Fault Bend Research Articles

Spontaneous rupture processes on a bending fault

We simulated spontaneous rupture processes on a vertical, bending strike slip fault in a three‐dimensional half space, using a finite‐difference method. Rupture area and overall slip distribution on the fault vary with the initial stress field, which depends on strike change at the bend. Rupture velocity and detailed slip distribution around the bend, on the other hand, are affected by time‐dependent normal stress change caused by rupture. This dynamic stress change plays an important role in the rupture process ahead of the bend, as well as in the resulting ground motion. The numerical simulation method demonstrated here in a simplified geometry is equally applicable to modeling strong ground motion from geometrically complex ruptures in realistic earth models.

Plate-scale stress fields driving the tectonic evolution of the central Ouachita salient, Oklahoma and Arkansas

Two stages of regional cross-fold jointing refl ect the rearrangement of a lithosphericplate-scale stress fi eld during the Ouachita (i.e., Alleghanian) orogeny. These joints overprint northward-verging thrust-related folds in the Ouachita foreland. Stage-one jointing during the Ouachita orogeny is associated with a stress fi eld recorded by an Atokan and earlier regional joint set, which has a NNE strike. Stage-one jointing is separated into two phases in the central Ouachita salient, where a secondorder recess is marked by a prominent bend in the Windingstair fault below the forelandmost sheet of the central thrust belt. The Big Cedar recess developed when the Windingstair sheet overrode the frontal imbricate zone, thereby causing the Big Cedar pinch zone, a structure refl ecting fold-parallel shortening proximal to localized dextral transpression in the Choctaw thrust sheet. A later regional joint set, representing the second stage of jointing during the Ouachita orogeny, affects rocks in the Arkoma foreland as well as in the fold belt. Stage-two jointing records a stress fi eld associated with NNW-directed closure during the fi nal stage of plate convergence; this stage persisted into the Desmoinesian.

Characterizing a large shear‐zone with seismic and magnetotelluric methods: The case of the Dead Sea Transform

Seismic tomography, imaging of seismic scatterers, and magnetotelluric soundings reveal a sharp lithologic contrast along a ∼10 km long segment of the Arava Fault (AF), a prominent fault of the southern Dead Sea Transform (DST) in the Middle East. Low seismic velocities and resistivities occur on its western side and higher values east of it, and the boundary between the two units coincides partly with a seismic scattering image. At 1–4 km depth the boundary is offset to the east of the AF surface trace, suggesting that at least two fault strands exist, and that slip occurred on multiple strands throughout the margin's history. A westward fault jump, possibly associated with straightening of a fault bend, explains both our observations and the narrow fault zone observed by others.

Late Cenozoic deformation and uplift of the western flank of the Altiplano: Evidence from the depositional, tectonic, and geomorphologic evolution and shallow seismic activity (northern Chile at 19°30′S)

We analyze the west vergent thrust system (WTS) along the western flank of the Altiplano in northern Chile (18°S–21°S). In our study area (19°20′S–19°50′S), the WTS consists of three thrust propagation monocline folds (flexures) developing growth strata. The relative uplift accommodated by the flexures is rapid between 26 and 8 Ma (0.1 mm/yr), diminishing to 0.02 mm/yr after 8 Ma. Approximately 2000 m of relative surface uplift was accommodated by the flexures since the late Oligocene. Sedimentological and geomorphological analysis shows that westward tilting of the forearc occurred after 10 Ma, coeval with the shifting of deformation from the Altiplano to the sub‐Andean zone, where the underthrusting of the Brazilian Craton would have resulted in crustal thickening, surface uplift in the orogen, and westward ductile subcrustal flow. Forearc tilting is accommodated by east vergent thrusts (ETS) issued from the Benioff zone beneath the Central Depression emerging into the Western Cordillera, contributing 500–1400 m of surface uplift. The WTS connects the ETS in the brittle‐ductile crustal transition (∼25 km depth), continuing farther east as the Altiplano low‐velocity zone, configuring the western Altiplano as a crustal‐scale fault bend fold. Forearc tilting would be caused by westward ductile flow in the lower crust pushing the rigid forearc in the ETS. Meanwhile, between 19°S and 21°S, the WTS accommodates dextral strike slip, and ∼3 km of N‐S shortening occurred in the Coastal Cordillera. Transcurrence and strain partitioning are probably the result of slight plate convergence obliquity, strong coupling within the interplate zone, westward continental concavity, and high elevation opposing horizontal contraction.

