 On 20 January at 06 : 03 local time ( 11 : 03 UTC ) the strongest aftershock since the earthquake , measuring magnitude 5 @.@ 9 Mw , struck Haiti . USGS reported its epicenter was about 56 km ( 35 mi ) <unk> of Port @-@ au @-@ Prince , which would place it almost exactly under the coastal town of Petit @-@ Goâve . A UN representative reported that the aftershock collapsed seven buildings in the town . According to staff of the International Committee of the Red Cross , which had reached Petit @-@ Goâve for the first time the day before the aftershock , the town was estimated to have lost 15 percent of its buildings , and was suffering the same shortages of supplies and medical care as the capital . Workers from the charity Save the Children reported hearing " already weakened structures collapsing " in Port @-@ au @-@ Prince , but most sources reported no further significant damage to infrastructure in the city . Further casualties are thought to have been minimal since people had been sleeping in the open . There are concerns that 12 January earthquake could be the beginning of a new long @-@ term sequence : " the whole region is fearful " ; historical accounts , although not precise , suggest that there has been a sequence of <unk> progressing <unk> along the fault , starting with an earthquake in the Dominican Republic in 1751 . 
