.S. I explore the dispersive properties and noise characteristics of the multiple-frequency measurements and find that dispersion is a significant signal, especially in the amplitude measurements. Amplitude patterns are spatially coherent over hundreds of kilometers.

The signal processing is scaled and automated to process the entire database of ~2000 suitable earthquakes that occurred worldwide between 1999 and 2007. In the first application of multiple-frequency body-wave tomography, the subset of traveltimes and amplitudes measured in North America is jointly inverted for P-wave structure and attenuation of the North American mantle. New USArray data represent an ideal testbed for this study.

We obtain very detailed velocity structure down to ~1800 km depth that reveals some major surprises. Not one but two whole-mantle subduction systems are present beneath North America. Presently, the Farallon slab descends from the Pacific Northwest coast to 1500 km depth beneath the Great Plains, whereas its stalled predecessor occupies the transition zone and lower mantle beneath the eastern half of the continent. We argue that the separation between them is linked to the end of the Laramide era 50 million years ago, a time of unusual tectonic and volcanic activity during which the flatly subducting slab is inferred to have caused the uplift of the ancestral Rocky Mountains.

Download Ph.D. thesis as pdf:
  author = {Karin Sigloch},
  month = {mar},
  school = {Princeton University},
  title = {{Multiple-frequency body-wave tomography}},
  type = {Ph.D. thesis},
  year = {2008},
  url = {http://www.geophysik.uni-muenchen.de/~sigloch/papers/2008{\_}Sigloch{\_}CompleteThesis.pdf},
%0 Thesis
%A Sigloch, Karin
%D 2008
%T Multiple-frequency body-wave tomography
%U http://www.geophysik.uni-muenchen.de/~sigloch/papers/2008_Sigloch_CompleteThesis.pdf
%8 mar
%I Princeton University
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Printed 20. Mar 2019 03:54