The GeoTraverse Workshop

Held at the first EarthScope National Meeting

March 28, 2005

Tamaya Resort, New Mexico



Basil Tikoff (University of Wisconsin);

Ben van der Pluijm (University of Michigan);



Ramon Arrowsmith (Arizona State), Sam Bowring (MIT), Mike Brown (Maryland), Cathy Busby (Santa Barbara), Rick Carlson (Carnegie), David Evans (Yale), Gary Fuis (USGS), Kevin Furlong (Penn State), George Gehrels (Arizona), John Geissman (New Mexico), Robert Hatcher (Tennessee), Kip Hodges (MIT), Dan Holm (Kent State), Mary Hubbard (Kansas State), Gene Humphries (Oregon), Jim Knapp (South Carolina), Luc Lavier (Texas Inst Geophysics), Thorne Lay (Santa Cruz), Chris Marone (Penn State), John Oldow (Idaho), Roberta Rudnick (Maryland), Jane Selverstone (New Mexico), Christian Teyssier (Minnesota), Martyn Unsworth (Alberta), Mike Williams (Massachusetts), Kelin Whipple (MIT), Robert Wintsch (Indiana).
Find contact information at end of the report.



Background and Motivation................................. 1

Schedule.................................................. 2

Breakout groups........................................... 3

Details of the GeoTraverse concept........................ 3

Results of the workshop................................... 4

Models for Geological involvement......................... 4

I. Strict GeoTraverse..................................... 5

II. CD-model.............................................. 6

III. Flexible GeoTraverse................................. 7

Summary of the GeoTraverse concept........................ 7

Participants ............................................. 9

Background and Motivation

GeoTraverse is a cross-continent, transect-based research concept that supports integrated, multidisciplinary (geologic and geophysical) study of the three-dimensional structure and temporal evolution of the crust and uppermost mantle of the United States.


The purpose of the GeoTraverse workshop was to evaluate a geologically-based scheme on how to design and coordinate one or more transects for high-resolution, coast-to-coast coverage of the conterminous United States.  The primary motivation of the GeoTraverse concept is the great need for systematic integration of geologic data into the EarthScope initiative. Additionally, we assert that broad involvement by the geologic community and recognition by the general public is essential for the ultimate success of EarthScope.  Among the EarthScope products, an over-arching synthesis of all regional EarthScope studies, such as provided by one or more geologic transects, is critical to define and understand the structure and evolution of the North American continent. The difficulty with the current deployment of USArray is that the arrangement offers insufficient spatial resolution of the crust, which is essential to geologic analysis.  Therefore, the meeting primarily focused on geologically relevant and reasonable use of the USArray flexible seismic array, utilizing both passive- and active-source seismology.  The combination of geophysical and geologic data   envisioned under GeoTraverse is scientifically integrative and synoptic, and would optimize public interest and outreach.


A group of ~30 experienced geoscientists from a broad spectrum of the community were invited to explore the possibility of the GeoTraverse concept.  The workshop was held at the Tamaya Resort at Santa Ana Pueblo, New Mexico, on the day before the first annual EarthScope meeting.  The preliminary outcomes of the workshop were presented during a 15-minute presentation on the first day of the EarthScope meeting (see ).



2:00p Welcome and workshop goals

van der Pluijm - Introduction and Logistics

Tikoff – details of GeoTraverse concept

2:30p Selected presentations. 

Humphreys – The role of active source seismology

Fuis – The role of active source seismology  

Selverstone – The role of petrology and geochemistry

Teyssier – The role of structure and rheology

3:30p Break

3:45p Two break-out groups (pre-arranged grouping)

4:45p Break-out group feedback on GeoTraverse concept (detailed discussion after dinner)

5-7 Dinner and break; opportunity to meet with other ES meeting participants

7:00p Plenary session: Discussion of break-out groups' discussions

8:00p Toward a "white-paper" on GeoTraverse and meet with representatives of other, interested groups

9:00p Adjourn


Breakout groups

The break-out groups were asked to explore questions that examine both process and research.  These questions were:

1. What process-oriented, geologic questions can be answered though imaging of the US lithosphere? 

2.  Specific questions about the GeoTraverse, including: a) Where are particular places to locate a traverse?; and b) What is the best strategy for a traverse (large swath, a few small swaths, multiple lines)?  

