报告地点：教学行政楼 706 会议室
报告时间：2024-05-31 从 15:00 到 16:30
报告人：焦利青（中国地质科学院深地科学与探测技术实验室）
报告人简介：
焦利青，中国地质科学院研究员；曾在新加坡南洋理工大学土木与环境工程学院项目工作员以及在南洋理工大学新加坡地球观测研究所博士与博士后，法国巴黎地球物理研究所合同研究员与教师研究员。曾受邀在加州理工学院，法国科学院里昂一大，格勒诺布尔阿尔卑斯大学，南希洛林大学，道达尔石油公司研究院，北京大学，南京大学，中国科技大学等等多次访问并给多个受邀报告。主要研究领域为运用数值方法研究印亚板块碰撞下喜马拉雅弧形山脉的形成机制；印亚板块碰撞下的大陆构造变形以及火山喷发过程中断裂变形；运用数值方法研究印尼苏门答腊俯冲带区域的地震周期；以及走滑断层地表破裂数值模拟研究与力学分析。部分研究成果发表于PNAS, JGR, EPSL, GRL, Tectonophysics, Acta Geologica Sinica 等国内外知名杂志。
报告题目：The shape of the Himalayan “Arc”: an ellipse pinned by syntaxial strike-slip fault tips
报告内容简介
Trans-Himalayan GPS data confirms that, between both syntaxes, India/Asia convergence is steadily oriented ≈ N20°E, perpendicular to the range trend. However, measurements of co-seismic and Holocene surface faulting near both syntaxes, along the 2005 and 1950 earthquake ruptures, imply long-term thrusting directed ≈ 130° apart, and post-LGM shortening rates of only ≈ 5-6 mm/yr, ≈ 2 to 3 times slower than in Nepal (≈ 15-20 mm/yr). Syntaxial earthquakes' return-times are also ≈ 3 times longer (> 2000 yrs) than those in Nepal (≈ 700 yrs). In a structural frame centered halfway between the syntaxial cusps, the tectonic features of the range show remarkable symmetry. In map view, the overall shapes of the Main Frontal Thrust (MFT) and the Main Central Thrust (MCT) closely fit ellipses, with major-to-minor axis ratios of ≈ 2.5 to 3. This suggests that the range growth atop subducting India was “pinned” by the strike-slip faults that bound it to the east and west. 3D Discrete Element Modelling corroborates a late-Tertiary elliptical range growth. This accounts for the ≈ 65° angles and 2-3-fold decrease in active thrusting between Nepal and the syntaxis, for the maximum Himalayan heights (≥ 8000 m), larger magnitudes (≥ 8), and shorter return times (≈ 700 years) of great earthquakes in Nepal, for the existence of two 500 to 600 km-long, south-concave mountain ranges north of both syntaxes and for the ≈ 9 mm/yr, N100-110°E extension across southern Tibet. It also suggests that predictions of impending or frequent great earthquakes in the eastern- and westernmost Himalayas may be overstated. In this talk, Dr Jiao will analyze geometry/kinematics of the entire range and of its two main megathrusts (MFT and MCT), in keeping with broad-scale, along-strike geodetic measurements, earthquake’s focal mechanisms and field-studies of thrust faulting. She will show by using a simple, planar, laterally bounded Discrete Element Modelling (DEM) simulation, that, as predicted by solid mechanics, the range’s shape and growth best fit those of ellipses pinned at both syntaxes by ≈ NS, nearly orthogonal, conjugate strike-slip fault tips. Dr. Jiao will also discuss the mechanisms behind the formation of the Himalayan Arc.