Estimating the slip rates of normal faults in the Great Basin, USA

Abstract

A reconnaissance slip‐rate‐estimation technique is needed for hundreds of uncharacterized normal faults in the Great Basin. We use the occurrence and/or absence of primary tectonic geomorphology, alluvial fault scarps and fault facets, to distinguished between categories of faults that have differences of orders of magnitudes in slip rate. Normal faults that lack alluvial fault scarps and fault facets (Type 3) have vertical slip rates on the order of 0.001 m kyr−1. Faults with alluvial fault scarps but that lack active fault facets (Type 2) have vertical slip rates on the order of 0.01 m kyr−1. Faults with active fault facets with a minimum height of 30 m (Type 1) are the most important faults in the Great Basin with respect to seismic hazard, tectonic deformation, and basin development and deposition. These faults generally have vertical slip rates of 0.1 m kyr−1 and faster. For better precision we have developed a relationship between vertical slip rate and maximum basal facet height: Log10 Sv=0.00248H−0.938 where Sv is vertical slip rate in m kyr−1 and H is maximum basal facet height in metres. The standard deviation of this relationship is 0.239, which corresponds to plus or minus a multiplicative factor of 1.7 in vertical slip rate.These criteria were used to estimate vertical slip rates for major normal faults in Nevada, USA. Based on the rates and orientations of these faults, seven Quaternary tectonic subprovinces are distinguished. The fastest faults (≥0.5 m kyr−1) are generally located in the Walker Lane belt, perhaps because of higher extension rates created by the addition of strike‐slip tectonics. Earthquake occurrence rates based on the faults in Nevada and their estimated slip rates are about a factor of two lower than historical earthquake rates.