Papua, Indonesia (offshore)

January 3, 2009; M7.7, 7.4 Earthquakes

EERI REPORTS The Papua Earthquakes of January 3, 2009

West Papua earthquake epicenters (click to enlarge)

On January 3, 2009 (Indonesian time), a M7.6 earthquake in the pre-dawn hours and a M7.4 earthquake three hours later, almost certainly triggered by the first event, shook the remote east Indonesian province of West Papua. The region nearest the epicenter is sparsely populated and attracts tourists thanks to its diving sites, wildlife, and spectacular scenery. The capital city of Manokwari is the nearest major city (population 161,000) and is located about 145 km and 85 km from the first and second large shocks respectively. Depths of the two events were 17 km for the M7.6 and 23 km for the M7.4. A tsunami warning was issued and cancelled an hour later. Liquefaction was observed on beaches and in river banks. According to EERI Member Teddy Boen, these events and their aftershocks resulted in little damage to buildings and infrastructure. The Badan Geologi (Geological Agency) reported that in Manokwari, about 250 houses were lightly to heavily damaged with one collapse. Two people were killed and 74 injured. Numbers may have been two or three times larger throughout the entire province. Widespread fleeing from homes occurred not because of damage but because of fears of tsunamis and additional large shocks. Upwards of 17,000 evacuees filled tent cities. Fear coupled with illness within these camps and rainy weather has impeded the populace’s return home. The 2009 events were both associated with subduction of the Pacific plate beneath the Australian plate. Relative plate motion in this area is 12 cm/yr; the convergence rate on these two plates is probably a few cm per year on a plane dipping about 30 degrees south beneath the north shore of West Papua. The Sorong fault, a major onshore transform fault that could have a sliprate as high as 10 cm/yr, has not had a large event for at least 100 years and may have been stress-loaded during this recent activity. Therefore there is concern that these recent events may lead to another large earthquake on the Sorong fault, which is located much closer to the cities of Manokwari and Sorong. The original newsletter article can be read here.