SITE SUMMARY

Site: JT-4

To 186 Site JT-4 Track Line

To 186 KH96-3 Line 4

Priority: 2
Position: 39°05.11´N, 143°18.77´E
Water Depth: 2510 m
Sediment Thickness: ~1300 m
Target Drilling Depth: 1000-1400 m
Approved Maximum Penetration: PPSP approval needed Seismic Coverage: Near intersection of KH96-3 Lines 1 and 4

Objectives: This is an alternate site for JT-1C. The objectives of Site JT-4 are:

1. Install long-term geophysical borehole observatory to monitor strain, seismicity, tilt, and temperature. Quantify episodic plate motions within seismically active part of the interplate seismogenic zone.
2. Constrain subsidence history of the Japan Trench forearc.
3. Determine nature of Cretaceous basement if time permits.

Drilling Program: APC to 250 mbsf, XCB to 450 mbsf, and RCB to 1000 mbsf. Drill the instrumented borehole, install reentry cone, and case through unstable section.

Logging and Downhole Operations: Triple combo, FMS/sonic/temperature, 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); and silicified claystone (~100 m).

To 186 Site 439

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