Geodetic Extension Across the Southern Basin and Range and Colorado Plateau

Abstract

Elastic strain accumulation in the Earth's crust is the primary driver of continental earthquakes and can pose significant seismic hazards. Regional studies of seismic hazard in the southern Basin and Range Province (SBR) and Colorado Plateau Province (CP) include assessments of risk to transportation (Euge et al., 1992), buildings (Ghanat et al., 2015, hydro-electric power, and water resources (Lockridge, Fouch, Arrowsmith, & Linkimer, 2012) and the Palo Verde nuclear power plant (U.S. Nuclear Regulatory Commission, 2016). Strain rates can be used with seismicity, fault location, and slip rate data to characterize areas of deformation and enhance regional assessments of potential seismic hazard.The crustal strain-rate field in diffuse plate boundary zones can be affected by both long-term and shortterm processes. Improved understanding of the long-term deformation patterns can be incorporated into models of plate boundary zone hazards (e.g., Petersen et al., 2014) and provide constraints for studies of the forces that act on the lithosphere (e.g., Flesch & Kreemer, 2010). Strain rates along the Wasatch fault zone of the northwestern margin of the CP have been the focus of numerous studies (e.g., Bennett et al., 2003;Niemi et al., 2004) and are better constrained than along the southern and southwestern margin. The poor constraints in the latter areas are due to the low levels of deformation and, until recently, the sparseness of data in southern Utah, southern Nevada, Arizona, and New Mexico.In this study, we analyze crustal motions in the SBR and southern portion of the CP (Figure 1) using two regional densifications of the EarthScope Plate Boundary Observatory (PBO) (Herring et al., 2016) network established with funding from the National Science Foundation (NSF) EarthScope Science Program (Berglund et al., 2012;Kreemer et al., 2015). GPS sites installed by us in 2010 in the SBR and on the CP are referred to in the text and figures as EarthScope (ES) sites (Figure 2a). The expanded network is used in conjunction with the existing EarthScope PBO, MAGNET network (Blewitt et al., 2009) and Rio Grande Rift stations

Tectonics of the Colorado Plateau and Its Margins

“…Relative stability of the Colorado Plateau within the slowly deforming western US Cordillera is constrained by satellite geodesy (Berglund et al 2012, Murray et al 2019, Broermann et al 2021. Earthquake activity is tracked by sparse regional seismographs, except near the Wasatch Front where more extensive monitoring exists and strain rates are an order of magnitude greater (Murray et al 2019).…”

“…Earthquake activity is tracked by sparse regional seismographs, except near the Wasatch Front where more extensive monitoring exists and strain rates are an order of magnitude greater (Murray et al 2019). The interior of the Colorado Plateau (Colorado Plateau Interior Block of Broermann et al 2021) is deforming more slowly than its margins but exhibits dilatation strain rate near the margin of detectability, −0.5 +/− 0.5 nanostrain/year, indicating slight compression or a nondeforming block embedded among adjacent extensional provinces (Broermann et al 2021). The region spanning from the western rim of the Colorado Plateau to the western Great Plains shows broadly distributed slow extension of 1.2 (+/− 0.2) nanostrain/year (Berglund et al 2012).…”

“…Geophysical imaging and geodynamic studies of the modern Colorado Plateau indicate that its core, with a mean elevation of ∼1.6 km, is nearly stable from the perspectives of geodetic surface horizontal displacements (Murray et al 2019, Broermann et al 2021, isostatic support (Becker et al 2014), and the ongoing presence of thick lithosphere (Schmandt & Humphreys 2010, Shen & Ritzwoller 2016. How and when did this stable, high-standing core emerge?…”

Western US intraplate deformation controlled by the complex lithospheric structure

“…Generally, the Basin and Range (B&R) is continuously extending in the northwest direction 17,18 , while the Great Valley (GV) and Colorado Plateau (CP) remain relatively undeformed [17][18][19][20] . Notably, the crustal motion within the southern B&R is lower than that further north 21 . From the northwestern B&R to the Pacific Northwest (PNW), the crustal motion transitions from northwest to northeast 15,22 .…”

New Insights Into Lithospheric Structure and Melting Beneath the Colorado Plateau

“…It is noteworthy as an area of high present‐day topography and historical uplift, anomalous for its current location far from any plate boundaries (Karlstrom et al., 2012; Morgan & Swanberg, 1985; Thompson & Zoback, 1979). A relatively thick lithosphere and little internal deformation have been noted within the Plateau, in stark contrast with the adjacent Basin and Range province, which is characterized by thin lithosphere and broadly distributed extension (Bennett et al., 2003; Broermann et al., 2021; Colgan et al., 2006; Hamilton, 1987; Hammond, 2014; Stewart, 1971; Zandt et al., 1995). It has been proposed, based on both petrologic and seismic evidence, that fluids released from the foundering Farallon slab metasomatically hydrated and weakened the lithospheric mantle below the Colorado Plateau (Butcher et al., 2017; Humphreys et al., 2003).…”