Additional sedimentation occurred until a subduction zone formed off the coast .
直至一个潜没带在距离海岸处形成前，额外的沉积作用一直存在。
How do earthquakes arise in undersea subduction zones , which account for 90 per cent of all seismic energy released worldwide ?
占全球地震能量释放90%的地震是怎样发生于海底俯冲区的？
The cascadia subduction zone , just 50 miles off the coast and stretching from northern california to southern british columbia , is accumulating stresses that could unleash an earthquake of magnitude 9.0 and generate its own tsunami .
