Paleoseismic transect across the northern Great Basin

Abstract

The relationship of strain accumulation to strain release over different timescales provides insight to the dynamics, structural development, and spatial and temporal pattern of earthquake recurrence in regions of active tectonics. The Great Basin physiographic province of the western United States is one of the Earth's broadest regions of ongoing continental extension, encompassing an area reaching ∼800 km in width between the Sierra Nevada to the west and Wasatch mountains to the east. We present observations arising from excavations, scarp profiling, optically stimulated luminescence, and radiocarbon dating to place limits on the late Pleistocene paleoseismic history of faults bounding eight ranges across the interior of the northern Great Basin, specifically, the Shawave, Hot Springs, Humboldt, Sonoma, Shoshone, Tuscarora, Dry Hills, and Pequop ranges. Combining the observations with similar previously published studies within and at the margins of the Great Basin yields a transect that extends eastward across the basin between the 40th and 41st parallels. The sum of observations provides a picture of the patterns and rates of earthquake recurrence over the region during the last ∼20–45 kyr that may be compared to patterns of contemporary seismicity and recently reported measures of strain accumulation across the area using GPS. The recurrence rate of large surface rupture paleoearthquakes along ranges at the margins of the Great Basin is systematically greater than observed along ranges in the interior. The pattern is similar to seismological and geodetic measurements that show levels of background seismicity and strain accumulation are also concentrated along the margins of the Great Basin. An east‐west extension rate across the interior of the Great Basin on the order of 1/2 mm yr−1 (strain rate of ∼1 nstrain yr−1) over the last ∼20–45 kyr is estimated by summing the record of paleoseismic displacements across the 400 km breadth of the transect, as compared to ∼2 mm yr−1 of strain accumulation indicated by a recently reported analysis of a collinear GPS survey. The comparison is hindered by significant uncertainties coupled to the geologic rate estimate. The transect also crosses the northern limit of the central Nevada seismic belt. The central Nevada seismic belt is defined by a north‐northeast trending alignment of historical surface rupture earthquakes, increased levels of background seismicity, and strain accumulation rates greater than observed elsewhere in the interior of the Great Basin. The reported recurrence rate of late Pleistocene surface rupture earthquakes within the central Nevada seismic belt is also generally greater than observed along our transect. The observations when taken together suggest that the characteristics of strain release observed historically within the central Nevada seismic belt have been operative over the latest Pleistocene and that the apparently greater rates of strain accumulation and release in the central Nevada seismic belt are diminished or less localized in regions to the north and east. Thus, while the historical alignment of surface ruptures that defines the central Nevada seismic belt remains a unique clustering of earthquakes in time and space, the likelihood of the cluster at its observed location appears greater than would be expected to the north or eastward in the interior of the Great Basin.