Masters Thesis

Salt Marsh Response and Recovery to Coseismic Subsidence

This study utilized the stratigraphic record from the Seal Beach Wetlands (SBW), a coastal wetland in southern California straddling the active Newport-Inglewood Fault Zone, to: 1) Identify evidence of paleoseismic events and 2) Characterize wetland response and recovery to these events. The goal of this study was to better understand how a southern California coastal wetland evolves in response to seismic activity. To accomplish this, a suite of sedimentary and geochemical analyses were performed on one core collected from the SBW to characterize environmental changes resulting from seismic events, and the subsequent recovery following the events. Integrating results from these analyses, we classified sedimentary layers into three dominant facies: subtidal, mudflat, and vegetated marsh that represented paleo-elevation at this location in the wetland. Five possible coseismic events were identified, distinguished by a sharp contact at an abrupt facies change suggesting a decrease in elevation. When marsh facies were overlain by sandy subtidal sediment, we interpreted this to have represented the most substantial subsidence event. Apparent subsidence estimates diminished with time, culminating in a lack of subsidence evidence associated with the 1933 Long Beach earthquake. We interpreted this as evidence of the wetland becoming more resilient to coseismic subsidence overtime. This study highlights wetland response to rapid changes in sea level and places extreme events (i.e., earthquakes) in the context of wetland development that may provide insight into improving stratigraphic interpretation.

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