Fault Dip Angle Research Articles

Joint Inversion of GPS, Leveling, and InSAR Data for The 2013 Lushan (China) Earthquake and Its Seismic Hazard Implications

On 20 April 2013, a moment magnitude (Mw) 6.6 earthquake occurred in the Lushan region of southwestern China and caused more than 190 fatalities. In this study, we use geodetic data from nearly 30 continuously operating global positioning system (GPS) stations, two periods of leveling data, and interferometric synthetic aperture radar (InSAR) observations to image the coseismic deformation of the Lushan earthquake. By using the Helmert variance component estimation method, a joint inversion is performed to estimate source parameters by using these GPS, leveling, and InSAR data sets. The results indicate that the 2013 Lushan earthquake occurred on a blind thrust fault. The event was dominated by thrust faulting with a minor left-lateral strike–slip component. The dip angle of the seismogenic fault was approximately 45.0°, and the fault strike was 208°, which is similar to the strike of the southern Longmenshan fault. Our finite fault model reveals that the peak slip of 0.71 m occurred at a depth of ~12 km, with substantial slip at depths of 6–20 km. The estimated magnitude was approximately Mw 6.6, consistent with seismological results. Furthermore, the calculated static Coulomb stress changes indicate that the 2013 Lushan earthquake may have been statically triggered by the 2008 Wenchuan earthquake.

Performance of segmental and shotcrete linings in shallow tunnels crossing a transverse strike-slip faulting

Abstract In this paper, three-dimensional numerical modeling is performed to study the effects of strike-slip fault movement on the performance of shotcrete and segmental linings in shallow tunnels that transversely cross the fault. For this purpose, a parametric study is conducted on lining thickness, soil geo-mechanical properties, tunnel depth, and fault dip angle to assess their influence on the tunnel movements and deformation. A comparison between the segmental and the shotcrete tunnels is made to highlight their performance. The results show that the greater strike-slip fault dip angle increases the separation of the lining segments. As well, after faulting, the maximum tunnel displacement in denser soils is greater than in loose soils.

Three‐dimensional structural‐material models of the formation of the Nyurbinskaya and Botuobinskaya kimberlite pipes (Yakutian Diamondiferous Province, Russia)

The Nyurbinskaya and Botuobinskaya kimberlitic pipes were in the focus of a comprehensive study aimed to investigate their structural and material positions as the main deposits in the Nakyn field (Yakutian Diamondife‐ rous Province, Russia). This paper present the study results and 3D structural‐material models showing the formation of these deposits. In application to geological studies, the 3D modeling technologies allow taking into account the ani‐ sotropy of material complexes comprising kimberlite pipes, as well as inconsistencies in the structural and morpho‐ logical properties of ore‐bearing structures. In order to discover the structural positions and features of the fault‐ block structures of the deposits, tectonophysical methods were used in combination with tacheometric surveys. Based on this more comprehensive and integrated approach, the existing fault patterns were clarified in detail; elements of the internal fault structure were mapped; fault azimuths and dip angles were estimated; and thickness values were obtained. Computer processed data were used to construct 3D models showing the fault‐block structures of the Nyurbinskaya and Botuobinskaya pipes. The mineralogical, petrographic and diamond‐bearing features of various kimberlite generations comprising these pipes were investigated in order to reconstruct the morphology and spatial positions of each of the selected complexes in the current cross‐section and in accordance with intrusion phases. The 3D frame models of geological bodies were constructed for all the magmatic phases, including porphyry kimberlite and eruptive and autolithic kimberlite breccia. The structural‐material models for the Nyurbinskaya and Botuobin‐ skaya pipes were based on a synthesis of their material and structural features discovered in the previous stages of the study. The models presented in this paper are used to discuss temporal relationships between faults in the kim‐ berlitic structure and material complexes comprising the pipes. The models show that the pipes occurred in the near‐ surface structures of shear tension, which developed in the areas where the NNE‐striking fault was conjugated with the ENE‐ and NE‐striking faults in the fault zone resulting from several stage of the tectono‐magmatic activity. In this case, the kimberlite melt material was transported in discrete portions from the source through deep‐seated faults, and the faults acted as channels characterized by an increased permeability. Disjunctive elements identified in this study facilitated magma movements and localization of kimberlite bodies.