3. How does one organize a traverse and should there be an (small) organizational superstructure?

4. Given realistic resolution of passive source seismology (~10 km), how critical is active source seismology?

5. How can we utilize data delivery structure of EarthScope to collect/distribute geologic information in a digital format?


Details of the GeoTraverse concept

A GeoTraverse is a coast-to-coast geologic transect across the conterminous US that focuses on 3-D visualization of the crust and uppermost mantle.  We distinguish between literal transects and conceptual transects. A literal transect is a specific path on a map that combines targeted studies, and best captures the intent of the GeoTraverse concept as proposed.  Conceptual transects focus on specific regions of the continent in which studies will be conducted, although no specific data are collected across regional boundaries.  The latter might also be viewed as mini-traverses, following past and current integrated continental dynamics projects.


Any form of the GeoTraverse is not a one-dimensional line, but rather a swath with varied degrees of resolution along and perpendicular to the swath.  We envision a ~100 km wide (or broader?) passive source swath that represents a significantly enhanced spacing from the 70 km spacing utilized by the USArray Bigfoot array.  To provide greater crustal resolution, the GeoTraverse must locally add an active-source component that specifically includes reflection profiling, allowing the integration of geology, seismology and other geophysical approaches. 


A GeoTraverse is not necessarily straight, nor oriented EW.  Rather, a GeoTraverse is likely curved and occasionally segmented to link scientific targets and include critical geographic logistics.  Importantly, any form of GeoTraverse would ideally proceed in concert with planned USArray deployment to optimize outcomes and maximize the outreach potential, country-wide research opportunities.


The GeoTraverse concept could fundamentally change how geologists carry out continental science.  By identifying a national priority for obtaining geologic information, the community would embrace a “data-collection” model of operation, similar to that in the geophysics community.  The GeoTraverse must cultivate interaction among different geologic sub-disciplines.


Perhaps equally important to intellectual, science-driven considerations, the GeoTraverse will be a key element in the Education and Outreach component of EarthScope, as observable geological phenomena strongly interest the public and students.  Therefore, GeoTraverse should incorporate, where possible, recognized natural laboratories and iconic settings, such as National Parks and Monuments. Further, because of national extent of a GeoTraverse, it could potentially link EarthScope to urban populations.  Passing a transect or swath through an urban area would make a significant contribution to the visibility of EarthScope, with obvious links to area high school science programs, science museums, and other educational outlets.


Results of the workshop

The geologic community has a reputation for being individualistic, partially in response to the demands of field-based study by small groups and the fact that large collaborations are considered less critical for collecting geologic data. Initial responses at the workshop typically reflected this perspective. In particular, individual participants were concerned about the fact that identifying research targets would necessarily require that some areas would not get attention and/or that a particular process may not be examined in the best location.  Illustrating the diversity, an informal poll of target areas and research topics resulted in a list with as many specific features as participants.  The realization that this culture may have to change in the EarthScope environment was understood and grew significantly during the course of the meeting. Given the short duration of the workshop, many participants lacked definitive opinions and positions, but verbalized both the positive and negative features of the GeoTraverse concept.  Subsequent comments further shaped discussion.


Notably, the GeoTraverse concept, as broadly defined, was recognized for its very appealing components.  First, the potential, longer-term benefits of a broad research framework could outweigh initial reservations, especially when carefully coordinating regional interests.  Specific priorities were discussed in regional workshops, and these results must be considered in determining the path of a GeoTraverse.  Second, the participants emphasized that the geologic component of EarthScope does not have any organizing intellectual framework, and that a GeoTraverse could provide this context.  Last, it was generally agreed that geologists could benefit from a change in their approach to community-wide science, and that GeoTraverse may provide this opportunity.


In general, the workshop concluded that EarthScope offers a tremendous opportunity to the geological community, but that utilization and involvement of this community is presently limited in scope and purpose, and requires a broader framework to be established.


