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Empirical constraints on magnitude-distance relationships for seismically-induced submarine tsunamigenic landslides

Salamon, Amos, Di Manna, Pio
Earth-science reviews 2019 v.191 pp. 66-92
coasts, earthquakes, landslides, tsunamis, India, Italy
Seismically-Induced submarine Landslide Tsunamis (here called SILTs) attract growing attention due to their unique setting, damage potential and short warning time. A question of key importance, especially for tsunami early warning, is: how far can an earthquake trigger a tsunamigenic slump? Here we investigate the relationships between earthquake magnitude and the maximal distance between the seismogenic fault and the tsunamigenic slumps (Rf) and between the earthquake epicenter and the slump (Re), and propose empirical constraints on these Magnitude-Distance (M-D) relations.The 49 identified SILTs are spread in various seismotectonic and bathymetric settings in different seas around the globe. We found that the maximal distance of the tsunamigenic submarine landslide from the parent earthquake grows with the magnitude and is bounded by an envelope constrained by Mw as low as 4.9 for several kilometers (the 1968, Liguria Coast, Italy) and as far as 250 km for Mw 7.7 (the 1819, Rann of Kachchh, India). Higher earthquake magnitudes also produce SILTs, seemingly distances lower than 250 km, however, it is suspected that the available data is limited and unable to reflect the true nature of SILT's generation.Generalized empirical relations between the earthquake magnitude (Mw) and the maximal distance from the seismogenic fault to its generated SILT (Rf, in km) are: Log Rf = −1.17 + 0.49 Mw (R2 = 0.78). The empirical distance between the earthquake epicenter and the corresponding tsunamigenic slump (Re, in km), is: Log Re = −0.87 + 0.45 Mw (R2 = 0.83). Although many earthquakes within the M-D bounding envelope did not produce tsunamis, the ‘successful’ events still enable the delineation of the M-D zone vulnerable to tsunami generation, which, in turn, can be applied to tsunami early warning procedures. This is particularly important for near-coast inland earthquakes, as their tsunamigenic potential might be overlooked.