“Red”, “Green” and “Blue” Tsunamigenic Earthquakes and their Relation with Conditions of Oceanic Sedimentation in the Pacific

Abstract

The theoretical relationship between tsunami intensity I (on the Soloviev-Imamura scale) and the moment magnitude of an earthquake M _w , has been obtained (I = 3.55M _w − 27.1) by Chubarov and Gusiakov (1985). This relationship was used to calculate the expected tsunami intensity for 293 Pacific tsunamigenic earthquakes with known moment-magnitude M _w . The present study introduces the formal classification of these earthquakes on the basis of their ΔI parameter, that is the difference between observed and expected tsunami intensity. Based on the ΔI value, all events are divided into three groups: “red” (ΔI>1), “green” (−1≤ΔI≤1), and “blue” (ΔI<−1). The geographical distribution of events in these groups shows their clear correlation with climatic and circum-continental zonation in oceanic sedimentation, as described by Lisitsyn (1974). Specifically, the equatorial humid zone, characterized by the highest rate of oceanic sedimentation, is clearly indicated by an increased level of “red” tsunamigenic earthquakes. The circum-continental zonation is clearly expressed by the fact that all tsunamigenic events that occurred in this century in the East China, the Yellow, the Japan, the Okhotsk and the Bering Seas belong to the “red” group. On the other hand, all major submarine earthquakes that occurred in such remote subduction zones as Guam, Tonga, and New Zealand are designated as “green” or “blue”. Despite their large M _w values (greater than 7.9), these events generated very minor tsunamis with run-up heights less than 1 meter. The present study indicates that earthquake-induced disturbances of bottom sediments that result in submarine slumping can be a significant factor in the tsunami generation mechanism. Therefore, the potential slumping process should be taken into account in operational tsunami warning as well as in coastal tsunami zoning.