b. Depth (km)
440 435
Depth (km)
680 675
420 660
405 645
390 630
380 620
c. First, he found seismic discontinuities that bound the
transition zone, commonly attributed to phase chang-
es of olivine at depths of around 410 and 660 km, are
d. Covariance
1.00 Covariance
1.00 0.75
0.75 0.50
0.50 0.25
0.25 0.00
0.00 rough at every scale we can resolve. The figure to the
right from his paper shows this graphically. The second
figure, from a paper in review, argues that the transition
zone is full of small-scale, low-velocity heterogeneities
Inferred roughness of the mantle 410 and 660 discontinuities.

(a) and (b) show picked depth to 410 and 660 discontinuities
respectively. (c) and (d) are related maps showing a measure
of roughness defined in the paper by Wang and Pavlis (2016).

attributed to hydrous phases trapped in the transition
zone. This has broad implications for Earth’s history and
the origin of water on the planet.

A second important recent result with this technology
was published recently by Ph.D. student Xiaotao Yang
who completed his Ph.D. in fall 2016. He used the plane
wave migration method to image the Moho under the
area covered by the OIINK experiment (see 2016 HGR
section by Hamburger). A major discovery from Yang’s
paper was the inference of surprisingly thick crust un-
der central Illinois and a remarkable step in the Moho
along a trend parallel to the Mississippi River south of
St. Louis. The existence of mountainless roots under the
Illinois Basin is a puzzle we will be working on for years
to come.

Moho geometry inferred from P to S conversion imaging in the cen-
tral US by Yang et al. (2017). (a) was produced from the OIINK data
and (b) was produced from the Earthscope Transportable Array (TA)
data. The dashed box in (b) is the map area of (a). (a) is a higher reso-
lution image made possible by the higher station density of the OIINK
experiment compared to the TA.

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