Project Abstract
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As much as 43 cm of co-seismic subsidence occurred in upper Tomales Bay, California during the 1906 San Francisco Earthquake. This nearly 0.5 m of subsidence suggests the stratigraphy within the bay may contain a record of past earthquakes along the northern San Andreas Fault. As part of earlier work, we created a foraminifera-based transfer function for identifying past periods of co-seismic subsidence and collected 36 cores in Tomales Bay. The purpose of this work was to determine the abruptness and age of potential co-seismic subsidence events identified in the stratigraphy of the bay and determine if the events occurred at the same time as other documented earthquakes along the northern San Andreas Fault. To accomplish these objectives, we proposed to 1.) use our foraminifera transfer function across contacts in the cores to test for submergence and 2.) acquire more radiocarbon ages across potential co-seismic subsidence events. From our work we have 1.) refined our facies analysis of the cores, 2.) identified 5 possible co-seismic events (inclusive of the one previously identified), and 3.) compared the preliminary age of these possible events to other records of earthquakes along the northern San Andreas Fault. The four younger possible co-seismic events at 765±190, 1110±185, 1345±40, and 2055±260 cal yrs BP overlap within error with the age of earthquakes recorded in multiple paleoseismic records. The oldest at 3300±65 cal yrs BP dates to a time period older than any other known record of earthquakes along the northern San Andreas Fault. |
