Geometry of seismically active faults and crustal deformation within the Basin and Range-Colorado Plateau transition in Utah

Evaluation of the seismicity of the southern Great Basin and its relationship to the tectonic framework of the region

“…This lack of correlation suggests that these earthquakes reflect effects of deformation processes other than those directly related to the basin and range topography. Small earthquakes occurring in central Utah are also uncorrelated with the fault boundary between the Colorado Plateau and the Great Basin (Arabasz and Julander, 1986), although abundant Holocene fault scarps occur along that zone. Thus, this lack of correlation should not be taken as evidence that range front faults are unlikely to be associated with large earthquakes in the SGB.…”

“…A number of earthquakes in the Colorado Plateau-Great Basin transition zone can be interpreted as sinistral motion on northeast trending faults (Arabasz and Julander, 1986). Focal mechanisms from the Sevier Valley region, for instance, exhibit both dextral and sinistral slip on parallel nodal planes (Arabasz and Julander, 1986); in addition, Anderson and Barnhard (1987) find geologic evidence that they interpret as southwest-directed lateral transport or rafting of crustal blocks. They suggest, however, that these blocks are limited in vertical extent to about 5 km.…”

“…A schematic model demonstrating this concept is shown in Figure 5la. In fact, some evidence exists in both the current seismic record and the late Cenozoic geologic record that significant components of strike-slip movement have occurred or are occurring along the Great Basin-Colorado Plateau boundary (Arabasz and Julander, 1986;Anderson and Barnhard, 1987). A number of earthquakes in the Colorado Plateau-Great Basin transition zone can be interpreted as sinistral motion on northeast trending faults (Arabasz and Julander, 1986).…”

“…In fact, some evidence exists in both the current seismic record and the late Cenozoic geologic record that significant components of strike-slip movement have occurred or are occurring along the Great Basin-Colorado Plateau boundary (Arabasz and Julander, 1986;Anderson and Barnhard, 1987). A number of earthquakes in the Colorado Plateau-Great Basin transition zone can be interpreted as sinistral motion on northeast trending faults (Arabasz and Julander, 1986). Focal mechanisms from the Sevier Valley region, for instance, exhibit both dextral and sinistral slip on parallel nodal planes (Arabasz and Julander, 1986); in addition, Anderson and Barnhard (1987) find geologic evidence that they interpret as southwest-directed lateral transport or rafting of crustal blocks.…”

“…The presence of shallow active detachments would further complicate the assessment of the regional seismic hazard (Anderson and others, 1983;Arabasz and Julander, 1986), particularly in a zone undergoing substantial deep-seated strike slip. If active detachment surfaces exist in the upper crust of this region, motions in the lower plate might not be wholly reflected in the upper plate or they might be translated to the upper plate in a complex fashion (Hardyman, 1978).…”