Seismites(地震岩)等术语的概念与名称

seismites,按其字面意思理应翻译成地震岩,即与地震有成因联系或受发震断裂改造、变形的岩石。按发震时地质材料的固结程度与力学性质,地震岩可分为震积岩(地震时尚未固结成岩的含水沙土层,即软沉积物)和脆性断层岩(地震时已经固结成岩的沉积岩、岩浆岩和变质岩)。脆性断层岩包括断层角砾岩、碎裂岩、超碎裂岩、假熔岩和断层泥等。发育由沙土液化形成的软沉积物变形构造的沉积岩,统称为“沙土液化岩”(liquefactites),但是长期以来一直被误译为seismites。大量的研究表明,并不是所有的沙土液化和软沉积物变形都是由地震造成的,也并不是所有地震都能导致沙土液化。只有那些所在区域存在重要发震断层、真正由地震引起的区域性的沙土液化造成的软沉积物发育变形构造的岩层才能称之为震积岩(seismic liquefactites)。震积岩不应再翻译成seismites。零星出现的软沉积物变形构造与沙土液化构造(例如:砂涌丘)不足以作为古地震的证据。

On Seismites,Liquefactites and Fault Rocks

Seismites are tectonites or fault rocks that were deformed in a brittle manner by seismic faulting in the Earth’s lithosphere. They broadly include seismic liquefactites (soft sediments such as water-saturated sandy soils) and brittle fault rocks such as incohesive breccia, cataclasite, ultracataclasite, pseudotachyllyte and fault gouge (solid state sedimentary, igneous and metamorphic rocks). The sedimentary rocks that developed liquefaction-induced soft-sediment deformation structures, which have long been erroneously called ‘seismites’ in the literature, should be named as liquefactites. A large number of studies have shown that soil liquefaction and soft-sediment deformation structures can be caused not only by seismic shaking but also by any other instability events in various geological settings (e.g., water waves, tides, floods, ice floes, upward escape of water, differential stress-induced lateral displacement, landslides, and mudflow). Furthermore, not all earthquakes can cause liquefaction, depending on their moment magnitudes, the distances from the seismic fault, the thickness, water content and properties of the sediments (e.g., grain size distribution, porosity, and grain surface roughness) and the vertical overburden stress. Only the earthquake-induced liquefaction deposits can be called seismic liquefactites, which should be mainly distributed about a regionally important seismic fault associated with brittle fault rocks such as gouge, breccia, cataclasite and pseudotachylyte. A sporadic occurrence of small scaled soft-sediment deformation structures and sandy liquefaction structures (e.g., sand blows) are not sufficient evidence to support the presence of paleo-earthquakes.