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Associate Researcher Lu Renqi of IGL Paid an Exchange Visit to the Department of Geosciences of National Taiwan University

2016/12/30 8:35:24

At the invitation of Distinguished Chair Professor Mr. John Suppe of the Department of Geosciences of National Taiwan University, Associate Researcher Lu Renqi of IGL Research Room of Active Tectonics paid a 27-day exchange visit to National Taiwan University May 21~June 17, 2016. During this exchange visit, in-depth discussion and study was conducted mainly on 3D tectonic modeling of Lushan seismogenic structure and Tanlu fault zone, and preliminary result and cognition was achieved.

Firstly, the aftershock relocation data of the 2013 Sichuan Lushan Mw6.7 Earthquake was analyzed.  3D depiction of the seismogenic fault surface was conducted in Gocad software and a 3D space structure and model (Fig. 1) of “Y”-shaped active fault surface of Lushan Earthquake was established. Through double restraints of focal mechanism solution and man-made earthquake reflection characteristics, it is believed that Lushan Earthquake is a thrust fault developed on deep detachment layer (the depth is about 20km); the dip of the seismogenic fault is 45°-50°, and the tectonic style is fault-propagated drape; the structural interpretation tallies with coseismic deformation GPS and leveling data observation structure. The slip of the seismogenic fault is limited and terminated below Lower and Middle Triassic detachment layer. Based on the relevance between the geometric construction f the seismogenic fault and the deformation of local structure, the research explored the relation between shallow surface structure and deep structure and preliminarily believes the seismogenic fault of Lushan Earthquake may be an early normal fault, or thrust active fault formed by Cenozoic tectonic inversion. The research superposed and verified the published deep seismic sounding results, 2D man-made earthquake reflection profiles, drilling data, earthquake catalogue, and deep 3D seismic tomography, and further deepened cognition to the regional sedimentary-tectonic background of the seismogenic fault of Lushan Earthquake. Professor John Suppe gave many valuable suggestions on research approach and method (Fig. 2). During the research, fault-related drape theory and principle were applied to quantitatively analyze and calculate typical structures. The research revealed the earthquake region of Lushan has complex characteristics of multi-phase tectonics, layered detachment, and overlapped deformation.

Fig. 1. 3D tectonic characteristics of the seismogenic fault of the 2013

Lushan Earthquake and 3D display of its main fault surface

Fig. 2. Professor John Suppe carried out exchange and study in tectonic analysis and seismic structure model

Secondly, in respect to Tanlu fault zone tectonic segmentation model and 3D common fault model (CFM) to be established soon, the research preliminarily established a 3D seismic tomography database of Tanlu Fault Zone under the support of the data of global seismic network. By summarizing data of shallow surface geology, topography and geomorphology, and DEM, catalogue of historical earthquakes and distribution of main fractures,  3D structural interpretation work areas were established; next step, related research results will be collected and the existing fault interpretation models will be digitalized. With the help of Dr. Jonny Wu of National Taiwan University, Lu Renqi carried out in-depth study and exploration to SKUA-GOCAD 3D tectonic modeling technology and its software. During this exchange visit, Lu Renqi learned a lot  in the aspects of analysis of active tectonics, and modeling of seismic structure, which is great help and inspiration to future research.