Abstract:

The delineation of seismic zones and belts forms the basis for seismic zonation and seismicity analysis, among which the definition of seismic-zone boundaries is particularly critical. Accurate boundary delineation helps distinguish regions with different levels of seismic hazard and provides a scientific basis for earthquake-resistant engineering, urban planning, and infrastructure development. It also supports the rational allocation of disaster-mitigation resources, strengthens earthquake monitoring in key areas, and reduces potential casualties and economic losses. Ultimately, improved seismic-zone delineation contributes to enhanced seismic resilience and societal safety.

Seismicity in China exhibits pronounced regional variations. In eastern China, seismic activity is relatively frequent in North China, whereas the Northeast seismic zone is characterized by lower earthquake frequency and magnitude. In previous revisions of the Seismic Ground Motion Parameter Zonation Map of China, the southern boundary of the Northeast seismic zone was defined along the Chifeng-Kaiyuan Fault. However, its northern, eastern, and western boundaries were largely aligned with national borders, which is not well justified from seismological or geological perspectives. For the next generation of seismic zonation maps, the boundaries of the Northeast seismic zone should therefore be revised by considering the regional tectonic setting, contemporary tectonic stress field, and spatial pattern of seismicity. This study aims to provide a more geologically consistent delineation of the Northeast seismic zone based on the structural characteristics of Northeastern China and adjacent regions.

We conducted an integrated analysis of the tectonic setting, geophysical field characteristics, seismicity, and contemporary tectonic stress field of northeastern China and its neighboring regions. The tectonic features, block composition, evolutionary history, and geomorphological characteristics on both sides of the national borders show a high degree of similarity. Geophysical evidence further indicates that the region is generally tectonically stable and may be regarded as an independent block. Analysis of the relationship between seismicity and fault structures shows that the Sikhote-Alin mountains share similar fault orientations and seismicity patterns with northeast China and can reasonably be incorporated into the same seismic zone. In terms of the contemporary stress field, both northeast China and adjacent regions are mainly affected by the subduction of the Pacific plate, resulting in a near east-west compressional stress regime that extends eastward to Sakhalin island and northward to the northeastern segment of the Outer Xing'an Range.

On the basis of these multidisciplinary constraints, we propose a revised boundary for the seismic zone in northeast China. The southern boundary remains along the Chifeng-Kaiyuan Fault. The northern boundary is extended to the southern margin of the Outer Xing'an Range, the eastern boundary reaches the eastern foothills of the Sikhote-Alin mountains near the western coast of the Sea of Japan, and the western boundary is expanded by approximately 150~200km beyond the current national border.

This revised boundary has important practical implications. First, it improves the precision of seismic-hazard delineation in northeastern China and its surrounding regions, thereby enhancing the scientific reliability and accuracy of regional hazard assessment and providing a stronger basis for seismic zonation mapping. Second, the revised boundary offers useful guidance for urban disaster-prevention planning, seismic design of major engineering projects, and optimization of regional seismic monitoring networks.

Key words: seismic zone in northeastern China, tectonic setting, geophysical field, contemporary tectonic stress field

摘要：

地震区、 带划分是分析地震活动空间和时间分布特征的重要基础, 也是开展地震危险性评估与地震预测研究的前提条件之一。在划分地震区的工作中, 确定地震区的边界尤为重要。中国东北及邻区作为一个地震活动强度小、 频度低的地区, 可单独划分为东北地震区。传统的东北地震区边界划分方案存在局限, 边界的确定更多考虑中国的边境线, 未充分考虑地质背景。在新的中国地震动参数区划图修订过程中, 依据中国东北及周边地区的大地构造背景、 地形地貌、 地球物理场、 地震活动与断裂构造特征, 以及区域现代构造应力场特征等相关资料与数据, 重新对东北地震区进行了边界修订。研究结果显示, 中国东北及邻区的块体整体性、 构造一致性较好, 可作为一个独立块体进行分区, 并将其西、 北、 东边界进行外扩至更合理的构造边界上。在新的东北地震区边界划分中, 南界依旧沿赤峰-开原断裂分布, 北界则向外扩展至外兴安岭南缘, 东界延伸至锡霍特山脉东麓(日本海西岸), 西界按照国境线外扩150~200km。

关键词: 东北地震区, 构造背景, 地球物理场, 现代构造应力场