USArray Workshop II

September 26-27, 1999 - Houston, Texas

USArray Background:

Over the past several years, the seismology community has begun to develop an initiative to vastly improve the resolution at which we can image the structure of the continental lithosphere and the deep Earth beneath North America. The scientific rational for the development of an enhanced facility, called USArray, can be found in articles published in EOS (Levander et al., 1999) and the IRIS Newsletter (Ekström et al, 1999) [see additional information below for references]. A USArray workshop in Albuquerque, New Mexico (March 15-17, 1999) helped define the technical components of the USArray facility [see USArray and EarthScope below], identified scientific goals, and discussed an operation and management scheme for the facility. The first workshop led to new momentum for the initiative and also increased recognition that this initiative needs to integrate geological and geophysical investigations into a single unified effort to best achieve its scientific goals. Our hope is that the USArray will help facilitate new ways of conducting multidisciplinary research across the geoscience communities. This second workshop (September 26-27, 1999) is designed to involve a wider community of Earth scientists in the early planning stages of this initiative to enhance its scientific goals; better define its multidisciplinary component; and to identify ways in which USArray can best be used to advance Earth science research, education and outreach.


USArray Workshop II: Purpose and Format:

In this second workshop we seek to bring together a diverse group of Earth scientists to explore ways in which other branches of the Earth Sciences can expand the USArray concept and continue to refine the scientific goals and organizational structure of USArray. We also wish to examine ways the entire project can contribute to advancing Earth Science research, education, and outreach. Specific objectives include:

The workshop will be a working meeting. Formal presentations will be limited focusing on the current working models for the technical components of USArray and overviews of the types of scientific investigations that could benefit from such a facility. Working groups will be asked to refine the details of the technical and scientific goals for the project, to identify new geoscience targets that can be addressed with the advanced imaging capabilities of USArray, evaluate the types of data that can be integrated into the Geoscience Information System, and determine the types of systematic measurements that can benefit from the infrastructure provided by the facility. Each working group will prepare reports that will be presented and discussed during plenary sessions. A writing group will be tasked with preparation of the final report.

The workshop will produce a report outlining the recommendations of a broad segment of the geoscience community for scientific issues to be addressed by USArray, ways to facilitate multidisciplinary integrated research, and further development of the concept of USArray as an integrated field laboratory. The report will be provided to NSF by the end of 1999. In addition to the formal report, a Web version will be prepared providing expanded details on both the facility and scientific applications.


USArray and EarthScope:

The main scientific goal of USArray is to address continental structure, evolution, and deformation by imaging crustal and mantle structures over a wide range of scales to obtain an integrated "whole continent" view of the North America. In addition to advancing integrated research in basic continental structure and tectonics, the facility will improve: seismic hazard assessment in North America; imaging of deep-Earth structure (e.g., lower mantle and core-mantle boundary); and Earth Science education and outreach. A core facilities component of USArray is a transportable array of seismometers that systematically samples the subsurface. Funding to enable these facilities will be sought from the NSF Major Research Equipment (MRE) Program. MRE is an NSF-wide program created in FY1995 to provide funding for the construction and acquisition of major research facilities that are beyond the funding resources of any one Directorate. To create what will hopefully be a successful proposal to the MRE competition, the GEO Directorate of NSF working with the EAR Division and members of the steering committees of the initiatives involved, has bundled USArray into a package known as "EarthScope — A Look into Our Continent". Earthscope includes the USArray and initiatives for a Plate Boundary Observatory, San Andreas Fault Observatory at Depth, and Interoferometric Synthetic Aperture Radar (InSAR). EarthScope is very much in its formative stages, but, if successful, would represent a significant input of new funds and resources for earth science research in the United States.


USArray Facilities:

The working model for the facility component of USArray consists of three parts:

Transportable Array - To provide resolution of crustal and upper mantle structure on the order of tens of kilometers and increased resolution of structures in the lower mantle and core from teleseismic events, USArray will include a dense transportable array of broadband seismometers. The core of the transportable component will be a telemetered array of 400 broadband instruments designed to provide data from a regular grid with nominal spacing of 50-70 km (~1000 km aperture). Approximately 50 magnetotelluric field systems will be embedded within the array to provide controls on temperature and fluid content within the lithosphere. The transportable array will roll across the country with a 1-2 year deployments at each site. Multiple deployments will cover the entire continental US over a period of 8-10 years.

Flexible Array- One of the developments of the first workshop was increased enthusiasm for a problem-oriented approach to regional tectonic, seismic, and ground water issues. Additional portable instruments will provide the ability to enhance the transportable array with high-density, shorter-term observations of special targets using natural and explosive sources. These instruments will travel from region to region with the Transportable array, and will involve a spectrum of geophysical and geological tools for addressing specific local and regional problems. Both this component and the Transportable Array will need to be closely integrated with geologists in order to achieve maximum scientific benefit.

Permanent Reference Network- This component provides fixed reference points for calibration of the transportable array and permanent coverage of the continent with a uniform spacing of 300-350km. The permanent reference network also adds an important fourth dimension, time, to the USArray facility by providing a platform for continuous long-term observations. This component of USArray compliments the initiative underway at the US Geological Survey to install an Advanced National Seismic System. Some or all of the stations of the permanent component of USArray will be equipped as expanded geophysical observatories, with GPS receivers to provide direct real-time data on crustal deformation. Other geophysical instruments can take advantage of the platform provided by the permanent installations.

A shared and critical requirement for all USArray facility components is communication (telemetry), data archive, and access and management of diverse data sets that include both geophysical and geological data. A goal of USArray is to develop a geoscience information system that can be easily accessed by the broad earth science community, educators, and government agencies. All data from USArray will be archived and available in near- real time and provided openly to the research community, educators and agencies responsible for hazard assessment.


For additional information refer to:

or contact anyone of the USArray Steering Committee:

Rick Carlson, <>
Tim Dixon, <>
Göran Ekström,<>
Mike Gurnis, <>
Gene Humphreys, <>
Karl Karlstrom, <>
Alan Levander, <>
Anne Meltzer, <>
Roberta Rudnick, <>
Peter Shearer, <>
Paul Silver, <>
Rob van der Hilst, <>
Peter Zeitler <>