SSA 2005 Field Trip Information

Behind the Scenes: Tour of the Nevada Seismological Laboratory and the shake tables at the James E. Rogers and Louis Weiner Jr. Large Scale Structures Laboratory

Glenn Biasi (Nevada Seismological Laboratory) and Gokhan Pekcan (Department of Civil Engineering, University of Nevada, Reno)

When: Friday Afternoon (2:00 PM until 8:00 PM)

Field trip participants will tour the Nevada Seismological Laboratory and the shake tables at the James E. Rogers-Louis Wiener, Jr. Large-Scale Structures Laboratory. The tours will be followed by a catered dinner on the UNR campus.

The first half of the tour will focus on the inner workings of the Nevada Seismological Laboratory, which has overall responsibility for instrumental studies of earthquakes in the Nevada region. The laboratory operates a statewide network of seismographic stations and investigates the sizes, frequencies of occurrence, and distribution of earthquakes in the region, and other problems related to seismic risk in Nevada.

The second half of the tour will highlight the Network for Earthquake Engineering Simulation (NEES) equipment site at the University of Nevada, Reno, a biaxial, multiple shake table facility (with three identical biaxial shake tables) that is suitable for conducting of research on long, spatially distributed, structural and geotechnical systems. The facility is also capable of testing conventional structural and non-structural systems by using the tables in large-table mode, and operating them as a single unit. The facility is managed as a national shared-use NEES equipment site, with teleparticipation capabilities, to provide new earthquake engineering research testing capabilities for large structural systems through 2014.

More information on these facilities can be obtained at http://nees.unr.edu/ and http://seismo.unr.edu/.

Precarious rock constraints on ground motion from normal and trans-tensional strike-slip earthquakes

James Brune and Richard Briggs

When: Friday afternoon (12:00 PM to 8:00 PM)

Numerous precarious and semi-precarious rocks have been documented within a few km of normal faults and trans-tensional strike-slip faults north of Reno. Some of these rocks are less than 1 km from the trace of the most recent breaks. These precarious rocks provide important constraints on ground motion from recent earthquakes.

An impressive field of precarious rocks is located 1-2  km from the Fort Sage Mountains normal-fault zone, on the footwall, and 1-7 km from the Honey Lake trans-tensional strike-slip fault.  Field tests suggest that these rocks would be toppled by 0.2-0.3g accelerations.  In contrast, USGS-CDMG hazard maps predict much higher accelerations (e.g., 0.8g for 2%-in-50-years probability), most of the hazard coming from strike-slip earthquakes along the Honey Lake trans-tensional fault (none from the Fort Sage Mountains normal fault, which was not included in the hazard study).

Preliminary analysis of trench exposures on the Fort Sage Mountains normal fault indicate near-field displacements of at least a meter during the latest Pleistocene/early Holocene, overlapping with the lifetime of the precarious rocks, which sit untoppled 1-2 km away.  Regressions of displacement and magnitude suggest that the offsets correspond to earthquakes of Mw 6.8 - 7.1.  If an Mw 6.8 - 7.1 earthquake has indeed occurred without toppling the rocks, then the precarious rocks near the Fort Sage Mountains fault suggest that existing attenuation curves over-predict ground motions on the footwall of normal faults, as well as ground motions from trans-tensional strike-slip faults. . The field trip will include a short trek to the precarious rocks, and a visit to one of the trenches.

A 50th anniversary visit to the 1954 surface ruptures in the Central Nevada Seismic Belt

Andrew Barron and Rich Briggs (Center for Neotectonic Studies, University of Nevada, Reno)

When: Saturday (8:00 AM until 6 PM?)

In 1954, four large earthquakes (Ms 6.3 - 7.2) produced surface rupture in central Nevada. We'll observe the 50th anniversary of these earthquakes by revisiting the surface ruptures and highlighting important past and present work in the region. We'll visit scarps and secondary deformation features along the rupture trace in Dixie Valley and discuss geologic fault slip rates across the Central Nevada Seismic Belt in the context of recent GPS geodetic and INSAR measurements.

Active fault architecture of the Lake Tahoe Basin

Graham Kent (University of California, San Diego-Scripps Institution of Oceanography) and Gordon Seitz (San Diego State University)

When: Saturday (9:00 AM until 4:00 PM)

This trip will highlight geophysical and geological studies conducted during the past half-decade that document active extension (≥0.5 mm/yr) across the Lake Tahoe Basin. A variety of field trip stops will focus on three, en-echelon normal faults that are responsible for basin formation, and the role that glacial damming and associated lake-level changes have played in helping geoscientists unravel the tectonic history of the basin. A three-dimensional, virtual Lake Tahoe model will also be presented during the field trip; CDs including the model and software will be distributed to field trip attendees. Points of interest include: Emerald Bay, Eagle Rock, Tahoe City Dam, Incline Village Elementary School, and Mt. Rose Highway lookout.