solid Earth dynamics
KAJ JOHNSON Associate Professor of Geological Sciences
Kaj is a geophysicist who works primarily
with geodetic data and numerical and an-
alytical modeling to investigate active de-
GARY PAVLIS Professor of Geological Sciences |
Geophysics, Seismology, and Tectonics
formation of the lithosphere. In particular,
Although Gary Pavlis is plan-
he studies how deformation within plate
ning to retire from teaching in
boundary zones is accommodated by fault-
summer 2018, he continues
ing and folding in the crust and viscous flow
an active research program.

in the lower crust and upper mantle.

Over the past 20 years Pav-
lis and students have been
working on elements of the
BRUCE DOUGLAS Senior Lecturer | Structural Geology
Director, IU Judson Mead Geologic Field Station
technology for seismic imag-
ing of the deep interior. They
have developed a novel form
Bruce Douglas continues to work with col-
of imaging adapted from 3D migration methods used in
leagues from UNAVCO and other academic
the petroleum industry. The method migrates scattered
institutions including Mt. San Antonio Col-
P to S conversions produced by teleseismic P waves to
lege and Idaho State University to develop
produce an image of P to S scattering strength in true
teaching resources that involve various
geometry and with true relative amplitudes. The result
types of geodetic data (e.g. airborne and
is a 3D volume that is handled much like modern 3D
terrestrial LiDAR, InSAR, GRACE gravity,
seismic reflection data. In fact, their most recent work
GPS). These resources will ultimately be
has made extensive us of the seismic interpretation el-
added to the Geodesy Tools for Societal Is-
ements the Petrel package made possible through a re-
sues (GETSI) teaching resources package
cent software grant from Schlumberger.

supported by three NSF grants and hosted by the SERC web-
Profoundly new results have proven possible due to
site. The GETSI collaboration was an outgrowth of the incor-
deployment of large array experiments like the Earth-
poration of Terrestrial Laser Scanning (TLS) into the concen-
scope Transportable Array (TA) and the OIINK project.

tration week within course G429g.

Recent work by Ph.D. student Yinzhi (Ian) Wang using
The UNAVCO connection also has led to the use of Post-Pro-
data from the TA has produced images of the transition
cessing Kinematic (PPK) GPS data collection and analysis for
zone he showed in a recent paper are diffraction limited,
two M.S. projects undertaken in SW Montana under Bruce’s
which means they are the highest resolution possible
supervision. Donald Tripp and Kirstyn Cataldo are both work-
from these data. His work promises to greatly change
ing on M.S. degrees that address the displacement history for
understanding of the area of the mantle called the tran-
active normal faults that are found in the region north of the
sition zone. His Ph.D. work revealed two new insights on
Field Station. A third M.S. student, Ciara Mills recently com-
the transition zone.

pleted her degree analyzing the mechanics of the Carmichael
Fault that runs just south of the Field Station.

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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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