Tsunami hazard assessment in the southern Colombian Pacific basin and a proposal to regenerate a previous barrier island as protection

Abstract

Abstract. In this study, the tsunami hazard posed to 120 000 inhabitants of Tumaco (Colombia) is assessed, and an evaluation and analysis of regenerating the previous El Guano Island for tsunami protection is conducted. El Guano Island was a sandy barrier island in front of the city of Tumaco until its disappearance during the tsunami of 1979; the island is believed to have played a protective role, substantially reducing the scale of the disaster. The analysis is conducted by identifying seismotectonic parameters and focal mechanisms of tsunami generation in the area, determining seven potential generation sources, applying a numerical model for tsunami generation and propagation, and evaluating the effect of tsunamis on Tumaco. The results show that in the current situation, this area is vulnerable to impact and flooding by tsunamis originating nearby. El Guano Island was found to markedly reduce flood levels and the energy flux of tsunami waves in Tumaco during the 1979 tsunami. By reducing the risk of flooding due to tsunamis, the regeneration and morphological modification of El Guano Island would help to protect Tumaco.

Tsunami hazard assessment for the central and southern pacific coast of Colombia

“…On Cascajal Island, there is much less variability in terms of inundation extent and inundation depth: 12.6% of the island is flooded between 0.3 m and 0.01 m. Restrepo and Otero (2007) found that the maximum tsunami wave height for Cascajal Island in Buenaventura ranged from 2.6 to 4 m depending on the generation scenario evaluated, in contrast to the maximum heights obtained for the same area in this study which did not exceed 0.7 m. In the case of Tumaco, these differences are not as marked with respect to what was found by Quiceno and Ortiz (2001), Cardona et al (2005), Sánchez and Puentes (2012) and Otero, Restrepo, and Gonzalez (2014). Beyond the seismic scenario used in each study, this heterogeneity in results concerning Buenaventura Bay could plausibly be explained by considering the role of the marine and coastal morphology, both in the exterior and interior zone of the bay.…”

“…The present study calculated maximum height and inundation depth to evaluate the tsunami hazard through a deterministic approach in the areas of Tumaco and Buenaventura, specifically the islands of Tumaco, Morro, and Cascajal. Previous studies have evaluated the tsunami hazard in the same areas (Quiceno and Ortiz 2001;Cardona et al 2005;Restrepo and Otero 2007;Sánchez and Puentes 2012;Otero, Restrepo, and Gonzalez 2014); however all defined the tsunami generation source via a homogeneous slip which does not best represent the initial condition of tsunami waves in nearby fields (Ulutas 2013). We argue that our approach which considered non-homogeneous slip distribution better represents initial condition of tsunami.…”

“…The inundation depth allows the differentiation of areas with relatively high or low probability of damage (Renou et al 2011). A deterministic method was applied (Renou et al 2011;Otero, Restrepo, and Gonzalez 2014;Mas et al 2014), taking into account advances in the definition of the source models provided by Poveda and Pulido (2019) as explained in the previous section. The source models used in this study made it possible to define more realistic megathrust scenarios, this allowed to calculate with more precision the tsunami initial conditions.…”

“…The methodology was used to determine average sea level values in Tumaco and Buenaventura based on the separate analysis of astronomical and meteorological tides since no instrumental records exist. From Figures 4 and 5 it can be established that the maximum average sea level value for Tumaco is 3.6 m and for Buenaventura it is approximately 4.8 m. In sites such as the bays of Tumaco and Buenaventura on the Colombian Pacific coast where the tidal range is approximately 4 m, it is important to take into account sea level in tsunami simulations, since sea level is a variable that strongly influences tsunami height and inundation (Sánchez and Puentes 2012;Otero, Restrepo, and Gonzalez 2014).…”

“…In terms of structural damage, approximately 3,080 homes were destroyed and another 2,100 were damaged (Ramírez and Goberna, 1980). Given that the Colombian Pacific coast has been affected by strong earthquakes, which have been precursors of tsunamis, it is important to evaluate extreme scenarios of strong ground motion and tsunami impacts (Quiceno and Ortiz 2001;Cardona et al 2005;Restrepo and Otero 2007;Sánchez and Puentes 2012;Otero, Restrepo, and Gonzalez 2014).…”