More Haiti aftershocks felt; more expected for possibly years

PORT-AU-PRINCE, Haiti, January 22, 2010 – Haiti was rocked by more aftershocks yesterday and the news coming from the United States Geological Survey (USGS) is that there will be more in months, and even years to come. And one of them could be even bigger than last Tuesday’s devastating earthquake that killed up to 200,000 people, injured some 250,000, and made 1.5 million homeless.

“The frequency of events will diminish with time, but damaging earthquakes will remain a threat. 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,” it said yesterday evening in an assessment of aftershock hazards in Haiti.

The report was issued at the end of a day of aftershocks that jolted survivors of the quake. The first, with a magnitude of 4.9, occurred around 11:45 am with its epicentre 30 miles west of the already stricken capital Port-au-Prince. Nine minutes later, a 4.8 magnitude tremor hit, 15 miles closer to the capital.

There were reports of at least one other shock later in the night but that has not yet been confirmed by the USGS.

These events occurred a day after the biggest aftershock to date – a 5.9 magnitude tremor that occurred about 30 miles west south west of Port-au-Prince – crumbled already compromised buildings, sent more debris flying and scared residents running.

Based on the activity so far the USGS estimates that during the 30-day period beginning January 21st, there will be two or three more earthquakes of magnitude 5 or greater.

Additionally, it said, “the probability of one or more earthquakes of magnitude 7 or greater is less than three percent, the probability of one or more earthquakes of magnitude 6 or greater is 25 percent and the probability of one or more earthquakes of magnitude 5 or greater is about 90 percent”.

The USGS has cautioned that because any aftershock above magnitude 5.0 has the potential to cause additional damage, particularly to vulnerable, already damaged structures, anyone living in Haiti or involved in relief work there must be on alert.

It also noted that all the pressure that has built up in the faults running through the Caribbean region may not have been released in the Haiti quake and the fault zone near Port-au-Prince still stores sufficient strain to be released as a large, damaging earthquake during the lifetime of structures built during the reconstruction effort.

“It is essential that the rebuilding effort in Haiti take into account the potential for, indeed the inevitability of, future strong earthquakes,” it advised.

“The development of more resilient structures and infrastructure is a long-term goal, particularly in the face of economic limitations. Over the short-term, it is critical that the rebuilding effort be undertaken with an awareness of the potential for subsequent damaging events during the next months and years. It is essential that structures such as hospitals, schools, and critical facilities be reconstructed with greater resilience for the preservation of life and functionality.”

Other Caribbean countries, it said, should take a cue from what happened in Haiti: “The experience of the Port-au-Prince, Haiti earthquake reveals a need for better understanding of the nature and extent of earthquake and tsunami hazard in the Caribbean region.”

According to the agency, thorough seismic hazard assessments of countries in the Caribbean should be used to provide the basis for establishing or improving building codes and strengthening building resilience over the long-term.