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

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.