DisastersAssessing the risks of global aftershock
The entire world becomes an aftershock zone after a massive magnitude (M) 7 or larger earthquake — but what hazard does this pose around the planet? Researchers are working to extend their earthquake risk estimates over a global scale, as they become better at forecasting the impact of aftershocks at a local and regional level.
The entire world becomes an aftershock zone after a massive magnitude (M) 7 or larger earthquake — but what hazard does this pose around the planet? Researchers are working to extend their earthquake risk estimates over a global scale, as they become better at forecasting the impact of aftershocks at a local and regional level.
A Seismological Society of America release reports that there is little doubt that surface waves from a large, M≥7 earthquake can distort fault zones and volcanic centers as they pass through the Earth’s crust, and these waves could trigger seismic activity. According to Tom Parsons, seismologist with the U.S. Geological Survey, global surveys suggest that there is a significant rate increase in global seismic activity during and in the forty-five minutes after a M≥7 quake across all kinds of geologic settings. It is difficult, however, to find strong evidence that surface waves from these events immediately trigger M>5 earthquakes, and these events may be relatively rare. Nevertheless, seismologists would like to be able to predict the frequency of large triggered quakes in this global aftershock zone and associated hazard.
Studies of hundreds of M≥7 main shock earthquake effects in twenty-one different regions around the world has provided some initial insights into how likely a damaging global aftershock might be. Initial results show that remote triggering has occurred at least once in about half of the regions studied during the past thirty years. Larger (M>5) global aftershocks appear to be delayed by several hours as compared with their lower magnitude counterparts. Parsons suggests that local seismic networks can monitor the rate of seismic activity immediately after a global main shock quake, with the idea that a vigorous uptick in activity could signal a possible large aftershock.
Parsons presented his research at the annual meeting of the Seismological Society of America, an international scientific society devoted to the advancement of seismology and the understanding of earthquakes for the benefit of society.
