SCEC Award Number 23149 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Uplift of the Isla Vista Marine Terrace: A potential record of earthquakes?
Name Organization
Alexander Simms University of California, Santa Barbara
Other Participants Ryan Owings, graduate student
SCEC Priorities 5b, 1a, 4b SCEC Groups Geology, Geodesy, FARM
Report Due Date 03/15/2024 Date Report Submitted 02/24/2024
Project Abstract
The marine terrace underlying the campus of the University of California Santa Barbara dates to ~40 ka. Its current elevation suggests uplift of approximately 2 mm/yr. However, the role of earthquakes in the uplift is unknown. A recent seismic survey within the lagoon contains no fewer than 2 strong reflections exhibiting onlap onto older reflections that may represent periods of co-seismic uplift of the lagoon and its encasing marine terrace through the Holocene. We obtained 5 new sediment cores, new geochemical data, and 20 new radiocarbon ages from the lagoon with the intent of sampling and characterizing that surface in order to determine if it was exposed during past earthquakes. Although the surface is marked by carbonates, they are not of pedogenic origin as would be expected if they were created by exposure due to co-seismic uplift. Thus, although uplift during an earthquake cannot be ruled out as a contributing factor to the formation of the onlap, carbonates, and strong reflections, desiccation of the lagoon due to its isolation from the open ocean by the formation of a larger barrier or drier climates from 1-3 ka during the Holocene are just as likely a cause of the reflection pattern. Thus, although the lagoon has uplifted through the Holocene we cannot unequivocally call upon earthquakes as the cause of that uplift.
Intellectual Merit We tested whether a series of strong reflections in seismic profiles from the sedimentary fill of Campus Lagoon, which is cut into an uplifted marine terrace, represents periods of desiccation driven by earthquake-induced uplift. We sampled one of these surfaces. The surface likely represents a thin bed of evaporites, but the formation of the beds cannot be unequivocally attributed to uplift. They have a marine signal, not a pedogenic signal as originally hypothesized. Thus although a co-seismic origin is not ruled out, its origin may also be just as likely driven by a period of isolation of the lagoon from the ocean by other mechanisms (e.g. more sand in the littoral system).
Broader Impacts It supported a first-generation college student who completed his MS based on this research. He is now employed as a geologist for a geotechnical firm in Irvine.
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