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Conjugate Strike-Slip Faulting in the Truckee Basin of California, Northern Walker Lane

Description: 

The Walker Lane belt is a ~150 km wide zone of distributed and discontinuous transtensional faulting that roughly follows the California-Nevada border from Death Valley to Mohawk Valley, CA. This belt accommodates ~25% of the relative dextral transform motion between the North American and Pacific Plates. In the Northern Walker Lane, this dextral shear is accommodated across a series of normal-fault bound basins in conjunction with both northwest-striking right-lateral faults and conjugate northeast-striking left-lateral faults.

We present new lidar-based mapping in the Truckee Basin showing that the Polaris, Truckee, and Dog Valley are active conjugate strike-slip faults cutting a prominent sequence of glacial landforms and deposits emanating from the adjacent Sierra Nevada crest. Our paleoseismic trenching study of the ~25-km-long northeast-striking left-lateral Dog Valley fault provides evidence for one earthquake that occurred ~8.5–8.3 ka and a younger earthquake that postdates 8.3 ka. Three-dimensional trenches show that the most recent earthquake produced 115 cm of left-lateral slip. We present 29 new preliminary ¹⁰Be and ³⁶Cl cosmogenic exposure ages of boulders from glacial moraines and outwash terraces in the Truckee basin. These ages provide limits on the late-Pleistocene (post-140 ka) slip rates of the ~35-km-long northwest-striking Polaris and Truckee faults. The age of a displaced glacial outwash channel shows that the Polaris fault has a right-lateral slip rate of 0.45+^0.28/-_0.06 mm/a. Our mapping shows that the Truckee fault is a right-oblique slip fault and forms the northerly continuation of the West Tahoe fault. Glacial moraines displaced by the Truckee fault provide a right-lateral slip rate of 0.22^+0.09/_-0.04 mm/a and a vertical slip rate of 0.12^+0.09/_-0.06 mm/a. The sum of these two faults' dextral slip rates is less than half the maximum limit of ~3 mm/a of northwest-directed right-lateral shear measured by GPS across the basin. Taken together, these three conjugate faults raise questions in light of recent conjugate earthquake sequences in both the Walker Lane and abroad.

Session: Illuminating Complex, Multiplet Earthquake Sequences at Kahramanmaras (Turkiye), Herat (Afghanistan), and Beyond - II

Type: Oral

Date: 5/2/2024

Presentation Time: 11:00 AM (local time)

Presenting Author: Ian

Student Presenter: No

Invited Presentation: 

Authors