Search

The Daliang Shan is a tectonic unit that connects the active southeastern Tibetan Plateau with the stable South China block. As a newly generated (formed later than the Xianshuihe–Xiaojiang active fault system) seismotectonic zone induced by the Tibetan tectonics, the detailed constraints of the crustal deformation are central to the understanding of the kinematics and dynamics of the Tibetan expansion. This paper establishes and analyses a high-spatial resolution global positioning system (GPS) velocity field from a dense GPS network in this region. Our modelling results indicate that, in contrast to the equivalent sinistral strike-slip rate of approximately 5 mm yr–1 on the Anninghe–Zemuhe and Daliangshan faults, their inferred interseismic locking depth varies within a large range. The southern segment of the Anninghe Fault and the middle segment of the Daliangshan Fault have deep locking depths of ∼13 km, indicating that the seismic risk is high in these areas. In addition, the detectable counter-clockwise rotation rate of 0.35 ± 0.12° Myr–1 of the Mabian block makes a significant contribution of ∼50 per cent to the strike-slip motion on its boundary faults. This counter-clockwise rotation may be induced by a left-lateral shear gradient with southeastward motion relative to the South China-fixed reference frame, indicating the significance of a simple-shear pattern in exploring the kinematics of the encroachment of the Tibetan tectonics upon a stable block (craton). [ABSTRACT FROM AUTHOR]

Tarim Craton is a Precambrian block situated in northwest China, just north of the Tibetan Plateau, where a large sedimentary basin with abundant hydrocarbon potential has developed. Accurate heat flow data for Tarim is vital for understanding the lithospheric evolution and hydrocarbon generation in this area; however, there were unavailable until now, due to a lack of high quality steady-state temperature logging data. Here, we report 10 new heat flow values derived from steady-state temperature logging and measured thermal conductivity data. New heat flow values range from 40.1 to 49.4 mW m-2, with a mean of 43.1 ± 3.0 mW m-2. In addition, radiogenic heat production from the sediments accounts for 20 per cent of the observed surface heat flow, whilst the mantle heat flow is estimated to be as low as 6-15mWm-2; this indicates a dominant contribution from crustal heat, to the observed heat flow. The average heat flow and crustal temperature in the Tarim Craton are markedly lower than those in the Tibetan Plateau, whilst the calculated rheological strength of the lithosphere, beneath Tarim, is sufficiently large to resist the elevation-induced gravitational potential energy difference between Tarim and Tibet. This inherited thermal and rheological contrast, between the craton and Plateau, can be traced back to before the India-Asia collision; this accounts for the differential active deformation pattern in the Tarim Craton and adjacent areas. [ABSTRACT FROM AUTHOR]

We use InSAR and body wave modelling to determine the faulting parameters for a series of five 5.9-7.1 normal faulting earthquakes that occurred during 2008, including the March 20 Yutian earthquake ( 7.1), one of the largest normal faulting events to have occurred recently on the continents. We also study three earlier normal faulting earthquakes that occurred in southern Tibet between 1992 and 2005. Coseismic deformation for each of these eight events is measured with ascending and descending interferograms from ENVISAT, ERS and ALOS SAR data. Elastic dislocation modelling of the line-of-sight InSAR displacements and body wave seismological modelling of and waves are used to estimate fault parameters and are found to be in good agreement for all the events studied. The use of InSAR to measure deformation allows a relatively precise determination of the fault location in addition to resolving the focal plane ambiguity. Only five of the eight events are associated with a clear surface topographic feature, suggesting that an underestimation of the amount of extension would result from using the surface expressions of normal faulting alone. The observations, in all cases, are consistent with slip on planar surfaces, with dips in the range 40-50°, that penetrates the uppermost crust to a depth of 10-15 km. We find no evidence for active low-angle (dip less than 30°) normal faulting. The contribution of the normal faulting to overall extension estimated by summing seismic moments over earthquakes for the past 43 yr is 3-4 mm yr−1, or 15-20 per cent of the rates of extension measured across the plateau using GPS. 85 per cent of the moment release in normal faulting over the past 43 yr has occurred in regions whose surface height exceeds 5 km. This observation adds weight to the suggestions that the widespread normal faulting on the plateau is the result of variations in the gravitational potential energy of the lithosphere. [ABSTRACT FROM AUTHOR]

The shallow seismic velocity structure of the Kunlun fault zone (KLFZ) was jointly deduced from seismic refraction profiling and the records of trapped waves that were excited by five explosions. The data were collected after the 2001 Kunlun Ms8.1 earthquake in the northern Tibetan Plateau. Seismic phases for the in-line record sections (26 records up to a distance of 15 km) along the fault zone were analysed, and 1-D P- and S-wave velocity models of shallow crust within the fault zone were determined by using the seismic refraction method. Sixteen seismic stations were deployed along the off-line profile perpendicular to the fault zone. Fault-zone trapped waves appear clearly on the record sections, which were simulated with a 3-D finite difference algorithm. Quantitative analysis of the correlation coefficients of the synthetic and observed trapped waveforms indicates that the Kunlun fault-zone width is 300 m, and S-wave quality factor Q within the fault zone is 15. Significantly, S-wave velocities within the fault zone are reduced by 30–45 per cent from surrounding rocks to a depth of at least 1–2 km, while P-wave velocities are reduced by 7–20 per cent. A fault-zone with such P- and S-low velocities is an indication of high fluid pressure because Vs is affected more than Vp. The low-velocity and low- Q zone in the KLFZ model is the effect of multiple ruptures along the fault trace of the 2001 Ms8.1 Kunlun earthquake. [ABSTRACT FROM AUTHOR]