Imaging Tsunami Deposits in Oregon Using Ground Penetrating Radar


Holly J. Johnson

A thesis submitted in partial fulfillment of the requirements for the degree of


Department of Geography and Anthropology
University of Wisconsin - Eau Claire



Table of Contents









Results and Interpretations

Cannon Beach




List of Figures

bullet Figure 1. Location map of the study sites, Cannon Beach and Seaside, Oregon shown on left. The sites are situated on the Cascadia subduction zone, shown on right (Cascadia Regional Earthquake Workgroup, 2006).

bullet Figure 2. The transmitter antenna (1) sends EM waves into the ground and the receiver antenna (2) receives the EM waves that are reflected off underground layers. The information travels to the computer equipment by cables (3) and the computer equipment displays the raw data in real time on the screen (4).

bullet Figure 3. Common mid-point profile from Cannon Beach. Velocity is calculated by dividing antennae separation (distance) by two-way travel time.

bullet Figure 4. A laser level was used to collect elevation data in Cannon Beach.

bullet Figure 5. Core samples were collected at each site in Seaside.

bullet Figure 6. The four sites in Cannon Beach were located on roads and in a back-barrier wetland.

bullet Figure 7. The sites in Seaside were located on the shores of river channels and at the site of an assumed paleotsunami pour-over fan.

bullet Figure 8. Starting data collection on Larch Street (looking north).

bullet Figure 9. The profile of Larch Street shows cut and fill features (yellow), a continuous reflection (orange) and the internal stratigraphy of the ridge (red).

bullet Figure 10. Data was collected from west to east on Second Street (looking east).

bullet Figure 11. The Second Street profile shows a continous reflection in orange and possible cut and fill features in yellow.

bullet Figure 12. Data was collected on Spruce Street from south to north. Image on left looks south around middle of line. Image on right looks north at end of line.

bullet Figure 13. Possible cut and fill features, along with a possible paleosol are imaged in the Spruce Street profile.

bullet Figure 14. A line was run in the Spruce Street marsh from east to west using both the 225 and 450 MHz antennae.

bullet Figure 15. Possible cut and fill features (yellow) and sediment deposits are shown in the Spruce Street marsh profiles.

bullet Figure 16. These profiles of the Spruce Street marsh liquefation site were run from north to south and show possible cut and fill features (yellow). Sediment deposits are also shown.

bullet Figure 17. The east to west profiles show similar reflections.

bullet Figure 18. Data was collected on the west bank of the Necanicum River (river seen in background of left image) north of the 12th Avenue bridge. Lines were run east to west (A in right image and seen in left image) and south to north (B in right image).

bullet Figure 19. The east to west transects (12THC) show eastward dipping reflections along the Necanicum River. The first image shows 450 MHz data and the second shows 900 MHz data.

bullet Figure 20. The south to north transects (12THR) show southward dipping reflections. The first image shows 450 MHz data and the second shows 900 MHz data.

bullet Figure 21. HORNC (line A) was run south to north, perpendicular to the Neawanna Creek channel margin and HORNR (line B) was run west to east, parallel to the channel margin.

bullet Figure 22. The four profiles show mostly continuous horizontal reflections. 1) HORN-C450, 2) HORN-C900, 3) HORN-R450, 4) HORN-R900.

bullet Figure 23. PLUMC was run west to east as shown on left while the other line, PLUMR was run north to south, shown in the right figure looking north.

bullet Figure 24. Possible cut and fill features and several southward dipping reflection patterns are visible in the profile of PLUM-C450.

bullet Figure 25. The other profiles for North Roosevelt Drive show similar reflections. 1) PLUM-C900, 2) PLUM-R450, 3) PLUM-R900.

bullet Figure 26. One line (KAVEC) was run north to south at this site, perpendicular to the assumed Avenue K pour-over flow (looking south).

bullet Figure 27. A small creek running through the area approximately 33 m into KAVEC.

bullet Figure 28. The profile of Avenue K, running north to south, shows some possible cut and fill features are shown in yellow.

bullet Figure 29. Possible cut and fill features can also be seen in the profile running west to east.


List of Tables

bullet Table 1. GPR equipment configurations, survey parameters, and data processing parameters used during the survey.

bullet Table 2. Core log data collected in Seaside, Oregon by Dr. Curt Peterson.


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