89-5 Integrating Geologic, Geochronologic and Remote Sensing Data to Quantify the role of Active Faults on Surface Topography within the northern San Andreas Fault System

Session: Advancing Earthquake Geology and Surficial Deformation from Geologic Provinces to Political Entities through Multidisciplinary High-Resolution Data

Presenting Author:

Kimberly Blisniuk

Authors:

Blisniuk, Kimberly¹, Moon, Seulgi², Yeager, Simone³, Lord, Ian Duncan⁴, Ladinsky, Tyler⁵, Washburn, Hudson A.⁶, Brown, Nathan D.⁷, Madden, Elizabeth Hale⁸, Willenbring, Jane⁹

(1) San Jose State University, San Jose, USA, (2) University of California, Los AngelesE, Los Angeles, CA, USA, (3) San Jose State University, San Jose, CA, USA; USGS, Moffett Field, USA, (4) San Jose State University, San Jose, USA, (5) California Geological Survey, Seismic Hazards Division, San Mateo, CA, USA, (6) CoAdna Photonics, Santa Clara, CA, USA, (7) University of Texas at Arlington, Arlington, TX, USA, (8) San José State University, San Jose, CA, USA, (9) Stanford, Stanford, USA,

Abstract:

The complex geometry of the San Andreas Fault system, and how it steps and propagates across Earth’s surface, is revealed in the topography. This presentation highlights recent field, geochronologic and remote sensing studies on restraining bends of the northern San Andreas Fault System, specifically along the San Gregorio, Hayward, and Calaveras faults.  For the Hayward-Calaveras faults, cosmogenic radionuclides concentrations were measured to quantify denudation rates along the Diablo Mountain Range and Mission Hills, near the Arroyo Aguague Reverse and Mission Hills faults.  ¹⁰ Be-derived catchment-wide denudation rates for 15 watersheds between the Calaveras and Hayward faults range from 0.047 mm/y to 0.161 mm/yr, appear to support a landscape that is in topographic equilibrium. Low erosion rates from the southern Diablo Mountains, where the Calaveras Fault steps left to the Hayward Fault are consistent with similarly low mean slope, low local relief and low k_sn values. Erosion rates appear to steadily increase for catchments along the Hayward and Arroyo Aguague faults and are highest near Mission Peak. The observed pattern in catchment-average erosion rate suggests that crustal uplift and overall topography may control erosion rates here. For the San Gregorio a comprehensive stratigraphic and geochronologic study of displaced marine terrace sands from the subsurface at Pillar Point Bluff reveal a positive flower structure forming along a restraining bend of the fault that transfers slip to the Seal Cove Fault through a contractional stepover. These observations and initial dates bring into question previous assumptions of the fault structure within this on-land section of the San Gregorio fault and indicate that subsurface fault geometry likely plays a significant role in surface morphology.  These data suggest that the location and geometry of active faults impart a strong influence on the landscape in northern California. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8336

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