Geomagnetic exploration of the sea area around the northwestern part of Iki

Implementation plan (1987)
Planning agency: International Highway Construction Corporation
Executing agency: Far East Development Co., Ltd.

1. Overview

As a continuous survey of the geomagnetic exploration of the Iki Suido and the sea area around Iki, we planned "geomagnetic exploration of the sea area around the northwestern part of Iki" using a proton magnetometer.Geological surveys in the Japan-Korea Tunnel Project have been conducted extensively along the route, both on land and at sea.
In the sea area, since 1982, single-channel and digital multi-channel sound wave exploration using sparkers and water guns has been carried out for a total of 8,100 km at Iki Channel, Tsushima East Channel, and Tsushima West Channel.In 1986, marine boring was also carried out at Tsushima Nishi Suido, and the outline of the overall geological distribution, geological cross section, geological structure, etc. of this sea area was clarified.

2. Survey outline

Geomagnetic exploration with a proton magnetometer
XNUMX. XNUMX.Survey area Sea area around Iki northwest (map omitted)
XNUMX. XNUMX.Survey contents ① Total magnetic force measurement at sea, ② Land fixed point observation (diurnal cycle correction), ③ Sounding depth, ④ Test tide, ⑤ Positioning
XNUMX. XNUMX.Survey siding (map omitted)
Total distance: 530km
Test run: 50km
62.Survey period April 30, XNUMX-April XNUMX, XNUMX

3. Survey method

XNUMX. XNUMX.Ship position decision
Two-distance method using a sonic positioning machine (tri-sponder).The substation will use the existing reference point and will be installed so that the intersection angle of 30 distances will be within the range of 150 ° to XNUMX °.
XNUMX. XNUMX.Echo sounding
Continuous sounding with PDR-101
Insert a fixed line every XNUMX minutes
Ship speed XNUMXkt / h

XNUMX. XNUMX.Total magnetic force measurement
The proton magnetometer measures the frequency of free aging motion of protons (protons) in the earth's magnetic field by using the nuclear magnetism of hydrogen atoms in water, and absolutely measures the total magnetic force of the earth.The measurement principle is to enclose an aqueous solution in a coil combined in the north, south, east, and west, create a forced magnetic field by passing a strong exciting current through this coil, forcibly arrange hydrogen protons, and then turn off the current to earth. When the protons try to return to the magnetic field of, they make a staggered motion.The motion is represented by a frequency proportional to the strength of the magnetic field.
The formula is
XNUMXπf = rpF
rp = (2.67513 ± 0.00002) × 104 Sec-1 Γr-1
F = 23.4874 f F = total magnetic force
This equation shows the strength of the magnetic field.
(XNUMX) The average sea area around Tsushima is XNUMX r.
(30) The measurement interval shall be 60 to XNUMX seconds.
③ First try at XNUMXkt / h
④ Make fixed-point observations on land to see diurnal changes
The magnetic anomaly represents the magnetic strength of the rock in the crust, and its value is displayed as follows.
△ F = F - Fo – Fu
△ F: Abnormal value F: Total magnetic force observed value
Fo: Magnetic field strength inside the earth (IGRF) Fu: External diurnal cycle correction value
Based on the above principle, set the proton magnetometer as shown in the figure below (omitted), let the sensor flow backward about 50 m from the research vessel, and measure without the magnetic influence of the hull.
The measurement interval is 30 seconds / time.

4. Data processing

(XNUMX) The measurement time, sounding depth, positioning, and geomagnetic field values ​​are finally digitized and recorded.
(XNUMX) Calculate the geomagnetic anomaly value by correcting the regional and daily changes in the geomagnetism by IGRF and fixed point observation.
③ Perform model analysis of important points as necessary.
④ Make a batch file of data such as gravity, geomagnetism, sound wave exploration, and sediment.

5. Deliverables

(XNUMX) Report, (XNUMX) Wake map, (XNUMX) Survey line map, (XNUMX) Magnetic cross-section map, (XNUMX) Total magnetic force anomaly map, (XNUMX) Reference map, (XNUMX) Seafloor topographic map

  • Survey report (summary)

  • Geology of the Japan-Korea Tunnel
    Construction survey

  • Geology of the Japan-Korea Tunnel
    Construction survey

  • Overview of the Japan-Korea Tunnel

  • project

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