Receiver function structures beneath the Haiyuan fault on the northeastern margin of the Tibetan plateau

We performed a receiver function analysis on teleseismic data recorded along two dense seismic profiles and from 4 broadband regional seismic stations across the northeastern Tibetan plateau.The crustal thickness and vP/vS ratio were measured by the H-κdomain search algorithm.The Moho discontinuity across the Haiyuan arc fault zone was also revealed by common conversion point(CCP)imaging.Our study results show that the crustal thickness and the vP/vS ratio were 42–56 km and 1.60–1.88,respectively.The crustal thickening on the northeastern margin indicates that the crust is shortening or that there was a superimposition of crusts during the collision of the Tibetan plateau with Eurasian block.Our results suggest that Haiyuan fault likely resulted from the interactions of high temperature and pressure conditions during the collision of the Indian and Asian continents.The Moho beneath the Haiyuan tectonic region exhibits an obvious offset and a vague discontinuity according to CCP imaging.This study suggests that the Haiyuan arc fault zone is a trans-crustal fault that cuts through the Moho in the northeastern Tibetan Plateau.Moreover,there are indications of strong deformation in the intensive crustal extrusion from the interior of the Tibetan Plateau to its northeastern margin.

Interseismic deformation rate of the Haiyuan fault system based on the modified SBAS method

Radar interferograms are usually influenced by factors such as atmospheric artifacts,orbital errors,and terrain errors.It is difficult to reduce the influence by using the conventional small baseline subset(SBAS)method when determining the deformation rate.This study uses the adjustment model with systematic parameters to improve the conventional SBAS method and employs it to determine the interseismic deformation rate of the Haiyuan fault system,providing a data reference for exploring the locking depth,strain accumulation state,and potential seismic risk assessment of different segments of the Haiyuan fault system.The results are as follows:(1)the simulation experiment verifies the feasibility and robustness of the modified SBAS method.This method can effectively reduce the influence of residual signals such as atmospheric artifacts,orbital errors and terrain errors in the interferograms.The deformation rate map can be significantly improved;(2)the deformation rate field in the radar’s Line of Sight(LOS)direction shows that there are obvious differences between the north and south sides of Haiyuan fault system,which is consistent with the characteristics of the left-lateral strike-slip movement of the Haiyuan fault system.The deformation rate field and profiles reflect the complex trends among different segments of Haiyuan fault system in detail.(3)the deformation rate of the Jingtai pull-apart basin is higher than that of the surrounding areas,possibly indicating strong regional activity,which provides a reference for studying the seismic risk of the Jingtai pull-apart basin;and(4)the interseismic deformation rate and profiles across the fault show that the middle section of the Lao Hu Shan(LHS)segment and the western and middle sections of the Haiyuan segment are locked.

Dual threshold search method for asperity boundary determination based on geodetic and seismic catalog data

As an important model for explaining the seismic rupture mode,the asperity model plays an important role in studying the stress accumulation of faults and the location of earthquake initiation.Taking Qilian-Haiyuan fault as an example,this paper combines geodetic method and b-value method to propose a multi-source observation data fusion detection method that accurately determines the asperity boundary named dual threshold search method.The method is based on the criterion that the b-value asperity boundary should be most consistent with the slip deficit rate asperity boundary.Then the optimal threshold combination of slip deficit rate and b-value is obtained through threshold search,which can be used to determine the boundary of the asperity.Based on this method,the study finds that there are four potential asperities on the Qilian-Haiyuan fault:two asperities(A1 and A2)are on the Tuolaishan segment and the other two asperities(B and C)are on Lenglongling segment and Jinqianghe segment,respectively.Among them,the lengths of asperities A1 and A2 on Tuolaishan segment are 17.0 km and 64.8 km,respectively.And the lower boundaries are 5.5 km and 15.5 km,respectively;The length of asperity B on Lenglongling segment is 70.7 km,and the lower boundary is 10.2 km.The length of asperity C on Jinqianghe segment is 42.3 km,and the lower boundary is 8.3 km.

A joint InSAR-GNSS workfow for correction and selection of interferograms to estimate high-resolution interseismic deformations

Knowledge of the spatial distribution of interseismic deformations is essential to better understand earthquake cycles.The existing methods for improving the reliability of the obtained deformations often rely on visual inspection and prior model corrections that are time-consuming,labor-intensive,and do not consider the spatial distribution of interseismic deformations.Interferometric Synthetic Aperture Radar(InSAR)data provides wide-scale coverage for interseismic deformation monitoring over a wide area.However,the interseismic signal featured as millimeter-scale and long-wave deformations is often contaminated with noise.In the present study,a new workfow to correct the interferometric phase and quantitatively select interferograms is proposed to improve the accuracy of interseismic deformation measurements.Initially,the Generic Atmospheric Correction Online Service(GACOS),Intermittent Code for Atmospheric Noise Depression through Iterative Stacking(I-CANDIS),and plate model are combined to correct the atmospheric screen and long-wave ramp phase.Subsequently,the Pearson’s Correlation Coefcient(PCC)between the interferometric phase and the Global Navigation Satellite System(GNSS)constrained interseismic model as well as the STandard Deviation(STD)of the interferometric phase are introduced as criteria to optimize the selection of interferograms.Finally,the intermittent stacking method is used to generate an average velocity map.A comprehensive test using Sentinel-1 images covering the Haiyuan Fault Zone validate the efectiveness of our workfow in measuring interseismic deformations.This demonstrates that the proposed joint InSAR-GNSS workfow can be extended to study the subtle interseismic deformations of major fault systems in Tibet and worldwide.

The impacts of base level and lithology on fluvial geomorphic evolution at the tectonically active Laohu and Hasi Mountains,northeastern Tibetan Plateau

Previous researches had emphasized tectonic impacts on the fluvial system at the tectonically active areas,while the effects of lithology and local base level change have received relatively rare attention.Here we investigated fluvial landforms at different spatial scales,focusing on knickpoints and channel network reorganization from an area affected by the Haiyuan Fault in the northeastern Tibetan Plateau.The geomorphic indices,i.e.,drainage pattern andχanomalies,were calculated and investigated.The results show that two regional radial drainages formed around the Laohu and Hasi Mountains.Within the interior of the radial drainage,tributaries from the southeast side of the Laohu Mountain experienced near 180°direction change.We interpret this as the gradual drainage capture originating from the height difference(~190 m)of the local base level between the two catchments.Some tributaries from the Hasi Mountain show alternating gorges and broad valleys controlled by lithology.Besides,tectonic uplift and the lowering of base level(from the incision of the Yellow River)triggered an autogenic positivefeedback transition from parallel to dendritic drainage patterns.These observations suggest that base level change and lithology play a crucial role in landscape evolution,even in a tectonically active region.