The Nepal earthquake was so large that its aftershocks could persist for years, as a forecast released by US Geological Survey (USGS) predicts major tremors until May 31, 2016, many of them between the potentially risky magnitudes of 6 and 7 next month.
There’s even a small chance of an aftershock of “greater” intensity than the April 25 event during the one-year period.
The geological agency expects aftershocks to occur in the “zone of current activity and at its edges”, which means it will be felt in areas already devastated, complicating recovery and weakening structures further. Aftershocks felt so far in the Himalayan nation have been in line with the USGS projections.
According to the USGS, aftershocks of magnitude 5 and larger are “as a rule of thumb” considered potentially damaging.
Until May 3 this year, up to 14 aftershocks of magnitude 5 or greater are expected, along with a 54% chance of a magnitude 6 aftershock.
Chances of major tremors are highest throughout May this year, with a better-than-50% probability of at least three tremors greater than magnitude 6. According to the forecast’s classification, more than 50% translates to a “significant chance”. There’s very little doubt that Nepal will continue to feel more than dozen quakes of up to magnitude 5 in May.
Between now and May 31 next year, the “potential for an aftershock larger than the mainshock remains, but is small (1-2% in each time period),” the forecast, viewed by HT, says.
Aftershocks, or additional quakes arising from landmasses reshuffling after a big incident, are usually smaller than the mainshock, but sometimes may be large enough to be “felt widely throughout the area” and cause additional damage, particularly to structures already weakened by the main quake.