Fault dip variations related to elastic layering

Summary In this paper we model the crack growth in an elastic medium constituted by two welded half-spaces with different rigidities. We implement a 2D Boundary Element Method (BEM) computing shear and normal tractions acting on the crack and the slip accommodating stress drop from an arbitrary initial configuration to a final frictional configuration. The direction of crack growth follows the criterion of maximum energy release (strain and gravitational energy) provided that it overcomes the surface fracture energy and the work dissipated by friction. The energetic criterion leads to estimates of the dip angle of seismic faults depending on the amplitude of the initial stress and it includes the classical Anderson's results as a particular case. Moreover, in presence of a sharp rigidity contrast, the direction of crack growth is strongly deflected. The model simulates non-planar, complex, fault geometries, as in the case of detachment and listric faults and it explains the increase of dip angles for both normal and reverse faults, when they enter soft sedimentary layers.

The Decollement Depth of Active Thrust Faults in Italy: Implications on Potential Earthquake Magnitude

AbstractThrust fault ruptures during earthquakes do not often propagate down to the brittle‐ductile transition. Lithological variations control the behavior and depth of regional basal thrusts and decollement planes. Thrust fronts may be discontinuous along strike, limiting the dimension of single coseismic ruptures. These factors control the maximum expected magnitude in one region. This is the case of Italy where the convergence of few millimeter per year in the Apennines accretionary prism and along the retrobelt of the Alps generates compressional earthquakes with moderate to strong magnitudes. Here, using geological and geophysical data, we first compile a map of the undulated active basal thrust decollement for Italy that occurs from 1 to 17‐km depth. Then, we verify the relationship between the length of seismogenic ruptures in thrust faults (Lf) and the maximum depth of thrust faulting (zmax) of related earthquakes and find that their ratio (Lf/zmax) ranges between 2 and 4. Finally, we compute the potential seismogenic volume and estimate the maximum magnitude using an empirical relationship that multiplies the decollement depth and the Lf/zmaxratio. Maximum calculated magnitude is 6.7 ± 0.37 (depending on Lf/zmaxand fault dip angle), consistent with the largest magnitude of thrust‐related earthquakes recorded in Italy (6.5–7.0). Lower magnitudes are predicted in the Ionian Seas at the external front of the Apennines where smaller crustal volumes are involved, whereas higher magnitudes are expected in the southern Po Basin, the western Adriatic Sea, Sicily offshore, and the Southern Alps where the decollement is deeper and the brittle volumes are far greater.

Dynamic Rupture Modeling to Investigate the Role of Fault Geometry in Jumping Rupture Between Parallel‐Trace Thrust Faults

AbstractInvestigations of historic surface‐rupturing thrust earthquakes suggest that rupture can jump from one fault to another up to 8 km away. Additionally, there are observations of jumping rupture between thrust faults ∼50 km apart. In contrast, previous modeling studies of thrust faults find a maximum jumping rupture distance of merely 0.2 km. Here, we present a dynamic rupture modeling parameter study that attempts to reconcile these differences and determines geometric and stress conditions that promote jumping rupture. We use the 3D finite‐element method to model rupture on pairs of thrust faults with parallel surface traces and opposite dip orientations. We vary stress drop and fault strength ratio to determine conditions that produce jumping rupture at different dip angles and different minimum distance between faults. We find that geometry plays an essential role in determining whether or not rupture will jump to a neighboring thrust fault. Rupture is more likely to jump between faults dipping toward one another at steeper angles, and the behavior tapers down to no rupture jump in shallow dip cases. Our variations of stress parameters emphasize these toward‐orientation results. Rupture jump in faults dipping away from one another is complicated by variations of stress conditions, but the most prominent consistency is that for mid‐dip angle faults rupture rarely jumps. If initial stress conditions are such that they are already close to failure, the possibility of a long‐distance jump increases. Our models call attention to specific geometric and stress conditions where the dynamic rupture front is the most important to potential for jumping rupture. However, our models also highlight the importance of near‐field stress changes due to slip. According to our modeling, the potential for rupture to jump is strongly dependent on both dip angle and orientation of faults.

