2019年5月18日松原M5.1地震构造机制分析

基于区域地震台网的数字化波形资料，使用ISOLA方法对2019年5月18日吉林松原M5.1地震进行矩张量反演，研究地震的震源机制，并且收集了地震序列中M_L2.5以上地震的震源机制解，采用FMSI（focal mechanism stress inversion）方法反演震中区构造应力场。结果显示：松原M5.1地震的矩震级为4.9，矩心深度为6 km，双力偶分量为91.5%，主压应力P轴方位角、倾角分别为76°和3°，主张应力T轴方位角、倾角分别为166°和16°，震源机制解显示典型的构造地震特征；震中区构造应力场理论应力轴σ₁方位角、倾伏角分别为88.0°和0.9°，σ₂方位角、倾伏角分别为178.2°和9.6°，σ₃方位角、倾伏角分别为352.5°和80.4°，这一结果与区域构造应力场一致。推断认为区域构造应力场触发了2019年松原M5.1地震活动，地震震源机制解的北西向节面与震中区附近的第二松花江断裂现今活动性质完全一致，认为第二松花断裂可能是松原M5.1地震的发震断层。

Analysis of Tectonic Mechanism of Songyuan M5.1 Earthquake on May 18, 2019

Based on the digital waveform data of the regional seismic network, we inverted the seismic moment tensor solution for the Songyuan M5.1 earthquake by using the ISOLA method. Also,we inverted the stress field of the focal mechanism of the M_L>2.5 events in the aftershock sequence by FMSI method. The study results show that the Songyuan M5.1 earthquake has a moment magnitude of M_w 4.9, centroid depth of 7 km, and double couple components of 91.5%. The azimuth and plunge of P-axes are 76° and 3° respectively, and those of T-axes are 166° and 16° respectively. The reduced stress tensor shows that the azimuth and plunge of σ₁ are 88.0° and 0.9°, those of σ₂ are 178.2° and 9.6°, and those of σ₃ are 352.5° and 80.4° respectively, which agree with the region stress field. We suggest that it is the region stress field that triggered the Songyuan M5.1 earthquake, which occurred on the second Songhuajiang fault near the source region.