Tsunami hazard and buildings vulnerability along the Northern Atlantic coast of Morocco –the 1755-like tsunami in Asilah test-site

Abstract

Background: The Atlantic Coast of Morocco is prone to tsunami inundation. Therefore, in this region, earthquakeinduced tsunami hazard has been intensively investigated leading to the development of a number of coastal inundation models. However, tsunami vulnerability remains not well understood to the same extent as the hazard. In this study, we use high-resolution numerical modeling, detailed field survey and GIS-based multi-criteria analysis to assess the building tsunami vulnerability and its sensitivity to the tide variations. Asilah located in the northwestern Atlantic coast of Morocco, where the impact from the 1755 tsunami is well documented, constitutes the area of this study. Results:To model the source-to-coast tsunami processes we used the COMCOT (Cornell Multi-grid Coupled Tsunami Model) numerical code on a set of bathymetric/topographic grid layers (640 m, 160 m, 40 m and 10 m resolutions) with an initial sea-surface perturbation generated using Okada's formulae and assuming an instantaneous seabed displacement. The tsunami source models in this study correspond to four 1755-like earthquake scenarios. Results show that Asilah's built environment is highly vulnerable to the tsunami impact that can range from 1.99 to 2.46 km 2 of inundation area, depending on the source and the tidal level considered. The level of building vulnerability decreases considerably when moving away from Asilah's coastline. Moreover, the variation in the tidal level introduces large change in the modeled tsunami impact and, therefore, affects the level of building vulnerability.Conclusion: Thus, we suggest considering the effect of the tide when simulating tsunami hazard and vulnerability, particularly, in coasts where tidal variations are significant. This study provides hazard and vulnerability maps that can be useful to develop the tsunami awareness of the Moroccan coastal population.

Quantitative risk assessment in El-Jadida (Northern Atlantic Coast of Morocco) for a tsunami scenario equivalent to that of the 1755 Lisbon earthquake

“…In fact, the impact of past occurrences, such as that of 1755, have been documented in old towns that have now grown into big cities close to, or on, the Atlantic shoreline (El Mrabet 2005;Blanc 2009). Several attempts to model the effects of these events and to estimate the risk to human life and goods, show that the region is widely exposed if similar events were to recur (Omira et al 2010;Atillah et al 2011;Renou et al 2011;Mellas et al 2012;Moussaoui et al 2017;Ramalho et al 2018). In addition to historical documents, material evidence (geomorphic and sedimentary indices) for tsunamis or high energy events in Morocco have been found in many sites alongside the Moroccan Atlantic coast: (1) in Larache and Rabat (Medina et al 2011), (2) Tahadart estuary (Talibi et al 2016;Khalfaoui et al 2020) and (3) close to the Loukkos river mouth, (Mhammdi and Medina, 2015).…”

“…From a socioeconomic point of view, such events would be disastrous for Morocco as well, given that a large portion of its population (10.3 million people) (Laouina 2019), and large segments of its economy are tied to important coastal cities alongside its Atlantic shoreline. For this reason, several studies have attempted to evaluate the impact of a potential tsunami on some of the populous (i.e., Casablanca, Rabat and El-Jadida; see for example Omira et al 2009;Mellas et al 2012;Moussaoui et al 2017), but these studies have been limited to qualitative risk assessments. Such methods are subjective and lack a numerical basis for the estimation of potential economic and societal losses.…”

Coastal Vulnerability Study on Potential Impact of Tsunami and Community Resilience in Pacitan Bay East Java

“…It means that people do not understand the dangers of a tsunami coming from the sea (Hall et al, 2017;Kafle, 2012). Due to this existing condition, if a tsunami occurs, it will destroy the villages around the coast and is predicted to cause high casualties, as recorded in the tsunami events in Aceh in 2004 and Palu in 2018 (El Moussaoui et al, 2017;Suhita et al, 2021).…”

“…It refers to changes intended to make available land suitable for human use, such as settlement, rice fields, built-up areas, and forests (vegetation). According to the land use map (Figure 4 Settlements near the coastline are a type of land use extremely vulnerable to tsunami disasters (El Moussaoui et al, 2017;Hall et al, 2017;Kim et al, 2017). Settlements in the study area range from near the coast to about 2-3 kilometres inland.…”

“…Meanwhile, vegetation covered a large portion of the area on the west side of the river. Settlements are a type of land use extremely vulnerable to tsunami disasters(El Moussaoui et al, 2017;Hall et al, 2017;Kim et al, 2017).…”