Fault interpretation in seismic reflection data: an experiment analysing the impact of conceptual model anchoring and vertical exaggeration

Abstract. The use of conceptual models is essential in the interpretation of reflection seismic data. It allows interpreters to make geological sense of seismic data, which carries inherent uncertainty. However, conceptual models can create powerful anchors that prevent interpreters from reassessing and adapting their interpretations as part of the interpretation process, which can subsequently lead to flawed or erroneous outcomes. It is therefore critical to understand how conceptual models are generated and applied to reduce unwanted effects in interpretation results. Here we have tested how interpretation of vertically exaggerated seismic data influenced the creation and adoption of the conceptual models of 161 participants in a paper-based interpretation experiment. Participants were asked to interpret a series of faults and a horizon, offset by those faults, in a seismic section. The seismic section was randomly presented to the participants with different horizontal–vertical exaggeration (1:4 or 1:2). Statistical analysis of the results indicates that early anchoring to specific conceptual models had the most impact on interpretation outcome, with the degree of vertical exaggeration having a subdued influence. Three different conceptual models were adopted by participants, constrained by initial observations of the seismic data. Interpreted fault dip angles show no evidence of other constraints (e.g. from the application of accepted fault dip models). Our results provide evidence of biases in interpretation of uncertain geological and geophysical data, including the use of heuristics to form initial conceptual models and anchoring to these models, confirming the need for increased understanding and mitigation of these biases to improve interpretation outcomes.

Analysis Of Concrete Tunnel Frameworks Subject To Fault Removal

An earthquake fault rupture generates two types of ground motion: permanent quasi-static dislocations and dynamic oscillations, characterized by strong pulses. This study investigates tunnel’s response to two different conditions using a 2D finite element program; the first one has a static dislocation corresponding to different earthquake magnitudes, while the second combines near-field seismic motions with three specific peak ground accelerations along with permanent dislocations. The impulsive ground motions affect the lining response further to other influential factors such as fault type and dip angle, making changes in sectional forces, displacement, and shear distortion of the lining. Moreover, pulse intensity, period, and frequency content are effective characteristics of impulsive motions that change in final response of the lining, subjected to subsequent static dislocations. Based on the second condition, at low PGAs, the pulse type is more effective to final response of the lining, due to forward and backward momentum specifications in impulsive motions. For earthquakes with high PGA and larger values in nearfield parameters, both the pulse type and period are effective. The tunnel displacement increases at PGAs as large as 0.7 and 1g, unlike the low PGA as large as 0.35g, because of increasing soil stress and plastic strain, respectively.

Constraints on deformation kinematics across the Yumu Shan, NE Tibetan Plateau, based on fluvial terraces

Abstract In compressive ranges, the kinematics of thrusts and related folds are the key to understanding mountain building processes; however, relatively little attention has been paid to folding on the hanging-wall of a thrust fault which has broken the surface. On the hanging-wall of the Yumu Shan thrust fault, which lies on the north side of the Yumu Shan at the NE edge of the Tibetan Plateau, we found that significant folding deformation had occurred simultaneously with faulting at the surface. To determine the kinematics of the folding and faulting, we surveyed deformed fluvial terrace surfaces across the fold and fault. The geometry of the surface of terrace T4 of the Liyuan River exhibits a faulting displacement of 55 ± 11 m at the fault trace, while in the hinterland, there is an active anticline with a wave length of ~4000 m. Limb rotation on the forelimb is recorded by the terrace geometry. Based on terrace geometry and the deformation of bedrock strata, we infer the geometry of the fault and fold, and conclude that the forelimb was formed by simple-shear deformation above the fault ramp, and that the backlimb was formed by the down-lowering of the fault dip angle. Using the geometry of the fault and fold and previous age control for the terraces, an average rock uplift of 1.2 ± 0.1 mm/a is estimated across the range, which produces a total fault slip rate of 1.8 ± 0.4 mm/a below the Yumu Shan. This new uplift rate indicates an onset age of 2.5 ± 0.5 Ma for the uplift of the Yumu Shan, suggesting that this is a young mountain range. This result suggests that the outward accretion of the NE Tibetan Plateau occurred at ~3 Ma, and it provides an insight into the kinematics of deformation within relatively recently deforming structures, suggesting that folding is a significant process in accommodating the crustal shortening where the thrusting has broken the surface.

