Filippo Zaniboni

Large, deepwater slope failures: Implications for landslide-generated tsunamis

Deepwater landslides are often underestimated as potential tsunami triggers. The North Gorringe avalanche (NGA) is a large (~80 km3 and 35 km runout) newly discovered and deepwater (2900 m to 5100 m depth) mass failure located at the northern fl ank of Gorringe Bank on the southwest Iberian margin. Steep slopes and pervasive fracturing are suggested as the main preconditioning factors for the NGA, while an earthquake is the most likely trigger mechanism. Near-fi eld tsunami simulations show that a mass failure similar to the NGA could generate a wave >15 m high that would hit the south Portuguese coasts in ~30 min. This suggests that deepwater landslides require more attention in geo-hazard assessment models of southern Europe, as well as, at a global scale, in seismically active margins.

Comment on “On the cause of the 1908 Messina tsunami, southern Italy” by Andrea Billi et al.

[1] The December 28th 1908 Messina Earthquake has been ranked as one of the most destructive events of the last centuries [Davison, 1936] The damages produced by ground shaking were aggravated by the effects of a remarkable tsunami, with up to 11 m of run-up height, that followed the earthquake [Omori, 1909; Baratta, 1910; Tinti et al., 2004]. The location of the causative fault is still a matter of debate [e.g., Argnani et al., 2009], the modelling of the associated tsunami [Tinti and Armigliato, 2003] allowing uncertainty. [2] Billi et al. [2008] have recently proposed that the tsunami that stroke the coast of the Strait in December 1908 originated from a large submarine landslide (20 km) located offshoreGiardini-Naxos. The hypothesis is based on the study of tsunami arrival times [Platania, 1909; Baratta, 1910] and is supported, according to Billi et al. [2008], by inspection of: a multibeam morphobathymetry [Marani et al., 2004] and of a crustal-scale seismic profile [Scrocca et al., 2004]. [3] The arguments of Billi et al. [2008], however, have weak points that cast doubt on their interpretation. But most importantly, data collected in the last few years by the authors of this comment (A. Argnani and F. Chiocci), and work on tsunami modelling (S. Tinti and his group) cast further doubt on the proposed hypothesis that a large submarine landslide that was caused by the 1908 earthquake is located offshore Giardini-Naxos. These issues will be discussed in the following.

The Double Landslide‐Induced Tsunami

The 2002 crisis of Stromboli culminated on December 30 in a series of mass failures detached from the Sciara del Fuoco, with two main landslides, one submarine followed about 7 min later by a second subaerial. These landslides caused two distinct tsunamis that were seen by most people in the island as a unique event. The double tsunami was strongly damaging, destroying several houses in the waterfront at Ficogrande, Punta Lena, and Scari localities in the northeastern coast of Stromboli. The waves affected also Panarea and were observed in the northern Sicily coast and even in Campania, but with minor effects. There are no direct instrumental records of these tsunamis. What we know resides on (1) observations and quantification of the impact of the waves on the coast, collected in a number of postevent field surveys; (2) interviews of eyewitnesses and a collection of tsunami images (photos and videos) taken by observers; and (3) on results of numerical simulations. In this paper, we propose a critical reconstruction of the events where all the available pieces of information are recomposed to form a coherent and consistent mosaic.

The 1963 Vajont Landslide: A Numerical Investigation on the Sliding Surface Heterogeneity

The 1963 Vajont landslide is a key case in landslide literature, because it was catastrophic and because a lot of accurate data were collected before and after its occurrence. In this paper, the main focus is on the possible heterogeneity of the sliding surface involved by the landslide motion, which is reflected by a heterogeneous distribution of the dynamic basal friction coefficient μ. Assuming a given zonation of the sliding surface, our strategy was to apply a 2D Lagrangian model to compute the landslide motion and to find the values of μ for each zone, leading to the best agreement between the computed and the observed final deposit. Following some hints from the literature, we have explored heterogeneous configurations composed of up to four different zones, including also the homogeneous case, by means of a 2D numerical model (UBO-BLOCK2) that handles the landslide as a mesh of blocks and runs quickly enough to allow the computation of tens of thousands of simulations in a reasonable computing time. It is found that the four-zone zonation produces the best fit (or the least misfit), which is a strong hint that the gliding surface involved different geotechnical units.

Chapter 15 – Geoethical and Social Aspects of Warning for Low-Frequency and Large-Impact Events like Tsunamis

Real-time warning of large-impact events like tsunamis, that may attack the nearest coast soon after the generation, implies that there is no time to collect enough data before tsunami arrival to provide accurate estimates of the wave height and tsunami duration, which may result in issuing inaccurate alarm messages to the population. Assessments of tsunami hazard and analyses of tsunami risk, that are at the basis of long-term prevention policies, can be affected by large uncertainties as well, since they suffer from systematic scarcity of real observations because large tsunamis are very infrequent events. This paper discusses the role of geoscientists in providing predictions and the related uncertainties. It is stressed that through academic education geoscientists are formed more to improve their understanding of processes and the quantification of uncertainties, but are often unprepared to communicate their results in a way useful for society. Filling this gap is crucial for improving the way geosciences and society handle natural hazards and devise effective means of protection.