1. Heat flow measurement in shallow seas through long-term temperature monitoring Hamamoto Hideki (Earthquake Research Institute,Univ. of Tokyo) Yamano Makoto (Earthquake Research Institute,Univ. of Tokyo) Goto Shusaku (Aso volcanological laboratory, Kyoto Univ.)

2. Research purpose To obtain heat flow data in shallow sea areas. Remove influence of bottom water temperature variation using results of long-term temperature monitoring

3. Conventional measurement method in deep-sea areas k ： Thermal conductivity ： Temperature gradient Q ： Terrestrial heat flow

4. κ ： Thermal diffusivity Amplitude decay Phase shift Thermal diffusion equation Propagation of bottom water temperature variation T （ 0,t ） T(z,t)

5. Pop-up heat flow instrument er recorder

6. pic tur e

7. Measurement station A D B C Kumano area Eurasian plate Philippine Sea plate Pacific plate

8. Sub-bottom temperature data CH1 CH2 CH3 CH4 Station B (water depth: 2055m)

9. Heat transfer between CH1 and CH2 CH1 CH2 CH ３ CH ４

10. Correction for the effects of bottom water temperature variation

11. Temperature gradient = 58 mK/m Heat flow c.a 60 mW/m 2 Thermal conductivity 1 W/m/K

12. A D B C Kumano area Eurasian plate Philippine Sea plate Pacific plate Measurement station

13. A (water depth 1040m) Time(days) After correction Raw data Temperature （℃）

14. Time(days) Temperature （℃） C(water depth 2008m) After correction Raw data

15. Time(days) Temperature （℃） D(water depth 2070m) After correction Raw data

16. Heat flow cross section Conventional prove Estimated from BSR

17. Monitoring of sea-bottom water temperature 1. Estimation of appropriate monitoring period and probe length 2. Determination of heat flow in combination with ordinary probe measurements Purposes

18. Measurement stations in Kumano Sediment temperature Bottom water temperature (in progress) Sediment temperature (in progress)

19. Bottom-water temperature records

20. Temperature record for two years

21. Spectrum analysis Period (days) Amplitude

22. Summary 1.Long-term temperature data over 220 days were obtained with pop-up heat flow instruments. 2. Heat flow values can be obtained by removing the influence of bottom water temperature variation. Long-term temperature monitoring may be a useful method for heat flow determination in shallow sea areas.

23. Summary 3. Dominant periods of bottom-water temperature variations are 150 to 200 days. Heat flow can be determined well from 250 to 300 days temperature records.

24. BSR (Bottom Simulating Reflector) BSR

25. Station A Temperature ( ℃ )

26. Station A (water depth1040m) Spectrum Amplitude

27. Thermal diffusivity CH1 CH2 CH3 CH4

28. Thermal conductivity (Hyndman’s equation )

29. Thermal conductivity of sediment sample The sample was obtained near the station B (about 15miles away).

30. Disturbance from sea-bottom water temperature variation Depth(m ) 0.01K Temperature

31. Example of temperature profiles Deep sea Shallow sea

32. Temperature Time Sea-bottom Sub-bottom Example of thermal diffusion Amplitude decays Phase delays

33. 水温変動が海底下の温度分布に与える影響を計算 複数の地点で長期間の海底水温データが得られ た 海底水温が温度勾配に与える影 響 通常の方法による測定が可能かどうかを検 討

34. 1.5m 2.5m D 地点 ( 水深 1040m) 海底水温が温度勾配に与える影響 G=50mK/m κ ＝ 2.4×10 -7 m 2 /s 2.5m 4.5m

35. B 地点 ( 水深 2026m) 海底水温が温度勾配に与える影響 1.5m 2.5m 4.5m G=50mK/m κ ＝ 2.4×10 -7 m 2 /s

36. * D 地点（水深 1040m ）では，温度勾配は通常の方法で は測 定できない * A ～ C 地点（水深 1230 ～ 2026m ）でも, プローブが４～ ５ m の 深さまで貫入しなければ温度勾配を求めるこ とが困難 長期観測が必要 海底下の温度データから水温変動の影響を取り 除いて熱流量を求める ここまでの結果 （プローブを 4 ～ 5 ｍ貫入させることは難しい場合が 多い）

37. CH2 CH3 CH4 CH5 CH6 CH7 CH1 1.47 1.75 1.99 2.16 2.23 2.29 Thermal diffusivity （ ×10 -7 ）（ m 2 / ｓ） CH1 と各センサー間の熱拡散率

38. CH2 CH3 CH4 CH5 CH6 CH7 CH1 1.47 2.05 2.42 2.70 2.48 2.99 thermal diffusivity （ ×10 -7 m 2 /s ） 隣り合った各センサー間の熱拡散 率

39. A 地点における計算値と実測値 計算値と実測値が一致しない

40. 各センサー間の熱伝導率 (Hyndman の経験式 ) k: 熱伝導率 κ ：熱拡散率

41. C 地点の海底下の温度データ

42. 日変化 年変化 日変化と年変化の温度プロファイ

43. Long-term temperature monitoring Long-term temperature monitoring system has been deployed with submersibles. ＊ Few chances for deployment and recovery. ＊ Submersibles can handle short probes only. (max. 1m) We have developed Pop-up temperature monitoring system which can be deployed from surface vessels. Demerits