At 4 of January 2009, a powerful earthquake hit the area, 4 people died and over 66 people injured and evacuated while more than 500 building damaged. The first earthquake struck at 02:43:51 local time on 4 January 2009 on 7.2 Richter magnitude scale, located in 135 km Northwest of Manokwari, followed by 7.6 Mw at 05.33:40 WIB located on 95 km west of Manokwari both onshore in depth of 10 km. A tsunami warning was initially issued but lifted within an hour of the quake.
Area near the epicenter formed by pre Tertiary metamorphic rock, tertiary sedimentary rock and Quaternary sediment. Quaternary sediment mostly deposited along the coastline and this loose unconsolidated sediment amplifying the seismic wave propagation and so this area becomes the mostly damaged area. Another part of the area that was highly weathered also gives the similar response to the seismic wave. Earthquake also induced landslide and liquefaction in some places, mostly in area along the fault zone.
This earthquake generated by the activity of the Sorong fault. The Sorong fault zone is a broad zone of inferred left-lateral shear at the triple junction of the Indo-Australian, Eurasian, and Pacific plates. Its shear zone continue westward through the eastern margin of Eurasia in the region of Sulawesi Island. According to USGS its strike slip mechanism with parameter N 308o E/ 55o, slip 99o. In Modified Mercalli Intensity (MMI) this earthquake implied VI-VII MMI scale.
The community suggested to be aware of the aftershock even it will be more decresing in the intensity, people living near and along the slope must be aware of the landslide triggered by the aftershock activity. For the reconstructruction it is highly recommended to build with the earthquake resistant construction and community based future preparedness should be assess in the area.
Data source : USGS, Geology Agency, Ministry of Energy and Mineral Resources Republik of Indonesia and so many others
Map Links :
Epicenter, Intensity, Historical Earthquake Map
Rapid Investigation Result from the Geological Agency, RI
A collapsed hotel (image source : The Spec)
Residents sit outside of their damaged houses (image source : Daylife)