The results show that the vertical displacement of the three stations has a large and rapid subsidence within 1 hour before the Wenchuan earthquake, and the PIXI(Pixian) station, 36km from the epicenter,
has a subsidence of 300mm. So far, only GPS can measure such rapid and large vertical displacement anomalies. The GPS observation of Wenchuan earthquake has created many unique and first in the history of earthquake precursor monitoring.
It was the first large earthquake of magnitude 8 with long, medium and short crustal deformation anomalies observed by GPS. These anomalies provide information about the location, magnitude, and time of the earthquake in different ways.
Later, Professor Gu Guohua studied the M9 East Japan earthquake and found that although the M9 East Japan earthquake did not occur in the interior of the GPS continuous observation network of more than 1200 stations in Japan,
the epicenter was nearly 100km away from the nearest GPS continuous observation station in Japan. The horizontal displacement peaks near the epicenter of the earthquake. A large range of coseismic horizontal displacement was obtained after the earthquake.
The observation results obtained after the earthquake show that the coseismic horizontal displacement is also the elastic rebound of the horizontal displacement accumulated before the earthquake, which once again proves that there is precursor crustal movement before the earthquake,
which greatly enhances the confidence of exploration. The observed coseismic horizontal displacement of this earthquake is up to 5.6 meters. In addition, the ionospheric TEC short-term anomaly was also observed by GPS before the earthquake.
Post-earthquake studies show that the horizontal displacement observations accumulated before the 2013 M7 Lushan earthquake in Sichuan province and some other earthquakes, while the horizontal displacement near the epicenter tends to be closed (that is, no significant displacement),
abrupt change during the earthquake, resulting in coseismic horizontal displacement, and the earthquake makes the horizontal movement of the crust in a large range tend to be consistent,
indicating that the coseismic horizontal displacement is an elastic rebound in space. The horizontal displacement before the two large 7.8-magnitude earthquakes in Turkey in 2023 appeared in the above two ways respectively.
Due to the stable plate (horizontal) motion, the precursory horizontal displacement time process of each station is the simplest straight line except for the earthquake in the post-seismic deformation area after a huge earthquake.
A large number of observation results show that the horizontal displacement accumulated before the earthquake and the coseismic horizontal displacement are exact causal relationship, and can be reproduced in different earthquake occurrence processes.
Before the earthquake, the observation station moves horizontally along a straight line, and when the earthquake occurs, the horizontal displacement of the same earthquake suddenly reverses,
which is the process of the big earthquake from gestation to occurrence, from quantitative change to qualitative change, and the action and reaction, which fully shows that the earthquake has precursor crustal movement.
Coseismic displacement not only provides abundant data for the study of focal mechanism besides seismic waves, but also provides the most powerful observation basis for the existence of precursory deformation. Coseismic horizontal displacement is a key phenomenon in understanding earthquake precursory deformation.
Since the beginning of this century, the GNSS observation network and the large earthquakes occurring in or around the major seismic regions of the world are good opportunities to study earthquake prediction.
After the Wenchuan earthquake and the East Japan earthquake, in order to obtain more research results, Professor Gu Guohua has seized the opportunity to conduct more than 90 large earthquakes of 6-9.3 magnitude at home and abroad,including the 7.6-magnitude earthquake in Japan in early 2024 and the 7.3-magnitude earthquake in Taiwan, China in early April, and analyzed a large number of GNSS observation data. He has published more than 20 papers in domestic and foreign journals.
The earthquake types studied are diverse; A large number of crustal deformation observations from more than 5000 GPS observation stations at home and abroad are studied, about half of which are continuous observation stations.
The most available GPS continuous observation stations for an earthquake are nearly 1,600 stations, covering a distance of thousands of kilometers from the epicenter. The GPS continuous observation station was less than 1km away from the epicenter;
The longest observation time is nearly 30 years, and there are high-frequency sampling observations near the epicenter before the earthquake. The GPS observations have obtained the key results of continuous observation of the key areas near or near the epicenter of the major earthquake and the key periods before and after the earthquake. The results are compelling. Acquiring such a wealth of GNSS observations is costly and extremely valuable.
The results show that the horizontal displacement process of the observation stations within a certain range of the epicenter before and after the big earthquake is similar to the deformation process of the rock rupture test.
