State of stress and modern deformation of the Northern Basin and Range Province

Abstract

Constraints on the current stress regime of the actively extending northern Basin and Range province are provided by deformation data (focal mechanisms and fault slip studies), hydraulic fracturing in situ stress measurements, borehole elongation ("breakouts") analyses, and alignment of young volcanic vents. The integrated data indicate significant variations both in principal stress orientations and magnitudes. An approximately E-W least principal stress direction appears to characterize both the eastern and western margins of the Basin and Range province, whereas in the active interior parts of the province extension occurs in response to a least principal stress oriented NW to N60øW. The contrast in stress orientations between the province boundaries and in the interior suggests that along the margins the least principal stress direction may be locally controlled by the generally northerly trending profound lithospheric discontinuities associated with these margins. Active deformation along the southeastern and western province margins is characterized by a combination of strike-slip and normal faulting. Focal mechanisms along northeastern province margin (Wasatch front) and in central Nevada indicate a combination of normal and oblique-normal faulting. Temporal, regional, and depth-dependent variations in the relative magnitudes of the vertical and maximum horizontal stresses can explain much of the observed variations in deformation styles. However, some depth variation in faulting style inferred from focal mechanisms may be apparent and simply a function of the attitude of fault planes being reactivated. Evidence for significant temporal variation (or multiple cycles of variation) in relative stress magnitude comes from the Sierran front-Basin and Range boundary region where recent earthquakes are predominantly strike slip, whereas the profound relative vertical relief across the Sierra frontal fault zone in the last 9-10 m.y. implies a normal faulting stress regime. Using the best data on stress orientation, relative stress magnitudes are constrained from slip vectors of major earthquakes and young fault displacements. Analysis of well-constrained slip vectors in the Owens Valley, California, area indicate that large temporal variations in the magnitude of the approximately N-S oriented maximum horizontal stress are required to explain dominantly dip-slip and strike-slip offsets on subparallel faults. Similar faulting relations are observed throughout much of the boundary zone between the Basin and Range-Sierra Nevada (including the Walker Lane belt). Along the eastern province margin in the Wasatch front area in Utah, available data suggest that the maximum and minimum horizontal stresses may be approximately equal at depths of <4-5 km. Earthquake focal mechanisms in this area suggest more variability in relative magnitude of the two horizontal stresses with depth. Furthermore, superimposed sets of young fault striae along a segment of the Wasatch fault also indicate temporal variations of relative stres...

Gravity anomalies, Quaternary vents, and Quaternary faults in the southern Cascade Range, Oregon and California: Implications for arc and backarc evolution

“…This regional stress apparently is accommodated differently in the two regions. The western margin of the Basin and Range province including the Walker Lane, is characterized by spatial or temporal alternations between right lateral strike slip and normal faulting controlled by variations in the magnitude of the maximum horizontal stress relative to other components of stress Zoback, 1989] The correlation between fault orientation and gravity boundaries is excellent at the south edge of the Mount McLoughlin gravity low and the north edge of the Mount Sha. sta-Medicine Lake gravity low and less so at the south edge of the Mount Shasta-Medicine Lake gravity low and north edge of the Lassen Peak gravity low (Figure 4).…”

Cenozoic tectonic evolution of the central Wassuk Range, western Nevada, USA

“…3), consistent with modern geodetic data (Kreemer and Hammond, 2007;Kreemer et al, 2009). These fault motion indicators echo contemporary strain measurements along the western margin of the northern Basin and Range (e.g., Zoback, 1989;Dilles and Gans, 1995;Schweickert et al, 2000) and suggest that there has been a clockwise rotation of the direction of maximum strain from E-W to WSW-ENE during the Miocene to WNW-ESE from the late Pliocene to the present.…”

Systhesis of Volcanism Studies for the Yucca Mountain Site Characterization Project

“…Earthquakes are consistent with a northwest-trending orientation of the least principal stress axis, which is rotated clockwise relative to surrounding regions (Carr, 1974;Zoback, 1989). …”