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Scientists look at drilling sea floor to study 'silent' quakes

WELLINGTON, July 29 — Scientists from around the world will gather on the east coast of New Zealand next week to discuss proposals to study "silent" earthquakes by drilling into the seabed.

Silent quakes, also known as slow slip events, occur on the boundaries of the earth's tectonic plates, where one plate dives under another in areas known as subduction zones, and are slower than normal quakes, taking weeks or months to occur rather than seconds, and are rarely felt on the surface.

About 70 scientists from 10 countries will convene in the city of Gisborne, which lies near the site of a major fault line and where scientists first identified silent earthquakes in 2002.

Slow-slip events were first discovered with the advent of new measurement technologies on the west coast of Canada about 15 years ago and have since been recorded at about a dozen locations around the world, including four sites around New Zealand, said a spokesperson for New Zealand's Institute of Geological and Nuclear Sciences (GNS Science).

About eight slow-slip episodes have occurred under Gisborne since 2002 at roughly two-year intervals.

Scientists have proposed numerous theories to explain the phenomenon, but testing the theories is difficult as silent quakes happen many kilometers below ground.

"The best way to understand the true cause of slow-slip events is to drill into and sample the area on the plate boundary fault where they are known to occur, and monitor a whole range of physical and chemical properties at the plate interface," said Laura Wallace, of GNS Science.

Offshore Gisborne offered one of the best opportunities in the world to study the silent earthquakes because they occurred 5 to 15 km below the seafloor, making the shallow part of the slip zone accessible with modern ocean drilling methods, while they normally occurred at depths of 30 km to 40 km.

Other possibilities for studying slow-slip events with drilling techniques were in central Japan and Costa Rica.

Workshop participants would discuss a framework on how ocean drilling could be used to understand the origin of silent earthquakes.

Any international project to drill off Gisborne would take many years and be done in stages, and depend on the availability of a scientific ocean drilling ship, which were usually booked years in advance, said Wallace.

"Findings from such a project would have global significance as it would have the potential to significantly boost our understanding of the mechanics of subduction zone faults and the earthquakes that occur on them."

The workshop from Aug. 1 to 5 is funded by New Zealand's Ministry of Science and Innovation, the Integrated Ocean Drilling Program, to which New Zealand belongs, and the National Science Foundation in the United States. (PNA/Xinhua) LAP/utb

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