2021年漾濞6.4级地震前地壳形变分析

利用2019-05-20~2021-05-20云南及周边54个GNSS基准站观测数据，基于最小二乘配置法求取云南地区速度场、应变场，并结合2021-05-21漾濞6.4级地震近场、远场区域的GNSS基线长度时间序列，分析地震前地壳形变特征。结果表明，震前云南西边界SSW方向运动增强，沿怒江断裂带呈发散性运动状态，震中附近的近场速度值变化不大，区域速度场异常变化不明显；震前研究区整体面膨胀率值下降至原来的0.37倍左右，同时最大剪应变率、主应变率也急剧下降，说明震前区域地壳应变积累明显减弱，而震中位于张、压交替的零值线上。GNSS基线长度时间序列结果显示，震前地震近场区域的GNSS基线异常变化不明显，而远场区域的GNSS基线出现偏离长期背景的趋势异常变化，基线KMIN-YNYM在趋势压缩背景下反向加速拉张，背离趋势运动8.4 mm，基线YNLP-KMIN在趋势压缩背景下加速压缩，背离趋势运动6.4 mm，基线YNLP-YNDZ在趋势变形较平稳的背景下加速压缩，背离趋势运动8.1 mm，基线YNSM-YNLP在趋势拉张背景下加速拉张，背离趋势运动7.8 mm，可判断震前区域应力平衡状态被打破，诱发了地震。

Analysis of Crustal Deformation before the 2021 Yangbi MS6.4 Earthquake

Using 54 GNSS reference station observations in and around Yunnan from May 20, 2019 to May 20, 2021, we obtain the velocity field and strain field in Yunnan based on the least squares configuration method.We combine the time series of GNSS baseline length changes in the near-field and far-field regions of the 2021-05-21 Yangbi M_S6.4 earthquake to analyze the crustal deformation characteristics before the earthquake. The results show enhanced motion in the SSW direction at the western boundary of Yunnan before the earthquake, and a dispersive motion along the Nujiang fault. The near-field velocity values near the epicenter did not change much, and the anomalous changes in the regional velocity field are not obvious. The value of the surface expansion rate of the study area as a whole before the earthquake dropped to about 0.37 times its original value, while the maximum shear strain rate and principal strain rate also dropped sharply, indicating that the crustal strain accumulation in the area before the earthquake weakened significantly, and the epicenteris located on the zero value line of alternating tension and compression.The GNSS baseline length time series results show that the GNSS baseline anomalies in the near-field region before the earthquake changed insignificantly, and the GNSS baseline in the far-field region has trend anomalous changes that deviate from the long-term background before the earthquake. The baseline KMIN-YNYM accelerates backward in tension against the background of trend compression, deviating from the trend motion by 8.4 mm. The baseline YNLP-KMIN accelerates in compression against the background of trend compression, deviating from the trend motion by 6.4 mm; the baseline YNLP-YNDZ accelerates in compression against the background of relatively smooth trend deformation, deviating from the trend motion by 8.1 mm. The baseline YNSM-YNLP accelerates in tension against the background of trend tension, deviating from the trend motion by 7.8 mm. Weinferthat the stress equilibrium state in the region before the earthquake was broken and induced the earthquake.