MONITORING SHORELINE CHANGE AND TSUNAMI HAZARD ON PLAYA GUIONES, GUANACASTE, COSTA RICA

Costa Rica forms the southern province of Central America and lies within the Caribbean Plate, adjacent to the subducting Cocos Plate at the Middle American Trench. The objectives of this project are to monitor shoreline change during the period 1940 to 2005 at Playa Guiones and to assess the site's tsunami risk.

Monitoring shoreline change along the Costa Rican coastline is important for two main reasons. First, tourism within Costa Rica has exploded in the past fifteen years with in excess of 625 million tourists visiting the country annually (Windevoxhel et al., 1998). Many of these tourists are attracted to coastal regions that boast miles of sandy beaches, coral reefs and waves for surfing. This attraction to the coastal environment places it under considerable land use stresses, thus, understanding the nature of the shoreline is important for making effective decisions regarding land use practices.

Secondly, Fernandez et al., 2000 demonstrate that 43% of large earthquakes (Ms °Ý 7) along the Pacific coast of Central America generate tsunamis. During the period 1850-1996, 49 tsunamis have impacted Central America with 37 along the Pacific coast. These tsunamis have resulted in 455 deaths (Fernandez et al., 2000). Given the large number of tourists to this region who have minimal understanding of tsunamis it is important to fully understand the tsunami risk to effectively mitigate the risk.

The analysis involves the creation of a detailed digital elevation (DEM) model from real-time kinetic global positioning system data collected during June 2005 at 5 m intervals. Comparisons between the DEM and the recent satellite imagery permit an assessment of the validity of using satellite data for detailed analysis of the beach morphology at this site. After validation, a time-series of air photo and satellite imagery (1940-2005) informs an analysis of the temporal changes along this subsiding coastline. The modern coastline morphology will be combined with seismic risk maps to identify coastal areas in this region at risk from potential tsunami inundation.