The Japan Trench Earthquake and Tsunami Monitoring Network Project of Cable‐linked 150 Seafloor Observatories (the *S‐net Project) 

T. KANAZAWA, K. UEHIRA, M. MOCHIZUKI, T. SHINBO, S. NOGUCHI, H. FUJIMOTO (**NIED), and T. YAMADA (ERI, Univ. of Tokyo)

After the 2011 Tohoku‐Oki earthquake, a new ocean bottom observation project has been started to deploy the large‐scale ocean‐bottom network of cable‐linked 150 observatories along theJapan Trench (S‐net). The project is undertaken by NIED and supported financially by ***MEXT. S‐net provides progressively the in‐situ and real‐time geophysical data in the subduction zonewhich will be used to forecast the next‐generation early tsunami warning and to forecast an earthquake warning much earlier than the present system.

S‐net: A unique seafloor observation network of real‐time cabled multipoint observatories

A total of 150 observatories (each equipped with seismometers andpressure sensors (tsunami meters) ) are connected by an opticalcable of 5,700 km in a total length.

Spacing concept: One observatory site in a source region of M7.5earthquake (30 km spacing almost in an east-west direction and 50- 60 km spacing almost in a north-south direction).

S-net is composed of six subsystems S1-S6. Cable lengths areabout 800 km for S1–S5 and about 1600 km for S6 (outer risesegment).

T3.1‐P30

Construction of subsystem S‐net 

Two landing stations A and B make it possible to dual power supply systems and data transmission in two directions.

Data distribution 

Real time data are transmitted to landing stations via bidirectional fiber cables, and distributed to associated groups through IP-VPN network.

Seismometers andPressure sensors 

Each observatory is equipped with seismometers of several types and two hydro-pressure gauges of the same type (tsunami meters).

1. Direct detection of remote tsunami far from land, predictions of precisetsunami wave propagation, wave height and arrival times at various shorelines.

2. Development of early tsunami warning system, serving as effective andprompt evacuation.

3. Monitoring of crustal movement and seismic activity at the shallow subductionzone near trenches, detailed investigation of oceanic crustal structure andearthquakes and tsunami generating process.

4. Effective disaster mitigation countermeasure against tsunami and planning ofcity reconstruction in coastal areas.

Expected results from S‐net

Earlier detection of events by S‐net

S-net makes it possible to detect tsunami events by 10-20minutes earlier and earthquake events by around 10-20 seconds earlier along the Japan Trench.

*** MEXT: Ministry of Education, Culture, Sports, Science and Technology, Japan.** NIED: National Research Institute for Earth Science and Disaster Prevention.* S-net: Seafloor observation network for earthquakes and tsunamis along the Japan Trench.

Land Sea

Landing Station B

Terminal Equipment• Supervisory Equipment• Power Feeding Equipment • Optical Receiver Transmission Equipment• Data Conversion & Transmission Equipment• Power supply backup system• Timestamp by GPS clock

Power feed from both stations

Power feed from both stationsLanding Station A

Data

NIED Data Center

JMA

Other institution

Data

Optical Bidirectional TransmissionEarthLAN

(IP-VPN Network)

GPS Antenna

Observatory

Observatory 25

Observatory

Submarine Cable

Beach Manhole

Observatory 1

Backup Data Center

V= 623km/h V= 7km/h