A study of the Kunlunshan earthquake of MS = 8.1 based on observed coseismic strain steps from the borehole strain monitoring network over China has been carried out with some interesting results. Firstly, many recordings disagree with theoretic calculation using static dislocation model. Secondly, abnormally large strain steps are ob-served at quite a few stations in the tectonically active east-northern China, while in the relatively inactive east-southern China no obvious steps are recorded. It is inferred that seismic stress triggering may significantly affect remote seismic strain field. In other words, whether remote faulting be seismically triggered or not may de-termine the pattern of local seismic strain changes. Further comparison study results of March 11, 1999 Zhangbei earthquake and November 1, 1999 Datong earthquake show that the specific pattern of seismic zones has obvious influence on seismic strain changes in the region. This supports the idea that observed abnormal strain steps might be produced by coseismicly stress-triggered local faulting.
Borehole strain observation is playing an increasingly important role in the study on the crustal movements. It has been used by many countries such as China, USA, Japan, Peru, Australia, South Africa, Iceland and Italy, in re- search fields of plate tectonics, earthquake, volcanic eruption, dam safety, oil field subsidence, mining collapse and so on. Borehole strainmeter has been improved rapidly and tends to get more and more components included in one probe. Based on observations by this kind of instruments, studies on seismic strain step, slow earthquake, earthquake precursor and volcanic eruption forecasting have made remarkable achievements. In the coming years, borehole strain observation is going to become one major geodetic means, together with GPS and InSAR.
