Source models for the 2016 Mw6.0 Hutubi earthquake, Xinjiang,China: A possible reverse event

South and north-dipping nodal planes from the U.S. Geological Survey moment tensor solution were used to invert global teleseismic body waves to reveal the source rupture process of the December 8, 2016, Mw6.0 Hutubi earthquake. The results show that a compact pattern is the main feature of this event for only one main slip zone located at the hypocenter for both models, The slip distributions are dominated by a nearly pure-thrust fault, and there is no apparent surface rupture. The inversion revealed that the slip zone extends 10 km along strike and 12 km along dip. The released total seismic moment was about 9.0 -1017 Nm, corresponding to a magnitude of Mw6.0. It is difficult to solve for a best-fit rupture plane due to the sample slip pattern without obvious rupture directivity. This makes the far- field teleseismic data not sensitive enough to determine the fault geometric parameters. The source model of the reverse north-dipping plane fits well with the observed waveforms, and the results of the aftershock relocation outline a trend of north-dipping profiles, indicating the possibility of a reverse event. The inverted normal fault beneath the Qigu fold, interpreted by geological and seismic studies, may be the seismogenic fault for this reverse event.

Coulomb stress evolution along the Kongur Extensional System since 1895 and present seismic hazard

The present-day tectonic activities on the northeastern margin of the Pamir Plateau are mainly E-W oriented extensions, among which the Kongur Extensional System(KES) plays an important role in the internal expansion of the Pamir. As the largest earthquake since Taxkorgan earthquakes in 1895 and 1896, the Aketao earthquake occurred on the Muji fault on the northern portion of the KES in 2016. Since then, the trend of seismic activities along the KES has been paid much attention to. Based on the visco elastic layered lithosphere model, we calculate the co-seismic and post-seismic stress changes caused by five historical earthquakes on the KES and its adjacent areas since 1895, and analyze the interaction among strong earthquakes. The results show that all of the historical earthquakes after 1895 occurred in the areas where the co-seismic and post-seismic Coulomb stress increased. Coulomb stress loading at the hypocenters of the 1896 Taxkorgan earthquake, the 1974 Markansu earthquake and the 2016 Aketao earthquake were 0.251 MPa, 0.013 MPa and 0.563 MPa, respectively. The three earthquakes were catalyzed by such variations. The historical earthquakes increased the stress state on most segments of the Southern Kungai Mountain fault and Kongur fault along the KES. In particular, we can identify 2 visible earthquake gaps with increasing seismic hazard formed on the Qimugan segment and Bulunkou segment of the KES. The Qimugan section and the Bulunkou section are located at the fault transition zone with concentrated stress and high extension rate, so great attention should be paid to their seismic hazard at present day.

Multiplicity of solutions to geophysical inversion reflected by rupture slip distribution of the 2015 Nepal earthquake

The equivalence of geophysical fields, the finiteness of measurements and the measurement errors make the result of geophysical inversion non-unique. For example, the measurements and inversion method used, the priori rupture model determined and the slip distribution smoothing factor selected will have significant influences on the earthquake rupture slip distribution. Using different data and methods, different authors have given different rupture slip distribution models of the 2015 Mw7.9 Nepal earth- quake, with the maximum slip ranging from 3.0 m to 6.8 m. In this paper, geometry parameters of the single rectangular fault model in elastic half-space were inferred constraining with the Global Posi- tioning System （GPS） and Interferometric Synthetic Aperture Radar （InSAR） coseismic deformations and bounding the slip with approximate average value; and then, the single rectangular fault was divided into multiple sub-faults, and the final slip smoothing factor, the final slip distribution and the maximum slip were determined with the misfit-roughness tradeoff curve, the cross-validation sum of squares （CVSS） and the third-party observation data or indexes being comprehensively taken into account. The results show that, the rupture of the Nepal earthquake extended by over 100 km east by south. The maximum slip of the earthquake was about 6.5-6.7 m, and most of the slip is confined at depths of 8 -20 kin, consistent with the depth distribution of aftershocks. The method for reducing the multiplicity of solutions to rupture slip distribution in this paper was ever used in inversion of rupture slip distri- bution for the 2008 Wenchuan and 2013 Lushan earthquakes, and the third-party measurement - surface dislocation has very large effect on reducing the multiplicity of solutions to inversion of the Wenchuan earthquake. Other priori information or indicators, such as fault strike, dip, earthquake magnitude, seismic activity, Coulomb stress, and seismic period, can be used for beneficial validation of and comparison with inversion results.

