20 D7. Paleoearthquake Records and Slip Rates Across the Southern California Plate Boundary (Posters)

Wednesday, 13 May 2020
9:00 AM - 6:00 PM
Fountain Ballroom

QUATERNARY MAPPING OF THE GOOSE LAKE FAULT, VAN DUZEN RIVER TERRACES, AND YAGER CREEK TERRACES, HUMBOLDT COUNTY, CALIFORNIA

Paper number: 20-4
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

The transition between the San Andreas fault and Southern Cascadia subduction zone is a tectonically complex, broad zone of deformation where southerly dextral strike-slip motion meets northerly relative contraction, and the Gorda, Pacific, and North America plates convene to form the Mendocino triple junction. We observe an array of dextral, oblique, and thrust faults along northern California, accommodating deformation from these highly active structures—the Mendocino triple junction, for example, migrates north ~40 mm/yr. The Little Salmon fault is the southernmost known major thrust fault in the Cascadia subduction zone, trending northwest with south vergence. About 2 km south of the central segment of the Little Salmon fault, near the town of Hydesville, California, the Goose Lake fault trends subparallel. The Goose Lake fault has three strands, is mapped ~10 km in length, and has apparent thrust-dominant, oblique northside-up motion. Additionally, well-preserved fluvial terraces associated with the Van Duzen River and Yager Creek are present in immediate proximity.

Using newly available 1m resolution LiDAR data, we present the results of our Quaternary mapping of terrace surface extent and morphostratigraphic position. We also present the results of our mapping of topographic escarpments possibly associated with the Goose Lake fault that appear to deform the mapped terraces. We identify four terraces possibly associated with the Van Duzen River (QD1-QD4) and 10-13 terraces possibly associated with Yager Creek (QY1-13). Preliminary results from 10Be cosmogenic analyses show minimum dates for Van Duzen terraces of 50ka and 23ka. These minimum dates may provide information on the time-averaged incision rate for these terraces. If we assume the landscape is in steady state and incision mimics localized uplift rate, calculated maximum uplift rate is 2.5—4.0 mm/yr. Given that these terraces are within the footwall of the Little Salmon fault, it may be unlikely that Little Salmon or Goose Lake fault slip are driving such locally high uplift rates. We suggest terrace uplift and formation is controlled by deformation from the Southern Cascadia subduction zone and San Andreas fault. These observations may offer insight into structural relations between minor crustal structures and major tectonic forces.

Geological Society of America Abstracts with Programs. Vol. 52, No. 4

doi: 10.1130/abs/2020CD-347421

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