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My research can be divided into several broad themes, and programs
therein. Much current effort has gone into large broadband seismic
field experiments, which continue to offer exciting student
opportunities.
Imaging the
Central America Subduction Factory (TUCAN: Tomography and other things
Under Costa Rica And Nicaragua)
Why do volcanos form in subduction zones? Many of the largest
volcanoes on the planet form in subduction zones, implying that melting
occurs there, yet the causes of melting remain poorly understood. To better
understand the origin of arc magmas, we are conducting a broadband seismic
field experiment in the Central American Subduction Factory, using PASSCAL instruments. The main
deployment started July 1, 2004, continuing through March, 2006. This NSF -
Margins
experiment should provide images of slabs and the mantle wedge where
geochemical indicators of melting show large along-strike variations.
Initial results show an unusually slow layer atop the Nicaragua slab,
inferred to be strongly hydrated (Abers et al.,
2003). This major broadband seismic project is in
collaboration with Brown University, OVSICORI/Univ. Nat. Aut. Costa Rica,
and INETER Nicaragua. (ftp
proposal here in 6Mb PDF) or just the (Project
Summary PDF)
The Central America
experiment (TUCAN) has a web page found here.
Subducting
slabs, structure, metamorphism, and earthquakes
A long-term project has been the unravelling of the processes that take
place within subducting plates at sub-arc depths (50-250 km). Most
processes are in some way affected by or control the release of fluids into
the subduction system. We are imaging the dehydration of downgoing
plates using a variety of seismological tools, primarily through the
propagation of high-frequency signals that can image features as small as
subducting crust. The dehydration also seems tied to the generation of
earthquakes in some way, and we are exploring models for earthquake
generation. Through the NSF CSEDI program, we are funded to work with
petrologists and thermal modelers to better understand these systems.
The projects in Alaska and Central America directly tie to this broader
goal. We are working closely
with geodynamic model development to make better sense of these and other
observations.
Recent work includes a global
compilation of subduction zone parameters (Syracuse and Abers, 2006
G-cubed), a useful reference for a wide variety of subduction zone studies.
(web page
with text and data)
Multidisciplinary Onshore
Observatories for Subduction (MOOS) Project Page
This Alaska-based field experiment features broadband imaging of the
subduction zone updip of BEAAR, through the Kenai Peninsula area where the
great 1964 Good Friday Earthquake (Mw 9.2) ruptured the worlds largest
asperity. (pdf of Summary) (6 Mb proposal here) The deployment,
of 34 broadband seismographs, began in June 2006 with full deployment in
the summer of 2007. This is
probably the best place on the planet to observe deep subduction of thick
crust and its effects on tectonic process; these processes may include the
link to the behavior of great earthquakes. We will be investigating the
relationship between interplate thrust zone seismicity, surface deformation
with GPS, and the postulated subduction of the Yakutat terrane. This
work is in collaboration with D. Christensen and J. Freymueller at the Geophysical Institute of the University of
Alaska Fairbanks.
Cascadia Arrays For
Earthscope (CAFE)
A two-year field campaign
began in July 2006 with the deployment of 62 seismographs in the Cascadia
subduction zone, in western Washington State (PDF
map). This project aims to understand the relationship between
subduction, the transport of water into the earth’s mantle, and unusual
Episodic Tremor and Slip events, recently discovered in the Pacific
northwest. The BU parts of
this project relate to seismic imaging with broadband instruments of the
forearc and arc in Washington State. This project is collaborative with
several other (Univ. Washington, MIT, Central Washington, UC Santa
Barbara), and is part of the Earthscope initiative, a major US effort to
sample strain and image the mantle beneath the continent. Click
here for a UW early press release on this project.
BEAAR:
Broadband Array across the Alaska Range (click this for project page)
This 36-station broadband experiment (map)
sampled the crust, mantle, and subducting plate beneath central Alaska
between Anchorage and Fairbanks (regional map).
Here are some 1999
field pictures and some 2000
pictures. It samples the roots of the region around Mt. McKinley,
and lies atop a subducting Pacific slab as it descends from 60 to >150
km depth. The deployment lasted from June 1999 to August 2001.
Work by Aaron Ferris, a graduate student, has made an impressive image of the subducting
Pacific plate to nearly 150 km depth using receiver function techniques (Ferris et al., 2003, EPSL). This work is
a collaboration with the Geophysical
Institute of the University of Alaska Fairbanks.
Woodlark-D'Entrecasteaux
Seismic Experiment
This Woodlark Rift includes the world's fastest opening piece of
continental crust, so makes a natural laboratory for exploring the
processes leading to continental breakup and the consequences of high
strain (regional map). We have observed
evidence for normal faults at unusually shallow dips (to 25 degrees) in a
region of active metamorphic core complex formation. A joint land-sea
seismic experiment, from July 1999 - June 2000, provided the first direct
sampling of local earthquakes and deep structure in the region. At BU
we have been responsible for the 20 on-land PASSCAL broadband sites. First results from this seismic experiment (Abers et al., 2002, Nature) show that the
crust is thinning by >10 km in the region directly under the area of
maximum unroofing of the upper crust, and that this region is compensated
by hot mantle. This shows how extension in the mantle plays a
dominant role in extension. Click here for
a picture of our most remote site, Egum Island.
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