Abstract
There is a fairly strict relation between maximum tsunami wave heights and causation earthquake magnitudes. This provides a new tool for estimating the magnitude of past earthquakes from the observed wave heights of related paleo-tsunami events. The method is subjected to a test versus two paleoseismic events with multiple independent estimates of corresponding earthquake magnitude. The agreement to the tsunami wave height conversion is good, confirming very high magnitudes of M 8.5 - 9.0 and M 8.4 - 8.5. Applying the same method to two Late Holocene events of methane venting tectonics indicates a ground shaking of forces equivalent to a M 8.0 earthquake, seriously changing previous long-term crustal hazard assessments.
Highlights
Major tsunami events are primarily generated by submarine earthquakes [1] [2]
Two paleoseismic events were selected for a test of the significance of Figure 1 relations established; viz. the 10,430 vBP and the 9663 vBP events, because both of these event were established by means of a multiple criteria [10] [11], besides they both represent very strong events with well-established tsunami heights
The tsunami height of the 2900 BP event is consistent to a magnitude ground shaking of M 8.0, which seems to harmonize with the violence of the structures observed (Figure 5)
Summary
Major tsunami events are primarily generated by submarine earthquakes [1] [2]. In principle, there is a relation between earthquake magnitude and tsunami wave height. Mörner and 8) the Tihoku-oki 2011 event with a wave height of 19.5 m and a magnitude of Mw 9.0. Because these 8 events are known both to tsunami wave height and causation earthquake magnitude, they can be used to establish the relationship between tsunami wave height and seismic magnitude [3] [4].
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