Search for: All records

Landscape disturbance events (e.g., earthquakes, slope failures) play key roles in landscape evolution in tectonically active areas. Along the Teton fault, fault scarps vary in height by up to tens of meters. LiDAR-based mapping indicates that scarp height is affected by glacial geomorphology, slope failure, and alluvial processes. LiDAR data, digital and field mapping were used to characterize fault scarps and slope failure deposits along the Teton fault zone. Based on vertical separation (VS; the vertical offset between faulted surfaces) across fault scarps and the expected behavior of normal faults, we propose a four-section model of the Teton fault. At a broad scale, VS is greatest along the southern fault zone. At a finer scale, VS is least at the ends of the fault and at three areas within the central fault zone. Transitions between these four sections may represent segment boundaries with potentially important implications for geohazards assessment. 

ABSTRACT The 72-km-long Teton fault in northwestern Wyoming is an ideal candidate for reconstructing the lateral extent of surface-rupturing earthquakes and testing models of normal-fault segmentation. To explore the history of earthquakes on the northern Teton fault, we hand-excavated two trenches at the Steamboat Mountain site, where the east-dipping Teton fault has vertically displaced west-sloping alluvial-fan surfaces. The trenches exposed glaciofluvial, alluvial-fan, and scarp-derived colluvial sediments and stratigraphic and structural evidence of two surface-rupturing earthquakes (SM1 and SM2). A Bayesian geochronologic model for the site includes three optically stimulated luminescence ages (∼12–17  ka) for the glaciofluvial units and 16 radiocarbon ages (∼1.2–8.6  ka) for the alluvial-fan and colluvial units and constrains SM1 and SM2 to 5.5±0.2  ka, 1σ (5.2–5.9 ka, 95%) and 9.7±0.9  ka, 1σ (8.5–11.5 ka, 95%), respectively. Structural, stratigraphic, and geomorphic relations yield vertical displacements for SM1 (2.0±0.6  m, 1σ) and SM2 (2.0±1.0  m, 1σ). The Steamboat Mountain paleoseismic chronology overlaps temporally with earthquakes interpreted from previous terrestrial and lacustrine paleoseismic data along the fault. Integrating these data, we infer that the youngest Teton fault rupture occurred at ∼5.3  ka, generated 1.7±1.0  m, 1σ of vertical displacement along 51–70 km of the fault, and had a moment magnitude (Mw) of ∼7.0–7.2. This rupture was apparently unimpeded by structural complexities along the Teton fault. The integrated chronology permits a previous full-length rupture at ∼10  ka and possible partial ruptures of the fault at ∼8–9  ka. To reconcile conflicting terrestrial and lacustrine paleoseismic data, we propose a hypothesis of alternating full- and partial-length ruptures of the Teton fault, including Mw∼6.5–7.2 earthquakes every ∼1.2  ky. Additional paleoseismic data for the northern and central sections of the fault would serve to test this bimodal rupture hypothesis. 

Abstract Prominent scarps on Pinedale glacial surfaces along the eastern base of the Teton Range confirm latest Pleistocene to Holocene surface‐faulting earthquakes on the Teton fault, but the timing of these events is only broadly constrained by a single previous paleoseismic study. We excavated two trenches at the Leigh Lake site near the center of the Teton fault to address open questions about earthquake timing and rupture length. Structural and stratigraphic evidence indicates two surface‐faulting earthquakes at the site that postdate deglacial sediments dated by radiocarbon and optically stimulated luminescence to ∼10–11  ka. Earthquake LL2 occurred at ∼10.0  ka (9.7–10.4 ka; 95% confidence range) and LL1 at ∼5.9  ka (4.8–7.1 ka; 95%). LL2 predates an earthquake at ∼8  ka identified in the previous paleoseismic investigation at Granite Canyon. LL1 corresponds to the most recent Granite Canyon earthquake at ∼4.7–7.9  ka (95% confidence range). Our results are consistent with the previously documented long‐elapsed time since the most recent Teton fault rupture and expand the fault’s earthquake history into the early Holocene.