Models of geological involvement in the USArray component of EarthScope

A major question facing the USArray initiative is whether part or all of the flexible array instrument pool should be systematically deployed to focus study on specific areas of the coterminous United States.  Although the GeoTraverse workshop did not reach consensus on this issue, systemic deployment of the USArray flexible seismic array was a critical topic.  An overarching outcome of the workshop was the increased realization that geologists have an important role to play in EarthScope, but that role is poorly defined and presently poorly influenced.  Consequently, the geologic community, as a whole, is not involved in the EarthScope initiative.  The workshop was successful insofar as it outlined the possible roles of geologists and had frank discussions about the advantages and limitations of all approaches. 


We briefly summarize three plans that were discussed at the workshop: A strict GeoTraverse “swath” across the country, a Continental Dynamics (CD) model approach, and a modified GeoTraverse approach.


Option 1: A “Strict” GeoTraverse

We describe selected benefits of a coast-to-coast, planned traverse.  We neither specify the traverse location nor the equipment utilization, but rather advance the concept of a continent-wide traverse in anticipation of community discussion on specific location(s).


1) It would provide the portal for a geologic component into EarthScope.  Geologists working together would provide the continent-scale approach that is compatible with the EarthScope initiative’s goals.

2) It would highlight transitions between different tectonic provinces, rather than focusing exclusively on problems, often of parochial interest, specific to a region.  This is perhaps the richest intellectually, yet least recognized potential of the GeoTraverse concept, given the unusually diverse tectonic settings in the US.

3) All areas of the country would be covered, thereby enhancing the involvement of geoscientists in the EarthScope initiative.  This nationwide involvement can only increase the possible success of EarthScope.

4) It would engage the broader geologic community by offering a framework that embraces regional activities and opportunity for new discoveries. This motif is broadly summarized under the heading “Building a continent” (Structure and Evolution of the North American Continent).

5) It would transform how geologists do continental science, as it would specifically recognize “data-collection” as a complementary aspect of “hypothesis-testing” science.  This approach, used by the geophysical community, would undoubtedly allow us to recognize new process-based questions, to test new hypotheses that would otherwise not be possible.

6) It would facilitate the inclusion of numerous geologists, rather than selected groups, because an individual can contribute to data collection along the specified transect. 

7) It would offer a highly visible framework for outreach and education, by tying observable geologic phenomena (geology) to deeper lithospheric processes (determined from geophysics) across the entire continent.  The diversity of tectonic setting guarantees that interest will remain high during the project’s tenure.

8) Given the cost of studying the crust with active-source seismology and other techniques and the declining budgets that earth science institutions are currently facing, it is important that efforts be concentrated in a study such as GeoTraverse to maximum EarthScope results.




We recognize that there are several major challenges to adoption of the GeoTraverse concept by the geological (and geophysical) community.

1) How is a traverse located to optimize the outcomes, including both process- and discovery-oriented science?   As opposed to solely PI-driven research, in which the reviewers ultimately determine those areas/processes that are funded, the location of the transect will limit what can be studied.  Therefore, it is crucial that the process of choosing the transect is determined carefully by maximizing the amount of new information to be learned, given the exposure of the field area, resolution of specific seismic instruments, and logistics of their installation.

2) How will a location be decided upon in collaboration with regional groups?  Several regional groups have prioritized geologic problems in a particular area, and this information should be included in any larger, more encompassing initiative.  We recognize, however, that different regional groups may have geographically disparate areas that do not allow inclusion into any specific GeoTraverse (e.g., Southern Rocky Mountains and Northern Rocky Mountains).  We also recognize that specific regional priority areas are not equally compelling.

3) How many seismometers should be utilized in the GeoTraverse initiative?  Two-dimensional coverage along a GeoTraverse will require a large part of the USArray seismometers, yet excellent scientific arguments can also be made for areas outside the specific traverse.  We recognize that some compromise is required for these competing needs, which should be possible within the GeoTraverse concept.

4) How is the logistical effort realized?  Because a GeoTraverse requires putting instruments on a grid, it will require a major permitting and installation effort.  If and how this effort could be coordinated with the USArray Bigfoot array must be determined.

5) How can we integrate both the geophysical and geologic communities?  The GeoTraverse approach requires the participation of both the active and passive source seismology communities.  There are many enthusiastic supporters of this effort in these communities and we recognize that their cooperation is essential. The multidisciplinary, multi-institutional, and often multi-national transects that have been conducted to date, including LITHOPROBE, the  Trans-Alaska Crustal Transect, and the trans-European transects, have provided excellent models for GeoTraverse.

