| Research
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Hot
spots and mantle plumes |
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I
play a major role in co-ordinating the current global
debate on whether deep mantle thermal plumes exist and
give rise to “hot spot” volcanism. This
has been described as the most important controversy
in Earth Science today. A critical element of the subject
is development of alternative models. My main activites
are:
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I founded and manage the website www.MantlePlumes.org,
an international forum for the debate, which currently
contains contributions from ~250 scientists and over
300 web pages, ~100 of which are purpose-written scholarly
articles.
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I initiated and convened two recent international
conferences, Plume
IV: Beyond the Plume Hypothesis, a Penrose
Conference held in Iceland in 2003 and sponsored by
the Geological Society of America, and The
Great Plume Debate, a Chapman Conference
held in Scotland in 2005 and sponsored by the American
Geophysical Union.
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Examples
of recent significant publications:
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Foulger, G.R., J.H. Natland, D.C. Presnall and D.L.
Anderson (Eds.), Plates,
Plumes, and Paradigms, Geol. Soc. Am. Special
Volume 388, pp. 881+xi, 2005.
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The
Coso producing geothermal area, California |
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The
Coso geothermal area is utilized to generate ~250 Mw
of electricity. Steam removal induces intense microearthquake
activity suitable for advanced seismic analysis techniques
that are powerful to monitor the reservoir and optimize
production strategies. I have used the ~80,000-earthquake
dataset currently available for time-dependent seismic
tomography, relative event relocations and moment-tensor
analysis.
These
studies have yielded a 3D image of the entire reservoir,
and show changes in reservoir properties with time caused
by production. Fracture enhancement is conducted using
hydraulic stimulation to improve steam recoverability.
A unique proof-of-concept of the moment-tensor technique
to image stimulated fractures and their mode of failure
was recently achieved. During 2006, hydraulic stimulations
in additional wells will be monitored and studied. The
huge dataset available has the potential to generate
numerous other studies.
This
project is conducted in collaboration with the U.S.
Geological Survey, the U.S. Navy and the University
of Utah, and is funded in part by the Department of
Energy. It comprises a strategic element in the development
of alternative energy resources.
Examples
of recent significant publications:
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Julian,
B.R., G.R. Foulger, K. Richards-Dinger and F. Monastero,
Time-dependent
seismic tomography of the Coso geothermal area, 1996-2004,
Proceedings, Thirty-First Workshop on Geothermal
Reservoir Engineering, Stanford University, Stanford,
California, January 30-February 1, 2006.
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Foulger,
G.R., B.R. Julian, D.P. Hill, A.M. Pitt, P. Malin
and E. Shalev, Non-double-couple
microearthquakes at Long Valley Caldera provide evidence
for hydraulic fracturing, J. Volc. Geotherm.
Res., 132, 45-71, 2004.
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The
Iceland Hotspot Project |
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In
1996 I led a multinational, NERC-, NSF- and EC-funded
consortium that deployed in Iceland the largest regional
broadband seismometer network ever installed in the
world at the time. Over a two-year period it returned
several hundred Gbyte of seismic data that are now publicly
available on the Internet. These data have fueled, and
continue to fuel, numerous research projects and Ph.D.
theses.
Major
discoveries include the shallow nature of the low-velocity
mantle anomaly beneath Iceland and an extensive low-velocity
body in the crust that may represent a submerged oceanic
microplate. Seismic velocity anisotropy suggests ridge-parallel
flow; the absence of the predicted radial pattern is
consistent with the lack of radial coherence in surface
geochemistry.
The
results have generated numerous published papers and
furthered understanding of hot spots globally. The unexpected
complexities revealed raise many new questions, inspiring
a wealth of further topics for study, including graduate-student
theses.
Examples
of recent significant publications:
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Exotic
earthquake focal mechanisms |
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It
is commonly assumed that earthquakes are caused
by shear motion on geological fault planes. Such
motion is expected to generate seismic source mechanisms
consisting of two mutually orthogonal force couples,
the so-called “double couple” model.
For several decades, this model was used as an a-priori
assumption to constrain seismic data interpretation.
Working
in the Hengill geothermal area, Iceland, I achieved
the first observation of earthquakes whose sources
unambiguously involved an explosive, crack-opening
component in addition to shear. Such sources can
be explained by the motion of fluids, e.g.,
magma or water, into cracks – a process fundamental
to the hydraulics of volcanoes and geothermal areas.
This work has relevance to volcanic hazard reduction
and geothermal resource utilization.
I
have applied the results to active volcanoes in
Iceland and the USA, and to geothermal areas in
Iceland, the USA, Indonesia and Papua New Guinea.
This research theme has generated many field projects,
publications and Ph.D. theses. I presently apply
the methods developed to the Coso geothermal field,
southern California.
Examples
of significant publications:
- Julian,
B.R., A.D. Miller and G.R. Foulger, Non-double-couple
earthquakes 1. Theory, Rev. Geophys.,
36, 525-549, 1998
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- Foulger,
G.R., R.E. Long, P. Einarsson and A. Bjornsson,
Implosive earthquakes at the active accretionary
plate boundary in northern Iceland, Nature,
337, 640-642, 1989
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Foulger,
G. and R.E. Long, Anomalous focal mechanism solutions:
evidence for tensile crack formation on an accreting
plate boundary, Nature, 310,
43-45, 1984
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Crustal
deformation using the Global Positioning System |
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In the period
1986 – 1995 I led 7 multinational GPS surveys in
Iceland, Turkey and the Basin & Range Province, western
USA. These surveys involved teams of up to ~20 fieldworkers
who occupied up to ~100 survey stations distributed over
regions up to ~800 km wide. The objectives were to establish
and measure networks of survey points to centimetre-level
accuracy, and then to re-measure them in order to constrain
crustal deformations due to geological processes. This
huge surveying effort, and the massive data-processing
and software-development effort required to extract the
results, led to several major discoveries.
A
great dyke-injection episode along the spreading plate
boundary in Iceland 1975-1985 loaded the crust with stress,
which was subsequently gradually released by slow deformation
that continued at a detectable level until 1995. Our observation
of this phenomenon remains a unique achievement and enabled
us to calculate the viscosity of the asthenosphere. Surveying
across the Basin & Range Province revealed that most
of the ~1 cm/year of expansion there is concentrated in
two seismically hazardous zones.
The
project generated significant papers, M.Sc. and Ph.D.
theses and post-doctoral projects. It laid the groundwork
for ongoing investigations of the study regions that continue
to the present day.
Examples of
significant publications:
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Thatcher,
W., G.R. Foulger, B.R. Julian, J. Svarc and E. Quilty,
Present
day deformation across the Basin and Range Province,
western United States, Science, 283,
1714-1718, 1999
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Foulger,
G.R., C.-H Jahn, G. Seeber, P. Einarsson, B.R. Julian
and K. Heki, Post
rifting stress relaxation at the accretionary plate
boundary in Iceland, measured using the Global Positioning
System, Nature, 358, 488-490,
1992
last
update 22nd January, 2009 |
