Within five years of each megathrust shock that struck since 1960, aftershocks on the high-slip portions of the rupture surface had shut down. At the same time, large aftershocks light up the surrounding area, menacing coastal population centers. In a study published last week in Nature Geoscience, we argue that after a megathrust earthquake, aftershocks on the rupture surface quickly shut down. But there is abundant evidence that megathrusts and other very large earthquakes abruptly and profoundly alter the hazard to depart, leading to damaging aftershocks and progressive mainshocks. Most seismic hazard assessments attempt to reflect the long term earthquake rates, which are assumed to slowly change as stress builds on faults. The largest instrumentally recorded megathrust was the 1960 Valdivia, Chile, magnitude-9.5 event. On average, there are about five megathrust shocks per century (Kagan and Jackson 2013). However, they occur at a rate only one hundredth of a magnitude-7. Such shocks release one thousand times the energy of a magnitude-7 event, and thus play a dominant role in the global seismic energy release. Subduction zones spawn the planet’s largest earthquakes, termed ‘megathrusts’ once they reach magnitude-9. Stein, Ph.D., Temblor, Inc., and Shinji Toda, Ph.D., International Research Institute of Disaster Science, Tohoku University New evidence has emerged of both a shutdown and a persistence of such shocks following megathrust events throughout history. Aftershocks of large earthquakes can be highly destructive.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |