Technical Note 20/6


TABLE 1:

PROPOSED SITE INFORMATION AND DRILLING STRATEGY


SITE
: JT-1B
PRIORITY: 1
POSITION: 39°10.878´N, 143°20.095´W
WATER DEPTH: 2700 m
SED. THICKNESS: ~1300 m
TOTAL PENETRATION: 1400 m
SEISMIC COVERAGE: Intersection of KH96-3, Lines Leg 2-1 and Leg 2-4

Objectives: (1) Install long-term geophysical borehole observatory to monitor changes in strain, seismic signals, tilt, pressure, and temperature. Quantify episodic plate motions within seismically active part of the interplate seismogenic zone. (2) Recover past 3 m.y. volcanic ash stratigraphy for comparison with other western Pacific ash deposits in relation to eruptive processes and transport mechanisms. (3) Constrain subsidence history of the Japan Trench forearc. (4) Determine nature of Cretaceous basement.

Drilling Program: Double APC to 250 m, XCB to 450 m, RCB to 1400 m, reentry cone. Case through unstable section

Logging and Downhole Operations: Triple combo, FMS/Sonic/Temp, BHTV; install long-term sensor package and cement at the bottom

Nature of Rock Anticipated: Sandy, silty, pebbly clay with ash layers (50 m); clayey diatom ooze, diatomaceous clay, ash layers (~350 m); diatomaceous claystone, clayey diatomite (~250 m); claystone, diatomaceous claystone, calcareous claystone (~200 m); sandy claystone, diatomaceous claystone (~200 m); turbidite sand silty claystone (~100 m), sandstone and siltstone (~100 m), boulder to pebble conglomerate and breccia, dacite and mudstone clasts (~50 m); silicified claystone (~100 m)



SITE
: JT-2B
PRIORITY: 1
POSITION: 38°43.312´N, 143°20.852´E
WATER DEPTH
: 2123 m
SED. THICKNESS: ~1300 m
TOTAL PENETRATION: 1400 m
SEISMIC COVERAGE: Near intersection of KH96-3,Lines Leg 2-2 and KH90-1 Line JT90

Objectives: (1) Install long-term geophysical borehole observatory to monitor changes in strain, seismic signals, tilt, pressure, and temperature. Quantify episodic plate motions within seismically inactive part of the interplate seismogenic zone. (2) Constrain subsidence history of the Japan Trench forearc. (3) Determine nature of Cretaceous basement.

Drilling Program: APC, RCB to 1400 m; reentry cone; case through unstable section

Logging and Downhole Operations: Triple combo, FMS/Sonic/Temp, BHTV; install long-term sensor package and cement at the bottom

Nature of Rock Anticipated: Sandy, silty, pebbly clay with ash layers (50 m); clayey diatom ooze, diatomaceous clay, ash layers (~350 m); diatomaceous claystone, clayey diatomite (~250 m); claystone, diatomaceous claystone, calcareous claystone (~200 m); sandy claystone, diatomaceous claystone (~200 m); turbidites and silty claystone (~100 m), sandstone and siltstone (~100 m), boulder to pebble conglomerate and breccia, dacite and mudstone clasts (~50 m); silicified claystone (~100 m)


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