American scientists have just discovered a fearsome link between the two most dangerous fault lines and the largest subduction zone on the US West Coast - San Andreas and Cascadia. An earthquake in Cascadia could trigger a super-field earthquake in San Andreas, creating an unprecedented double disaster in modern history.
For decades, geologists have believed that two giant seismic engines on the US West Coast - the Cascadia suction zone and the San Andreas fault zone - operate separately, one slide, one sink, each containing unpredictable destructive power. However, new research by marine geology expert Chris Goldfinger (Oregon State University) is shaking that belief.
By analyzing 137 sedimentary corees under the seabed along the two fault lines, the team followed the 10,000-year-old seismic event of the planet.
When major earthquakes occur, mud and sand are washed away, forming characteristic sedimentary layers called turbidite, recording the time of each change.
By comparing the size of particles, thickness and geological age using radioactive carbon methods, Mr. Goldfinger's team discovered a surprising thing: Many sedimentary layers in Cascadia and San Andreas appeared at the same time, only a few decades apart, even a few years apart.
In particular, the eight pairs of sediment clearly show a pair form, with the smoother layer (Cascadia) covered with a rougher layer ( San Andreas) - suggesting that an earthquake in Cascadia may have triggered the next match in San Andreas.
The phenomenon is most concentrated around the intersection of Mendocino triple Junction - where the three tectonic plates of North America, the Pacific Ocean and Juan de Fuca collide violently.
According to Mr. Goldfinger, "broken joints can work synchronously like joint eating cakes". A slide in Cascadia could put pressure on San Andreas, causing it to pull earlier than the natural cycle; on the contrary, San Andreas could also respond with an earthquake pushing back towards Cascadia.
If this theory is correct, the Big One scenario - a super earthquake predicted a long time ago in California - may not happen alone, but a chain reaction.
History has seen a similar phenomenon in Sumatra (Indonesia) in 2004-2005, when two consecutive 9-degree earthquakes were less than 1 year apart.
The discovery not only changes people's understanding of the seismic mechanism, but also rings a new warning bell: The US West Coast may be " Suppressing" the energy for two consecutive earthquakes, once one of the two zones is broken or the Zone is recovering.
