DISCOVERY OF A STRONG PALEOSEISMIC EVENT IN THE CHENGHAI-BINCHUAN FAULT ZONE

doi:10.3969/j.issn.0253-4967.2025.01.013

Abstract

Abstract:

The Chenghai-Binchuan fault zone is an active Holocene fault zone approximately 200km in length. The region is characterized by sharply uplifted mountains and canyon landforms, intense erosion, and frequent geological hazards such as collapses, landslides, and debris flows. These factors have obscured the preservation of displaced landforms, making it difficult to identify paleoearthquake relics and hindering the study of paleoearthquakes.

The Taoyuan Basin, a tectonic basin formed along the Chenghai-Binchuan fault zone, has undergone extensive land planning and hillside improvements as part of the resettlement efforts linked to the Ludila hydropower project on the Jinsha River. As a result, many artificial slopes have been excavated in the area. Approximately 500m northeast of Chitian village, southwest of Taoyuan town, near the confluence of the Jinsha and Kumu rivers(100.4489°E; 26.1926°N), farmers excavated a large slope for land planning and slope stabilization. This slope, approximately 50m in length and over 10m in height, exposes a relatively continuous sedimentary sequence, including sand and gravel layers. The exposed strata display typical paleoearthquake features, such as fault displacements, seismic wedges, sand veins, and soft sediment deformation, all of which are well-preserved and provide valuable insights into paleoearthquake activity.

Paleoearthquake research was conducted through satellite remote sensing interpretation, field geological and geomorphological surveys, slope profile excavation and measurement, detailed stratigraphic description, and chronological testing of sediment samples.

The findings are as follows: 1)Two fault sets, striking NW and NE, were identified on the profile. The sedimentary characteristics of each stratigraphic unit, along with the relationships between stratigraphic displacement, marker layer offsets, and features such as colluvial wedges, soft sediment deformation, and sand veins, suggest that a significant earthquake occurred in the area. Radiocarbon dating(AMS ¹⁴C)indicates the paleoearthquake event occurred between(5910±30)aBP and(4100±30)aBP. 2)The maximum vertical co-seismic displacement along the fault is 4.0m. Using the empirical relationship between fault displacement and earthquake magnitude, the moment magnitude(M_W)is estimated at 7.3, similar to the historical 1515 Yongsheng earthquake(M_W7.3). These results fill a critical gap in paleoearthquake data for the Chenghai-Binchuan fault zone and extend the region's paleoearthquake record. This research holds significant practical value for earthquake hazard zoning and seismic risk analysis for major regional projects.

Key words: Chenghai-Binchuan fault zone, earthquake fault, seismic wedge, soft sediment deformation structure, sandblow

摘要：

程海-宾川断裂带是一条长达200km的全新世活动断裂带。近期研究发现, 在该断裂带上的赤田村边坡剖面揭露出错距很大的地震断层、地震楔、软沉积物变形、砂脉等古地震现象。通过卫星遥感影像解译及野外地质地貌调查、边坡剖面的清理与实测和详细的地层描述, 并结合地层年代学样品测试等工作开展了古地震研究。研究结果表明: 1)边坡剖面揭露出NW向和NE向2组断层。根据各地层单元的沉积特征、地层切盖关系和标志层位错, 以及崩积楔、软沉积物变形、砂脉等现象, 认为这里存在1次强烈地震事件, 据AMS ¹⁴C年龄推算, 古地震事件发生的时间为( $5$ 910±30)~( $4$ 100±30) $a$ BP。2)地震断层产生的最大垂直同震位移量为4.0m, 据震级与断层位移量的经验公式估算出其矩震级(M_W)为7.3级, 与云南地区历史强震的同震位错量相比, 其震级可能与1515年永胜 7.3级地震的规模相似。文中研究结果弥补了程海-宾川断裂带上古地震资料的不足, 延长了古地震记录的历史, 对开展本区地震危险性区划、重大工程地震危险性分析具有重要的实际价值。

关键词: 程海-宾川断裂带, 地震断层, 地震楔, 软沉积物变形, 砂脉

LUO Lin, CHANG Zu-feng, YIN Gong-ming, MAO Ze-bin, HUA Jun, CHEN Gang. DISCOVERY OF A STRONG PALEOSEISMIC EVENT IN THE CHENGHAI-BINCHUAN FAULT ZONE[J]. SEISMOLOGY AND GEOLOGY, 2025, 47(1): 214-234.

罗林, 常祖峰, 尹功明, 毛泽斌, 华钧, 陈刚. 程海-宾川断裂带一次古强震事件的发现[J]. 地震地质, 2025, 47(1): 214-234.

Figures/Tables 9

Fig. 1 Location of main active faults in northwest Yunnan(a) and distribution of Chenghai-Binchuan fault zone(b).

Fig. 2 Schematic diagram of the location of paleoearthquake remains in the Chenghai-Binchuan fault zone.

Fig. 3 Photo and sketch of NW strike fault at the southwest corner of the slope.

Fig. 4 Photo and sketch of NW strike fault on the northeast side of the slope.

Fig. 5 Photo and sketch of NE strike faults at the southwest end of the slope.

Fig. 6 Photo and sketch of NE and NW strike faults at the northeast end of the slope.

Fig. 7 Photo of soft sediment deformation developed in the silty fine sand layer at the southwest end of the slope.

Fig. 8 Photo of liquefied sand vein developed in the middle of the slope.

Fig. 9 Photo and sketch of liquefied sand vein.

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