| The Upper Minjiang Basin,located in the eastern Tibetan Plateau,is characterized by complex rugged terrains,and vulnerably subjected to geological hazard such as landslides.Surface deformation monitoring plays an important role in predicting landslides,and thus it is quite beneficial and necessary to explore distribution characteristics of surface deformation and its underlying regulating factors.However,the interal and external factors of landslides in this area is quite complicated,so it is difficult for regional field investigation with conventional in-situ methods.Therefore,satellite remote sensing,with the spatial advantage,can provide the efficient approach for analyzing regional surface deformation,which may reveal associations of surface deformation with ecological environment factors.Based on interferometric synthetic aperture radar data,this study used the small baseline subset(SBAS-In SAR)method to detect possible surface subsidence during the period of 2015-2019.Then the distribution characteristics of high risk areas of deformation were explored,and the relations between subsidence and environment factors were also discussed.The folowing results were reached:(1)The average subsidence rate along the radar sight is-0.03 mm/a,and most areas are in relatively high surface stability.But distinct spatial differences in surface deformation are observed.The fast subsidence rate and the high-risk landslide areas are widely distributed in the slopes of typical river valleys,most of which are southward.(2)The topographic influence on landslides is relatively limited and has the difference in slope aspects.Due to the aspect effect of hydrothermal conditions,the count of fast decending points on sunny slope is about twice of that on shady slope.The average deformation rate of sunny slope is-33.02 mm/a,while the rate of shady slope is-9.33 mm /a.The south(sunny)slope experiences the higher subsidence rate than the north(shady)though with similar elevation.The topographic slope also exerts a certain control influence on landslides,and the slope in the range of 20°～45° is more likely to induce landslide hazard.(3)Mainly regulated by water and heat conditions combinedly,vegetation shows distinct aspect characteristic,and thus the vegetation effect on surface stability also exhibits aspect related difference.In the study area,sunny slopes are dominated by grassland,while forest as the main vegetation covers on shady slopes.In terms of the surface stability due to vegetation protection,the subsidence rate is highly correlated with the factor C of vegetation cover(R~2=0.85,p<0.005),which reflects the sparse vegetation cover usually responded by distinct subsidence.(4)Precipitation is one of main factors inducing landslides.As the vapour of precipitation mainly comes from the southeast,the annual precipitation and intense precipitation are more in the south than in the north.The physical erosion induced by orographic rain is not beneficial to the stability of south slopes.As for seasonality in precipitation,landslides triggered by intense rainfall occur frequently in summer,and the continuous low intensity precipitation in summer may also cause the acceleration of slow-moving landslides.(5)The influence of human activities on surface stability is also typically characterized by terrain aspect.Cultivated land and residential areas are mostly distributed on sunny slopes due to the preferable condition of solar radiance,but the acitivties of cultivation and construction generally weaken the stability of sunny slopes.In conclusion,this paper revealed the aspect difference in surface subsidence in the upper Minjiang region and the underlying envirometnal regulation of topography,precipitation,human activities and other factors.Our study emphasized the distinct vulnerability in surface stability of south slopes in this region,which should be carefully taken into account in hazard mitigation and avoidance. |
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