A Seismic Design Method for Subsea Pipelines Against Earthquake Fault Movement

As there are no specific guidelines on design of subsea pipelines crossing active seismic faults, methods for land buried pipelines have been applied to. Taking the large seismic fault movement into account, this paper proposes improved methods for seismic designs of subsea pipelines by comprehensively investigating the real constraining of soil on the pipelines, the interaction processes of soil with the pipeline, the plastic slippage of the soil, and the elastic-plastic properties of the pipeline materials. New formulas are given to calculate the length of transition section and its total elongation. These formulas are more reasonable in mechanism, and more practical for seismic design of subsea pipelines crossing active faults.

The movement age of hidden fault and analysis on width of its effect zone from shallow seismic sounding and drilling data

Field experimental seismic sounding permitted us to obtain optimal shallow seismic reflection sounding parameters.In process of data processing,we obtained a high-qualitative shallow seismic reflection sounding profile by using the techniques such as filtering,edition surgical blanking,prediction deconvolution,fitting static correlation of first arrival time,and velocity analysis.Comprehensive analysis on the information of reflection wave groups along the seismic sounding profile and the stratigraphic and neogeochronological data obtained from many drills near the sounding line reveals that the upper termination of the detected fault zone is located at depth of 75~80 m,in the Middle Pleistocene deposits dated to be about 220 ka BP.The continuity,discontinuity,increasing and decreasing amount of reflection wave groups and change of their configurations,in combination with geological columns of drills,permitted us to know that the width of upper termination of the fault zone is 100 m.It can be inferred from the variation of number of reflection wave groups along the profile that the scarp of hidden fault is 200 m wide and the fault is a synsedimentary active fault in the Early Pleistocene and the early stage of Middle Pleistocene.No tectonic movement,which offset the covering deposits,had occurred since the late stage of Middle Pleistocene.

Response analysis of a submarine cable under fault movement

Based on the performance of submarine cables in past earthquakes, an analytical method to determine cable performance under seabed fault movement is proposed in this paper. First, common types of earthquake damage to submarine cables are summarized, which include seabed displacement induced by fault movement, submarine landslides and seabed soil liquefaction, etc. The damage is similar to damage observed to buried pipelines following land earthquakes. The Hengchun earthquake of Dec. 26, 2006 is used as a case study. The M7.2 earthquake occurred in the South China Sea at 20：26 Beijing Time, and caused 14 international submarine cables to sever and break. The results show that the proposed method predicts damage similar to that observed in the Hengchun earthquake. Based on parametric studies of the influence of the water depth and the magnitude of the submarine earthquake, countermeasures to prevent damage to submarine cables are proposed.

Robust inversion analysis of local gravity anomalies caused by geological dislocation model of faults

Theoretical analysis and practical observations show that fault dislocations can change the gravity field around the fault. Gravity changes which were caused by the repeated dislocations over a long period of time were superimposed on the Bougeur gravity anomalies. These anomalies became the evidence of historical movement of fault as well as provide a way for the study of paleo earthquakes. This paper investigates inversion methods for the geological dislocation modeling of faults using the local Bouguer's gravity anomalies. To remove the effects of the irrelevant part of gravity anomalies to fault movements, we propose the robust nonlinear inversion method and set up the corresponding algorithm. Modeling examples indicate that the Marquardt's and Baye's least squares solutions depart from the true solution due to the attraction of gross errors in the data. The more seriously the data is contaminated, the more seriously the solutions are biased. In contrast, the proposed robust Marquardt's and Baye's inversion solutions can still maintain consistency with the solution without gross errors, even though 50 percent of the data is contaminated. This indicates that the proposed robust methods are effective. Using the proposed methods, we invert the geological dislocation models of the faults around the Erhai Lake in West Yunnan. The results show that the Northern Cangdong fault and the Erhai fault are normal dip slip faults with about 4 to 5 km dislocations; and that the Southern Cangdong fault has a less dip slip compared with the former two. A satisfactory fitting between the theoretical values of the inversion solution and the actual local gravity field is achievable.

Synthetic aperture radar interferometry—based coseismic deformation and slip distribution of the 2022 Menyuan MS6.9 earthquake in Qinghai,China

On January 8,2022,a 6.9 magnitude earthquake occurred in Menyuan County,Qinghai Province,with the epicenter located at the intersection of the Tuolaishan Fault and the Lenglongling Fault,which are part of the Qilian—Haiyuan fault zone.This study investigated the sliding characteristics and seismic mechanism of the earthquake to understand the activity and seismic risk of the fault on the northeastern margin of the Qinghai—Tibet Plateau.This paper analyzed Sentinel-1 synthetic aperture radar images to obtain the coseismic deformation field of the earthquake,which was then used to invert the slip distribution of the seismogenic fault and the coseismic Coulomb stress on the surrounding faults caused by the earthquake.It was found that the earthquake was primarily characterized by sinistral strike-slip movement.Along the satellite line of sight,the south wall of the fault had a maximum deformation of 0.62 m,and the north wall had a maximum deformation of 0.48 m.The coseismic slip distribution results indicated that the maximum slip of the earthquake was 4.51 m,and the moment magnitude was MW6.7.The Coulomb stress analysis showed that the 2016 Menyuan earthquake promoted the occurrence of the 2022Menyuan earthquake.

Paleoseismic activity on Wujiahe segment of Serteng piedmont fault, Inner Mongolia

Geomorphic study on Wujiahe segment of Serteng piedmont fault, Inner Mongolia is made. Through analysis of the available data in combination with the results of predecessors studies it can be obtained that average vertical displacement rate is 0.48~0.75 mm/a along the Wujiahe segment since the late Pleistocene (14.450~22.340 ka BP) and 0.56~0.88 mm/a since the early-middle Holocene (5.570~8.830 ka BP). Analyzing paleoseismic phenomena revealed in the excavated 5 trenches in combination with the results of predecessors studies of paleoearthquakes on the fault, we determine five paleoseismic events on the Wujiahe segment of Serteng piedmont fault since 27.0 ka BP and the recurrence interval to be about 4.300~4.400 ka. A cluster of paleoearthquakes occurred probably during 8.000~9.000 ka BP and two paleoseismic events in 10.000~20.000 ka BP may be missed. A comparison between height of fault scarps and sum of displacement caused by paleoseismic events revealed in trenches, and recurrence interval of paleoseismic events obtained from average displacement rate along the fault and the disloca-tion by one event suggest that three paleoseismic events are absent in Alagaitu trench. Two paleoseismic events may be absent on the whole active fault segment.

Estimating the Degree of Earthquake Risk from Fault Characteristics

A theoretical model considering the relationship between fault characteristics and tectonic stress is proposed to quantify earthquake risk degree. The model is applied in practice to the fault along the southern margin of Weihe basin in Shaanxi Province, Northwestern China and fitted well with reality.