Influence of tectonic stress regime on the magnitude distribution of induced seismicity events related to hydraulic fracturing

Hydraulic fracturing is today the primary means of initiating, increasing, and maintaining well productivity in unconventional shale gas reservoirs. However, hydraulic fracturing is attracting public concern over its rapid growth in use and environmental footprint, including potential hazards such as induced seismicity. To mitigate these concerns, there is a need to better understand the level of hazard present with respect to the magnitudes of the events possible, recognizing that these are not equal across different shale gas plays due to regional differences in the geological conditions or even within the same shale gas play due to local differences.An empirical study is presented here along with a series of numerical simulations to investigate the influence of the tectonic stress regime on the magnitude and magnitude distribution of induced seismicity events related to hydraulic fracturing practices. A database of determined earthquake focal mechanisms was first used to determine the tectonic stress regime for different North American shale gas basins. Next, induced events associated with hydraulic fracturing operations were identified to determine the magnitude distributions and b-values for these different shale gas basins. To support these empirical analyses, 3-D numerical modelling was performed to further investigate the mechanistic responses and event magnitudes under different simulated stress regimes. The empirical analysis results show that thrust faulting stress regimes have lower b-values than strike-slip stress regimes and therefore are more susceptible to larger induced seismicity events. The numerical simulations show that this is related to the stresses acting on a thrust fault (relative to the fault dip angle) being higher and more concentrated across a larger slip area. Slip in this case, and the stored strain energy being released, was observed to occur as a single large magnitude event. In contrast, numerical simulations for the other faulting types showed the stresses to be more distributed across the fault plane. This results in multiple slip events involving smaller slip areas and therefore with smaller event magnitudes, assuming all other factors are kept the same.

Evolution of Low-Angle Normal Faults in the Enping Sag, the Northern South China Sea: Lateral Growth and Vertical Rotation

Low-angle normal faults (dip <30°, LANFs) are widespread in the northern margin of the South China Sea where the maximum crust thickness is approximately 30.0 km. Based on 3D seismic survey data and drilling wells in the Enping sag, evidences for LANFs that initially formed at high-angles are discussed. After a detailed investigation of extensional fault system and description of 3D fault geometry, the initial fault dips under the model of distributed vertical simple shear are also calculated. The results indicate that the present-day dip angles of the LANFs are in the range of 12° to 29°, and the initial fault dip angles are in the range of 39° to 49°. Deep seismic imaging suggests that the upper crust in the footwall block of the LANFs was tilted at an angle of ~14° to 22° due to the isostatic rebound during rifting. Moreover, the temporal and spatial sequences of the lateral growth of the LANFs have been investigated by the seismic interpretation of four isochronous stratigraphic interfaces, which demonstrates that two individual fault segments propagated towards each other and subsequently, were hard-linked during the Early Eocene.

Failure mode analysis of X80 buried steel pipeline under oblique-reverse fault

As the main way of oil and gas long-distance transportation, buried pipelines will inevitably pass through the active fault zones. Fault displacement induced by earthquake, especially the oblique-reverse fault displacement, will cause large compressive, tensile and bending strain in the pipeline, resulting in buckling, rupture or warping, which seriously threaten the safety operation of pipelines. A 3-D numerical model considering the role of underground rock stratum was proposed for failure mode analysis of X80 buried steel pipeline under oblique-reverse fault displacement. Referring to the engineering parameters of the Second West-to-East Gas Pipeline Project (China), the strain evolution of X80 steel pipeline for local buckling, tensile fracture and cross-section ovalization failure was obtained, and the effects of fault dip angle, pipeline diameter-thickness ratio, burial depth and internal pressure on the failure modes were discussed. Finally, according to the failure criteria of buried steel pipeline, the critical fault displacements corresponding to different failure modes were obtained, and the conversion relationships between different failure modes were further derived, which provide a reference for failure analysis and safety design of pipelines crossing oblique-reverse faults.

Calculation of hydraulic fracture induced stress and corresponding fault slippage in shale formation

The casing deformation problems during hydraulic fracturing process in shale gas wells seriously affect multi-stage hydraulic fracturing treatment and cause significant impact on efficient exploitation of shale gas in Sichuan, China. But by now, the mechanism of these casing deformation problems has not been completely understood. The tests of the casing deformation show that the shear failure is the main type of casing deformation. Combined with the detected seismic data, the fault slip caused by hydraulic fracturing is identified as the main reason for casing deformation in shale gas wells. A deep understanding of fault reactivation and slip is significant important. Hence, a semi-analytical model for calculating induced stress along the fault caused by hydraulic fracture is established in this paper. Based on the induced stress along the fault, semi-analytical models for calculating two types of fault slip are established, including the reactivated zone located at one fault tip and the reactivated zone located away from fault tips. Additionally, the effects of fluid pressure, dip angle of fault, scale of fluid stimulated area and the friction coefficient on fault slippage are discussed. At last, the method for calculating fault slippage proposed in this paper is applied in field and the calculated result is consistent with the field data. The semi-analytical model proposed in this paper provides a reasonable way for identifying casing deformation in shale gas wells or other wells which need hydraulic fracturing treatments.

