Strain accumulation process and interplate coupling in the Nankai region, Southwest Japan

日本西南部南海地区的应变积累过程和板间耦合

• 批准号: 06640549
• 负责人: TABEI Takao
• 金额: $ 1.34万
• 依托单位: Kochi University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1994
• 资助国家: 日本
• 起止时间: 1994 至 1996
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06640549/
• 关键词: GPS; Interplate interaction; Crustal strain; Nankai trough; プレート間カップリング

The Nankai region is located in one of the most active plate-subduction zones in Japan, where earthquake deformation cycle caused by the subduction of the Philippine Sea plate beneath the Eurasian plate is very clear as shown by the occurrence of great interplate earthquake within the short span of 100-130 years. We deployed GPS observation network to clarify strain accumulation process and discuss dynamics of the interplate interaction.Results obtained from three-year GPS measurements are as follows : 1. All stations have been displaced toward the west-northwest to northwest direction, 2. Displacement velocity is maximum at the southernmost site and rapidly dicreases with increasing distance from the plate boundary, and 3. Large displacement gradient exists in a narrow region extending parallel to the strike of the plate boundary. These results imply that current interplate coupling at the Nankai trough is strong ; much of the relative plate motion has been taken up by deformation of the leading edge of the Eurasian plate.Using an inversion technique of GPS-derived displacement velocity, we estimated strength of interplate coupling at the Nankai trough. Strong coupling thus estimated is in striking contrast to the weak interaction in the Tohoku region where considerable part of relative plate motion may be taken up by aseismic "slow" or "silent" slip. Furthermore, we discussed more regional deformation field based on the results by the nationwide GPS network by Geographical Survey Institute. We pointed out eastward motion in Chugoku region, which is small but systematically contradictory to the subduction of the Philippine Sea plate. One of the interpretations is that southwest Japan belongs to the "Amurian" microplate which is considered to have a slight eastward velocity and eastward motion of southwest Japan is constrained to reduce by the collision with northeast Japan and/or by the interaction with the Philippine Sea plate.

南海地区位于日本板块俯冲最活跃的地区之一，菲律宾海板块俯冲到欧亚板块之下引起的地震变形周期非常明显，在短短100-130年的时间内发生了板间大地震。我们部署了GPS观测网络来阐明应变累积过程并讨论板间相互作用的动态。三年GPS测量结果如下：1.所有站点均向西北偏西向西北方向位移，2.位移速度在最南端最大，并随着距板块边界距离的增加而迅速减小，3.在狭窄的延伸区域存在较大的位移梯度 平行于板块边界走向。这些结果表明南开海槽当前板间耦合较强；大部分相对板块运动已被欧亚板块前缘的变形所占据。利用 GPS 导出的位移速度反演技术，我们估计了南开海槽处的板间耦合强度。由此估计的强耦合与东北地区的弱相互作用形成鲜明对比，东北地区相当一部分相对板块运动可能被地震的“缓慢”或“无声”滑动所占据。此外，我们还根据地理测量院全国GPS网络的结果讨论了更多的区域形变场。我们指出了中国地区的向东运动，该运动虽小，但与菲律宾海板块的俯冲系统地矛盾。一种解释是，日本西南部属于“阿穆里亚”微板块，该板块被认为具有轻微的向东速度，日本西南部的向东运动因与日本东北部的碰撞和/或与菲律宾海板块的相互作用而受到限制。

项目成果

Tabei, T.et al: "Crustal deformation at the Nankai subduction zone, southwest Japan, derived from GPS measurements" Geophysical Research Letters. 23 (21). 3059-3062 (1996)

Tabei, T.et al：“日本西南部南海俯冲带的地壳变形，源自 GPS 测量”地球物理研究快报。

木村昌三: "1946年南海地震直前の南海地域における地震活動の低下" 地震第2輯. 48. 213-221 (1995)

木村正三：“1946 年南海地震前夕南海地区地震活动的减少”《地震》卷 2. 48. 213-221 (1995)

Tabei, T.et al: "Horizontal crustal deformation in southern part of Shikoku, southwest Japan, deduced from GPS surveys" Zisin (Journal of Seismological Society of Japan). 47 (3). 303-310 (1994)

Tabei, T.et al：“日本西南部四国南部的水平地壳变形，根据 GPS 调查推断”Zisin（日本地震学会杂志）。

田部井隆雄: "GPS -地球科学へのインパクト-" 月刊地球. 号外11. 107-112 (1995)

Takao Tabei：“GPS - 对地球科学的影响 -” 地球月刊特刊 11. 107-112 (1995)。

Date, Y.et al.: "Crustal deformation in Shikoku region, southwest Japan, derived from GPS surveys-Results from 1990 to 1994" Proceedings of the Japanese Symposium on GPS (1994). 203-209 (1994)

Date, Y.et al.：“日本西南部四国地区的地壳变形，源自 GPS 调查 - 1990 年至 1994 年的结果”日本 GPS 研讨会论文集（1994 年）。