Sandbox models of downward-steepening normal faults

Two deformational styles resulted from sandbox experiments examining the hanging-wall deformation above a downward-steepening normal-fault bend comprised of two planar segments dipping at 40 and 60. In the first, hanging-wall layer-parallel extension dominated, with synthetic normal faults forming an upward-widening fault-bound wedge above the fault bend. Early forming, arcuate, vertical-to-reverse faults bound the wedge on its downthrown side and were followed by a planar, large-displacement synthetic normal fault bounding the wedge on the upthrown side. This later fault accommodated almost all of the subsequent displacement that occurred on the underlying 60 fault. Slip variably occurred along the 40 segment of the fault. Good analogs in nature exist for this deformation geometry. In the second deformational style, hanging-wall layer-parallel compression dominated, forming a monocline with antithetic hinge surfaces dipping downward to the fault-bend surface. Antithetic reverse faults formed in the limb of the monocline. The upper hinge of the monocline intersected the footwall at the fault bend, whereas its lower hinge intersected the 60 fault below the fault bend. The lower hinge was older and formed near the location of the fault bend prior to its being translated down the 60 master fault as part of the hanging wall. Elements of this geometry correlate well with the results of some geometric-based numerical models, but strong analogs in nature are elusive.

An experimental study on variation of b value during deformation of rock samples with different structural models

A preliminary study of b value of rocks with two kinds of structural models has been made on the base of a new acoustic emission recording system. It shows that b value of the sample decreases obviously when the sample with compressive en echelon faults changes into a tensile one after interchange occurs between stress axis σ1 and σ2. A similar experiment is observed when the sample with tensile en echelon faults changes into that with a bend fault after two segments of the en echelon fault linking up. These facts indicate that the variation of b value may contain the information of the regional dominant structural model. Therefore, b-value analyses could be a new method for studying regional dominant structural models.

Rupture Process of the Chi-Chi (Taiwan) Earthquake in 1999

The rupture process of the 1999 Chi-Chi, Taiwan earthquake is investigated by using co-seismic surface displacement GPS observations and far field P-wave records. In according to the tectonic analysis and distributions of aftershocks, we introduce a three-segment bending fault plane into our model. Both the elastic half-space model and the layered-earth model are employed to invert the distribution of co-seismic slip along the Chi-Chi earthquake rupture. The results indicate that the shear slip model can not fit horizontal and vertical co-seismic displacements simultaneously, unless we add the fault-normal motion (tensile component) to inversion. And then, the Chi-Chi earthquake rupture process is obtained by inversion using the seismograms and GPS observations. Antidilatational fault normal motions determined by inversion, concentrating on the shallow northern bending fault, where the surface earthquake ruptures, reveal more complexities and the developed flexural slip folding structures than the other portions of the rupture zone. For understanding the perturbation of surface displacements caused by nearsurface complex structures, we have taken a numerical test to synthesize and inverse the surface displacements for a pop-up structure that is composed of a main thrust and a back thrust. Our result indicates that the pop-up structure, the typical shallow complex rupture that occurred in the northern bending fault zone, can be modelled better by a thrust fault added a negative tensile component than by a simple thrust fault. We interpret the negative tensile distributions, that concentrate on the shallow northern bending fault, as a synthetic effect including the complexities of property and geometry of rupture. The earthquake rupture process also exhibits more spatial and temporal complexities at the northern bending fault. And the results clearly show an inverse correlation between the aftershock distribution and the mainshock slip.

