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Research | Publications | Abstracts | Curriculum Vitae
Research statement:
My research involves using scattered seismic energy to infer Earth structure. This rather broad statement can be subdivided into two main areas of interest: 1) forward scattered elastic waves and 2) back scattered acoustic waves. Given a medium with know physical properties, (in my case, the Earth) solutions to the wave equation can give us very accurate models of the wavefield. However, the problem is the inverse to that: given the scattered wavefield, how do we predict physical properties of the Earth?
Computing near-receiver P-to-S converted phases (often times called "receiver functions"), it is possible to delimit major lower crustal and upper mantle impedance contrasts. My earliest research focused on how to use teleseismic earthquake data recorded on arrays of broadband seismic instruments (available from IRIS-PASSCAL) to image down to depths of 700km. Mainly, I'm concerned with the problem of imaging with such data. That is, because of structural complexities in the Earth, the wavefield diffracts and scatters predictably. By making use of full, vector (as opposed to acoustic, or single component) wavefield migration techniques, it is possible to reconstruct the impedance structure of the Earth (figure1), i.e. focus the wavefield. However, the two major assumptions in current imaging techniques is that 1) the scattering is weak; i.e. the Born Approximation and 2) we can adequately resolve the P-to-S (PdS) phases. The first of these assumptions is often violated by real data as evidenced by the preponderance of multiple reflected energy commonly seen on both teleseismic PdS images and reflection seismic sections. The second problem of accurately resolving the PdS phases is intricately folded into the imaging problem and requires much future work.
Recognizing the problems of the weak scattering assumptions has sparked interest in my latest research. Current imaging makes use of velocity models that have smoothly varying velocities. The part of the velocity model that's imaged is typically the small perturbations in the velocity. This means that if there are portions of the Earth's crust that have "unsmooth", and/or large velocity gradients, current imaging techniques fail. Also, current imaging techniques have problems when the Earth isn't nicely layered. The problem is that large portions of the Earth behave in exactly these ways! In fact, the crystalline portion of the Earth's crust can be modeled as a stochastic medium. Because of the complexities in such a medium, scattering, multipathing, and dispersion make imaging with reflected wavefields quite challenging. Indeed, the wavefield in such a medium is, well, a mess. But its only a mess because we lack the mathematical and computational tools to understand the behavior of the mechanical waves in such a regime. My current research involves a field that's been dubbed "statistical seismology", in which we are trying to develop the algorithmic tools to extract meaningful properties of the Earth given a wavefield that has propagated through a stochastic medium. This work involves the use of lots of synthetic velocity models, synthetic seismograms to confirm current theories, and applications to real field data. (figures 2, figure 3). A large portion of this work involves the age-old problem in reflection seismology: seismic source estimation. Without a reliable source estimate, deconvolution (and hence our estimate of the stochastic velocity model) becomes too error-prone to be useful (figure 4).
Publications:
Refereed articles:
C. Poppeliers and G. L. Pavlis, 2003; Three- dimensional, prestack, plane wave migration of teleseismic P-to-S converted phases: 2. Stacking multiple events. J. Geophys. Res. in press
C. Poppeliers and G. L. Pavlis, 2003; Three-dimensional, prestack, plane wave migration of teleseismic P-to-S converted phases: 1. Theory, J. Geophys. Res., vol 108, no B2 doi:10.1029/2001/\JB000216
C. Poppeliers and G. L. Pavlis, 2002; The seismic response of a steep slope: High-Resolution Observations with a dense, three-component seismic array, Bull. Sies. Soc. Am., vol 92, no. 8, pp.3102-3115
Abstracts, Meetings:
C. Poppeliers and G. L. Pavlis, 2000; Imaging the Cheyenne belt: Three dimensional plane wave migration of P-to-S converted phases, AGU 2000 fall meeting, Eos, Transactions, Am Geophys Union, vol 81, no 48, Suppl, pp F895, 28 November, 2000
C. Poppeliers and G. L. Pavlis, 1999; 3-D imaging of upper mantle P-to-S converted phases using broadband array data; applications of time-domain deconvolution and migration, AGU 1999 fall meeting, Eos, Transactions, Am Geophys Union, vol 80, no 46, Suppl, pp 704, 16 November, 1999
G. L. Pavlis and C. Poppeliers, 1999; The seismic response of a steep slope; direct observations of topographic site effects by a dense, three-component seismic array, AGU 1999 fall meeting, Eos, Transactions, Am Geophys Union, vol 80, no 46, Suppl, pp 709, 16 November, 1999
C. Poppliers, D. Danks, and M. L. Cummings, 1996, Wear due to physical and petrographic properties of rocks and their dynamic interactions with mining equipment, GSA, Cordilleran Section, 92nd annual meeting, Abstracts with Programs - Geol. Soc. Am. Vol 28 no 5, pp. 102, April 1996
Curriculum Vitae:
Education:
B.S. 1992, Purdue University, W Lafayette, IN; Geophysics
M.S. 1996, Portland State University, Portland, OR; Engineering Geology
Advisor, Michael Cummings
Ph.D. 2001, Indiana University, Bloomington, IN; Seismology
Advisor, Gary L. Pavlis
Employment/Teaching History:
2002-current, Post Doctoral Research Associate, Center for Computational Geophysics,
Rice University
2002, Research Geophysicist, ExxonMobil Upstream Research Company
2001-2002, Senior Geophysicist, ExxonMobil Exploration Company
1998, Adjunct Faculty, Portland Community College
1996-1998, Environmental Scientist, AGRA Earth and Environmental, Inc, Portland, OR
1995-1996, Adjunct faculty, Clark Community College, Vancouver, WA
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