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Twenty Years of Subduction Zone Science:
Subduction Top to Bottom 2 (ST2B-2)

G.E. Bebout*, Dept. of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA; D.W. Scholl,
emeritus, United States Geological Survey, Menlo Park, California 94025, USA, and University of Alaska Fairbanks, Fairbanks,
Alaska 99775, USA; R.J. Stern, Dept. of Geosciences, University of Texas at Dallas, Richardson, Texas 75083, USA; L.M. Wallace,
University of Texas Institute for Geophysics, Austin, Texas 78758, USA, and GNS Science, Lower Hutt, New Zealand; and P. Agard,
Institut des Sciences de la Terre de Paris, UPMC Université Paris 06, CNRS, Sorbonne Universités, Paris, France

ABSTRACT become increasingly interested in the pro- resultant publication encourages continued
cess since the term was introduced by efforts along these lines.
No other plate-tectonic setting has White et al. (1970; also see the prescient
attracted such diverse, multidisciplinary sketch of a subduction zone by Coats, “SUBCON” (Subduction Conference)
research as convergent margins. Under 1962) on the heels of the plate tectonic rev- was held in Avalon, Santa Catalina Island,
standing the dynamics of subduction is olution. Subduction zones are where litho- California, USA, on 12–17 June 1994,
particularly important for realistic assess- sphere is recycled into the mantle and they largely funded by the United States
ment of associated hazards such as earth- provide the third dimension for the Geological Survey (USGS) but with addi-
quakes, tsunamis, and volcanic eruptions. ~55,000 km length of convergent plate tional support from the National Science
A number of recent initiatives have been margins. The sinking of lithosphere in sub- Foundation (NSF). At this conference,
successful in building communities not duction zones provides most of the power ~120 scientists from around the world
only to investigate subduction processes, for plate motions and is directly respon- shared their understanding of subduction
but also to convey knowledge about sub- sible for crustal deformation and arc mag- zone dynamics as a function of depth—
duction zone processes to other scientists, matism. Convergent margin processes from top to bottom—bringing together
students, postdocs, and the broader pub- affect climate directly (volcanic gasses) observations and predictions from the
lic. These efforts must include synthesiz- and indirectly (producing relief and stimu- many diverse perspectives of the group.
ing and simplifying subduction-zone sci- lating weathering), contributing impor- Although it is now common to see multi-
ence for classroom presentations and to tantly to maintaining Earth’s habitability, disciplinary groups working together to
help prepare the public for subduction- at the same time producing societal ben- understand subduction, this was not so in
related disasters. efits (ore deposits and hydrocarbon-rich the mid-1990s. To many at SUBCON, the
basins) and some of the most dangerous audience to which they revealed their work
Tremendous advances over the past natural hazards (earthquakes, tsunamis, was unusually diverse in interests and
20 years or so have been made in subduc- and explosive volcanism). In spite of their expertise, resulting in some surprising and
tion zone science, with increasingly importance, subduction zones are not easy useful feedback. As a part of SUBCON,
multidisciplinary efforts producing some to study because they are hidden deeply in the group visited selected outcrops of the
of the greatest insights. We have initiated the Earth; teasing out their secrets has Catalina Schist exposed on the island and,
a publication effort in the GSA journal involved years of efforts by geologists, for many of the participants, this was a
Geosphere, with a Themed Issue geophysicists, and geochemists from many first view of an ancient subduction zone.
“Subduction Top to Bottom 2” (or different countries working on land, at sea, SUBCON and its aftermath helped lead to
“ST2B-2”) aimed at showcasing the and using observations from space. The some very productive multidisciplinary
recent advances, following up on the con- enormity of the challenge of studying sub- collaborations, including the 1996 publica-
ceptually similar Subduction Top to duction zones has spurred efforts to build a tion of Subduction Top to Bottom (Bebout
Bottom published in 1996 as an American cross-disciplinary community of govern- et al., 1996, American Geophysical Union
Geophysical Union Geophysical ment, academic, and industrial geoscien- [AGU] Geophysical Monograph 96, some-
Monograph. The ST2B-2 Geosphere tists from many nations, and for members times called “Big Purple” because of the
Themed Issue is accumulating papers of this community to learn how to explain cover). Big Purple contains 39 papers of
and is open to ALL wishing to contribute their findings to scientists with different either a review or case-study nature cover-
to this effort—we anticipate accepting expertise as well as to students and the ing all aspects of subduction zones and
manuscripts through all of 2018 and public. Workshops and edited volumes their products.
possibly beyond. play key roles in building this community.
An excellent early example of this commu- In the 20 or so years since SUBCON
INTRODUCTION nity-building effort was held 23 years ago, and Big Purple, many advances have been
and the success of this workshop and the made in the fields of geophysics, petrol-
Subduction is a uniquely powerful and ogy, geochemistry, and geodynamics, with
important Earth process, so it is no sur- the work increasingly conducted by highly
prise that the geoscientific community has

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