I spent a month out in the field collecting data with Lesley Perg and two other interns, Eugene Morgan and Lindsey Christiansen. Our location was near in Sinkyone Wilderness Park near Shelter Cove and Punta Gorda, near Petrolia; both located on the coast of northern California. We were looking at the marine terraces and the uplift rates associated with the Mendocino Triple Junction. At this junction, the uplift rates varied from less than 1mm yr-1 at Sinkyone Wilderness Park to 3-4 mm yr-1 at Punta Gorda.

Marine Terraces are striking stepped geomorphic features, common along actively uplifting continental margins, that form through the interaction of rock uplift and rapid, large-scale sea-level oscillations (Alexander, 1953). These are important to understand and study because they can tell us a lot about the seismic activity on the coast. We can assume that we know the sea-level based on tropical marine terrace sequences, so we can determine the uplift rates of a particular area. This will tell us about the seismic rates as well as the erosional landscape of the coastline. The uplift rates can also show development, with different aged soils mixed together in the same environment, which gives us an idea of where the sediment is coming from and how fast it is being deposited.

We used Ground Penetrating Radar (GPR) to achieve a representation of the soils beneath the surface. This is possible because GPR uses electromagnetic fields to probe lossy dielectric materials to detect structures and changes in material properties within the materials (Davis & Annan). In other words, light rays get transmitted by one antenna into the ground, reflected, and are received by the other antenna. This allows us to find structures under the soil by seeing the speed at which the speed at which the light if received.

This summer I took all the data that we collected from the Global Positioning System (GPS) and GPR and interpreted where zero sea-level was by finding the "notch" in the bedrock. With this, we will be able to determine the uplift rate for each area. In my time actually interpreting the data I was unable to obtain numerical results due to complications arising from working with new software so this project is still a work in progress to be continued at a later date.

References:
Alexander, C.S., 1953, The marine and stream terraces of the Capitola-Watsonville area: University of
California Publications in Geography, v. 10, p. 1-44.

Davis, J.L., and Annan, A.P., 1989, Ground Penetrating Radar for High-Resolution Mapping of Soil and Rock Stratigraphy, Geophysical Prospecting, Vol. 37, pp. 531-551.
 
 

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