Masters Thesis

Searching San Elijo Lagoon, Southern California for Paleotsunami Evidence.

Tsunami are a very real natural hazard for coastal Southern California; however, there are no geological records of past tsunami occurrence to determine their frequency and magnitude. For this study, a combination of five sedimentological analyses (sediment description, magnetic susceptibility, total organic matter, total carbonate content, and grain size analysis) were used to test our guiding hypothesis that the “wetlands of Southern California – specifically San Elijo Lagoon – record evidence for paleotsunami.”. And, provide the first geological evidence for paleotsunami in Southern California. The results of the study provide the first sedimentological record from San Elijo Lagoon that spans last 2200 years BP. Furthermore, the results indicate that depositional environment has changed significantly due to changes in the lagoon’s depositional environment over the last 2200 years BP. San Elijo Lagoon was selected for the investigation based on a number of factors, specifically: a historical tsunami database, generated mathematical models for Southern California tsunami, sedimentary structures reported from previous studies, and reconnaissance survey core results. Unfortunately, no sedimentological data were found in this study to support our hypothesis. Rather, the event unit we analyzed (CTU-I) is interpreted to reflect a storm deposit (or deposits) from the nearby Escondido Creek. So the main question now is why is there no unequivocal evidence for paleotsunami in San Elijo Lagoon? Absence of paleotsunami record in this region is may be due to following reasons: preservation potential of tsunami deposits, preservation potential of the catchment area, post-depositional alteration of tsunami deposits, Holocene sea level change, and limitation of paleotsunami proxies. Perhaps further research must be conducted to fill the gap between the geological records, a historical tsunami database and generated mathematical models for Southern California tsunami. Without such records, recurrence interval and vulnerability assessment is difficult to precisely reconstruct for this region.

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