After Haiti was hit by a massive 7.0 earthquake on January 12, 2010, huge aftershocks rippled through the already crippled city of Port-au-Prince and surrounding areas. On January 20, 2010, the ongoing rescue efforts were again delayed when a 6.1 magnitude aftershock struck the area at about 6:00 a.m. Between January 12th and January 20th, there were over 40 aftershocks. Experts say that aftershocks can last for weeks or months.http://news.yahoo.com/s/ap/20100120/ap_on_re_la_am_ca/cb_haiti_earthquake_287;_ylt=AowUERnSoUR7caAPqfTZdxNxieAA;_ylu=X3oDMTE2M3IwdWY0BHBvcwMxBHNlYwN5bi1yLWItbGVmdARzbGsDZXYtaGFpdGlhbnNm

The 6.1 aftershock on January 20th was said to be centered about 35 miles southwest of Port-au-Prince. The rumbling sparked panic among the Haitian people who have been displaced and homeless since the initial earthquake. Many people were still sleeping outside in tents, in fear that a large aftershock could bring down any remaining and damaged structures.http://www.csmonitor.com/World/Americas/2010/0120/Haiti-aftershock-stirs-panic-could-hinder-last-ditch-rescue-efforts

After the large aftershock in Haiti on January 20, 2010, geophysicist Bruce Pressgrave told the Associated Press that the aftershocks could be because of the "new reality of the rock layers." The expert said that the large earthquake on January 12th could have been the start more seismic activity; both in Haiti and elsewhere.http://abcnews.go.com/Technology/wireStory?id=9611586

The island of Haiti/Dominican Republic sits on top of the Enriquillo-Plantain Garden Fault line. To the north of Haiti, and crossing through the Dominican Republic is the Septentrional Fault line. The Haiti earthquake on January 12th was the biggest quake on the Enriquillo fault line. The nearby Septentrional fault system hasn't had a big earthquake in over 800 years.http://www.npr.org/templates/story/story.php?storyId=122531261