As can be seen from the results of recent geodetic measurement, the strong earthquakes were all companied by changes in topologies. So to speak, the Bohai earthquake in 1969, the Yangjiang earthquake in Guangdong Province, Tonghai earthquake in 1970, and Yuxin earthqake in Yunnan were all accompanied by ground deformation.
Take Xintan earthquake as an example, let's take a look at the elevation change of benchmark. There, the elevation increased sharply at a speed of 82-110mm per year from December of 1964, contrary to its usual trend of falling down. On March 15, 1996, the figure turned to another abrupt fall and the earthquake took place on March 22.
In 1968, before the earthquake of 8.5 magnitudes occurred in Tancheng of Shandong, there was a small island to the East of the epicenter area. Because the ground surface swelled slightly, that small island kept rising slowly. Afterwards, the small island even connected with the continent. When the earthquake took place, the ground to the East of the epicenter area rose up abruptly and held back the sea water 15 km to the East of Ganyu, Jiangsu province.
The US seismologist set up more than 80 observation stations along the St. Andrews Grant Fault. The activities of the Grant Fault cause earthquakes to occur most frequently along the Western Californian coast. The outstanding feature of that topology was of its horizontal deviation. The two sides of the Grant Fault deviated 6.4 meters away when an earthquake took place in 1906. Calculated by geological method, the displacement was as long as 500 km from Jurassic Period to the present. Judged by the satellite data, the horizontal shear relative speed somewhere in Grant Fault is 5 cm per year.
In Japan, before several severe earthquakes, unusual phenomena also occurred. 9 hours before Sinxie earthquake in 1964 in Japan, unusual things appeared.
As is known, the fault movements in the underground are the direct reasons for most of the earthquakes. The deformation measurement can monitor the fault activities. Together with other methods, such as to monitor the earthquake sounds to detect the micro split in faults, it is possible for mankind to judge the accurate state of the fault activity. If we go on with this chain of thought, we could conclude that deformation measurement could provide quite important evidence for the forecast of earthquakes.