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Is the Rocky Mountain – Tintina Trench Tectonically Active?

Description: 

The Rocky Mountain – Tintina Trench (RMTT) is one of the most conspicuous topographic lineaments on Earth, stretching from Montana through the eastern Canadian Cordillera and into Alaska. It is the locus of major Eocene transtensional faulting and marks a step-change in lithospheric thickness, strength, and thermal properties. There is a moderate level of seismicity in the vicinity of the RMTT, and several historical earthquakes have caused shaking and minor damage. However, little is known about the paleoseismic record of the RMTT and the potential for larger and more damaging earthquakes along it. Improving this record is important for the safety of the ~135k people that live along the RMTT, as well as the dams, pipelines, highways, and rail corridors that cross it. Here we review high-resolution topographic data (drone and airborne lidar and ArcticDEM) along the Canadian portion of the RMTT and examine in detail several potentially fault-deformed Quaternary landforms. In the southern RMTT near the town of Fairmont Hot Springs (50.3°N), a Holocene alluvial fan surface is disrupted by a 4-m-high west-facing scarp. Electrical resistivity tomography reveals a listric normal fault beneath the scarp – kinematics that are at odds with contemporary compressive crustal stress patterns. Near the town of Mackenzie (55.1°N), seismic reflection surveys and outcrop observations are suggestive, but not conclusive, of fault-deformed glacial till. At the British Columbia - Yukon border (60°N) a subtle linear mound disrupts glaciofluvial outwash gravels, indicating Holocene strike-slip rupture. In northwestern Yukon, near Dawson City (64°N), a 120-km-long series of scarps and “mole-tracks” disrupts a ~3 Ma landscape, but a 200 ka glacial moraine overlying the fault is undeformed, suggesting that activity on this segment of the RMTT has waned in the mid-to-late Quaternary. These results are the first conclusive evidence of Quaternary surface-rupturing earthquakes along the RMTT and, in addition to the implications for seismic hazard, significantly change our understanding of the Cenozoic evolution of the Canadian Cordillera.

Session: Cordilleran Strike-Slip Faults as Seismogenic and Seismological Features - I

Type: Oral

Date: 5/2/2024

Presentation Time: 04:30 PM (local time)

Presenting Author: Theron

Student Presenter: Yes

Invited Presentation: 

Authors