GSA home

Log In | GSA Community | GSA Store | Join GSA | Donate | Contact Us

GSA home

| GSA Community | GSA Store | Donate | Contact Us

About GSA

Connected Community

Divisions &
Associated Societies

Education & Outreach

GSA Foundation

GSA International




Public Policy


Resources & Jobs


Find Your Science at GSA
Penrose Conference

Association of Environmental & Engineering Geologists
Seismological Society of America

Penrose Conference Announcement

Extensional Reactivation of Thrust Faults, Coseismic Surface Rupture, and Crustal Evolution in the Eastern Basin and Range Transition Zone

Evanston, Wyoming, USA  • 22–27 June 2015

Download the
Conference Summary



Co-Chair Michael W. West
Michael W. West & Associates, Inc.,
Co-Chair Stephen A. Sonnenberg
Colorado School of Mines,
Paul M. Santi
Colorado School of Mines,
Tarka Wilcox
Pacific Lutheran University

figure 1
Figure 1. (A) Low-sun angle aerial view of the Big Burn scarp (dotted yellow line at midpoint of scarp) at the south end of the Bear River fault zone (BRFZ). The scarp is 15+ m high in glacial tills and outwash. (B) View of trench wall excavated across the Lester Ranch scarp, BRFZ, showing colluvial wedges, surface soil, and two buried organic soils delineating surface faulting events at about 4.6 ka and 2.2 ka. (C) Low sun angle views to the south along Holocene fault scarps, BRFZ, showing tilting of flood plain. The active stream channel, due to back-tilting, is eroding the scarp. The former channel is preserved on upthrown block. (D) View of block faulting, looking south, along the west side of the Bigelow Bench outwash surface. Note displacement of the outwash surface, eastward back-tilting, and possible graben development. Click on image to enlarge.

Rare geologic terranes exist in intraplate areas of the North American continent that illuminate nascent crustal-scale tectonic processes, fault nucleation/evolution, interaction of geologic structures in changing stress fields, tectonic effects on topography and fluvial systems, and issues in seismic hazard/risk assessment. These terranes, if recognized, are ideally suited to multidisciplinary research, leading to greater understanding of crustal evolution from the crust-mantle interface to surface geomorphology. Conference participants will have the opportunity to examine and assess active crustal deformation in an area encompassing the Laramide Uinta Mountains uplift; the Absaroka and Darby/Hogsback thrust plates of the Sevier orogenic belt (Wyoming and Utah); the late Holocene Bear River fault zone (BRFZ); and the transition between the contemporary margin of the Basin and Range province and the adjacent Laramide Green River Basin (Figs. 1A–1D and 2). The Bear River fault zone exhibits the largest reported paleo-displacements in the Basin and Range province, indicating the terrane encompassing the BRFZ and extensionally reactivated thrust faults is among the most tectonically active in the transition zone.

Specific conference topics include (1) crust/mantle interaction in the eastern Basin and Range transition zone, 100+ km east of the Wasatch Front; (2) stress, strain, and rheology at the intersection of the Uinta Mountains, Sevier thrust belt, Green River Basin, and active Basin and Range extension; (3) kinematics and evolution of crustal-scale structures from compression through contemporary extension; (4) relation of late Holocene co-seismic fault ruptures to preexisting Sevier and Laramide thrust faults; (5) refinement of seismogenic fault histories and surface-rupture parameters; (6) seismogenesis and hazards related to surface rupture along low-angle faults; (7) tectonic effects on glacial and fluvial geomorphic systems; (8) glacial loading/unloading effects on fault surface-rupture; (9) geophysical imaging of structures from the near subsurface to the crust/mantle interface; (10) applications of geodesy, LiDAR, and INSAR to crustal deformation and comparison to paleoseismological methods; and (11) relation of hydrocarbon occurrence to active, extensional tectonism.

figure 2
Figure 2. LiDAR image (evening illumination) of the south end of the BRFZ at the intersection with the Uinta Mountains uplift, showing the Big Burn scarp, antithetic scarps, and scarps sub-paralleling the north flank of the Uinta Mountains. Inset: Low-sun angle aerial view, looking S-SW, of the intersection of the Big Burn scarp, BRFZ, with the north flank of the Uinta Mountains. Click on image to enlarge.

The conference area provides an important, largely untapped field laboratory in which to study the interaction of contemporary extensional tectonic processes with older structures, reflected in modern topography and geomorphology. We suggest that this part of the eastern Basin and Range transition zone may be a “Rosetta” terrane, highlighting tectonic interactions in a complex geologic setting. Late-onset extension illuminates subsurface structural relations, reflected in surface deformation, which would likely not be recognized either in unextended terranes or, conversely, in highly extended terranes where initial structural relations may become indecipherable. Moreover, the juxtaposition of active extension against the relatively stable geomorphology of the Green River basin provides an opportunity to assess the timing and effects of late-onset extension on landscape development. We expect that the conference will yield new insights related to the region’s crustal evolution with applications transferable to other terranes affected by changing stress fields. Conference participants will be tasked with determining if the project area should be designated as a prototype “national field laboratory” to encourage focused research on crustal-scale tectonic processes.

The conference, including focused technical presentations, field trips, and workshop, will be held in Evanston, Wyoming, USA, at the historic Union Pacific Railroad Roundhouse Conference Center. Attendees are invited to arrive 22 June by 5:30 p.m. (MST) for welcome reception and dinner.

As currently planned, the conference will encompass five days:

Conference Proposal

GSA Bulletin article

Meeting Registration will be approximately US$1500. Registration will include 5 nights lodging in Evanston, 2 field outings, and dinner Monday, 22 June. Breakfast, lunch, and dinner on Tuesday, 23 June through Friday, 26 June. Breakfast and lunch on Saturday, 27 June. Attendees will be responsible for airfare and transportation to and from the conference site. 


Deadline 13 March 2015. Please see details above.