Hiroshi ISHII and Tsuneo YAMAUCHI (1) Tono Research Institute of Earthquake Science (TRIES)

Transcription

1 Geophysical study of an active fault by using a deep borehole with 1000 m depth --- Initial stress measurements and continuous multicomponent monitoring of crustal activities --- Hiroshi ISHII and Tsuneo YAMAUCHI (1) Tono Research Institute of Earthquake Science (TRIES) ishii@tries.gr.jp (1) Graduate School of Environmental Studies, Nagoya University

2 Multi-component observation system for crustal activities in deep boreholes Hiroshi ISHII Tono Research Institute of Earthquake Science(TRIES) Our principle for borehole observation 1. Multi-component observation a. Obtain much information as possible as we can as borehole construction is expensive. b. At the present time 7 strain components (4 horizontal, 2 inclined (shear) and a vertical), 2 tilts, 3 seismic waves, 4 geomagnetisms and a temperature of high resolution. Arbitrary combination and more addition off the sensors are possible.. c. stress measurement 2. High S/N ratio observation Deeper borehole observation. 1km installation experience of multi-component instrument at the present time.. 3. Surely installation and data acquisition a. Protect lightning damage b. Data monitoring during installation process *Cooperating work with Nagoya Univ. and ERI Univ. of Tokyo

3 6300 Coaxial cable Cable support part Cable head Centralizer Wireless circuit and seismometers Centralizer A/ D parts Detector parts Motor control parts Magnetometer (4 Comps) Tilt meter ƒ Ó117 Quartz thermometer Strain meter (horizon.) Strain meter (horizon.) Strain meter (horizon.) Strain meter (horizon.) Strain meter (shear 2 Comps.) Strain meter (vertical) ƒó117 ƒó117 Tilt meter Centralizer ƒ Ó117 ƒ Ó83mm ƒ Ó90mm ƒ Ó83mm ƒ Ó66mm ƒ Ó66mm ƒ Ó66mm ƒ Ó66mm ƒó117 Multi-component borehole instrument (a case of Byoubusann 1km depth station) Total length@93000mm Instrument weight 150 Kg Weight part 80Kg Total weight 230Kg Weight part Centralizer ƒ Ó Connection parts

4 Amplifying Mechanics Lever principle is employed

5 Principle of tilt meter No mechanical dumping but by electric filtering

6 Data acquisition transmission system A/D:SAR (successive approximate register) 16bits sampling: 10kHz/ch and accumulate 33 times, then resolution improves 6 bits 16--->22bits samplingseismometer(200hz), strain meter(20hz), tilt meter(10hz), thermometer(1hz) in case of Byoubusan 1km station

7 D=160m D=1030m D=150m D=207m D=165m Vault D=350m D=1020m

8 Location of observation stations of our institute Distribution of observation points and position of Byoubusan- fault

9 Characteristics of the Byoubusan station system --- measurement of the initial stress in the deep borehole and installation of small diameter multi-component instrument for borehole observation 1. This is the deepest multi-component observation in the world. The instrument developed here can observe such components as 7 strains (4 horizontal, 2 shear, a vertical), 2 tilts, 3 seismic waves, 4 geomagnetisms, and a temperature of high resolution by one instrument. And also arbitrary combinations ofsensors are possible. 2. In-situ stress measurements at depths of 350,700 and 1000m were performed during drilling by applying overcoring method by the use of wireless intelligent type strain meter developed by us. This is also the deepest in-situ measurement in deep boreholes by applying overcoring method in the world. 3. Data obtained from sensors are delivered to a coaxial cable by wireless way and then reach to surface devices. Therefore, the cable can be thin and the instrument is safe for various noises. 4. We can monitor outputs of all observation components during installation as wireless data transmission system. Therefore, we can immediately make sure if the installation succeed or not. Purposes of Byoubusan station construction 1. Geophysical research of Byoubu-san fault that is inland active fault. 2. Research for development and improvement of instrument for observing crustal activities in deep boreholes as 1km. 3. Research for development and improvement of methods for measuring in-situ stress in deep boreholes as 1 km. 4. Development research of data transmission system in deep boreholes as 1 km.

10

11 Multi-component instrument and tower

12 Installation of multi-component instrument Cable drum and head quarters

13 Headquarters and monitoring display Display showing the record that the instrument gets into grout

14 Display showing the record that the instrument gets into grout

15

16

17

18 Continuous measurement of Initial Stressis Important especially for earthquake prediction research

19 Intelligent type strain meter Ver.2 for measurement of in-situ stress.

20

21 In- situ stress obtained from both overcoring and DSC in the borehole EXT. COMP. 700m 350m DSCA 350m H1 Vertical MPa 28.8MPa MPa

22 Amplifying Mechanics (bird s-eye view)

23 Vertical component

24 Data obtained from well logging

25 Inclined (shear) component

26 Strain step of KII Hanto-oki EQ.

27 BYB.TOKACHI Vertical 0.2µ strain 1µ strain Fig.2a. CH1 2min CH4 CH2 CH3

28 Strain seismograph of Tokachi-oki-oki EQ. (2003/9/26, MW 8.1, delta 924km) Observed at Byoubu-san Borehole