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Hosgri Fault Zone-driven Uplift of the Irish Hills, Central Coastal California: Viscoelastic Crustal Deformation Modeling Results

Most of the central California coast west of the San Andreas fault (SAF) has slowly uplifted over the past 120 kyr. The offshore Hosgri fault zone (HFZ) in central coastal California has a reverse slip component that produces coastal uplift. Correlated and dated 120 ka emergent marine terrace bedrock surface elevation measurements provide coastal uplift rate data used with viscoelastic crustal-mantle deformation modeling to test the hypothesis that reverse-oblique earthquakes on the HFZ explain post-120 kyr observed coastal uplift rates of up to 0.2–.25 m/kyr. Model inputs include elastic seismogenic upper crust, viscoelastic lower crustal and upper mantle and HFZ geometry based on published crustal-mantle viscoelastic structure. Viscoelastic deformation modeling calculations of long-term uplift rates use a two-segment HFZ geometry based on published fault mapping and slip rates within the range published for the HFZ. The modeling shows that the rate and pattern of uplift of the coast and Irish Hills can be solely attributed to transpressional deformation of the HFZ. It is not necessary to add onshore thrust-reverse faults to explain observed ≤120 kyr coastal uplift rates. Modeled HFZ deformation explains observed folded Quaternary sedimentary structures observed in bathymetric and seismic reflection data in the offshore HFZ step-over region and the location and amplitude of the deep-crustal Santa Maria anticline in the hangingwall of the southern HFZ. These results suggest that viscoelastic deformation modeling of the reverse-slip components of other steeply-dipping, predominantly strike-slip offshore-nearshore faults along the California coast may explain portions of observed post-120 ka California coastal uplift rates across the region.

Session: Advances in Earthquake Geology: Spatiotemporal Variations in Fault Behavior From Geology and Geodesy [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/22/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Daniel R. H. O'Connell

Student Presenter: No

Additional Authors