Japan Geoscience Union Meeting 2015

Presentation information


Symbol S (Solid Earth Sciences) » S-GD Geodesy

[S-GD23] Gravity and Geoid

Wed. May 27, 2015 6:15 PM - 7:30 PM Convention Hall (2F)

Convener:*Jun Nishijima(Department of Earth Resources Engineering, Graduate School of Engineering, Kyushu University), Yuichi Aoyama(National Institute of Polar Research)

6:15 PM - 7:30 PM

[SGD23-P03] Minus anomaly region of gravity in Hyuganada and place that sinking-slab-block tears off shallow part are corresponding

*Hirofumi MASE

(Please refer to the figure)
In convergence zones, high temperature bodies are formed diagonally-on-and-under the plate of low temp. and the bodies are drawn each other. The mantle wedge and the plate, get on the high temp. body that heads westward from the east, head westward. And, they are placed by the high temp. body that heads eastward from the west and compressed. I think this is the main spring and structure in it. I explained in each respect of the theory, experiment, and application.(1)(2)(3),etc.
This time, I thankfully used (4) to be able to understand tomography data of 3D in seamless. And I thankfully used (5) about gravity chart(Bouguer anomaly). I have been interested in the existence of minus anomaly region of gravity where with center in Hyuganada(5). Result of the research is going out and I want to report. (the minus anomaly region of gravity:The Region)
The Region is divided roughly into the one in prefecture northern part and the prefectural boundary, and the one in Hyuganada. The latter has the plain center like eye and the long-drawn tail to the south and is impressive. The south end of ,the subducting slab(The SS), is exactly formed in the eye. Pulling Hot1 and Hot2 against each other is shown by black pair arrows in each Section. (Names of high temp. bodies, etc. are naming only of here.) Bearing capacity of land and intrusive pressure generated along with it are shown by pink arrows.
In Section 1-1',2-2', Hot1 invades under the land to the east to be deep and is pulled against each other again there with Hot2. The black arrows are mainsprings that wring and dent or thin The SS. Pressure in the invaded part rises and The SS is depressed(blue arrow). And the invaded part extends vertically. By the result of this calculation of going out and entering of density, The Region in the prefecture northern part and the prefectural boundary might exist.
It is thought that the sinking-block is formed and separates from The SS by the above-mentioned action. On the west side, it is divided into parts from the depth in the west due to the crack(blue broken line) and slips. On the east side, tightening and pull-tearing off(green arrow) are generated in shallow area(Hyuganada). Vertical subsidence of the sinking-block is understood underground in the whole area of Miyazaki Prefecture. Section 1-1'--9-9' are like fixed point scene sending animated cartoon of this change.
The site of pull-tearing off and separation(The Site) is in the Miyazaki Prefecture central part offing and is corresponding to the peak of The Region(Section 4-4'--7-7',a-a'). By pull-tearing off action, for hanging down part of The Site, the material is pulled out under the west, the shape is transformed into Rohto type. And, I think that the generation of the density reduction is a cause of the gravity anomaly. End of pull-tearing off and complete separation have already been generated in the southern part(Section 8-8',9-9'). However, the place is still in The Region and the tail expands to the south. The peak of the gravity anomaly came like the shadow along with The Site that keeps going north from the south and arrives now. Even if The Site passes, the gravity anomaly of the place remains as a track (tail) because it does not improve at once.
(1)Mase/SSJ2010/P3-47 (2)Mase/JpGU2012/SCG67-P06 (3)Mase/SSJ2014/S03-P01
(4)AIST/Visualization system for subsurface structures/tomography data by Abdelwahed and Zhao (2007)dVp
(5)AIST/same to (4)/gravity chart(Bouguer anomaly)