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the rheology and mechanical failure of
rocks lead to greater understanding of the
relationships between devolatilization and
other metamorphic reactions and observed
seismicity (e.g., Incel et al., 2017)? Can we
decipher the balance of material delivered
through an individual subduction margin
by combining knowledge of inputs derived
through deep-sea drilling, forearc heat
flow measurements, thermal modeling,
thermodynamic calculations, analysis of
ancient metamorphic rocks, and analyses
of volcanic gases?

Figure 2. Illustration of northern 2007 episodic tremor and slip (ETS) event in Cascadia (from Gom- THE MAKEUP OF ST2B-2
berg et al., 2010). The oceanic Juan de Fuca plate subducts beneath the North America plate at
~4 cm/yr roughly perpendicular to the coast (white arrow). The plates are coupled for part of their The ST2B-2 endeavor is intended to
interface (tan-colored surface) such that relative motion is inhibited or “locked” to a varying degree. generate a large, online themed issue in
Uncertain are the location and mechanism by which the locking changes to a freely slipping inter- the Geological Society of America jour-
face. The fraction of relative plate motion is portrayed as continuous aseismic slip that increases nal Geosphere. With this online format—
down-dip from 40% to 80% (dashed contours). Inland of the locked zone, tremor epicenters pro- in our view a clear example of the future
jected onto the plate interface (circles) overlie the area that experienced slow slip (gray area on of scientific communication—we are
plate interface) during the last two weeks of January 2007. Color shading of tremor epicenters unencumbered by page limits imposed by
shows its temporal migration. a physical book and by costs of color fig-
ures; furthermore, this format encourages
use of interactive graphics and online
data sets. Individual papers are published
soon after manuscripts are accepted; there
is no waiting for the slowest author(s).
Published works in Geosphere are land-
scape-format and so more amenable to

We particularly encourage manuscripts 50
employing diverse observations and meth-
ods to identify problems where differing British Columbia
disciplines examine similar processes.
To raise awareness of the new volume, we 70 Mexico
have been holding “Subduction Top to
Bottom 2” sessions (Fall 2016 AGU and Cas cadia
2017 GSA Annual and Fall AGU meetings).
90
As examples of where multidisciplinary
pursuits could be particularly fruitful, 110 N Peru gap
forearc seismic events commonly originate 130
along the active subduction interface or in depth (km) 150 C Peru gap
accreted sediments experiencing pressure- 170
temperature conditions preserved in 190 New Zealand Izu Solom on Nankai
forearc metasedimentary suites represent- 210
ing similar but ancient processes. Might 230 Colombia-Ecuador C Chile gap
examination of the metamorphic rock 250 0
record better tell us how slow slip events C Sumatra N-C Chile S Chile
and related seismic phenomena (such as N Sumatra
tremor) happen (see Fig. 2) and, more spe- Scotia Alaska Nicaragua
cifically, the roles of fluids in generating
such events? Could highly brecciated Bonin S-C Chile
zones of eclogite from ancient subduction N Chile
zones be the products of catastrophic New Britain
energy release along the interface that gen-
erated ancient earthquakes (see Fig. 5)? E Banda Sea N Kurile C Chile
Could laboratory experiments regarding S Kurile Costa Rica

Kam chatka AK Peninsula Peru
Guatemala-El Salvador
S Marianas Java C Honshu N Vanuatu Ryukyu
N Honshu S Vanuatu Kyus hu
S Lesser Antilles Bali-Lom bok
Aegean N Philippines Tonga

Hokkaido S Sumatra Calabria E Aleutians Kermadec
W Banda Sea
S Philippines
N Lesser Antilles
Sunda Strait W Aleutians

N Marianas C Aleutians

5 10 15 20 25 30

slab H2O loss (Tg/Myr/m)

Fsuigbudruec3t.inDgivienrtsoeeHa2cOh loss calculated as a function of depth for oceanic lithosphere and sediment
of Earth’s modern subduction zones (the “Tokyo Subway Map” from van
sKuebkdeuncettinagl.,s2la0b1s1)l.oTsheeswiganrimficeasnt tsuwbadteurctwiohnenzotnheesslloasbecmomosetsoifntthoeciroHnt2Oacbt ewniethatthhethheoftoorevaerrcly.iAngll
mantle wedge (in these models, at 80 km depth). For many slabs (e.g., Kamchatka, Calabria) further
dehydration is minor. Other slabs (e.g., Chile) continue to dehydrate significantly with increasing
depth principally due to the dehydration of the uppermost mantle. A few slabs (e.g., Marianas) are
very cool, and far less H2O is lost to even 230 km depths.

www.geosociety.org/gsatoday 7