Activity of the eastern Karakoram - Jiali fault zone in Tibet
Date Issued
2014
Date
2014
Author(s)
Chung, Ling-Ho
Abstract
The Karakoram-Jiali fault zone (KJFZ) is the only major dextral fault system in Tibet, and plays an important role in the eastward extrusion of the Tibetan Plateau. Armijo et al. (1989) first recognized the KJFZ and proposed it as the structural boundary along which eastward movement of the Qiangtang terrane relative to the Lhasa terrane. This study focus on the activity of the eastern KJFZ, including with the Jiali fault (JF) and the Gyaring Co fault (GCF). Using high resolution satellite images, I was able to remap those two faults. Several geochronological methods are used, including radiocarbon, in-situ cosmogenic exposure, and optically stimulated luminescence (OSL). The GCF, one of the en echelon faults of the KJFZ, has been reported as a dextral fault, striking N50°-60°W. According to our OSL ages, a slip rate of the GCF can be estimated as 14.6 ± 3.1 mm/yr since ca. 50ka. This study also focuses on a section of the western segment of the GCF, where the slip has been recognized to have occurred 3.0 ± 1.6 m more than 7 times. This ~3 m slip implies Mw 7.2-7.4 earthquakes recurring to the western segment in every 200 yrs, and may reach about Mw 7.7 if both segments break at the same time. Along JF, the main Jiali fault has become less active since ca. 20ka. The field investigation shows there may have been only one small possible event during the Holocene, but none in the Late Pleistocene. The Nagqu fault (NF), previously mapped as the horsetail branch of the JF, shows many evidences to indicate that it is an active fault. The slip rate of the NF is 13~26 mm/yr, as fast as the GCF.
The GCF and the NF are similar to another en echelon minor fault, named the Beng Co fault (BCF), which was located on the 1951 M8 event. Such a high slip rate suggests that the central en echelon minor faults of the original KJFZ are kinematically different from the Karakoram and Jiali faults. Turning to inactive along the main Jiali fault may be attributed to the orientation of the Jiali fault, which is parallel to the extensional axis and has no differential stress acting across it. On the other hand, the en echelon faults play essential roles in accommodating the stress in a certain tectonic system.
Subjects
活動斷層
西藏
特徵地震
Type
thesis
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