青藏高原东缘活动断裂带地壳岩体构造损伤特征与模式讨论

TECTONIC DAMAGE OF CRUSTAL ROCK MASS AROUND ACTIVE FAULTS AND ITS CONCEPTUAL MODEL AT EASTERN MARGIN OF TIBETAN PLATEAU

活动断裂带强烈复杂的构造运动会对地壳岩体产生不同程度的损伤,这些损伤能够显著影响地震破裂、地貌演化和地质灾害等地质过程,并对工程岩体稳定有较大影响,但目前鲜见对大型活动断裂地壳岩体构造损伤的深入研究。本文首次提出地壳岩体构造损伤的科学概念,揭示其具有不可逆性、累积性、非均匀性与愈合性。通过对青藏高原东缘鲜水河断裂带等6条主要活动断裂带大范围岩体露头的实测分析,采用构造结构面面密度作为表征构造损伤的定量指标,将断裂带地壳岩体划分为损伤带与围岩,测得最宽损伤带达3100 m。分析了地壳岩体损伤分布特征、变形破裂特征和损伤分布影响因素,取得如下认识:(1)损伤带主要沿活动性较强的主断裂分布,其内部具有高、低损伤区交替的分区损伤特征;(2)损伤带与围岩岩体分别表现为高应变速率与低应变速率状态下脆性损伤特征,损伤带的形成与断裂近期区域应力场密切相关;(3)表征断层发展阶段的累积位移量控制损伤带的总体规模,而其局部变化主要受控于断裂的几何展布与岩石性质;(4)提出了典型活动断裂带地壳岩体构造损伤模式。研究成果可为地震动力学、构造地貌、地质灾害和大型工程建设等提供约束地壳岩体结构的科学证据,有助于深化对活动断裂带地壳岩体力学环境的认识和理解。

The strong and complex movement of active fault zones inevitably causes different degrees of damage to the crustal rock mass.These damages can significantly affect the processes of earthquake rupture,geomorphic evolution,geological disaster,and engineering rock mass.However,the tectonic damage of crustal rock mass around large active faults is still not well understood.The concept of the tectonic damage of crustal rock mass is firstly proposed.The tectonic damage is irreversible,accumulative,heterogeneous,and healable.We measure tectonic discontinuities of the outcrops in the six major fault zones on the eastern margin of the Tibetan Plateau.They are the Xianshuihe fault zone,the Longmenshan fault zone,the Anninghe fault zone,the Daliangshan fault zone,the Zemuhe fault zone,and the Xiaojiang fault zone.The crustal rock mass outside fault core can be divided into a damage zone and wall rock according to the intensity of tectonic discontinuities.This intensity is a quantitative index of tectonic damage.Then we analyze the spatial pattern,the characteristics of damage,and the influence factors of the tectonic damage of crustal rock mass.The main conclusions are as follows:(1)Damage degree shows a decrease with perpendicular distance from the main fault trace.High damage areas alternate with low damage areas in the damage zone.The widest damage zone is 3100 m;(2)The rock mass in damage zone and wall rock is damaged in brittle regime at high strain rate and low strain rate,respectively.And the orientations of tectonic discontinuities in damage zone show a strong correlation with recent crustal stress field;(4)The cumulative displacement that characterizes the development stage of faults determines the scale of the damage zone,and the local variations are mainly controlled by fault geometry and lithology;(5)A new conceptual model based on cumulative displacement,fault geometry,lithology,and depth is proposed to explain the pattern of the tectonic damage of crustal rock mass around the active fault zone.This study can provide evidences for constraining the structure of crustal rock masses in seismic dynamics,tectonic geomorphology,geological disaster,and engineering,and help to deepen the understanding of the crustal rock mass of active fault zones.