A new method for complete quantitative interpretation of gravity data due to dipping faults

Abstract We have developed a simple method to determine completely the model parameters of a buried dipping fault from gravity data (depths to the centers of the upper and lower portions of the faulted thin slab, dip angle, and amplitude coefficient). The method is based on defining the anomaly values at the origin and at four symmetrical points around the origin on the gravity anomaly profile. By defining these five pieces of information, the dip angle is determined for each value of the depth of the lower portion of the faulted thin slab by solving iteratively one nonlinear equation of the form f(α)= 0. The computed dip angles are plotted against the values of the depth representing a continuous depth-dip curve. The solution for the depth to the lower portion of the faulted thin slab (down-thrown block) and the dip angle of the buried fault is read at the common intersection of the depth-dip curves. Knowing the depth to the center of the lower portion of the faulted layer and the dip angle, the problem of determining the depth to the center of the upper portion of the faulted slab (up-thrown block) is transformed into the problem of solving iteratively a nonlinear least-squares equation, f(z) = 0. Because the depths and the dip angle are known, the amplitude coefficient, which depends on the thickness and density contrast of the thin slab, is determined using a linear least-squares equation. The method is applied to theoretical data with and without random errors. The validity of the method is tested on real gravity data from Egypt. In all cases examined, the model parameters obtained are in good agreement with the actual ones and with those given in the published literature.

Variation in geometries and displacement along thrust faults: a quantitative analysis from sandbox models

The present work combines theoretical analysis, laboratory experiments, and field examples together with quantitative analysis to understand displacement variation along fault surfaces with varying dip angle. Two sandbox experiments are described to quantitatively analyze the interactions between shortening and sedimentation during late stages of deformation. The two models consisted of sand layers with single and two microbeads layer/s within the sandpack, sieved over horizontal frictional detachment. The models demonstrate that the overlying sediment load bears a major role on kinematic of developing structures. Fault displacement varied along imbricate thrusts due to variation in fault dip angle in the listric geometry. Maximum displacement occurred in the up-dip direction (up-section or near fault tip) along the faults where fault dip angles were shallower and favourable for thrust displacement. In contrast, the displacement was limited in the down-dip direction (down-section or near basal detachment) where fault dip angles were steeper. The variation in fault displacement with fault dip along the fault surfaces made it possible to establish an inverse relationship between the fault dip and related displacement values, i.e. lower is the dip angle, greater the displacement and vice versa. Despite the inherent limitations and assumptions of laboratory experiments, application of results to natural examples sheds new light on the mechanics and geometry of thrust faults from the deep to shallow structural levels as well as structural patterns that could appear as anomalous at a first sight.

Evaluation of EPS wall effectiveness to mitigate shallow foundation deformation induced by reverse faulting

A comprehensive study is presented to illustrate the effect of an expanded polystyrene sheet (EPS) wall for absorbing fault rupture and its effects on shallow embedded foundations. Numerical modeling has been thoroughly validated through centrifuge test results. Various embedment depths and fault dip angles were considered to specify the critical foundation position on the soil surface. Furthermore, the impact of vertical trenching of an EPS wall, next to a rigid foundation, was investigated to mitigate surface foundation deformation. Results indicated that, due to high compressibility and low shear resistance that is not time dependent, an EPS wall panel protects the foundation by absorbing fault induced shear strains in the soil stratum. The effectiveness of such walls depends mainly on the geometry, location and mechanical characteristics of the walls, foundation location, bedrock fault offset, and fault dip angle.

Finite Element Analysis of Overlying Soil Failure Based on Fault Dip Angle

When the strong earthquake occurs, the deformation response and rupture of the overlying soil are very complicated. In this paper, the influence of fault dip angle on the surface deformation and rupture of overlying soil is analyzed by means of finite element numerical simulation. When the vertical dislocation of the fault is about 3∼5% of the thickness of the overlying soil layer, the surface rupture occurs only when the fault dip angle is 45°. When the vertical displacement of the fault increases to 10% of the thickness of the overlying soil layer, surface rupture occurs under three working conditions of 45°, 70° and 90° of fault dip angle. With the increase of the dip angle from 45°, 70° to 90°, the surface equivalent strain is gradually smaller, the deformation of the overlying soil is smaller, and the deformation width of the upper wall will change from about 2 times that of the lower wall to the same as the lower wall. The deformation and rupture of the overlying soil first begin with the fracture of the soil mass at the interface between the fault bedrock and the soil. With the increase of the dislocation quantity, the surface also will appear 1 breakpoint when the fault angle is 45° and 70°, the ground surface will appear 2 breakpoints when the fault angle is 90°, and at last overlying soil is broken through.

