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Physical Experiments of Tectonic Deformation and Processes:
Building a Strong Community
Michele L. Cooke, University of Massachusetts–Amherst, Amherst,
Massachusetts 01003-9297, USA; Jacqueline E. Reber, Iowa State
University, Ames, Iowa 50011-3212, USA; Saad Haq, Purdue University, investigations provides a strong three-legged stool upon which we
West Lafayette, Indiana, 47907, USA
ABSTRACT
The recent revolution in the analysis of physical experiments of
tectonic processes has provided new quantitative tools to analyze
their outcomes. Physical experiments using scaled analog models
are unique in providing information on complex three-dimensional
deformation where processes can be directly observed. These
observations critically complement insights gained from field and
analytical/numerical investigations. Recent innovations in rheo-
logic testing, digital image processing, and data collection are
revolutionizing how we use experiments to provide insight into
crustal deformation. At the same time, we are seeing the benefits
of physical experiments in classroom teaching by engaging students
in hypothesis testing and hands-on laboratory experience.
Strengthening of the community of physical experimentalists and
instructors using analog materials to simulate tectonic processes
will enhance our understanding of these processes, lend more
power both to interpretations of field observations and to valida-
tion of numerical models, and deepen student understanding of
tectonic mechanisms. A step toward a stronger community has
been made with a recent workshop on physical modeling of tectonic
processes, and this report is one outcome of that workshop.
THE REVOLUTION IN PHYSICAL EXPERIMENTS
Two hundred years ago, Hall (1815) published the first research
GSA TODAY | DECEMBER 2016
paper to use physical experiments using analog materials to inves-
tigate mountain belt formation. Since these very first experiments0,.5cm 2cm
physical models in earth science have not only been useful tools
for visualizing deformation but also have great power to investi-
gate physical processes that govern deformation. For example, the
innovative experiments of Tapponnier et al. (1982) and Davis et
al. (1983), each with over 2,000 citations, have transformed our
thinking about tectonic processes. Carefully scaled analog models Figure 1. Deep understanding of crustal deformation relies on three approaches:
provide a means to directly observe deformational processes that field measurements of deformation, physics-based predictions of deformation,
within Earth’s crust are too slow and too large to directly docu-
ment (Hubbert, 1937). Furthermore, within such experiments we
have control over boundary conditions and material properties so
that we can directly assess their effect on deformation. While
fieldwork and analytical and numerical models are essential tools
for investigating crustal processes, they often do not inform all
GSA Today, v. 26, no. 12, doi: 10.1130/GSATG303GW.1.
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aspects of the deformational story. Using physical experiments in
conjunction with field observations and analytical/numerical
can build a robust understanding of crustal deformation processes
(Fig. 1).
Advances in experimental procedures have been developed at
physical modeling laboratories within both academia and the
petroleum industry. The past 10 years have seen a revolution
within physical modeling of crustal deformation spurred by the
utilization of new innovative analog materials (e.g., Di Giuseppe
et al., 2015), systematic rheologic testing (e.g., Klinkmüller et al.,
2016), incorporation of laser and image processing techniques for
data analysis (e.g., Haq, 2012), measuring in situ stress (e.g., Herbert
et al., 2015), and reconstruction of the evolution of complex 3D
structures (e.g., Colletta et al., 1991). These advances all strengthen
the quantitative rigor of physical modeling of tectonic processes.
The vanguard of this recent revolution has been in Europe, which
has many active laboratories staffed with technicians implementing
and advancing these new technologies. While presently a typical
experimental laboratory in the United States is run by a single
principal investigator with his or her students, European labs
are run with a team of lead scientists with tens of students.
Consequently, the core of the experimental community is in Europe,
where experimentalists host regular workshops and conference
sessions focused on physical modeling. Strengthening the U.S.
Tectonic Processes
A) Field Observations physics
C) Numerical/Analytical Models
proof
process
0.5cm 1cm
B) Laboratory Experiments
and direct documentation of deformational processes within laboratory
experiments. To illustrate the power of the tectonics three-legged stool, we show
results from a fully integrated study on the development of sheath folds in simple
shear. (A) Sheath fold from Cap de Creus, Spain. (B) Photo from a physical
experiment investigating the impact of layer viscosity contrast on the fold
formation (Reber et al., 2013). (C) Cross section from an analytical model
investigating the effect of total shear strain (Reber et al., 2012).