Geophysical study of the structure and processes of the continental convergence zones: Alpine-Himalayan belt

Studies of the structure of the continental collision zones using seismic and body waves, theoretical modelling of the thermal regime of the convergence processes, and studies of earthquake mechanisms and deformation aspects of the model are covered

The 2001 M_w 7.6 Bhuj earthquake, low fault friction, and the crustal support of plate driving forces in India

We present a source model for the 2001 M_w 7.6 Bhuj earthquake of northwest India. The slip distribution suggests a high stress drop (~35 MPa) and, together with the depth distribution of aftershocks, that the entire crust is seismogenic. We suggest that the active faults have an effective coefficient of friction of ~0.08, which is sufficient for the seismogenic crust to support the majority of the compressive force transmitted through the Indian lithosphere. This model is consistent with the midcrustal depth of the transition from extension to compression beneath the Ganges foreland basin where India underthrusts southern Tibet. If the coefficient of friction were the more traditional value of 0.6, the lithosphere would be required to support a net force roughly an order of magnitude higher than current estimates in order to match the observed depth of the neutral fiber

Crustal Azimuthal Anisotropy Beneath the Southeastern Tibetan Plateau and its Geodynamic Implications

The fast orientation and magnitude of crustal azimuthal anisotropy beneath the southeastern Tibetan Plateau and adjacent areas are measured by analyzing the sinusoidal moveout of the P to S converted phase from the Moho. Beneath the tectonically active plateau, the mean magnitude is 0.48 ±Â 0.13 s, which is about twice as large as that observed in the stable Sichuan Basin (0.23 ±Â 0.10 s). The two areas are separated by the Longmenshan fault zone, a zone of devastating earthquakes including the 12 May 2008 MW 7.9 Wenchuan earthquake. Fault orthogonal fast orientations observed in the southern Longmenshan fault zone, where previous studies have revealed high crustal Vp/Vs and suggested the presence of mid-lower crustal flow, may reflect flow-induced lattice preferred orientation of anisotropic minerals. Fault parallel anisotropy in the central segment of the fault zone is most likely related to fluid filled fractures, and fault perpendicular extensional cracks are probably responsible for the observed anisotropy in the northern segment. The crustal anisotropy measurements, when combined with results from previous studies, suggest the existence of mid-lower crustal flow beneath the southeastern margin of the plateau. Comparison of crustal anisotropy obtained before and after the Wenchuan earthquake suggests that the earthquake has limited influence on whole crustal anisotropy, although temporal changes of anisotropy associated with the earthquake have been reported using splitting of shear waves from local earthquakes occurred in the upper crust

Geodetic constraints on the translation and deformation of India: implications for future great Himalayan earthquakes

Because the elastic deformation of rock is fundamental to the earthquake process, geodetic surface measurements provide a measure of both the geometrical parameters of earthquake rupture, and a measure of the temporal and spatial development of elastic strain prior to rupture. Yet, despite almost 200 years of geodesy in India, and the occurrence of several great earthquakes, the geodetic contribution to understanding future damaging earthquakes in India remains minor. Global Positioning System (GPS) geodesy promises to remedy the shortcomings of traditional studies. Within the last decade, GPS studies have provided three fundamental constraints concerning the seismogenic framework of the Indian Plate: its overall stability < 0.01 μstrainlyear), its velocity of collision with Asia (58 ± 4 mm/year at N44E), and its rate of collision with southern Tibet (20.5 ± 2 mm/year). These NE directed motions are superimposed on a secular shift of the Earth's rotation axis. As a net result, India currently moves southward at 8 ± 1 cm/ year. In the next few decades we can expect GPS measurements to illuminate the subsurface distribution and rate of development of strain in the Himalaya, the relative contributions of along-arc and arc-normal deformation in the Himalaya and southern Tibet, and perhaps the roles of potential energy, plastic deformation and elastic strain in the earthquake cycle

Tectonic signals documented in gravel and silt beds : A comprehensive review of the eastern Tibetan plateau

Acknowledgements This project was supported by the National Natural Science Foundation of China (42207239) and National Nonprofit Fundamental Research Grant of China, Institute of Geology, China Earthquake Administration (IGCEA1906). We gratefully acknowledge the editors of the journal and the anonymous reviewers for their useful and detailed comments and suggestions to improve the original submission.Peer reviewedPostprin

