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The Mw ≥ 9.0 1952 Kamchatka, 1957 Aleutians, 1960 Chile, 1964 Alaska, 2004 Sumatra, and 2011 Japan earthquakes triggered destructive tsunami rupturing hundreds of kilometers along few specific segments of the subduction margins globally in a while. Such infrequent mega-events had shown their far-reaching effects and perplexed the world community. The 2004 mega-event in association with few other great earthquakes in the central and southern parts of the Sumatra margin (e.g., 1797 M ~ 8.4, 1833 M ~ 9.0, 1861 M ~ 8.5, 1905 Mw ~ 8.4, 2005 Mw 8.7, 2007 Mw 8.5) provided unprecedented opportunity for a critical reappraisal of hazard for the adjoining areas. We explore here the characteristics of seismic energy released along the eastern subduction margin, based on USGS catalogue for the period between 1976 and 2013. We consider the earthquakes with body wave magnitude 4.0 and above. We find the earthquake activities are mainly concentrated in four tectonic domains: first one covers the entire Myanmar margin (Segment I), second one includes Andaman-Nicobar-Northwest Sumatra margin (Segment II), third one is located in the Southeast Sumatra-West Indonesia (Segment III), and the fourth domain lies in the East Indonesia (Segment IV). The tectonics parameters, locations, great earthquake occurrences, seismic energy release, and the Wadati-Benioff zone geometry in these four segments also display distinct features. We find the aftershock activities of 2004 mega-event has been shifted from deeper to shallower level of the lithosphere in Segment II. The shifting of aftershocks of the 2005 Mw 8.7 Nias earthquake from deeper to shallower part of the subducting oceanic lithosphere was also noticed. Such shifting of seismicity towards the trench-axis after the 2004 MW > 9.0 earthquake was apparently caused by migration of the stress-field from deeper to shallower part of the Indian lithosphere. Similar shifting of aftershocks were also observed along the Kuril trench after the incidence of 15th November 2006 Mw 8.3 earthquake, and interpreted to be caused by stress transfer through the subducting lithosphere. Further, the energy bursts happened near the Northwest Sumatra and Car Nicobar areas are likely located in the zone of seismic quiescence during 2004 event. We find spikes in the plot of seismic energy distribution, which apparently indicates the stress energy transferring happened from east to west, towards the zone of occurrence of 2004 Mw>9.0 earthquake during the quiescence period. The b-values show a constant decrease in Segments II, III, and IV, whereas the Zone I does not show any such pattern prior to the 2004 mega-event. These typical observations account for dominant stress accumulation near the Sumatra area. We thus believe that the occurrence of 2004 mega-event was apparently concealed behind the long-term seismic quiescence existing near the Sumatra and Nicobar margin. A systematic study of the patterns of seismic energy release and b-values, and the long-term observation of collective behavior of the margin tectonics, might had given clues for the forecasting of the 2004 mega-event, and thus contribute to improve seismic hazard estimates.Keywords: Eastern Subduction Margin; Seismic b-value; Tsunami; Seismic quiescence; 2004 mega-event [ABSTRACT FROM AUTHOR]

Recent seismological and geodetic observations, as well as sophisticated regional models, indicate that similar physical processes are active during the earthquake cycle at different subduction margins. Part of the observed complexity at these margins is controlled by the fact that they are in different stages of the earthquake cycle. The observations capture critical physical processes like (partial) locking of the plate interface, the detailed co-seismic slip, and mantle relaxation and afterslip.We analyze geodetic observations along sections of the South America, Japan, and Sunda trenches during the interseismic part of the megathrust earthquake cycle. The results show that overriding plates shorten from the trench to a "backstop", where interseismic velocities become close to zero. In most, but not all, regions, the backstop location from trench-perpendicular GPS velocities agrees with that from parallel velocities. The distance of this interseismic backstop to the trench varies along major subduction margins. We explore what controls this distance by correlating backstop location with locking area on the plate contact, with boundaries of tectonic blocks in the overriding plate (mechanical contrasts), and with estimates of the recurrence time of the largest events.An enigmatic observation is that co-seismic geodetic displacements of great earthquakes, including the 2004 Sumatra earthquake, the 2010 Maule earthquake, and the 2011 Tohoku earthquake extended into the overriding plates well beyond what we infer to be the backstops. We use cyclic 3D geodynamic models to further understand and quantify these correlations. Co-seismic and subsequent slip on the subduction interface are dynamically (and consistently) driven. This setup allows us to access the sensitivity of the geodetic signals to mechanical components of the overriding plate and the slab system. We conclude that gradients in the effective elastic thickness of the overriding plate explain the observations. [ABSTRACT FROM AUTHOR]

Marine tsunamis have been increasingly discussed in the context of ocean-wide natural hazards since the 2004 Sumatra, the 2011 Tohoku earthquake and the more recent 2018 Palu tsunamis. However, as historical reports and recent studies have shown, tsunamis also occur in lakes. While ocean tsunamis are often caused by earthquake-related plate displacements, tsunamis in lakes are of seismic or aseismic origin, caused by mass-movement processes that displace large amounts of water, generating devastating waves. In Switzerland, historical reports document that tsunamis occurred in many lakes (e.g. 563 AD in Lake Geneva, 1601 and 1687 AD in Lake Lucerne) causing large damages and casualties. The causes of these historical tsunamis were diverse and include earthquake-triggered sublacustrine and subaerial mass-movements, spontaneous delta collapses. Today, the shorelines of many Swiss lakes are densely populated. Although tsunamis are known to have occurred in the past on various Swiss lakes, a workflow for a holistic tsunami hazard assessment is still missing. An interdisciplinary project, funded by the Swiss National Science Foundation, uses the outstanding field laboratory of Switzerland's lakes to better understand the key concepts of governing processes of lake tsunamis by investigating i) their trigger mechanisms, ii) the geotechnical and sedimentological properties of the unstable sediment, iii) the potentially unstable sediment volumes on charged slopes, iv) wave propagation and inundation, v) onshore tsunami deposits and vi) their related hazard. The results of this project will provide the basis for assessing the risk for people and infrastructure along lakeshores and coasts. [ABSTRACT FROM AUTHOR]