Cosmogenic tsunamic risk assessment: a first application to the European Atlantic coasts
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Cosmogenic tsunamic risk assessment: a first application to the European Atlantic coasts Damien Violeau1,2 Received: 24 February 2020 / Accepted: 18 September 2020 © Springer Nature B.V. 2020
Abstract We address the question of cosmogenic tsunamis, i.e., tsunamis due to the fall of an asteroid in the ocean, in particular on the Atlantic coasts of Europe. We apply Ward and Asphaug’s method (Deep-Sea Res II 49:1073–1079, 2002) for assessing this probabilistic return period of tsunami waves, with simplifying assumptions allowing writing their results in the form of analytic formulae, some of them involving simple integrals to be computed by numerical quadrature. We also account for uncertainties, (still following Ward and Asphaug (Deep-Sea Res II 49:1073–1079, 2002) on a simplified line. An upper bound of continental shelf shoaling is estimated ad hoc. The influence of several parameters is also analyzed, in particular the effect of tide is briefly addressed. Keywords Cosmogenic tsunami · Asteroid fall · Coastal flood · Risk assessment
1 Introduction We address here the question of cosmogenic tsunamis, i.e., tsunamis due to the fall of an asteroid in the ocean. Our goal is to estimate the risk of such an event on the Atlantic coasts of Europe. Note that, by "risk" we mean here the probabilistic analysis, not the impact on the coastline structures and populations, contrary to Chesley and Ward (2006), for example. The risk of asteroid fall on Earth has been studied since the end of the 1970s (CATWG 1979). These space bodies come mostly from the asteroid belt between Mars and Jupiter, and about 20,000 of them have been identified, about 900 of them having a radius RI above 500 m and a several thousands with a radius above 70 m (Bostrom 2002; Marcus et al. 2010; Hughes 2003; Bland and Artemieva 2006; Mathias et al. 2017; Wheeler and Mathias 2019). According to Ward and Asphaug (2000), the asteroids with radius higher than RI,min = 65 m reach the ground or the ocean. A more recent work Wünnemann and Weiss (2015) proposed RI,min = 50 m for metal bodies and RI,min = 200 m for rock bodies. Here, we will keep the value RI,min = 65 m to avoid underestimating the risk. The annual rate of asteroid fall given by Chesley and Ward (2006) is as follows: * Damien Violeau [email protected] 1
EDF R&D/LNHE, Chatou, France
2
Laboratoire d’Hydraulique Saint-Venant, Chatou, France
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Natural Hazards
( ) n RI =
𝛼 10∕3 RI
,
(1)
with 𝛼 = 1.816 × 10−14 m1∕3 yr−1 (yr stands for a year). The unit of n is [n] = L−3 T −1 , thus we can rewrite (1) as 1∕3
RI,min ( ) n RI = , 10∕3 𝜏RI
(2)
where 𝜏 = 2.21 × 1014 yr has the dimension of time.1 Note that current estimates resulting from recent additional observations lead to different laws for the rate of fall; in particular, it is worth mentioning the linear power law neglects the observed dip such as shown in Harris and D’Abramo (2015). However, the law (1) will be considered as sufficient for the sake of this study. Assessing the risk of asteroid fall and
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