以21世纪全球各具特色且最典型的6次大地震,尤其是巨大地震前后GNSS观测得到的地壳水平形变为重点,回顾探寻前兆形变,探索地震预测预报。6次地震为:2008年汶川8.0级、2010年智利8.8级、2011年东日本9.0级、2015年尼泊尔8.1级、2016年日本九州岛7.3级地震及2023年土耳其7.8级双震。地壳形变是物理问题,区域参考框架是利用GNSS连续观测研究前兆位移物理问题的基本前提,而同震水平位移是探寻前兆形变的关键现象。大震前震中及其附近既无明显的垂直位移积累,也无明显的水平剪切位移积累。大地震震中及其附近前兆水平位移主要有两种形态,水平位移达到峰值或为闭锁; 但近震中震前介质已非弹性,仅远场介质为弹性。GNSS观测结果表明震前震中主要为水平挤压,震时产生剪切破裂,这与岩石破裂实验结果一致,因此“压-剪”(弹性)回跳模型符合GNSS观测结果,但至今仅获得少数地震短临前兆形变观测结果。GNSS依然是探索地震预测的主要观测手段,但由于与地震断层破裂临界状态密切相关,利用各种观测技术探索地震断层破裂的临界现象,即地震短临前兆,是突破地震短临预报的关键,仍需要利用多学科各种观测技术。

The paper focuses on the horizontal deformations detected by the GNSS measurement before and after 6 typical large earthquakes of parculiar characteristics,particularly huge earthquakes,to explore crustal deformations precursory to earthquakes for the purpose of earthquake forecasting. They are the Wenchuan earthquake of M8.0,the earthquake of M8.8 in Chile,the Tohoku earthquake of M9.0 in Japan,the M8.1 earthquake in Nepal,the 2016 M7.3 Kyushu earthquake of and the doublet earthquakes of both M7.8 in 2023 in Turkiye. The regional reference frames are used in studies on the crustal deformations precursory to earthquakes to keep alignment for the requirement. And the coseismic horizontal displacements are the key phenomenon in exploring crustal deformations precursory to earthquakes. No accumulations of vertical and horizontal shear displacements were detected at or near the epicenters. There have been two patterns of precursory horizontal displacements at and near the epicenters of large earthquakes,that is,they reached peak values or were locked with no horizontal displacements. The media at and near the epicenters were non-elastic,but the media far from the epicenter were elastic. The GNSS observations showed that the epicentral areas were compressed before the events and there were shear break at the time of the earthquakes. The processes were similar to the rock failures in the rock tests. Therefore the “compression-shear”(elastic)rebound model is in agreement with the results of GNSS observations. But till now there were imminent precursory crustal deformations for only quite few earthquakes. Obviously even though there are problems in detecting imminent precursory deformations,GNSS has been one of the main observation techniques in earthquake forecasting. Because imminent precursory deformations are closely related with critical phenomenon in the failure process of earthquake faults,the critical phenomenon or imminent precursors are the key for the breakthrough in earthquake forecasting. Different observation techniques of multiple disciplines should be used to detect the imminent precursors.

P315

中国地震局老专家科研基金(202305)资助