An intermediate deep earthquake rupturing on a dip‐bending fault: Waveform analysis of the 2003 Miyagi‐ken Oki earthquake

Using waveform analysis, we propose a dip‐bending fault model for the 2003 Miyagi‐ken Oki earthquake. Dip angle of the upper fault plane is estimated as 87° on the basis of focal mechanism from P‐wave first motions. S‐wave polarization analysis leads to a dip angle of 60° for the lower portion of the fault plane. Inversion results show that the rupture started on the southern fault plane. In the beginning 5 seconds, slip was mainly confined in the hypocenter area on the southern fault. From 5 seconds on rupture propagated to the northern part, where the largest slip (3 m) occurred in the northern deep part. The complex stress field in the slab and compositional difference in the upper and the other portion of the slab account for such a bending fault even at intermediate depth.

Geomorphology, kinematic history, and earthquake behavior of the active Kuwana wedge thrust anticline, central Japan

We combine surface mapping of fault and fold scarps that deform late Quaternary alluvial strata with interpretation of a high‐resolution seismic reflection profile to develop a kinematic model and determine fault slip rates for an active blind wedge thrust system that underlies Kuwana anticline in central Japan. Surface fold scarps on Kuwana anticline are closely correlated with narrow fold limbs and angular hinges on the seismic profile that suggest at least ∼1.3 km of fault slip completely consumed by folding in the upper 4 km of the crust. The close coincidence and kinematic link between folded terraces and the underlying thrust geometry indicate that Kuwana anticline has accommodated slip at an average rate of 2.2 ± 0.5 mm/yr on a 27°, west dipping thrust fault since early‐middle Pleistocene time. In contrast to classical fault bend folds the fault slip budget in the stacked wedge thrusts also indicates that (1) the fault tip propagated upward at a low rate relative to the accrual of fault slip and (2) fault slip is partly absorbed by numerous bedding plane flexural‐slip faults above the tips of wedge thrusts. An historic earthquake that occurred on the Kuwana blind thrust system possibly in A.D. 1586 is shown to have produced coseismic surface deformation above the doubly vergent wedge tip. Structural analyses of Kuwana anticline coupled with tectonic geomorphology at 103–105 years timescales illustrate the significance of active folds as indicators of slip on underlying blind thrust faults and thus their otherwise inaccessible seismic hazards.

Fold–thrust styles in the Absaroka thrust sheet, Caribou National Forest area, Idaho–Wyoming thrust belt

The Bear Creek, Big Elk and Black Mountain anticlines are macroscopic structures located in the hanging wall of the Absaroka thrust within the Idaho–Wyoming fold–thrust belt. Structural mapping of the area was conducted by draping existing geologic maps and digital orthophotos over digital elevation models (DEM) to obtain a three-dimensional perspective of the area. The map was further refined by reconnaissance field mapping of selected outcrops. Construction of balanced cross-sections suggests that these structures detach at three stratigraphic levels, within the Cambrian Gros Ventre Formation, Devonian Darby Formation, and Triassic Dinwoody Formation. The folds in the upper stratigraphic package consist of symmetric to asymmetric detachment folds, which show variable vergence along trend. The structures in the lower stratigraphic packages primarily evolved as low-amplitude detachment folds, which were subsequently displaced over fault ramps to form fault–bend folds or duplexes. The duplex geometries in the Cambro–Ordovician units under the Bear Creek and Poker Peak anticlines vary from independent anticlines in the south to completely overlapping stacks in the north. The macroscopic structural patterns of folds proposed in this study will be useful in interpreting subsurface structures in other parts of the Idaho–Wyoming fold–thrust belt.

