Neotectonic (Miocene to recent) vertical movements in the Lao Cai Basin (Red River Fault Zone, Vietnam): An approach to seismic hazard assessment

D.P. Phan^a, A.K. Tokarski^b, A. Swierczewska^c,⁎, P.J. Strzelecki^c, M. Waliczek^c,

M. Krapiec^c,N.Q. Cuong^d

• Institute of Marine Geology and Geophysics, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Viet Nam
• Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Kraków, Senacka 1, 31-002 Kraków, Poland
• AGH University of Science and Technology, Faculty of Geology, Geophysics and Environmental Protection, Al. Mickiewicza 30, 30-059 Kraków, Poland
• Institute of Geological Sciences, Vietnam Academy of Science and Technology, 84 Pho Chua Lang, Dong Da, Hanoi, Viet Nam

ABSTRACT

In this contribution, we present a model of the neotectonic (middle Miocene to recent) development of the LaoCai Basin located in the Vietnamese segment of the Red River Fault Zone. The model is constructed on the basisof the analysis of mixed-layered illite-smectite composition and vitrinite reflectance analysis of middle Miocenestrata. The model is supported by new data on small-scale brittle tectonic structures cutting these strata and issupplemented with C14 dates of Quaternary river terraces. Furthermore, we present the first evidence for paleoseismicitypredating the last hundred years in the Lao Cai Basin. Our results show that: (1) the Lao Cai Basin is agraben formed during the left-lateral shift along the Red River Fault Zone due to oblique slip on graben-boundingand graben-cutting strike-slip faults as well as dip slip on graben-cutting normal faults; (2) the exhumation of themiddle Miocene strata filling the graben might have amounted up to 2.4 km and took place during the rightlateralshift along the Red River Fault Zone, possibly being affected by the reversal of slip on graben-boundingand graben-cutting faults and, (3) the Lao Cai Basin was affected by M5+ earthquakes, whereas the returnperiod of such earthquakes is more than 370 years but less than ca. 2300 years. Moreover, we tentatively estimatethe late Holocene surface uplift rate in the Lao Cai Basin at ca. 7 mm/year.

Keywords:Red River Fault Zone, Exhumation, Fractured clasts, Seismic hazard, Late Quaternary tectonics

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Journal of Asian Earth Sciences: https://doi.org/10.1016/j.jseaes.2019.103885