Summary Of the Late Quaternary Tectonics of the Basin and Range Province in Nevada, Eastern California, and Utah
(DERIVED FROM USGS DATABASE ON QUATERNARY FAULTS AND FOLDS IN THE UNITED STATES)
faults in the Great Basin portion
of the Basin and Range Province (Fig. 1) trend
slip displacement, and bound uplifted or tilted mountain
ranges. Although the uplifted ranges are spectacular geomorphic
features, the associated Quaternary faults whose relatively low
slip rates result in relatively long
or larger earthquakes. A small
percentage of the faults are quite active, especially those at
the eastern and western margins of the province, including the
Genoa (2-3 mm/yr), Death Valley (4-5 mm/yr), and Wasatch (1-1.5
mm/yr) faults. Hundreds of more typical Basin and Range faults
are clearly less active, but their long-term behavior is not well
studies show that some of
these faults have average slip rates of 0.05-0.15 mm/yr and recurrence
intervals of tens to hundreds of thousands of years for earthquakes
that rupture the ground surface. Although individual faults pose
relatively low hazard, the cumulative hazard is significantly
greater because hundreds of Quaternary faults riddle the province
and, therefore, increase the average rate of earthquake recurrence
in any particular region.
Michael Machette, Kathleen Haller, Richard Dart, and Susan Rhea
Map showing faults that had surface rupture in the past 1,600,000 yr (1.6 Ma, Quaternary) in the Great Basin
Except for aftershock activity associated with some historical ruptures in the province, it is difficult to associate recorded seismicity with specific faults and there are virtually no examples of foreshock activity preceding large earthquakes. For example, the Wasatch fault zone, the longest and most prominent fault in the province is poorly defined by earthquakes on Utah seismicity maps, and the Thousand Springs segment of the Lost River fault in Idaho was virtually aseismic at M>3.5 for at least two decades before it ruptured during the 1983 Borah Peak earthquake. Similar examples are common in the Great Basin, especially in its southern half. For the most part, normal faults of the Great Basin seem to be aseismic and locked, but some may be close to the point of failure as was the case with the 1954 Fairview Peak and Dixie Valley earthquakes.
Data from the global positioning system (GPS) of satellites shows some close associations with the fault data in the Great Basin. The entire province is between the Sierra Nevada Mountains in eastern California and the Wasatch Mountains in central Utah is expanding in a roughly east-southeast to west-northwesterly direction at a rate of about 13 mm/yr. Recent analyses of GPS data show a simple pattern in which the extension is concentrated in three belts: 1) along the Wasatch Front Utah, in the Intermountain seismic belt (ISB), 2) in the Central Nevada seismic belt (CNSB) in west-central Nevada, and 3) along the Eastern California seismic belt (ECSB) in extreme eastern California (Fig. 4).Miocene and Pliocene normal faulting, with minor rejuvenation during the Pleistocene.
The CNSB and ECSB have been the preferred areas where historical earthquakes larger than M 6.5 have occurred in the Basin and Range Province (Fig. 3). Between 1872 and 1954, seven large earthquakes caused surface ruptures along this NNE-trending belt yielding an incredibly high average of one rupture every 14 years. Recent summaries of paleoseismic investigations of the CNSB have shown that this rate of earthquakes that rupture the surface and the spatial pattern of activity is anomalous. There is no compelling evidence that a similar pattern of concentrated activity has occurred in this belt in the past 50,000 years, and there has been almost 50 years of quiescence since the last large earthquake. So, two of the most pertinent but unanswered questions about the CNSB are ?why here and where next?? Ultimately, the broader scientific challenge in the Basin and Range Province is to compare geologically determined rates and styles of deformation to contemporary strain fields determined by GPS to see if regions of accelerated extension are relicts of geologically recent activity or precursors of future activity. Hopefully, the new compilation of faults in the Basin and Range will provide an ever-growing archive of paleoseismic information that will encourage such comparisons.
Machette, M.N., Haller, K.M., Dart, R.L.; Thatcher, W.A., and Wernicke, B., 2002, Quaternary tectonics of the Basin and Range province of Nevada and Utah Faults, folds, and GPS: Geological Society of America Abstracts with Program, v. 34, no. 4, p. A-12.
Machette, M.N, 2003, Quaternary extensional tectonics of the Basin and Range province: Eos [Transactions of the American Geophysical Union], v. 84, no. 46, Fall meeting, Abstract S12E-01.
Machette, M.N, Haller, K.M., and Dart, R.L 2003, Quaternary fault database for the Basin and Range province of Nevada and Utah: Eos [Transactions of the American Geophysical Union], v. 84, no. 46, Fall meeting, Abstract G31B-0711.
Machette, M.N, Haller, K.M., Rhea, B.S., and Dart, R.L., 2004, Quaternary fault database for the Basin and Range province of Nevada and Utah: Proceedings of the Basin and Range Province Seismic Hazards Summit II, Western States Seismic Policy Council meeting, Reno, Nevada, May 16-91, 2004.
Machette, M.N, 2005, Summary of the late Quaternary tectonics of the Basin and Range province in Nevada, Eastern California, and Utah, in Lund, W.R., ed., Proceedings of the Basin and Range Province Seismic Hazards Summit II, Western States Seismic Policy Council meeting, Reno, Nevada, May 16-91, 2004: Utah Geological Survey Special Publication 05-2 (CD-ROM), 18 p., 12 full-color figures, 2 tables