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汶川地震破裂带上的近场震后变形,是一种震后的蠕滑行为,而且大部分表现为与同震滑移的方向相反.地震断层的活动通常划分成震前、同震、震后和震间4个阶段,反映了一次地震从孕育、发生到结束的整个演化过程,而不同活动阶段的变形特征反映出不同的应力状态和力学性质.汶川地震沿龙门山断裂带形成了两条长分别为250和72km的地表破裂带.为了了解汶川地震地表破裂带的震后变形特征,对中央主破裂带上人为破坏较轻的断层崖或断层挠曲崖进行反复测量,结果显示在19个观测点中,13个观测点(68%)的断层崖或断层挠曲崖的高度(垂直同震位移)震后降低回落,平均降低了9.7%;5个观测点(26%)没有发生变化;1个观测点(6%)的在震后继续抬升,抬升了12.8%,而且该观测点位于中央主破裂带的南西端部.尽管这种变化中存在着上冲断层盘虚假抬升后压实回落的影响,但主要是沿汶川地震破裂带发生的震后滑移造成的,而且大部分震后滑移(68%)与同震滑移的方向相反.除破裂端部存在同震位移亏损,弹性能释放不完全外,其他部位同震位移要么与震间累积达到平衡,要么过冲产生能量亏损,揭示了汶川地震的能量可能基本释放完全,发生7级以上强余震的可能性不大.此外,这种震后变形特征还告诉我们,在进行活动断层构造地貌研究时,特别是通过断层崖高度(或其他水平位错量)判断断层运动速率和估计古地震事件大小时,除侵蚀作用产生的误差外,还需要考虑10%左右来自震后滑移的系统误差.
The near-field post-earthquake post-earthquake deformation in the Wenchuan earthquake rupture zone is a kind of post-earthquake creep behavior, and most of them show the opposite direction of the coseismic slip. The seismic faults are usually divided into three types: pre-earthquake, coseismic, The post-earthquake and the epicenter 4 stages reflect the whole evolution process of an earthquake from inception to its occurrence, while the deformation characteristics in different stages reflect different stress states and mechanical properties. The Wenchuan earthquake formed two The length of the surface rupture zone of 250 and 72km respectively.In order to know the post-earthquake deformation features of the surface rupture zone of the Wenchuan earthquake, repeated measurements on the man-made damage of the central main rupture fault or the fault flexural cliff were carried out. Of the 19 observation points, the height (vertical coseismicity) of the fault cliffs or faulty flexure cliffs at 13 observation points (68%) decreased after the earthquake and averaged 9.7% lower; and the five observation points (26%) did not 1 observation point (6%) continued to rise up 12.8% after the earthquake, and the observation point is located at the south western end of the central main rupture zone, although there is a false uplift of the upwelling fault plate After the compaction down the impact, but mainly Resulting from the post-earthquake slippage in the Wenchuan earthquake rupture zone, and most of the post-earthquake slippage (68%) is opposite to the direction of the coseismic slip. Except for the loss of coseismic displacement at the end of the rupture, the elastic energy release is incomplete , Other parts of the coseismic displacement or balance with the cumulative earthquake balance, or overshoot energy loss, revealing the Wenchuan earthquake energy release may be complete, the occurrence of a strong aftershock 7 or more unlikely .In addition, this post-earthquake Deformation features also tell us that in the study of active fault tectonic geomorphology, especially when judging the fault movement rate and estimating the magnitude of paleoearthquakes by the height of the fault (or other horizontal dislocation), besides the error caused by erosion, It is necessary to consider about 10% of systematic errors from post-earthquake slippage.