Small slips and big earthquakes

RESEARCHERS have identified a “slow slip” pattern of gradual deformation that begins just before moderate and major earthquakes, according to Naoki Uchida of Tohoku University, Japan, and colleagues. A better understanding of such cycles of slow slip rates could help scientists refine earthquake forecasts in the region. The work has been published in a recent issue of Science.

Slow (or a seismic) slip is a process by which faults displace rocks like earthquakes do, but much more slowly and without generating seismic waves. A detailed understanding of the relationship between large earthquakes and a seismic slip is lacking because of the poor detectability and measurement of slow slip events and the rare occurrence of large earthquakes.

However, some evidence suggests that slow slips can increase stress in adjacent areas and may trigger damaging earthquakes.

This led Naoki Uchida and colleagues to analyse data of 6,126 seismic moments over a period of 28 years to detect slip-rate fluctuations in north-eastern Japan. Their analysis reveals that intervals of slow slip range from one to six years, and often coincide with clusters of large magnitude earthquakes, including the large 2011 Tohoku-oki earthquake in north-eastern Japan.

R. Ramachandran