After several years of planning, a massive new
Earth science research initiative is ready to dig deep and take
flight to expand the body of knowledge on the Earth's processes.
It's called EarthScope, an ambitious new earthscience
initiative designed to dramatically advance understanding of the
North American continent by comprehensively exploring its three-dimensional
structure, its evolution and its active dynamic processes.
By integrating scientific information derived from
geology, seismology, geodesy and remote sensing, EarthScope hopes
to yield a comprehensive, time-dependent picture of the continent
beyond that which any single discipline can achieve.
Land- and space-based technologies will make it possible
for the first time to resolve Earth structure and measure deformation
in real-time continental scales, according to Stanford University's
Mark Zoback, a member of the EarthScope Facilities Executive Committee.
The four EarthScope components are:
- The United States Seismic Array.
- The San Andreas Fault Observatory.
- The Plate Boundary Observatory.
- Interferometric Synthetic Aperture Radar
(InSAR).
"Each of these components has a separate history,
but in 2000 the National Science Foundation hit on the idea to combine
the different elements into EarthScope," Zoback said.
The program was developed by the scientific community
and the National Science Foundation, in partnership with other science
and mission-oriented agencies, including the U.S. Geological Survey
and NASA, with links to existing regional networks and state-based
agencies.
As with any scientific research, funding was a major
hurdle before EarthScope could become a reality, said Zoback.
"The big hurdle was congressional funding, and the
earth science community worked hard to push through the initiative,"
he added. "We can't celebrate yet until we get approval from NSF,
but we think it looks good.
"We are on the cusp of changing earth science forever."
Critical Areas
The EarthScope program will address scientific targets
in a number of critical areas of active research, including:
- Fault properties and the earthquake process.
- Fluids and magmas in the crust and upper
mantle.
- Crustal strain transfer.
- Convergent margin processes.
- Large-scale continental deformation.
- Continental structure and evolution.
- Deep Earth structure.
EarthScope resources will be accessible to the entire
scientific and educational communities, Zoback said. Data acquired
from the new observational facilities will be transmitted in near
real-time to central processing centers where it will be available
at no cost to the research community, government agencies, educators
and the public and private sectors.
End users also will have online access to software
that will aid in data integration, manipulation and visualization.
Numerous factors made EarthScope a reality, Zoback
said, including;
- Development of high-precision instruments
capable of being placed in remote locations for extended periods
of time.
- Availability of radio and satellite telemetry
that allows remote instruments to communicate directly and constantly
with operational support bases.
- An expanded capability for drilling,
sampling and taking measurements in active fault zones, and the
ability to instrument these holes to extract key information on
the physical conditions within earthquake nucleation zones.
- Widespread computer networks that bring
real-time data to the desktop and are capable of connecting scientists
and educators across the country into a united research and educational
enterprise.
- Analytical improvements in geochronology
that provide both higher precision and application to a wider
age range of events.
- Expanding data archival systems capable
of storing and manipulating huge data streams arriving from large
instrument arrays.
- A mature national infrastructure of Earth
science organizations and consortia that have developed extensive
experience in managing facilities similar to those in EarthScope.
A Better Understanding
The EarthScope facilities will use these new techniques,
approaches and data technologies to provide a framework for broad,
integrated studies across the Earth sciences. The USArray, SAFOD
and PBO observational systems will offer direct observations of
the spatial distribution and evolution of plate boundary deformation,
the space time pattern of earthquake occurrence, the initiation
and rupture sequences of earthquakes and the dynamics of magma rise,
intrusion and eruption.
These facilities also will advance the understanding
of earthquake and volcano hazards, as well as a number of important
problems in continental geodynamics and tectonics. The problems
include:
- Determining the mechanisms of continental
formation and breakup.
- The relationship between crustal tectonic
provinces and upper mantle structure.
- Rheological stratification and lateral
heterogeneity in the lithosphere.
- Role of fluids in the crust.
- Intraplate stress distribution and its
relationship to modern structures and seismicity.
- Development of dynamic topography.
- Feedbacks between surface and tectonic
processes.
"This is an exciting time for the Earth sciences,"
Zoback said. "This project promises to provide a wealth of knowledge
that can advance our science dramatically."
Organization
Regarding implementation, operation and maintenance
of EarthScope's facilities, Zoback said USArray, PBO and SAFOD facilities
will be under the direction of three community-based organizations:
- The IRIS Consortium.
- UNAVACO Inc.
- Stanford/USGS.
An EarthScope facilities office, however — including
a facilities executive committee and facilities project director
— will serve as the primary operational point of contact with NSF
and the user community for the entire project, noted Zoback, who
is a member of the EarthScope Facilities Executive Committee. The
office will coordinate the component facilities and interact with
NSF to ensure that EarthScope remains in compliance with NSF policies
and procedures, and is on-track and on budget.
The office also will work closely with a second committee,
the EarthScope Science and Education Committee, which will comprise
representatives from the Earth science community at large. This
committee will foster science integration, education and outreach
to ensure that the EarthScope facilities remain responsive to the
evolving needs of the research community, he said.
In addition, Zoback said, NSF will appoint an EarthScope
program manager as well as a new assistant director to oversee all
of NSF's large-scale facilities (which will include EarthScope).
"Exactly how the EarthScope committees will interface
with NSF's two-line manager approach to EarthScope will have to
be defined," he said, "but those things will work themselves out
as we move forward with the project."
