WELLINGTON, Sept. 12 (Xinhua) -- Last November's 7.8-magnitude Kaikoura quake in New Zealand's South Island triggered a series of major slow-slip events, or "silent" earthquakes, beneath the east coast of the North Island, showed a new research from GNS released on Tuesday.
It was the largest and most widespread episode of slow-slip observed in New Zealand, since scientists first recognized this phenomenon under the seafloor east of Gisborne on the east coast of the North Island in 2002, according to the paper published in Nature Geoscience by researchers from GNS Science.
Slow-slip events are very similar to earthquakes, as they involve more rapid than normal movement between two pieces of the Earth's crust along a fault. However, unlike earthquakes, where the movement occurs in seconds, movement in these "silent earthquakes" can take weeks to months to occur, the paper explains.
According to the study's lead author and geophysicist, Laura Wallace of GNS Science, "This is probably the clearest example worldwide of large-scale slow slip being triggered over long distances by seismic waves from a large earthquake."
"One of the most intriguing factors is that the quake triggered slow-slip off the Gisborne coast, up to 600 km away from its epicenter in North Canterbury," Wallace said.
Seismologist Yoshihiro Kaneko, of GNS Science, said the slow-slip was triggered by stress changes in the Earth's crust caused by passing seismic waves from the Kaikoura quake.
Kaneko said the study also suggested that the northward travelling rupture during the Kaikoura quake directed strong pulses of seismic energy towards the North Island, and this also influenced the long-distance triggering of the slow-slip events beneath the North Island.
The east coast slow-slip event was also responsible for sparking a series of small to moderate earthquakes off the east coast in November last year, Kaneko said.
