[Contents]
 
Abstract
   

To better understand tsunami processes associated with Cascadia subduction zone earthquakes, ground penetrating radar (GPR) transects were collected. Multiple mega-earthquakes, which often create tsunamis, have occurred in the Pacific Northwest of the USA and with increased population in the region, these multiple hazards pose a significant threat to the coastal communities. GPR, a geophysical tool used to image the subsurface, was used at numerous sites to investigate the extent of paleotsunami inundation and the magnitude of wave run-up. GPR transects (using 100, 225, 450, and 900 MHz antennae) were collected at four sites in both Cannon Beach and Seaside, Oregon. These transects ranged from 10 m to 690 m in length and depth of penetration ranged from 0.5 to 10 m. Laser leveling surveys were carried out to gather topographic data which was used to topographically correct the GPR transects. Both the 1964 (Alaska earthquake) tsunami and the 1700 AD Cascadia tsunami were imaged in the project. Both of these tsunamis left extensive sand sheets on the investigated landscape. The internal stratigraphy of the 1964 tsunami deposits was imaged, showing near continuous horizontal to sub-horizontal reflection patterns near or on the surface. The 1700 AD tsunami deposits, which lie beneath peat and marsh deposits, were imaged and analyzed. In addition, tsunami pour-over fans from the 1700 AD tsunami were also mapped using GPR.

   
[Contents]