Research
Highlights
North China Earthquakes
The
National Science Foundation’s PIRE Program (Partnerships for
International Research and Education) has recently awarded us a
five-year grant to partner with Chinese institutions in a joint study
of intraplate earthquakes in North China, where ~50 large (M≥6.5)
earthquakes occurred in the past 700 years. We will integrate seismic
imaging of earth structure, geodetic measurement of crustal
deformation, paleoseismic reconstruction of earthquake histories, and
geodynamic computer simulations to understand the causes of these
earthquakes. This project will provide both graduate and undergraduate
students with a unique opportunity to travel to China to work with
Chinese students and scientists on an exciting geological problem. For
more information, click on http://pire.missouri.edu.
Moving
Hotspots or Reorganized Plates?
The
theory of plate tectonics describes how tectonic plates, the dozen or
so pieces
of Earth's broken outer shell, move relative to each other. While
observations
in the past decades have greatly refined the relative motion of these
plates,
their motion relative to Earth's deep interior remains uncertain. Two
propositions suggested more than 30 years ago provide the framework for
relating plate tectonics to the deep mantle: 1) that hotspots, caused
by
upwelling plumes from the deep mantle, have remained fixed relative to
each
other, and 2) that the direction and rate of plate motions have not
changed
significantly in the past 40 million years. The former allows hotspots
to be
the most commonly used reference framework for studying plate motion
relative
to Earth's deep interior, and the later permits relative plate motion
established from young marine magnetic anomalies to be extrapolated to
the
geological past. We re-examined hotspot data with an up-to-date
relative plate
motion model and found that these two propositions cannot be tenable
simultaneously. Our statistical analyses indicate that plate motion did
not
reorganize significantly in the past 40 million years, but hotspots may
have
moved systematically, in the direction opposite to plate motion. Wang,
S., and M. Liu, Moving hotspots or reorganized plates?, Geology, 34
(6),
465468; doi: 10.1130/G22236.1, 2006
Related
News: Highlight in Geology :: Highlight
in Natural History Magazine :: MU
News
Release
The Ordos
Plateau is a relic
of the Archean Sino-Korean craton
which was thermally activated and split apart in the late Mesozoic. It
has
remained a stable block during the Cenozoic, while rift zones developed
on all
its margins but its southwestern side, where collision from the
expanding
Tibetan Plateau has produced the
Related
News: News
Report in
Science:: Associated
Press
News:: report at Physics
Today::Local News
Report
Fault
Evolution and Seismicity in the San Andreas Plate Boundary Zone
The
San
Andreas Fault (SAF) is the
Pacific-North American plate boundary,
but the relative plate motion and seismicity distributed over a broad
plate
boundary zone. In particular, the Eastern California Shear Zone (ECSZ)
accommodates up to 25% of present Pacific- North American plate motion;
in
southern California a significant portion of the relative plate motion
is taken
up by the San Jacinto Fault (SJF). We have developed a 3D viscoelasto-plastic
finite element model to simulate the initiation of theECSZ and the
SJF, their
impact on the regional stress field, strain partitioning, and
seismicity.
Preliminary results indicate a strong geometrical influence of the SAF
on the
along-strike variations of stress and deformation. In particular, the
Big Bend
is shown to reduce the slip rate on southern SAF and cause high shear
stress
and strain energy over a broad region in southern California,
consistent with
the spatial distribution of seismicity. It also facilitated the
development of
the ECSZ.