ASSESSING PUERTO RICO’S PHYSICAL TOPOGRAPHY IN RELATION TO RAINFALL-INDUCED MASS WASTING SITES POST HURRICANE MARIA

Puerto Rico is vulnerable to seismic and atmospheric hazards, both of which can trigger hazardous chain events. In 2017, Hurricane Maria caused thousands of landslides that caused damage to infrastructure and claimed lives. In order to better understand this phenomenon, a detailed landslide inventory of the island was created using aerial images provided by FEMA, NOAA, and Digital Globe to explore various landslide-inducing factors. More than 40,000 mass wasting scars were catalogued and analyzed with respect to elevation, curvature, slope, and aspect. Frequency ratios were then calculated for each factor to identify the most vulnerable values for each factor.

Landslide-to-elevation frequency ratios reveal higher values in areas of 200-900m above sea level, the peak being in 500-550m. A lower correlation in frequency ratios around values of 600-650m are due to remnant highland erosional platforms that have been tectonically uplifted in the past millions of years. Even though they occur almost equally, convex topography is statistically more susceptible to mass wasting than concave areas. These convex areas are typically found in the island’s Cordillera Central. Landslide probability increases with steeper slopes until approximately 45°, above which are surfaces that are usually more resistive material such as karstic limestone. The style of failure on slopes above 45° may also be less visible in aerial imagery. Landslide-to-aspect frequency ratios illustrate that terrains facing north to northwest were slightly more prone to landslides during Hurricane Maria, possibly as a result of the counterclockwise spin of the hurricane and accompanying directional rainfall caused by Earth’s Coriolis effect.

Puerto Rico’s juvenile topography has vast influence upon the amount and style of landslides that can occur via extreme rainfall events throughout the island. Using these four topographical characteristics and several other factors, the final goal of this ongoing endeavor is to create a revised and reliable high-resolution rainfall-induced landslide susceptibility map of Puerto Rico.