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Tectonics and the California Coast


Alex Simms – Assistant Professor, Department of Earth Science, University of California, Santa Barbara


One of California’s biggest draws is its nearly 1200 miles of scenic coastline. The distinctive features of this coastline are an excellent archive of past sea-level changes, tectonic uplift rates, storms, and in some places tsunamis. Marine terraces are the most common feature along the California Coast. These marine terraces are often used in conjunction with independent records of past sea-level changes to determine the amount of uplift experienced along many of California’s active faults. Here we show that previous studies of the marine terraces of the California coast are bias in the sea-level reconstructions used as a datum for uplift rates because they ignore the impacts of glacial-isostatic adjustment (GIA). Correcting for GIA reduced uplift rates by an average of 40% along the California coast. Accounting for GIA also brings uplift rates determined from different aged terraces into agreement and allows the identification of mistaken age assignments for other terraces. Although these marine terraces provide excellent records of past uplift, it is the estuaries of the California Coast that host the best archives of past tectonic events, sea-level changes, tsunamis, and even storms. One storm in 1861-1862 left an overwash fan comparable in size to hurricane fans in Carpinteria Slough of southern California. This storm is not isolated in time or space but produced similar deposits along much of the southern California Coast and similar storms struck the coast at least 3 times in the last ~2000 years. However, the biggest agents of coastal erosion to hit the California Coast are not caused by storms but earthquake-driven tsunamis and coastal subsidence. One such tsunami that hit the northern California Coast 900 years ago eroded the beach 110 m inland to depths of over 2 m removing 225,000 m3 of sand along a 1.7 km stretch of the coast. This is an order of magnitude more sand than removed during any historical El Nino experienced along the California Coast. Tsunamis are not the only agents of change experienced during earthquakes. Many of California’s coastal wetlands and estuaries undergo catastrophic sinking during large earthquakes. This process has long been known to impact the northern California coast but we provide some of the first evidence for a similar process occurring in southern California estuaries as well.


Alex Simms was raised in Oklahoma where he attended Oklahoma State University. Upon completing his BS in Geology at OSU, he went to work on a PhD at Rice University in Houston Texas. In 2005 he returned to Oklahoma State University as an Assistant Professor before coming to UCSB in 2010. His work focuses on coastal and shallow marine depositional systems and the records they hold of past sea-level, climate, and tectonic changes. He has published over 50 papers on his work along the Quaternary coasts of Texas, Antarctic, and California as well as the Permian Rocks of western Oklahoma.


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