Scientists get first look at cause of ‘slow motion’ earthquakes

An international team of scientists has for the first time identified the conditions deep below the Earth’s surface that lead to the triggering of so-called ‘slow motion’ earthquakes.

These events, more commonly known as slow slip events, are similar to regular sudden and catastrophic earthquakes but take place on much longer timescales, usually from days to months.

By drilling down to just over 1km deep in water depths of 3.5km off the coast of New Zealand, the team have shown that the fault zone areas in which slow slip events occur are characterised by a ‘mash up’ of different rock types.

The results, published today in the journal Science Advances, showed that the areas are comprised of extremely rough sea floor topography made of rocks that varied markedly in size, type and physical characteristics.

The lead author of the paper, Dr Philip Barnes of New Zealand’s National Institute of Water and Atmospheric Research (NIWA), described that ‘some rocks were mushy and weak, whilst others were hard, cemented and strong.’

This has given scientists the first-ever look at the types and properties of rocks directly involved in slow motion earthquakes and begins to answer some of the major outstanding questions surrounding these unique events, such as whether or not they can trigger larger, more damaging earthquakes and tsunamis.

Co-author of the study Dr Ake Fagereng, from Cardiff University’s School of Earth and Ocean Sciences, said: “This was the first effort to sample the rocks that host slow slip events, and the striking, immediate observation is that their strengths are hugely variable.”

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