A Paleoseismic Record Spanning 2-Myr Reveals Episodic Late Pliocene Deformation in the Western Qaidam Basin, NE Tibet

Acknowledgments This research was inspired by Prof. Lin Ding's comments on the doctoral thesis proposal of Yin Lu in May 2014 at the Institute of Tibetan Plateau Research, China. We thank Profs. Todd Ehlers, Erwin Appel, and Oliver Friedrich for fruitful discussions in the early stage of this research. We appreciate the editor Germán Prieto for handling our manuscript, Jérôme Nomade and one anonymous reviewer for constructive reviews. We thank Werner Fielitz for comments, A. Koutsodendris, K. S. Nakajima, and H. Campos for help with lab work, and W. Rösler and H. Schulz for help with core sampling. Financial support was provided by the German Research Foundation (# FR2544/13-1 to O. Friedrich) and the University of Liege under Special Funds for Research, IPD-STEMA Program (R.DIVE.0899-JF-G to Y. Lu).Peer reviewedPublisher PD

About the lithospheric structure of central Tibet based on seismic data from the INDEPTH III profile

Signals from 11 shots and 8 earthquakes, and numerous teleseismic events were recorded along the 400-km seismic line INDEPTH III in central Tibet and interpreted together with previous seismic and tectonic data. The abnormal behavior of various mantle phases reveals a complex Moho-transition zone, especially in the northern part of the line, in the Changtang Block, where the lower crust and the mantle show unusually low velocities, a shingled appearance of Pn and no low-velocity layer in the upper crust. The strong east-west anisotropy in the Changtang Block is related to an easterly escape movement of the whole lithosphere, facilitated by the warm and weak layers in the lower crust and the upper mantle, bounded apparently by two prominent west-east running fault zones

Qinghai-Tibet Railway, China and the Solutions to Its Major Geotechnical Problems for Construction

The Qinghai-Tibet Railway (QTR) is the highest-elevation one for passenger trains in the world and the first railway to connect central China to Tibet. Construction of this railway starting in 2001 had to contend with major geotechnical challenges, such as permafrost, environmental protection and seismic hazards. Its completion in 2006 is a remarkable feat in the world’s railway construction history and crystallization of wisdom of human beings. In this paper, the planning and preparing history and the construction project of QTR are introduced. The major three thorny problems, permafrost, lack of oxygen and environmental frangibility for the construction and their solutions are presented, which are active methods of riprap roadbeds, heat pipe roadbed and bridges over land for permafrost, health care system for lack of oxygen and environmental protection measures for construction and operation. Seismic safety assessment was carried out for earthquake damage mitigation of the railway. The laboratory test, field test and observation, and it’s operation have shown that design, construction, and measures for earthquake hazards mitigation and environmental protection of the Qinghai-Tibet Railway are completely successful

Kinematic fault slip evolution source models of the 2008 M7.9 Wenchuan earthquake in China from SAR interferometry, GPS and teleseismic analysis and implications for Longmen Shan tectonics

The M_w 7.9 2008 Wenchuan earthquake ruptured about 280 km of faults in the Longmen Shan of Sichuan province, China, at the eastern edge of the Tibetan Plateau. We use teleseismic waveforms with geodetic data from Global Positioning System, synthetic aperture radar interferometry and image amplitude correlation to produce a source model of this earthquake. The model describes evolution of fault slip during the earthquake. The geodetic data constrains the spatial distribution of fault slip and the seismic waveforms constrain mostly the time evolution of slip. We find that the earthquake started with largely thrust motion on an imbricate system of faults beneath the central Longmen Shan, including the Beichuan Fault and Pengguan Fault, with fault slip at depth extending up to 50 km northwest of the mountain front. The fault ruptures continued northeast along the Beichuan Fault with more oblique slip (right-lateral and thrust) and the proportion of lateral motion increasing in the northern Longmen Shan. The northernmost fault segment has a much steeper dip, consistent with nearly pure strike-slip motion. The kinematic source model shows that the rupture propagated to the northeast at about 2.5–3.0 km s^(−1), producing a cascade of subevents with a total duration of about 110 s. The complex fault ruptures caused shortening and uplift of the extremely steep central Longmen Shan, which supports models where the steep edge of the plateau is formed by thrusting over the strong crust of the Sichuan Basin