Earthquake-induced landslides in Haiti: seismotectonic and climatic influences, size-frequency relationships

Abstract. First analyses of landslide distribution and triggering factors are presented for the region affected by the August, 14, 2021, Nippes, earthquake (Mw = 7.2) in Haiti. Landslide mapping was mainly carried out by comparing pre- and post-event remote imagery (~0.5–1-m resolution) available on Google Earth Pro® and Sentinel-2 (10-m resolution) satellite images. The first covered about 50 % of the affected region (for post-event imagery and before completion of the map in January 2022), the latter were selected to cover the entire potentially affected zone. On the basis of the completed landslide inventory, comparisons are made with catalogues compiled by others both for the August 2021 and the January 2010 seismic events, including one open inventory (by the United States Geological Survey) that was also used for further statistical analyses. Additionally, we studied the pre-2021 earthquake slope stability conditions. These comparisons show that the total number of landslides mapped for the 2021 earthquake (7091) is smaller than the one observed by two other research teams for the 2010 event (e.g., 23,567, for the open inventory). However, these fewer landslides triggered in 2021 cover much wider areas of slopes (> 80 km²) than those induced by the 2010 event (~25 km² – considering the open inventory). A simple statistical analysis indicates that the lower number of 2021-landslides can be explained by the ‘under-mapping’ of smallest landslides triggered in 2021, partly due to the lower resolution imagery available for most of the areas affected by the recent earthquake; this is also confirmed by an inventory completeness analysis based on size-frequency statistics. The much larger total area of landslides triggered in 2021, compared to the 2010 earthquake, can be related to different physical reasons: a) the larger earthquake magnitude in 2021; b) the more central location of the fault segment that ruptured in 2021 with respect to coastal zones; c) and possible climatic preconditioning of slope stability in the 2021-affected area. These observations are supported by (1) a new pre-2021 earthquake landslide map, (2) rainfall distribution maps presented for different periods (including October 2016 – when Hurricane Matthew had crossed the western part of Haiti), covering both the 2010 and 2021 affected zones, as well as (3) shaking intensity prediction maps.