Aftershocks will last months, if not years

Jan 22, 2010 08:21 GMT  ·  By
Rescue workers pull a survivor from under concrete blocks, in the Haitian capital Port-au-Prince
   Rescue workers pull a survivor from under concrete blocks, in the Haitian capital Port-au-Prince

According to geologists at the US Geological Survey (USGS), the 7.0-magnitude earthquake that struck Haiti on January 12 will continue to generate aftershocks for many months to come, or maybe even years. Naturally, the strength of these tremors will decrease over time, as evidenced by the fact that the January 20 aftershock, a 6.1-magnitude earthquake, was less intense than the original. The agency also issued a warning detailing the risks that the already-battered population of Haiti would be subjected to over the upcoming months. The new assessment was ordered by USGS Director Marcia McNutt.

“The aftershock sequence of a magnitude-7 earthquake will continue for months if not years in the affected area. The frequency of events will diminish with time, but damaging earthquakes will remain possible in the coming months. There is also a small chance of subsequent earthquakes larger than the initial shock. The sequence from the Port-au-Prince earthquake continues to be very strong and active,” the agency reveals in its analysis, published on January 21.

The activity and the statistics of aftershock sequences allowed the USGS to also estimate the possible aftershock incidence over the coming month. By February 28, Haitians are subjected to a less than three-percent chance of experiencing a tremor of magnitude 7 or higher. However, the possibility of a 6-magnitude tremor is at about 25 percent, whereas the possibility of them experiencing an earthquake stronger than a magnitude-5 one is of over 90 percent. The USGS geologists also report that they expect about two or three such aftershocks to occur over the coming month.

“Any aftershock above magnitude 5.0 will be widely felt and has the potential to cause additional damage, particularly to vulnerable, already damaged structures. Anyone living in Haiti or involved in relief work there must maintain situational awareness with regard to their personal earthquake safety. They should always be aware of what action they are going to take if the ground starts to shake. Open spaces are generally safe but running through falling debris to get to an open space may be dangerous,” the agency also reports.

“Only qualified engineers can determine if a damaged building is safe for reoccupation. Until engineering assistance arrives, a general rule to follow is: If it does not look safe, it probably is not safe. Entry into or reoccupation of obviously damaged structures should be avoided,” the USGS advises. Full details of the investigation can be read here.