北京周围地区地震的分布特点与地壳屈曲

SOME FEATURES OF EARTHQUAKES DISTRIBUTION AROUND PEKING AND CRUSTAL BUCKLING

  • 摘要: 地震活动的规模常具有大尺度的特点,结合全球地震分布具有相当的似对称性,我们认为,地震的成因必然蕴含着地球的整体运动.地震活动具有块体性活动的特点.块体的边界线常与经纬线相交成45°.强震发生前也有这种情况.文中给出了与经纬线相交成45°的一个条块,近年华北的强震基本上都落在这个条块的两条边线上,且这些强震的分布具有较明显的等间隔分布特点,类似于地层中的褶皱所显示的一定的波长.我们分析了有历史记载以来我国全部八级地震,发现每次八级地震前后,都有另一次八级或七级半地震在它的一定距离上发生.这个间距有两个优势分布,一个短距的为480—550公里,另一个长距的为1100公里左右(后者约为前者的一倍).引用了柱壳轴向受力屈曲作为初步探讨.从分析可知,柱壳屈曲的半波长(1/2λ≈1.72 \sqrtRh )主要决定于圆柱半径与柱壳厚度:以 R=6000公里、h=15公里估算,得半波长为530公里,与我国强震分布间距较为符合.故我们的初步认识是地震的分布可能受着地壳屈曲的控制.

     

    Abstract: The large spatial distribution of the activity of strong earthquakes is a characteristic feature. And it seems that the World-wide seismic zones are somehow arranged in several regularly directions on the spherical surface. We suppose that the cause of earthquakes might be related to the movements of the whole earth.A feature relating to earthquakes activity in blocks, the boundaries of which usually make 45° with the latitude or longitude was found. The same situation happened before strong earthquakes occurred in recent years. A stripe making an angle of 45° with the latitude or longitude has been delineated. Strong earthquakes occurred in recent years are located essentially along the two boundary lines of this stripe, and obviously distribute themselves at equal distance span, which means that the distance span between the strong earthquakes resembles equal wave length during the folding of geological strata. We have studied all of the M8 earthquakes occurred in China during history. We found that before or after each earthquake (M8), another earthquake (M7.5) generally occurred at a definite distance away. The distance span has two predominant distributions, one at a shorter distance of 480—550km, the other at a longer distance of about 1100km (the latter distance is about twice the former).We take for a preliminary discussion the buckling process of a simple cylindrical shell under compression in the axial direction. From analysis we know that, whenthe cylindrical shell buckles, the buckling wave length (1/2λ≈1.72 \sqrtRh ) was de-termined only by the radius of the cylinder and the thickness of the shell. Now if we substitute R=6000 km; h=15 km, the halfwave length will be 530km. It agrees with the distance span for strong earthquake distribution.So we have the tentative opinion that the character of earthquakes distribution is controlled by crustal buckling.

     

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