EVALUATION OF RYUKYU-MANILA TRENCH TECTONIC BACKGROUND AND SEISMOGENIC ABILITY

doi:10.3969/j.issn.0253-4967.2021.06.003

Abstract

Abstract:

After the Fukushima nuclear accident caused by the “3·11” earthquake tsunami in Japan, whether the coastal nuclear power stations in China are liable to similar earthquake tsunami impact has been widely concerned by the whole society. According to the previous results of earthquake tsunami impact assessment conducted by professional departments on coastal nuclear power plants, China's coastal areas do not have the conditions for the occurrence of large-scale earthquake tsunami, but in order to fully learn from the experience and lessons of the Fukushima nuclear accident caused by Japan's “3·11” earthquake tsunami, definite conclusions have been drawn on the offshore tsunami and its impact on nuclear power plants in the early assessment work of potential tsunami impact of coastal nuclear power stations in China, combined with the structural background, historical seismic data and tsunami impact analysis. However, whether the earthquakes in the Ryukyu trench, Manila trench and other areas can generate tsunami has not been systematically considered. Therefore, in this paper, the seismogenic capacity of the Ryukyu trench and Manila trench is evaluated based on the seismotectonic background and relevant seismic source parameters.
Both Ryukyu and Manila trench belong to the west Pacific plate subduction zone, while the Japan's “3·11”earthquake is also located in the west Pacific plate subduction zone. Therefore, whether the former has the same tectonic background and conditions as the “3·11” earthquake does is the key factor to assess whether the Ryukyu trench and Manila trench have the same potential for M9 earthquake. Based on the analysis of a large number of data, this paper evaluates the tectonic background, segmentation characteristics and maximum potential earthquake generating capacity of the Ryukyu trench and the Manila trench. The Ryukyu trench and Manila trench are located in the west of the Philippine Sea plate. There are also subduction zones distributing in the east of the Philippine Sea plate from Izu-Ogasawara trench, Mariana trench to Yap Palau-Ayu trench. Since the Ryukyu trench-Manila trench subduction zones are not in the direct contact zone between the Pacific plate and the Eurasian plate, the plate tectonic setting is obviously different from the low-angle subduction zone where the Japan's March 11 earthquake locates. From the perspective of tectonic system, the Ryukyu trench belongs to the subduction tectonic system of trench-island arc-back arc basin. The island arc and trench are retreating eastward, showing the characteristics of weak coupling. The overall scale of the Manila trench is small, and affected by the “slab window” in the subduction slab formed by the ancient spreading ridge, the length of these two trench zones is much smaller than that of the subduction zones where M_W≥9 earthquakes have occurred.
Based on the comprehensive analysis of the differences in trench structure, earthquake data and etc., the Ryukyu trench can be divided into 6 rupture segments, and the section of the Manila trench concerned in this study can also be divided into 6 rupture segments. At the same time, the possibility of combined rupture of the rupture segment is considered from a conservative standpoint. The rupture segments RL5 and RL6 of the Ryukyu trench, RM2 and RM3 of the Manila trench all have the possibility of combined rupture, and rupture segments RM4, RM5 and RM6 also have the possibility of combined rupture. To sum up, the comprehensive estimation result of the maximum potential earthquake in the subduction zone is magnitude 8.5 in the Ryukyu trench and magnitude 8.8 in the Manila trench.

Key words: Ryukyu Trench, Manila Trench, structural segmentation, maximum potential earthquake

摘要：

琉球-马尼拉海沟属于西太平洋板块俯冲带, 2011年3月11日日本地震的震中同样位于西太平洋板块俯冲带, 前者是否与“3·11”地震具有相同的构造背景和条件, 是评估琉球-马尼拉海沟是否同样具备发生9级地震潜在能力的关键因素。文中对大量资料进行了分析, 对琉球-马尼拉海沟的构造背景、分段特征及最大潜在发震能力进行了评估, 认为琉球海沟属于海沟-岛弧-弧后盆地俯冲构造体系, 岛弧与海沟处于向E后退的状态, 表现为弱耦合特征, 构造上可分为6个破裂段, 最大潜在地震为8.5级; 马尼拉海沟受古扩张洋脊形成俯冲板块中的“板片窗”影响, 长度及规模远小于目前已发生9级以上地震的俯冲带, 构造上可分为6个破裂段, 最大潜在地震为8.8级。综合结果分析认为, 琉球-马尼拉海沟无论是在构造背景还是规模上都与日本“3·11”地震的构造样式存在较大差异。

关键词: 琉球海沟, 马尼拉海沟, 构造分段, 最大潜在地震

CLC Number:

P315.2

LI Zheng-fang, ZHOU Ben-gang, XIAO Hai-bo. EVALUATION OF RYUKYU-MANILA TRENCH TECTONIC BACKGROUND AND SEISMOGENIC ABILITY[J]. SEISMOLOGY AND EGOLOGY, 2021, 43(6): 1381-1397.

