Heki, K., G.R. Foulger, B.R. Julian and C.-H. Jahn, Plate dynamics near divergent boundaries: geophysical implications of postrifting crustal deformation in NE Iceland

J. Geophys. Res., 98, 14279-14297, 1993.

リスト上部のNatureのLetter to the editorをJGRでfull paper化したもの。 Natureの時点では一次元モデルで解析モデルにデータを当てはめていたが、JGR論文で はplane-stressの仮定のもとに二次元化、差分法で数値的に応力の拡散係数を求めて いる。当時使用していたUNIRASと呼ばれる描画プログラムを駆使した三次元プロットが 随所に登場。なおこの論文で仮定した薄いニュートン流体と弾性体の成層構造は後に後 継者のM.Hoftonによって薄い弾性体と半無限マックスウェル粘弾性体の成層構造モデル に進化し、同じくJGR誌上で近年発表された。

The bulk of a tectonic plate is thought to move continuously at a rate consistent with the geologic average. On the other hand, movements are highly episodic at plate boundaries. We study the plate dynamics that relate to these two different modes by modeling the displacements observed using the Global Positioning System (GPS) in Northeast Iceland 1997-1990. These observations were made about ten years after an episodic divergent movement between the North American and Eurasian plates 1975-1981. The horizontal displacement field fits well a two-dimensional model of post-rupture stress relaxation assuming a thin elastic layer overlying a layer of Newtonian viscosity. This analysis indicates values of about 10 m2/s for the stress diffusivity and 0.3-2 x 1918 Pa s for the Newtonian viscosity of the lower layer. However, no significant correlation exists between the observed and modeled vertical displacements probably because of the relative inaccuracy of the vertical component observations. Assuming that contemporary plate motion is the sum of many displacements that have diffused from boundaries where episodic displacements occur periodically, we simulate the spatial transition from episodic to continuous plate movements. The plate "boundary zone" where movements are episodic or quasi-episodic is of the order of 100 km wide, depending on the stress diffusivity (which may be fairly uniform throughout the world) and the frequency of episodic movements.


日置幸介 (email: heki@ep.sci.hokudai.ac.jp)