PALEOSEISMIC EVIDENCE FOR PRIOR BELT-LIKE BEHAVIOR IN THE CENTRAL NEVADA SEISMIC BELT

The central Nevada seismic belt (CNSB) is a zone of seven moderate- to large-magnitude historical earthquakes that produced a nearly continuous zone of surface faulting extending for 300 km from the 1932 Cedar Mountain zone on the south to the 1915 Pleasant Valley zone on the north. Our studies have integrated new paleoseismic data from trenching, radiocarbon dating, and tephrochronology with previous studies in the CNSB to look for evidence of older, similar belt-like rupture patterns that could indicate whether the CNSB is a zone of focused, long-term crustal strain or whether it is a temporal feature. Based on the number and timing of events determined for each historical rupture zone, the data show that the historical rupture belt pattern is unprecedented in the available paleoseismic record. In particular, the age of the penultimate event on the 1954 Fairview Peak fault is >35.4 ka (age of Wilson Creek bed 19 tephra), precluding the possibility of an identical belt in the last several tens of thousands of years. However, based on the timing and distribution of events in the historical zones together with paleoseismic data from associated Holocene faults, including the Stillwater seismic gap, several similar, but not identical, belt-like combinations can be postulated within the greater 1915-1932 rupture zone. If the Holocene-age Sand Springs fault zone is substituted for the adjacent 1954 Fairview Peak fault, three belt-like scenarios are possible for several intervals during the last 13 ka (nominal age of last lacustral highstand): 1) 2-4 ka 2), 6-9 ka, and 3) 10-13 ka. None of these rupture combinations would fully duplicate the historical sequence, however. We conclude that the paleoseismic histories of each of these faults are diverse, and that although some events may correlate between some faults, there is not a consistent pattern of belt-like behavior comparable to the historical sequence during the last 13 ka.