# Airborne Electromagnetics to Improve Landslide Knowledge in Tropical Volcanic Environments
###### Abstract  
Caribbean areas are particular volcanic territories in tropical environments. These territories juxtapose several landslide-prone areas with different predisposing factors (poorly consolidated volcanic materials, superimposition of healthy materials on highly weathered materials, high heterogeneity of thicknesses, etc.). In these environments, where rapid development of slopes and land use changes are noticeable, it is necessary to better characterize these unstable phenomena that cause damage to infrastructure and people. This characterization has to be carried out on the materials as well as on the initiation conditions of the phenomena and requires complementary investigations. This study, focusing on La Martinique, proposes a landslide analysis methodology that combines new information about landslide-prone materials acquired by an airborne electromagnetics survey with a physical-based model. Once the data are interpreted and compared with field observations and previous data, a geological model is produced and introduced into the physical model to test different instability scenarios. The results show that geophysical investigations (i) improve the knowledge of the internal structure of landslides and surficial formations, (ii) specify the spatial limits of the materials that are sensitive to landslides, and (iii) give a better understanding of landslide initiation conditions, particularly hydrogeological triggering conditions. a +
Footnote †: journal: Applied Sciences  
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The first step in achieving these actions consists of assessing hazards [19; 20; 21]. Several methods that are more or less complex and range from qualitative to quantitative can be used. A large review of their uses can be found in the scientific literature [19; 20; 21; 22; 23], and some of them are particularly suited to the French regulatory context [24]. Among them, methodologies using physical-based models (PBMs) at the site scale (<1:5000) are the only methods designed for works [25] or that modified and revised existing regulatory hazard maps, taking into account triggering factors [24]. At this scale of work, it is possible to reach a good understanding of the mechanisms and probabilities of failure or to analyze the runout phenomena by taking into account physical processes. However, in Martinique, the parametrization of PBMs can be difficult because of a lack of information about the nature and depth of materials. Indeed, the island presents a very complex geology with different types of lavas deposited from the Oligocene to the present and exhibits extreme spatial variability and heterogeneity with a high degree of weathering [26; 27; 28; 29; 30]. Geophysical investigations can be an alternative to classical field investigations (i.e., geotechnical surveys; [31; 32]) to obtain quick information about grounds in large areas. These investigations presuppose correlations between measured properties and physical or geotechnical characteristics [33; 34]. In the case of landslides, it is possible to delineate the body of the moving mass of stable grounds due to the changing geophysical parameters [34; 35]. However, with heterogeneous grounds, the indirect information that is provided can be biased or difficult to interpret. Therefore, calibrating them with direct observations is indispensable [31], thereby limiting investigations in time and space for very large areas [32]. Airborne electromagnetics (AEM) provides information on lithology and regolith over large surfaces and/or hard-to-access areas [36; 37; 38; 39; 40]. It is able to provide plentiful pseudo-3D information about geological structures reaching a few hundred meters [41; 42] and has been successfully used in many environmental studies [30; 43; 44; 45; 46; 47] particularly in volcanic settings.