Fault slip rates and initiation age based on diffusion equation modeling: Wasatch Fault Zone and eastern Great Basin

Abstract

Models of the evolution of fault scarp morphology provide time elapsed since slip initiated on a faulted surface and may therefore provide more accurate estimates of slip rate than the rate calculated by dividing scarp offset by the age of the ruptured surface. To accomplish this task, linear and nonlinear models of sediment transport are calibrated from the morphology of Lake Bonneville shoreline scarps and fault scarps formed by multiple, surface‐rupturing earthquakes along the Wasatch Fault Zone (WFZ). Profile modeling of scarps formed by several events distributed through time is done using a constant slip rate (CSR) solution and yields a value ofA/κ (1/2 slip rate/diffusivity). Time elapsed since slip initiated on a fault is determined by establishing a value for κ and measuring total scarp offset. CSR nonlinear modeling (κ0= 2.8 ± 1.1 m2/kyr, WFZ) of faults along the west slope of the Oquirrh Mountains indicates a slip rate of ∼0.1 mm/yr since 50 to 65 ka, which is corroborated by cosmogenic dating (10Be/26Al age = 75 ka). The slip rate along the west flank of the Stansbury Mountains varies from 0.04 to 0.2 mm/yr for time frames of 10 to >100 ka, with the most recent rupture on the northern portion of the fault zone ∼10 ka. Scarp analysis of the southern end of the Nephi segment, WFZ, suggests either temporal clustering or variable slip rate as indicated by differences in the short‐term (1.3 mm/yr for 4.3 ka) versus long‐term (0.4 mm/yr for 70 ka) slip rates.