EarthScope's Four Components
Each of EarthScope's four components will provide
important new information to the overall earth science community.
- The USArray will dramatically improve
the resolution of seismic images of the continental lithosphere
and deeper mantle. Scientists will integrate these images with
a multitude of geologic data to address significant unresolved
issues of continental structure, evolution and dynamics.
The USArray comprises a transportable telemetered
array of 400 broadband seismometers designed to provide real time
data from a regular grid, with dense and uniform station spacing
of 70 kilometers and an aperture of 1,400 kilometers.
The transportable array will roll across the country
with one- to two-year deployments at each site; multiple deployments
will cover the entire continental United States over a period of
eight to 10 years. When completed, this will provide coverage for
3-D imaging from over 2,000 seismograph stations.
While the initial focus of USArray is coverage within
the United States, extensions of the array into neighboring countries
and onto the continental margins in collaboration with scientists
from Canada, Mexico and the ocean science community would be natural
additions to the initiative, according to the EarthScope proposal.
An important second element of USArray is a pool of
more than 2,400 portable instruments that are a mix of broadband,
short period and high-frequency sensors that can be deployed using
flexible source-receiver geometries. These instruments will use
both natural and explosive sources, and will allow for high-density,
shorter-term observations within the footprint of the larger transportable
array.
The USArray also will include 40 permanent stations
in an augmentation of the National Seismic Network operated by the
USGS. Relatively dense, high-quality observations from a continental
network of about 130 stations, with uniform spacing of 300 to 350
kilometers, is important for:
- Tomographic imaging of deep earth structure.
- Providing a platform for continuous long-term
observations.
- Establishing fixed reference points for
calibration of the transportable array.
- SAFOD is a project designed to directly
monitor a creeping and seismically active fault zone at depth
to sample fault zone materials and to measure a wide variety of
fault-zone properties.
A four-kilometer deep hole will be drilled through
the San Andreas fault zone close to the hypocenter of the 1966 M-6
Parkfield earthquake, where the San Andreas fault slips through
a combination of small to moderate magnitude earthquakes and aseismic
creep.
SAFOD will provide new insights into the composition
and physical properties of fault zone materials at depth and the
dynamics that govern fault behavior. It also will provide direct
knowledge of the stress conditions under which earthquakes initiate
and propagate.
In addition to retrieval of fault zone rock and fluids
for laboratory analyses, intensive downhole geophysical measurements
and long-term monitoring are planned within and adjacent to the
active fault zone.
Observatory-mode monitoring activities will include
near-field, wide-dynamic-range seismological observations of earthquake
nucleation and rupture and continuous monitoring of pore pressure,
temperature and strain during the earthquake cycle.
- The Plate Boundary Observatory is a geodetic
observatory designed to study the three-dimensional strain field
resulting from plate boundary deformation. This requires that
plate boundary deformation be adequately characterized over the
maximum ranges of spatial and temporal scales common to active
continental tectonic processes.
The geodetic instrumentation must provide:
- Sufficient coverage of the plate boundary
zones so as to capture the secular tectonic component.
- Appropriate station density for detecting
localized phenomena.
- The necessary bandwidth — hours to decades
— to detect plausible transient phenomena ranging from fast and
slow earthquakes to interseismic strain buildup and post-seismic
viscoelastic relaxation.
A continuously recording, telemetered strain observatory
will be installed along the Pacific/North American plate boundary,
building upon and greatly expanding the capabilities of specialized
geodetic networks already in place.
PBO will consist of four elements:
- A network of GPS receivers to provide
a long-wavelength, long-period synoptic view of the entire plate
boundary. The network will extend from Alaska to Mexico and from
the West Coast to the eastern edge of the North American Cordillera.
Receiver spacing will be about 200 kilometers
and the data will be integrated with InSAR, when and where it
is available, to define the regional component of the strain
field.
- Focused dense deployments of GPS receivers
in tectonically active areas, such as along the San Andreas Fault
systems and around young magmatic systems. These areas require
the greatest temporal resolution, so integrated networks of borehole
strainmeters and GPS receivers will be deployed around these features.
On the order of 1,000 observing sites
will be needed to cover the most active tectonic regions.
- A pool of 100 portable GPS receivers for
temporary deployment for dense coverage of areas not sufficiently
covered by continuous GPS.
These systems will provide observations
in unmonitored regions and provide a rapid response capability
to detect strain transients following earthquakes and volcanic
eruptions.
- Establishing a national center for the
storage and retrieval of digital imagery and geochronological
facilities to support geologic and paleoseismic studies in PBO.
- Although not included in the request
for MREFC support, the Interferometic Synthetic Aperture Radar
(InSAR) satellite mission would provide spatially continuous strain
measurements over wide geographic areas. Plans are under way to
develop a dedicated InSAR mission as an integral part of the EarthScope
Observatory.
InSAR would allow scientists to:
- Map surface displacements before, during
and after earthquakes or volcanic eruptions.
- Image the time evolution of geologic
systems, provide insights into the mechanics of fault loading
and earthquake rupture.
- Map strain accumulation across broad
tectonic zones, potentially highlighting zones of strain concentration.
- Provide insight into the sources, migration
and dynamics of magma movement through a volcanic system that
may lead to an eruption.
- Improve understanding of the rheology
of the crust and upper mantle.