青藏高原东北缘推覆体构造稳定性定量化评价——以龙门山推覆体为例

2008年5月12日汶川特大地震震害调查及分析表明，目前以活动断裂和历史地震调查为重点的工程区域构造稳定性评价方法存在漏判与误判特大地震问题，从而为工程安全埋下重大安全隐患。以龙门山活动推覆体为例，在已有研究成果基础上，利用岩体结构控制论、拜尔利定律等普适性原理对龙门山地壳岩体结构力学特征、控震结构面的抗剪强度与地震震级的线性相关性、地震震级与抗震设防烈度的关系进行了定量研究，对评价区域构造稳定性的关键问题进行了探讨。结果表明,推覆体型活动地块边界带中的滑脱层是对推覆体区域构造稳定性起主要控制作用的构造结构面--控震结构面，地震震级与滑脱层的埋深、抗剪切强度存在显著相关性：8级地震的震源深度接近20 km、7级地震的震源深度接近14 km、6级地震的震源深度接近10 km,据此对研究区及邻近的古地震进行了深度核定，圈定了龙门山活动推覆体-岷山地块的6级以上强震可能发生的范围、对应Ⅶ－Ⅺ度的抗震设防烈度范围。此研究成果弥补了以往根据活动断裂-发震断裂-历史最大震级与对应地震烈度评价工程区域构造稳定性，因历史地震资料疏漏不全、活动断裂带研究平面与深度范围局限以及忽视区域构造稳定性的岩体力学实质而导致评价结果常常出现误判与漏判的诸多缺陷。

Quantitatively Study on Regional Tectonic Stability Evaluation at Nappe Boundary Zones in Northeast Margin of Qinghai-Tibet Plateau: Longmenshan Nappe as an Example

Investigation and analysis on 2008.5.12 Wenchuan earthquake damages shows that some  major security hidden trouble problems for projects will leave out because of misjudging large earthquake by means of taking investigation based on active faults and historical earthquakes as the key evaluation method for engineering regional tectonic stability. Taking Longmenshan active nappe as an example, based on the research results on the crustal rock mass structure, new tectonic activities, historical earthquakes, using rock mass structure cybernetics, Byerlee’ law, mechanics characteristics of the Longmenshan crustal rock mass, the relationship between the shearing-slip strength of the controlling-seismic structural layer and earthquake magnitude, the relationship between earthquake magnitude and the seismic fortification intensity are quantitatively studied, the key problems to assess the regional tectonic stability are discussed. The main result is that the detachment layer within nappe boundary zone plays a main control role which is called a control shock layer. There is significant correlation among the earthquake magnitude, buried depth of the detachment layer and shear strength, namely, 8 earthquake focal depth close to 20 km, 7 earthquake focal depth close to 14 km, 6 earthquake focal depth near 10 km. Based on depth of ancient earthquakes ratified, possible scope of 6 above earthquakes and corresponding seismic fortification intensity are delineated in Longmenshan nappe-Minshan block and adjacent area. The result makes up drawbacks of the previous evaluation method based on the relation among active fault, seismogenic fault, historical maximum magnitude and corresponding seismic intensity, in which such problems as oversight of historical earthquakes, limit of scope and depth of fault zone and ignore the essence of rock mass mechanics in regional tectonic stability for proposed construction project lead to miscarriage of justice and leakage evaluation.