构造稳定的西北印度克拉通拉贾斯坦邦的周期性地震活动

IF 1 Q4 GEOSCIENCES, MULTIDISCIPLINARY
H. Kumar, M. Pandit
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引用次数: 2

摘要

印度半岛地区由几个太古宙克拉通地块(Dharwar、Bastar、Singhbhum、Aravalli - Bundelkhand)组成,以元古代活动带为界。因此,该地区被认为是构造稳定的,并被指定为除仍然活跃的印度中部构造带(CITZ)外最不容易发生地震的地区。后者是印度南部和北部地块之间的主要缝合线。印度的地震活动在其北部和东北部(喜马拉雅)地区是常见的,这些地区界定了印度板块边缘,与欧亚(西藏)板块碰撞。由于构造活跃,这个地区有记录的频繁地震,包括一些高震级和破坏性的地震。西北印度地块是印度相对稳定的前寒武纪地区之一,被印度气象部门归类为II区,是地震最不脆弱的地区之一。然而,该地区一直是一个反复发生低到中等震级地震的地区。印度西北部拉贾斯坦邦的地震数据汇编记录了该地区在过去15年中至少发生了45次地震。其中有几次由于震级低而未被注意到。东北-西南走向的Aravalli山区(AMR)横跨拉贾斯坦邦的东半部,代表了印度西北部最重要的构造地貌特征。AMR是一个覆盖在太古宙基底(带状片麻岩杂岩- BGC)上的元古代Aravalli和Delhi超群岩石(变质沉积岩、火山岩和侵入岩)的集合。这些元古代的活动带经历了几次变形,形成了今天的地貌。该州西部的马尔瓦尔地块年龄相对较年轻,是在1ga俯冲事件期间被吸积到AMR的。AMR的西缘,又称西缘断裂,是两个地块之间的主要缝合线。然而,整个地区在元古代末被克拉通化,在显生宙期间保持构造稳定。太古宙基底和上覆的元古宙盖层发育多处大小断裂和剪切带。其中最突出的是与区域构造颗粒相对应的北东—南西走向的主界线和若干跨界的小界线。地震震中分布格局与这些特征有密切的空间联系。由于该地区没有任何重大的构造活动,并且由于岩浆活动或过度降雨导致孔隙压力上升,我们将该地区地震的复发归因于这些旧缝合线/较弱带的重新激活,这是对印度板块持续向北辐合导致印度板块北缘应力积聚的响应。西部的一些断裂可以追溯到南部的Cambay盆地活动断裂,这可能引发了拉贾斯坦邦西部的地震活动。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Recurrent seismicity in Rajasthan State in the tectonically stable NW Indian Craton
Indian peninsular region comprises several Archean cratonic blocks (Dharwar, Bastar, Singhbhum, Aravalli – Bundelkhand), bordered by Proterozoic mobile belts. Therefore, this region is considered as tectonically stable and designated as the least vulnerable region to earthquake hazard except the still active Central Indian Tectonic Zone (CITZ). The latter is a major suture between southern and northern Indian blocks. Seismicity in India is common along its northern and northeastern (Himalayan) region defining the Indian Plate margin, in collision with the Eurasian (Tibetan) Plate. Being tectonically active, this region has a documented record of frequent earthquakes including some high magnitude and devastating ones. The northwestern Indian block is amongst the relatively stable Precambrian regions of India and categorized under Zone – II by the Indian Meteorology Department, one of the seismically least vulnerable regions. However, the region has been a site of recurring low to moderate magnitude earthquakes. Compilation of the earthquake data from the Rajasthan State in NW India documents at least 45 earthquakes in this region during the last one and a half decades. Several of these have remained unnoticed because of their low magnitude. The NE –SW trending Aravalli Mountain Region (AMR), running across the eastern half of Rajasthan State represents the most significant tectonomorphic feature of NW India. The AMR is an ensemble of Proterozoic age Aravalli and Delhi Supergroup rocks (metasediments, volcanics and intrusives) that overlie an Archean basement (Banded Gneissic Complex – BGC). These Proterozoic mobile belts have evolved through several episodes of deformation that have shaped its present day geomorphology. The western part of the State, the Marwar Block, is relatively younger in age and was accreted to the AMR during the 1 Ga subduction event. The western margin of AMR, also called as the Western Margin Fault, represents a major suture between the two terranes. However, the entire region was cratonized by end Proterozoic and has remained tectonically stable during the Phanerozoic Eon. The Archean basement and overlying Proterozoic cover rocks are infested with several major and minor faults and shear zones. The most prominent ones are the NE-SW trending major lineaments corresponding with the regional tectonic grain and several minor ones across. The earthquake epicenter distribution pattern shows a close spatial association with these lineaments. In the absence of any significant tectonic activity in the region and rise in pore pressure either due to magmatism or excessive rainfall, we attribute recurrence of earthquakes in the region to reactivation of such old sutures/weaker zones as a response to stress build-up along the northern margin of the Indian Plate resulting from ongoing northward convergence of the Indian Plate. Some of the faults in western part are traceable into the Cambay Basin active faults in the south that may have triggered seismic activity in western Rajasthan.
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来源期刊
Iranian Journal of Earth Sciences
Iranian Journal of Earth Sciences GEOSCIENCES, MULTIDISCIPLINARY-
CiteScore
1.40
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12.50%
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