Option 2: CD-model approach

We view the CD-model as the “default” alternative to the GeoTraverse approach.  This approach is essentially “business-as-usual” for the tectonics community, with competing (individual or small team) PI-driven projects.  As is seen below, the benefits are less numerous, but so are the challenges.


1) It provides the least change in how geologists are accustomed to preparing proposals and conducting science.

2) It provides a focus on process-driven science and effort can be concentrated on areas that appear the most promising to provide information about aspects of continental processes and tectonic assembly of North America.



1) It is unclear how to combine results from different areas to provide a synthetic view of orogenic processes at the continental scale.

2) Can geologists compete successfully for funding with geophysics-only projects in this system?  The scale of USArray is larger than that of any individual group of geologists working in detail.  Further, it is not clear how to tie geologic data directly to questions about mantle structure and physical properties (with notable exceptions, such as xenolith studies).


Option 3: A “flexible” GeoTraverse

The concept of a “flexible” GeoTraverse is to provide some consistency on how the flexible part of USArray is employed across the country.  As such, this is a hybrid between a literal GeoTraverse model and the CD-model.  The benefits and challenges are intermediate between the two lists, depending on the exact nature of the “flexible” GeoTraverse and will not be repeated below.  Rather, we summarize only the salient points.

For a “flexible” GeoTraverse, the geological community must provide its focus and define questions associated with a range of length and time scales, associated with a flexible portion of USArray equipment.  Geological input is clearly essentially for dealing with issues related to time-specific questions, including the evolution of the North American lithosphere.  Geological research will provide the link between larger scale processes in the mantle and smaller scale deformation in the crust.  The geological community will also provide the link to deformation processes, by working at all intermediate scales, from that of the crust to the microscopic scale relevant to the experimental deformation community. 

Three main challenges exist for formulating such a “flexible” Geotraverse.  (1) An overarching theme or themes must make the Geotraverse a single entity rather than multiple individual problems (CD-model). This overarching theme may be crust-mantle interaction or time scales of deformation.  (2) Higher resolution seismic data will be needed in the focus areas and these will be expensive.  (3) A novel way to interact and a strong data gathering/storing infrastructure needs to be developed by geologists.  Integrative tools to link this information to geophysical data and for input into geodynamic models will be necessary, which fall more logically to GEON or CIG (Computational Infrastructure in Geodynamics).


Summary of the GeoTraverse concept

The GeoTraverse concept – in either its literal or more flexible form - takes full advantage of the unique opportunity provided by EarthScope, providing a synoptic, integrative, and four-dimensional view of the North American continent.   The flexible form has the logistical advantage that it is a more organized form of how the geological community has done science in the past.  The GeoTraverse concept has the possibility of fully integrating the geological component into EarthScope and thereby broadening how the geological community does research.  It also provides for the possibility of significantly enhancing the education and outreach components of EarthScope, potentially with collaboration of the National Parks.  Adoption of the GeoTraverse concept will require compromises with other research activities, but the benefits are huge.  GeoTraverse would more fully integrate geology into EarthScope, distribute geologic investigation throughout the United States, transform the scientific approach of the geologic community, and provide a synoptic view of the North American continent that will become an unprecedented example of continental structure and evolution. 



June 10, 2005




Basil Tikoff (co-conv)


Ben van der Pluijm (co-conv)


Cathy Busby


Chris Marone

Penn State

Christian Teyssier


Dan Holm

Kent State

David Evans


Gary Fuis


Robert Hatcher


Robert Wintsch


Gene Humphreys


George Gehrels


Jane Selverstone

New Mexico

Jim Knapp

South Carolina

John Geissman

New Mexico

John Oldow


Kelin Whipple


Kevin Furlong

Penn State

Kip Hodges


Luc Lavier


Mary Hubbard

Kansas State

Mike Brown


Mike Unsworth


Mike Williams


Ramon Arrowsmith

Arizona State

Rick Carlson


Robert Hatcher


Robert Wintsch


Roberta Rudnick


Sam Bowring


Thorne Lay

Santa Cruz