At https://phys.org/print436523070.html … giant earthquakes are not as random as thought. Analysis of sediment cores from lakes in Chile show that EQs reoccur at regular intervals. It is only when smaller EQs are added that the incidents show up randomly in time. A Chilean EQ in 1960 had a magnitude of 9.5 and produced a massive tsunami wave that pummeled the coastal regions and caused a wave that travelled right across the Pacific to kill 200 people in Japan. Strong EQs produce underwater landslides which are preserved in sedimentary layers. By sampling these layers, up to 8m in length, the researchers produced a history of EQs going back 5000 years. This included 35 EQs with a magnitude over 7.7.
The same story is at https://tallbloke.wordpress.com/2018/01/30/giant-earthquakes-not-as-rand… …..
… giant EQs re-occur at intervals of 292 +/- 93 years. Smaller EQs took place more frequently. Curious George, in a comment, suggests the periodicity is similar to lunar apsiical cycles. Is that a coincidence?