CAJ | 학술논문

使用小震机制解资料，分析了1975年海城7.3级和1976年唐山7.8级强震及1983年菏泽5.9级和1995年苍山5.2级中强震前，震源区及其周围不同构造部位应力场的时、空变化，证实震前震源区附近应力场曾有某些异常改变，如唐山强震前震源区周围出现长达4a多的小震机制解主应力轴一致性取向的现象，菏泽地震前小震机制解P轴“集中—转向”，苍山地震前P轴偏转且一致性增强。同时还发现，唐山地震前应力场异常变化开始时间可能早于1972年；震源区内的陡河台与源外区的昌黎台小震综合机制解反映出震前的受力差异；震源断层附近不同应力区内震源机制解和地震活动有时空动态差异。这些现象一定程度上提供了不同构造条件和应力背景下，中、强震前震源区不同构造部位力学状态的改变或地震孕育过程的信息，对研究不同地震的孕震过程及差异有一定意义。
사용소진궤제해자료，분석료1975년해성7.3급화1976년당산7.8급강진급1983년하택5.9급화1995년창산5.2급중강진전，진원구급기주위불동구조부위응력장적시、공변화，증실진전진원구부근응력장증유모사이상개변，여당산강진전진원구주위출현장체4a다적소진궤제해주응력축일치성취향적현상，하택지진전소진궤제해P축“집중—전향”，창산지진전P축편전차일치성증강。동시환발현，당산지진전응력장이상변화개시시간가능조우1972년；진원구내적두하태여원외구적창려태소진종합궤제해반영출진전적수력차이；진원단층부근불동응력구내진원궤제해화지진활동유시공동태차이。저사현상일정정도상제공료불동구조조건화응력배경하，중、강진전진원구불동구조부위역학상태적개변혹지진잉육과정적신식，대연구불동지진적잉진과정급차이유일정의의。
By using the data of mechanism solutions of small earthquakes, wehave analysed the temporal and spatial changes of stress field in different tecton ic positions of the focal region and its adjacent areas before the Haichang ear thquake of magnitude 7.3 in 1975，Tangshan earthquake of magnitude 7.8 in 1976, Heze earthquake of magnitude 5.9 in 1983, and Cangshan earthquake of MS 5. 2 in 1995. It is verified that there were some anomaly changes of stress field ar ound the focal region before earthquakes. For instance, the axes of principal st resses had orientation coincidence in focal area as long as 4 years before the Tangshan earthquake. The P axis azimuths of composite mechanism solutions of smal l earthquakes concentrated first , and turned then, before the Heze earthquake. The azimuths of Paxes deflected and its coincidence increased before the Can gsha n earthquake. In the meanwhile, the stress field changes before the Tangshan ear thquake may began earlier than 1972. The composite mechanism solutions of small earthquakes recorded by Douhe station, which is in the focal region, is differen t from that of Changli station, which is outside the focal area. The focal-mecha nism solutions and the seismic activity in different stress areas near the focal fault have dynamic differences. To a certain extent, these phenomena indicate that the mechanical state in different tectonic positions of foca l areas is not same and small earthquakes are developing in focal areas before strong earthquakes under different tectonic conditions and stress background. This has practical meanings for studying the earthquake preparation process and differences for different earthquakes.