A paleoseismic transect across the northwestern Basin and Range Province, northwestern Nevada and northeastern California, USA
AuthorPersonius, Stephen F.
Briggs, Richard W.
Maharrey, J. Zebulon
Angster, Stephen J.
Mahan, Shannon A.
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We use new and existing data to compile a record of similar to 18 latest Quaternary large-magnitude surface-rupturing earthquakes on 7 fault zones in the northwestern Basin and Range Province of northwestern Nevada and northeastern California. The most recent earthquake on all faults postdates the ca. 18-15 ka last glacial highstand of pluvial Lake Lahontan and other pluvial lakes in the region. These lacustrine data provide a window in which we calculate latest Quaternary vertical slip rates and compare them with rates of modern deformation in a global positioning system (GPS) transect spanning the region. Average vertical slip rates on these fault zones range from 0.1 to 0.8 mm/yr and total similar to 2 mm/yr across a 265-km-wide transect from near Paradise Valley, Nevada, to the Warner Mountains in California. We converted vertical slip rates to horizontal extension rates using fault dips of 30 degrees-60 degrees, and then compared the extension rates to GPS-derived rates of modern (last 7-9 yr) deformation. Our preferred fault dip values (45 degrees-55 degrees) yield estimated longterm extension rates (1.3-1.9 mm/yr) that underestimate our modern rate (2.4 mm/yr) by similar to 21%-46%. The most likely sources of this underestimate are geologically unrecognizable deformation from moderate-sized earthquakes and unaccounted-for coseismic off-fault deformation from large surface-rupturing earthquakes. However, fault dip values of <= 40 degrees yield long-term rates comparable to or greater than modern rates, so an alternative explanation is that fault dips are closer to 40 degrees than our preferred values. We speculate that the large component of right-lateral shear apparent in the GPS signal is partitioned on faults with primary strike-slip displacement, such as the Long Valley fault zone, and as not easily detected oblique slip on favorably oriented normal faults in the region.
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