Abstract:

Analyzing the statistical data on the widths of earthquake surface rupture zones is one of the most objective methods for determining the extent of active fault offsets and deformed zones. This information is crucial for establishing the setback distances for significant engineering projects in areas affected by active faults. In this study, we collected data from 92 cases to compute the widths of surface rupture zones and subsequently analyzed the extent of active fault offsets and deformed zones. Specifically, our dataset includes 75 cases with surface rupture zone widths extracted from published sources and 49 cases with available surface rupture vector data.

When compiling the statistical data on surface rupture widths, we categorized the data based on whether the ruptures occurred along straight fault segments or along more geometrically complex segments. For the vector data, we normalized the distributed rupture length and primary rupture length for each case to determine the distribution proportion of the rupture zones relative to fault distance.

The statistical analysis of document data shows that the total width of surface rupture zones in geometrically complex sections of normal, thrust, and strike-slip faults does not exceed 8100m, 3700m, and 10100m, respectively. In contrast, the widths of surface rupture zones in straight fault sections are generally narrower, with maximum widths of 160m, 120m, and 400m for normal, thrust, and strike-slip faults, respectively. The vector data further reveal that the maximum distances between the distributed ruptures and the primary fault are as follows: 19212m for the hanging wall of normal faults, 16244m for the footwall of normal faults, 7579m for the hanging wall of thrust faults, 4216m for the footwall of thrust faults, and 120456m for strike-slip faults. Moreover, the maximum distances from the primary fault to the margin of the closely distributed rupture zones are 700m, 200m, 1000m, 400m, and 500m, respectively. It is important to note that when excluding exceptional cases, such as earthquakes associated with fold-related faults or gently dipping thrust faults, the maximum distance from the margin of the closely distributed rupture zone to the primary fault is as follows: 400m for the hanging wall of normal faults, 200m for the footwall of normal faults, 500m for the hanging wall of thrust faults, 200m for the footwall of thrust faults, and 400m for strike-slip faults. Based on this comprehensive analysis, we suggest that the range of active fault offset and deformed zones should be considered as 400~500m from the primary fault. However, further research is needed to accurately determine the extent of fault offsets and deformed zones in areas with complex structural features, such as fault bends, step zones, fault tails, and the hanging walls of foreland thrust faults.

Future studies would benefit from incorporating more extensive and detailed surface rupture data. Continued data collection is essential to improve the accuracy and robustness of the results.

Key words: Width of earthquake surface rupture zone, Closed distributed ruptured zone, Active fault offset and deformed zone, Active fault setback distance

摘要：

基于大量震例的地表破裂带宽度统计是确定活动断层错断变形区范围最客观的方法, 能够为重大工程的活动断层避让原则和距离制定提供数据支撑。文中收集了75例文献记录的地表破裂带宽度和49例地表破裂矢量数据, 对文献记录的地表破裂带宽度进行了汇总, 并对地表破裂矢量数据进行了空间分析, 在考虑断层性质及几何结构的情况下, 获得各类地震地表破裂带宽度和分布式破裂密集分布区。根据文献记录数据统计, 正断层、逆断层、走滑断层在几何复杂段的地表破裂带宽度分别为8100m、3700m、10100m, 在平直段分别为160m、120m、400m。根据矢量数据分析, 正断层上盘、下盘, 逆断层上盘、下盘, 走滑断层在主破裂两侧连续分布地表破裂的最大范围分别约为14000m、7000m, 6400m、4300m, 17700m, 其中地表破裂密集分布区域边界与主断层的距离分别为700~800m、200~300m, 1000~1100m、400~500m, 500~600m。综合确定活动断层变形区范围边缘在正断层上盘、下盘, 逆断层上盘、下盘, 走滑断层两盘到主断层的距离分别为400~500m、200~300m, 500~600m、200~300m, 400~500m。考虑断层定位、地表破裂的新生性并排除特殊震例影响, 确定活动断层错断变形区范围边缘在边界清晰的断层平直段距主断层破裂带外围边缘的最小距离为400~500m。在断层的阶区、端部、拐折等几何复杂段及薄皮状逆断层上盘等特殊构造位置, 还应针对活动断层错断变形区范围进行专门研究。利用丰富详细的地表破裂数据能够得到更全面的认识, 文中的研究方法及结果可作为在活动断层附近选址的重大工程对活动断层避让的参考, 未来仍需要不断补充地震地表破裂数据完善文中的研究结果。

关键词: 地震地表破裂带宽度, 分布式破裂密集分布区, 活动断层错断变形区, 活动断层避让距离