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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.
Subducting slabs, structure, metamorphism, and earthquakes
A long-term project has been the unraveling
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. We are funded to work with
petrologists and thermal modelers to better understand these systems: to understand
how seismic velocities relate to rock composition, fluid content, melting
and other parameters of interest; to understand the global systematics of
subduction systems; to understand causes of subcrustal earthquakes; and to
understand the Earth’s deep volatile cycle and thermal structure.
Global Compilation of Subduction Parameters. 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) A
follow-up study underway is examining the biases in slab geometry due to
unmodeled three-dimensional variations in seismic velocities, and the
earthquake mislocations that they cause.
Useful Excel Macro/Spreadsheet for calculating velocities.
Calculates P and S velocities and other related properties from
mineral composition at arbitrary P and T, published as Hacker and Abers,
2004 G-Cubed. (Hacker’s
version of macro) Currently upgrading it, adding anelastic effects and
other enhancements.
Global systematics of subduction zone thermal structure.
Ellen Syracuse (PhD candidate) is completing a global suite of 2D
thermal models for all accessible subduction zones, in collaborative with
Peter van Keken (Michigan).
Field-based Projects: Broadband Arrays (reverse
chronological order)
CDPapua: Exhumation
of the worlds youngest ultra-high-pressure rocks.
This project, recently funded by the NSF
Continental Dynamics program, includes a wide array of geophysical,
geodetic, geodynamic, geochemical and petrological studies of the D’Entrecasteaux
metamorphic core complexes in Papua New Guinea. These rocks include UHP rocks exhumed from > 100 km
depth in the last 5 Ma (Baldwin et al., 2004). How do crustal rocks travel
vertically so fast? The seismology portion includes a 30 element PASSCAL
broadband array and 8 element broadband OBS array, designed to image the
source region of these rocks and to place constraints on their mode of
emplacement / exhumation. Abers
leads the on-land part, Gaherty leads the OBS deployment. Other Lamont-based scientists
include Roger Buck and Terry Plank; the project is being managed by Suzanne
Baldwin at Syracuse, and includes groups from UC Santa Barbara, U. Texas
Austin, New Zealand, and Macquarie Univ. Australia. Seismic deployment planned in 2010.
Multidisciplinary Onshore Observatories for Subduction (MOOS) Project Page
This Alaska-based field experiment features
broadband imaging of the subduction zone 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 includes 4 - 34 broadband
seismographs across the region.
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 are
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. Seismic deployment 2006-2009.
Cascadia Arrays For Earthscope (CAFE)
(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, through a coordinated
geophysical effort in western Washington State. The Lamont parts of this project include seismic imaging
with broadband instruments of the forearc and arc, to provide in situ
constraints on the structure associated with tremor and transport of
subduction zone volatiles. 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. Seismic
deployment 2006-2008.
TUCAN: Tomography and other things Under Costa
Rica And Nicaragua Project Page
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. This NSF - MARGINS
experiment images the slab and the mantle wedge where geochemical
indicators of melting show large along-strike variations. 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) (summary
in IRIS Newsletter – 8 Mb) Seismic deployment 2004-2006.
BEAAR: Broadband Array across the Alaska Range Project Page
This 36-station broadband experiment (map) sampled the crust, mantle, and subducting plate
beneath central Alaska between Anchorage and Fairbanks (regional map). 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. Seismic deployment 1999-2001.
Woodlark-D’Entrecasteaux Seismic Experiment: (Map)
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. This joint land-sea seismic experiment provided the first
direct sampling of local earthquakes and deep structure in the region. .
Results (Abers
et al., 2002, Nature) show rapid
thinning of crust and mantle upwelling under the area of core complex
exhumation. Seismic deployment 1999-2000.
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