2017年1月28日四川筠连地震震害特征与孕震构造

Damage Character and Magnitude Discussion for the Junlian Earthquake on January 28, 2017 in Junlian, Western China

2017年1月28日四川筠连县发生4.9级地震,四川地震台网测定微观震中位于维新镇。经现场调查,本次地震的宏观震中位于筠连县乐义乡,震中烈度达到Ⅶ度,给筠连县造成较为严重的破坏,特别是位于震中区的中坝村、黄金村和白云村的破坏尤为严重,主要表现为少量的山体崩塌和大量的房屋破坏。大量的房屋破坏表现为少数砖木、土木结构房屋毁坏或严重破坏,砖混结构房屋少数中等破坏。综合现场考察资料、震源机制解、余震分布和地震构造背景分析认为,此次地震的等震线形态是南西侧稍大的不规则椭圆形,长轴沿NNE向展布,Ⅶ度区面积约12平方千米,长短轴比为16:11;Ⅵ度区面积约230平方千米,长短轴比8:5。综合596个余震精定位结果、地震构造背景和相似地区的震例类比分析,认为乐义背斜可能是本次地震的孕育构造,震区内近南北向的扎子坳断裂NW盘的震害程度明显大于SE部,断裂限制了余震的分布,震害在震中附近表现为较为明显的上盘效应,且存在震害叠加效应,地震的实际震级应该大于速报的4.9级,应大于等于5.0级。

The 4.9 magnitude earthquake occurred in Junlian County, Sichuan province on January 28, 2017, and the microcosmic-epicenter was located at Weixin village in Sichuan seismic network. According to the site investigation, the macrocosmic-epicenter of the earthquake is located in Leyi village, with the epicentral intensity of VII degree, causing more serious damage, especially the destruction of Zhongba village, Huangjin village and Baiyun village located in epicentral area, mainly a small number of landslides and a large number of houses. Houses damage shows that a small number of brick wood houses and soil wood houses collapsed or were seriously damaged, and a small number of brick masonry buildings were moderately damaged. The comprehensive field investigation data, source mechanism solution, aftershock distribution and seismic tectonic background analysis show that the isoseismic shape of the earthquake is a slightly irregular elliptical in the south of the south, the long axis distribution, the VII degree area is about 12 square kilometers, and the major and minor axis ratio is 16:11. VI degree area is about 230 square kilometers, major and minor axis ratio 8:5. The damage level was more serious in NW, less in SE of the main fault Zha zi ao fault. According to the seismic tectonic background and the earthquake cases analogy analysis of similar areas, it is concluded that the seismic damage of this earthquake is obvious fracture reel effect, and the seismic damage superposition effect, the actual magnitude of the earthquake should be greater than or equal to 5.0 which is greater than the 4.9 magnitude of rapid report.