A study on the seismogenic structure of the 2016 Zaduo, Qinghai Ms6.2 earthquake using InSAR technology

On October 17th, 2016, a Ms6,2 earthquake occurred in Zaduo County of Qinghai Province, China. The aim of this study is to use synthetic aperture radar （SAR） technology aboard the Sentinel-lA satellite to obtain high-resolution co-seismic surface displacement data and then to confirm the geometric parameters of the fault and slip distribution model. To this end, linear and non-linear inversion algorithms based on an elastic half-space dislocation model were used. The results showed that a distributed slip model can explain the surface deformation field measured by InSAR very well. The surface deformation field caused by the earthquake was an oval-shaped region of subsidence with a maximum displacement of 5 cm along the line of sight of the radar waves. This earthquake was mainly the result of a normal-slip fault process with 72°N strike and 65% dip. The slip was mainly concentrated at depths of 9-15 kin. The maximum slip was 0.17 m, located at a depth of 12 km. The moment magnitude given by inversion was Mw5.9. This was basically in agreement with the moment magnitudes and surface magnitudes measured by USGS and CENC.

Measuring ground deformations caused by 2015 Mw7.8 Nepal earthquake using high-rate GPS data

The April 25, 2015 Mw7.8 Nepal earthquake was successfully recorded by Crustal Movement Observation Network of China （CMONOC） and Nepal Geodetic Array （NGA）. We processed the high-rate GPS data （1 Hz and 5 Hz） by using relative kinematic positioning and derived dynamic ground motions caused by this large earthquake. The dynamic displacements time series clearly indicated the displacement amplitude of each station was related to the rupture directivity. The stations which located in the di- rection of rupture propagation had larger displacement amplitudes than others. Also dynamic ground displacement exceeding 5 cm was detected by the GPS station that was 2000 km away from the epicenter. Permanent coseismic displacements were resolved from the near-field high-rate GPS stations with wavelet decomposition-reconstruction method and P-wave arrivals were also detected with S transform method. The results of this study can be used for earthquake rupture process and Earthquake Early Warning studies.

Source model of 2016 Mw6.6 Aketao earthquake,Xinjiang derived from Sentinel-1 InSAR observation

On 25 November 2016（14:24:30 UTC）, an Mw6.6 earthquake occurred in Aketao county of Xinjiang. We derived the coseismic deformation field of the earthquake from ESA’s Sentinel-1 B images and inverted the fault geometry and slip distribution by using a homogenous half-space elastic model and the Steepest Decent Method（SDM） program. The slip model shows that the rupture plane is about 68 km in length and 40 km in width and has an average strike of 105.2°SE and an average dip of 76.0°S. The average amount of slip is-0.16 m and the maximum amount of slip is 0.59 m. The estimated seismic moment is 1.31 × 1019 N·m and the corresponding moment magnitude is Mw6.68. The dislocation is mainly distributed in the depth of 5-22 km, where the rupture center is located at 39.170 E, 74.38°N, and a depth of-8.8 km, so this earthquake is a shallow earthquake. In terms of the tectonic settings, the earthquake was triggered by the release of residual stresses on the seismogenic Muji fault. The ruptures were stimulated simultaneously by the main shock, which made the slip distribution pattern of a strike-slip fault with a double fracture. Due to the tectonic setting and the seismic gap between the ruptures, the Muji fault would have a risk of rupture to some extent and trigger an earthquake in future.

The present-day kinematics of the Tianshan orogenic belt constrained by GPS velocities

Since the late Cenozoic,the reactivated Tianshan orogenic belt has accommodated crustal shortening exceeding 200 km,primarily due to the far-field effects of the India-Eurasia plate collision.However,the details of the strain partitioning in the Tianshan Mountain range remain elusive.We interpret a new compilation of GPS velocities covering the whole Tianshan range with a classic elastic block model.Compared to previous studies with a block modeling approach,the Tianshan orogenic belt is further subdivided into several blocks based on geological fault traces and a clustering analysis approach.In addition to obvious crustal shortening on the bounding thrust faults of the Tianshan,our inverted fault slip rates also reveal that faults within the Tianshan orogenic belt,such as the Nalati Fault and the southern margin of the Issyk-Kul Lake Fault,which plays a crucial role in accommodating the tectonic crustal shortening.In the 72°E-78°E region,the internal shortening rate within the mountain is approximately 5-7 mm/yr.Besides crustal shortening,strike-slip motion occurs on faults in the interior of the mountain range as well as in the foreland fold-and-thrust belts,especially in the southern margin of the Tianshan.These findings suggest that the crustal deformation in the Tianshan Mountain range is more complex than previously thought,and the oblique convergence between the Tarim Basin and the Tianshan probably results in both strike-slip and thrust motion.