GPS观测得的2023年2月土耳其双震前后的地壳形变

Crustal Deformations before and after the Doublet Earthquakes in February 2023 in Turkiye Detected by GPS Observations

摘要: 2023年2月6日土耳其发生7.8级双震，相隔仅9小时、相距近，都是近直立断层走滑型地震，是利用GPS观测研究地震前后地壳形变稀有震例。利用美国网站得到131个GPS站欧亚(板块)参考框架位移数据，分析了2次地震前后的地壳形变。同震水平位移是分析大地震前兆地壳运动的关键现象。GPS分别观测得的2次地震同震位移，特征显著：水平位移最大达4.4 m；向西、向东和向南水平位移3个分区明显，与区域内3个板块构造运动密切相关；而垂直位移较小，无明显分区。2次地震前震中附近的水平位移分别出现(第一次地震)峰值和(第二次地震)闭锁2种类型，但无明显的垂直位移积累。与其他震例一样，在震前两种类型的水平位移区域，同震水平位移是震前位移在时间或空间上的(弹性)回跳，表明大地震有前兆形变。2次地震重合的孕震区内，有对2次地震同震水平位移影响相近的区域。GPS观测明确显示，地壳水平运动是2次大地震的成因。尽管观测不足和未能预报2次地震，但仍突显GNSS可在地震监测、预警和地震预测中发挥作用的优势。

Abstract: In only about 9 hours and at a short distance, doublet large earthquakes of M7.8 occurred on Feb. 6, 2023 in Turkiye with strike slips on near-vertical faults. They have provided a rare earthquake case with GPS observations before and after the events. Displacement data at 131 stations in the Erasia reference frame downloaded from the website in America are analyzed. Coseismic horizontal displacements are key facts for the studies on the crustal deformations precursory to large earthquakes. The features of the coseismic displacements obtained separately from GPS observations for each event are quite obvious: the largest horizontal displacement was 4.4 m, 3 distinct areas of mainly westward, eastward or southward horizontal displacements, that are closely related with the motions of the 3 tectonic plates in the region, are identified while no distinct areas for small vertical displacements are identified. No preseismic accumulations of vertical displacements were detected. Near the 2 epicenters there were the area with peak horizontal displacements for first event and no or locked horizontal displacements for the second event. Similar to other earthquake cases, the coseismic horizontal displacements in the areas of 2 different types of preseismic horizontal displacements were the (elastic) rebound of the preseismic horizontal displacements shown in time series or in space. They show that there were crustal deformations precursory to the 2 events. Within the overlapping area of the preparation of both events, there was an area in which both events showed similar coseismic horizontal displacements. GPS observations have shown definitely that the horizontal crustal motions were the origin of the 2 events. The potential advantages of GNSS in monitoring seismic waves and crustal deformation for earthquake early warning and earthquake forecasting have exhibited quite strikingly in Turkiye though there were insufficiencies in the GPS observations and the 2 events were not forecasted.