李正芳, 周本刚, 肖海波. 琉球-马尼拉海沟的构造背景及发震能力评估[J]. 地震地质, 2021, 43(6): 1381-1397.

Figures/Tables 19

Fig. 1 Tectonic framework of the west Pacific and east Indian Ocean plates.

Fig. 2 Location of P wave inversion profile lines and geometry of subduction zones from Kuril Trench to Manila Trench(Lu et al., 2001).

Fig. 3 The relative plate motion rates(Slob et al., 1998).

Fig. 4 Location of six megathrust earthquakes along subduction zones.

Table1 Characteristics of the tsunami sources induced by the six subduction mega-thrust earthquakes in the world

日期	地点	震级 /M_W	震源深度 /km	海沟长度 /km	俯冲带类型	板块聚敛速率 /mm·a^-1
1960-05-22	智利	9.5	60	2 800	海沟-岛弧	80
1964-03-28	阿拉斯加州	9.2	23	3 760	海沟-岛弧	56
2004-12-26	苏门答腊	9.0	28.6	4 200	海沟-岛弧	30~40
2010-02-27	智利	8.8	24~36	2 800	海沟-岛弧	80
2011-03-11	日本	9.0	24	3 000	海沟-岛弧(弧后扩张停止)	105
1952-11-04	堪察加半岛	9.0	45	3 000	海沟-岛弧(弧后扩张停止)	78

Fig. 5 Schematic diagram of weak coupling characteristics between Ryukyu Trench and plate(Kao et al., 1991).

Fig. 6 Schematic diagram of strong coupling characteristics between Kuril Trench and plate(Kao et al., 1998).

Fig. 7 Focal mechanisms zoning of shallow-focus earthquakes in Ryukyu Trench and Okinawa Trough (1976-01—1997-02, focal depth<50km)(Fabbri et al., 1999).

Fig. 8 Dividing lines between differences of shallow focal mechanisms and distribution of forearc depressions(Fu et al., 2004).

Fig. 9 The NW-trending fault zone in the Miyako Islands(Kizak, 1986).

Fig. 10 Seismic source partitioning in Ryukyu Trench(The earthquake data are from ISC catalogue).

Table2 Segmentation of ruptures and earthquake magnitude in Ryukyu Trench

琉球海沟的破裂源	位置起点		走向/(°)	长度/km	矩震级规模限/M_W
	东经	北纬
RL1	132°44'	30°46'	30	290	8.5
RL2	131°14'	28°31'	32	256	8.4
RL3	129°50'	26°35'	45	282	8.5
RL4	127°49'	24°47'	53	215	8.3
RL5	126°01'	23°31'	72	130	7.9
RL6	124°46'	23°15'	81	170	8.1
终点	123°06'	23°08'
RL(5+6)				300	8.5

Fig. 11 Distribution of rupture segments in Ryukyu Trench (L represents the segmentation point, RL represents the rupture segment).

Fig. 12 Tectonic schematic diagram of Manila Trench(after Yang et al., 1996).

Fig. 13 Subduction geometry near the paleo-ocean-ridge(after LIU Zai-feng et al., 2007).

Fig. 14 Seismic survey lines in the Taiwan-Luzon region(after Ku et al., 2009).

Fig. 15 Rupture plane partitioning in Manila Trench based on HUANG Hui-juan's(2008)scheme.

Fig. 16 Distribution of earthquake rupture source in Manila Trench.

Table3 Basic parameters of rupture sources in Manila Trench

马尼拉破裂源	位置终点		走向/(°)	长度/km	震级 /M_W
	东经	北纬
RM1	119°51'	21°58'	350	210	8.2
RM2	120°21'	20°06'	29	310	8.6
RM3	118°56'	17°40'	3	135	7.9
RM4	119°09'	16°24'	351	140	7.9
RM5	119°05'	15°12'	353	166	8
RM6	119°16'	13°44'	308	142	7.9
终点	120°17'	12°55'
RM(2+3)				445	8.8
RM(4+5+6)				450	8.8

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