地震和干旱的定向迁移及其机制

ORIENTATIONAL MIGRATION OF EARTHQUAKES AND DROUGHTS AND FORMATION MECHANISM

本文介绍了中国大陆４条地震带和全球６条地震带地震的定向迁移和亚非中纬度地区干旱的迁移现象；探讨了亚非地区地震和干旱向东定向迁移的机制，认为这可能是由地球自转速度变化、大西洋脊间歇性张裂和板块的脉动式推挤引发的变形波的传播和这种变形波驱动地壳和上地幔内的热流体（液、气）周期性上涌引起的。

he orientational migration phenomenon of earthquakes in a seismic zone isrecognized through following steps. First a sketch map of space-time distribution forearthquakes larger than a given magnitude is made. Then those earthquakes aregrouped and connected by use of lines in one or two directions. Those lines are wellsub-parallel and include most of the earthquakes in the sketch map. They areearthquake migration lines drawn by use of eye-vision filter, showing the phenomenonof oriented migration with equal velocity (Vm).,Studies indicate that the earthquake migration is well oriented and keeps constantin migration velocity in North-South middle axial, Tianshan Mountians, Shanxi andYanshan seismic zones on the mainland of China. Furthermore, earthquake does notalways migrate along extend of a seismogenic faults, and activation of one fault willnot always trigger its neighbouring fault. The most probable model for suchearthquake migration may represent a massive oriented motion under effect of anoriented additional force, owing to an uneven stress concentration pattern atmulti-points of faults in the seismic zone.Analysis of earthquake oriented migration along seismic zones for 184 earthquakes(Ms>7.8) during 1900 to 1990 in 6 seismic zones at globe scale indicates that theearthquakes migrate from the west to the east and their velocities decrease eastwardsalong the Euro-Asian, Philippine-New Hebrides Isle, Ryukyu Isle - KamchatkaPeninsula, Alaska-Aleutian seismic zones. World-wide monthly rainfall data of thepast 100 years from NCAR (USA) shows that the drought periods always started inNorth Africe (region A) and expanded eastward to Northwest China (region D)through Middle East (region B) and Middle Asia (region C). Their eastward velocityreached 400km/a.The eastward migration phenomena of both the earthquakes and the droughtsshow that there is interaction between atmosphere and lithosphere or there is acollective dynamic origin for above two phenomena. According to the presentknowledge on crust-mantle structure , the eastward migration phenomena forearthquakes and droughts can be explained by use of the eastward propagation ofdeformation wave in the crustal and upper mantle. The deformation wave may beoriginated from following processes : (1) The material oscillation in the asthenospheretriggering periodic occurrence of earthquakes and droughts in the regions, owing tointermittence spreading and uplifting of hot material in the middle or lower crust fromAtlantic ridges. (2) Episodic vibration induced by stable or unstable northward pushof the African, Arabian and indian Plates on the south to the Eurasian Plate on thenorth. (3)Earth variable rotation. Besides, the stable sub-periods of 60, 40 and 30years in the Earth rotation variation, which is demonstrated by the length of day(LOD), may also cause periodic oscillation of the asthenosphere controlling theearthquakes and droughts occurrence. There is 20 years of sub-period of earthquakeactivity on the mainland and its adjacent regions and this sub-period corresponds to asub-period of 40 years in LOD. Five seismic active Periods in this century started atthe extremum of the 40 years' Period component. The drought period in the regionD is also associated with this component (Fig.2). The drought in the region A startedabout the extrumum of 30 years' sub-period, and this may show a close relationshipto a 30 years' sub-period.Thus, we can conclude that the oriented migrations of both the earthquakes andthe droughts are resulted from Periodic upwelling of hot fluids in the crust and uppermantle driven by periodic deformation waves. The occurrence and preparation forearthquakes are associated with deep hot fluid. The upwelling of hot fluid may warmthe crust and then affect atmosphere circulation, while drought may be resulted fromthe atmosphere circulation anomaly. This may explain why both the earthquake andthe drought migrate in the same direction with similar migration velocities. To furtherverify and recognize this mechanism may need longer observation data, especially t