Japan: JAMSTEC Conducts Seafloor Survey in Area of Earthquake on Pacific Coast

A series of photos taken by the JAMSTEC’s deep-sea submersible Shinkai 6500 reveals the appearance of fissures and bacterial mats on the seafloor, which are possibly associated with the 2011 Earthquake of the Pacific Coast of Tohoku on March 11.

The survey was conducted from 30 June to 14 August, 2011 at three sites along the continental-side slope of the Japan Trench , to investigate biological, geochemical and geological impacts of the earthquake on the deep seafloor environments. The depth of the sites ranges from 3,200 to 5,350 meters.

The images taken by the submersible include:

1. Fissures and step-like topography on the seafloor

2. Methane seepage  from the seafloor and the resulting colonization of bacteria (bacterial mats)

3. Partial discoloration of the seafloor

4. Colonies of white giant clams, (Calyptogena phaseoliformis)

5. Dense habitation of sea cucumbers (Elpidiidae)

Scientists will do an in-depth analysis of the collected images and data to report the results.

JAMSTEC plan to continue surveys in this area to gain better insights into the mechanism and impacts of the earthquake.

*1. Seafloor fissures:

The fissures suggest crustal movement of the seafloor associated with a series of seismic activity during the March 11 earthquake.

*2. Methane seepage:

The seepage of groundwater containing dissolved methane is often observed along the seduction zone faults. In the surface sediment down to a depth of several centimeters, sulfate reducing bacteria form hydrogen sulfide from methane and sulfate ions. A high concentration of methane and hydrogen sulfide can therefore be supplied to fluids seeping from the seafloor.

*3. A bacteria mat is a dense assemblage of bacterial colonies, which stretches like a mat. Bacteria mats at the surveyed sites are considered to use reduction substances (e.g. methane and hydrogen sulfide ) as energy sources.

*4. Calyptogena phaseoliformis

A white giant clam (15 cm long) living at depths of 4,700-6,400 meters along the Japan Trench and the Kuril–Kamchatka Trench. The clams live in symbiosis with sulfur-oxidizing bacteria, and feed on organic matters produced by them. They occur in colonies and are specific to cold seeps and hydrothermal vents. The bivalve sticks its strong foot into the sediment and incorporate hydrogen sulfide to funnel it to the bacteria.

*5 Elipidiidae: a sea cucumber. Elipidiid sea cucumber feed on the sediment surface.

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Source: Jamstec, September 02, 2011;