Study on seismic isolation measures for cross-fault embankment

Under the movement of fault, embankment can produce uneven displacement, deformation and even destruction. Consequently, it is necessary to adopt appropriate seismic measures to reduce the deformation or damage of embankment with the fault displacement. In view of this, the dynamic response of a cross-fault embankment with raft foundation as a seismic isolation measure was simulated by ABAQUS in this paper. Based on the reverse fault and normal fault, three kinds of setting positions of the raft foundation were set and then the displacement of subgrade surface and bending moments of raft foundation in all kinds of working conditions were calculated and compared. The results show that when s/b = 0.75, the fracture zone is shifted to the right compared with no foundation, indirectly reducing the dip angle of fault (“s” is the distance that from left endpoint of the foundation to the surface outer point of fault without foundation, “b” is the width of foundation). In addition, it is found that the vertical displacement curve of subgrade surface when s/b = 0.75 is gentler than other working conditions, furthermore, the curve’s largest inclination value and bending moment of raft foundation are the minimum. Therefore, the best condition for raft foundation as a seismic measure to cross-fault embankment is s/b = 0.75.

Casing Shear Deformation Based on Micro Seismic Data

Casing shear deformation, which is caused by fault slipping, is the main morphology of casing deformation occurred during multistage fracturing. In order to determine the relationship between fault slipping and casing shear deformation, the micro seismic data collected from engineering field which can reflect the reality of the formations was analyzed. A new numerical model was developed, and the influential factors on casing shear deformation were studied, including the fault slip distance of lower and upper interface, fault dip angle, the thickness of cement sheath and casing. The results of research shows that: (1) Fault is easily activated by fracturing, which was the main reason of casing shear deformation; (2) The greater the fault dip angel, the slip distance, the greater the casing shear deformation; (3) Increasing the wall thickness of casing or cement sheath is beneficial to decrease the degree of the shear deformation; (4) Two ways can be used to avoid and control the casing shear deformation, one is keeping the designed horizontal segment of well trajectory keep away from fracture-developed area, or be parallel to natural fracture, the other is using stage cementing technology. Research results can provide important reference for design and control of casing integrity during multistage fracturing in shale gas wells.

A nonlinear inversion of InSAR-observed coseismic surface deformation for estimating variable fault dips in the 2008 Wenchuan earthquake

Satellite Interferometric Synthetic Aperture Radar (InSAR) is playing an increasingly important role in the observation of coseismic surface deformation caused by earthquakes, and has been used to invert for subsurface fault structure and reveal earthquake source mechanisms. However, the mapping of complex non-planar or curved (e.g., listric-shaped) faults still remains a challenging task due to variable dips along the underground depth and the impenetrability of the deep crust. Here, we develop a set of new inversion algorithms to determine the listric fault geometry with InSAR- and GPS-observed surface deformation as the significant constraints. The fault surface with variable dip angles is discretized into consecutive sub-fault layers along the down-dip direction. A nonlinear iteration algorithm is used to minimize the objective function to determine the dip angle for each sub-fault layer. The proposed method is first tested using synthetic data to show its effectiveness for retrieval of varying fault geometry dips, and then applied to the 2008 Mw 7.9 Wenchuan earthquake that ruptured the Yingxiu-Beichuan fault for over 320 km along the southwest-northeast strike. The inversion shows that the dip angle of the seismogenic fault is up to 76° near the surface layer, and gradually decreases along the down-dip direction. A significant decrease in dip occurs within the depths of 6–15 km with a dip of 32° at a depth of 15 km. The dip angle decreases to 2° at a depth of 20 km, and finally merges with the subparallel PengGuan fault, which is basically consistent with geological investigations and seismic waveform data inversion. Using the inferred fault geometry, the slip model associated with the event is estimated. Five high-slip concentrations along the strike of the Yingxiu-Beichuan fault are recognized. The inversion misfit of InSAR data is reduced to 7.1 cm with a significant improvement compared to previous studies.