2023年12月18日甘肃积石山6.2级地震震源机制及其对周围区域的应力影响

Focal Mechanism and Stress Implication on the Surrounding Region of the Jishishan,Gansu M_(s)6.2 Earthquake on December 18,2023

为研究2023年甘肃积石山6.2级地震对周围地区的应力影响,本文首先根据各个机构和学者提供的震源机制数据确定了本次地震的震源机制中心解。节面Ⅰ:走向159.08°,倾角40.57°,滑动角112.46°;节面Ⅱ:走向310.52°,倾角53.05°,滑动角71.88°。此次地震为逆冲型地震。将当地的应力体系投影到震源机制中心解的两个节面上,得到相对剪应力分别为0.797和0.951,可以看出该地震是区域构造应力场作用下的一次正常能量释放。拉脊山北缘断裂呈NNW走向,SWW倾向,倾角为45°~55°,与震源机制中心解的节面Ⅰ较为一致,判断拉脊山北缘断裂为此次地震发震断裂。基于该地震破裂模型及均匀弹性半空间模型,计算此次地震对周边地区产生的同震位移场及应变场。体应变在震中呈现拉张,距离震中较远的东北和西南两侧呈现轻微拉张,震中周边呈现压缩,东侧压缩表现更为突出。水平位移场表现为在震中西北侧和小部分东南侧的物质向外涌出,而东北侧和西南侧的物质涌入震中;与水平位移场相对应,垂直位移场在震中表现为隆升,而四周表现为略微沉降。

In order to study the stress implication of the 2023 M_(s)6.2 earthquake in Jishis-han,Gansu on the surrounding areas,the central focal mechanism solution of the earth-quake is estimated based on the focal mechanism data provided by various institutes and scholars,with nodal plane I:strike 159.08°,dip 40.57°,and rake 112.46°,and nodal plane I:strike 310.52°,dip 53.05,and rake 71.88°.It can be judged as a reverse focal mechanism type of this earthquake.Projecting the local tectonic stress tensor on the two nodal planes of the central focal mechanism,the resulted relative shear stress on the nodal plane are 0.797 and 0.951,respectively,which mean that the earthquake is a normal ener-gy release under the action of the local tectonic stress field.The NNW striking of the Lajishan Northern Margin fault is dipping SwW and dip angle of 45°~55°by geological field investigation,and nearly consistent with the nodal plane I of the central focal mech-anism,we consider that the Lajishan Northern Margin fault is the seismogenic fault of the earthquake.Based on the rupture model and homogeneous elastic half-space model,we calculate the co-seismic displacement field and strain field generated by the earthquake in the surrounding areas.The volumetric strain at the epicenter area shows tensile tension,and the northeast and southwest sides far from the epicenter show slight tensile tension,and the periphery of the epicenter shows compression with strong compression on the east side.The horizontal displacement presents the outflow of material from the northwest and a small portion of the southeast side of the epicenter,while the material from the northeast and southwest sides of the epicenter is inflowed into the epicenter.Corresponding to the horizontal displacement field,the vertical displacement field is uplifted at the epicenter,while the surrounding area shows little subsidence.