Preliminary results from R/V NATSUSHIMA survey around the epicenter, off Sumatra

Contact information
Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
Institute For Research on Earth Evolution (IFREE)
Program for Deep-Sea Research (Attn: Kinoshita)
Tel +81-46-867-9323
Public Relations (Attn: Takahashi / Gocho)
Tel +81-46-867-9066 fax +81-46-867-9055
http://www.jamstec.go.jp/

1. Outline
　Japan Agency for Marine-Earth Science and Technology (JAMSTEC) conducted a research cruise in collaboration with the Agency for the Assessment and Application of Technology (BPPT) using the Research Vessel NATSUSHIMA and the Remotely Operated Vehicle HYPER DOLPHIN to investigate the deformation of the seafloor around the epicenter after the earthquake.
　The research cruise had been carried out in the west offshore of Aceh Province, the northern part of Sumatra for the total of 26 days and divided into two legs; Leg 1 (Feb 18-Mar 5) from Singapore to Penang and Leg 2 (Mar 10-Mar 19) from Penang to Bali.
　This survey was conducted by several researchers and scientists from Japan and Indonesia by the lead of Dr. Wataru Azuma (JAMSTEC) and Dr. Yusuf S. Djajadihardja (BPPT) with the participation of those from Germany and USA.This seafloor survey includes creating the seafloor bathymetric map by high-resolution multi-narrow beam echo sounder onboard the NATSUSHIMA, investigating the deformation of the seafloor through the visual observation by the HYPER DOLPHIN, and monitoring aftershock distribution using Ocean-Bottom Seismometers (OBS).
　This survey has been supported as [Urgent Study of the Great Sumatra Earthquake and Tsunami Disasters] by Special Coordination Fund of MEXT (Ministry of Education, Culture, Sports, Science and Technology), Japan in 2004.

2.Background
　The magnitude 9 earthquake, which was occurred in the west coast of northern Sumatra on December 26, 2004 had generated a series of Tsunami wave and devastated coastal area through the Indian Ocean with the loss of more than 300,000 lives.A thorough investigation by researchers and scientists to determine the cause of this disaster is desperately needed as a global unit with the hope of the immediate recovery in the disaster-stricken area.

3.The summery of the survey
At this research cruise (See Exhibit 1: Survey area, Exhibit 2: The navigational chart),

(1)	The visual observation of the crustal deformation by the Remotely Operated Vehicle HYPER DOLPHIN in the seafloor off Aceh, where was inferred to be a large scale of displacement zone (off Aceh LsDZ) near the epicenter was conducted to understand the cause and propagation mechanisms of M9 class Sumatran earthquake.
(2)	The seafloor topographical survey utilizing multi-narrow beam echo sounder system and Ocean Bottom Seismographs (OBS) were conducted to monitor the aftershock distribution.

4. The preliminary results from the survey

(1)	The extensive fissures and edges of collapse were found around the epicenter through the high vision camera by HYPER DOLPHIN for the first time in the world. (On Feb 22 / Mar 19, 2005: See Exhibit 3,4).
(2)	The high-resolution bathymetric map around the focal area (approx. 4000 km2), where was inferred to have caused maximum seafloor deformation by this earthquake was created.
(3)	Over 3,000 aftershock data was obtained by 17 OBSs in two weeks (On Mar 13).The rest of 2 OBSs for the long-term observation (approx. 4months) are planning to be retrieved afterwards.
(4)	A large scale of open fissures (see Exhibit 3// The maximum width of the fissure: approx. 40m. The depth of the collapse: approx. 15m) were found intermittently approx. 45km across the seafloor at the depth of 2,300 m (On Mar 22).

5. As a future plan
　It has been continued to analyze the bathymetric map, aftershock data, and the image data, which were obtained by this survey and make clear the location of the fault, size, gradient, the strength of the energy emission, the process of the deformation, and the effects occurred around the epicenter.Furthermore, along with making best effort to clarify the mechanism of the occurrence of this earthquake, it is expected to contribute to make the alleviation system against Tsunami damage and promote our technology for earth science and disaster prevention.

Exhibit 1:Survey area off Sumatra, Indonesia
Exhibit 2:The navigational chart off Sumatra, Indonesia
Exhibit 3:Edge of collapse(photo 3/19/2005)
Exhibit 4:Open fissures(photo 3/19/2005)