Strong ground motion estimation in the Sea of Marmara region (Turkey) based on a scenario earthquake

We perform a broadband frequency bedrock strong ground motion simulation in the Marmara Sea region (Turkey), based on several fault rupture scenarios and a source asperity model. The technique combines a deterministic simulation of seismic wave propagation at low frequencies with a semi-stochastic procedure for the high frequencies. To model the high frequencies, we applied a frequency-dependent radiation pattern model, which efficiently removes the effective dependence of the pattern coefficient on the azimuth and take-off angle as the frequency increases. The earthquake scenarios considered consist of the rupture of the closest segments of the North Anatolian Fault System to the city of Istanbul. Our scenario earthquakes involve the rupture of the entire North Anatolian Fault beneath the Sea of Marmara, namely the combined rupture of the Central Marmara Fault and North Boundary Fault segments. We defined three fault rupture scenarios based on the location of the hypocenter, selecting a preferred hypocentral location near a fault bend for each case. We analysed the effect of location of the asperity, within the Central Marmara Fault, on the subsequent ground motion, as well as the influence of anelasticity on the high-frequency attenuation characteristics. The fault and asperity parameters for each scenario were determined from empirical scalings and from results of kinematic and dynamic models of fault rupture. We calculated the resulting time series and spectra for ground motion at Istanbul and evaluated the sensitivity of the predictions to choice of model parameters. The location of the hypocenter is thus shown to be a critical parameter for determining the worst scenario earthquake at Istanbul. We also found that anelasticity has a significant effect on the regional attenuation of peak ground accelerations. Our simulated ground motions result in large values of acceleration response spectra at long periods, which could be critical for building damage at Istanbul during an actual earthquake.

The complexity of a ramp–flat–ramp fault and its effect on hanging-wall structuring: an example from the Njord oil field, offshore mid-Norway

The Njord oil field of the mid-Norwegian continental margin comprises a hydrocarbon trap structure, which is delineated by segments of master faults with complex geometry. The Vingleia Fault Complex includes the major fault segments that delineate the Njord structure to the southeast and east. Three master fault segments with a change in strike orientation are recognized. Reflection seismic sections reveal that these segments show strong variations in fault plane geometry. The central part is characterized by a pronounced ramp–flat–ramp geometry, which diminishes both southwestward and northeastward, so that the northeastern and southwestern segments have a more listric geometry. Hence, an along-strike profile shows an antiform-like culmination in the master fault surface. To the characteristic deformation of ramp–flat–ramp faults, additional deformation in the Njord Field is obvious and marked by extensional horses, extensive roll-over folding, varying strata rotation, characteristic fault bending and variable influence of synthetic and antithetic faults. The occurrence of the style of deformation and geometrical variations in fault pattern are closely related to the structural position above the detachment fault. The following steps in the development of the Vingleia Fault Complex and the associated deformation of the hanging-wall fault block are proposed. (1) Initiation of the master faults in early Triassic. This stage was characterized by slow, extensional displacement. The positions of the master fault segments were possibly influenced by basement in homogeneities marked by a magnetic/gravity anomaly. (2) It is likely that the ramp–flat–ramp had already become established at this stage and that the master fault geometry and a proposed weak salt layer promoted this. (3) During accelerating extension in mid to late Jurassic, the master fault segments became connected by one-sided, lateral linking of fault tip and fault plane or by mutual curved linking of the fault tips. (4) Simultaneously, a roll-over anticline developed within the hanging wall of the master fault. Its relatively large amplitude is produced by a differential movement on the fault surface in combination with a dip-parallel shift of the vertical displacement maximum, which is positioned above a change in the footwall dip.

From transpression to transtension: changes in morphology and structure around a bend on the North Anatolian Fault in the Marmara region

The east–west-trending North Anatolian Fault makes a 17° bend in the western Marmara region from a mildly transpressional segment to a strongly transtensional one. We have studied the changes in the morphology and structure around this fault bend using digital elevation models, field structural geology, and multi-channel seismic reflection profiles. The transpression is reflected in the morphology as the Ganos Mountain, a major zone of uplift, 10 km wide and 35 km long, elongated parallel to the transpressional Ganos Fault segment west of this bend. Flat-lying Eocene turbidites of the Thrace Basin are folded upwards against this Ganos Fault, forming a monocline with the Ganos Mountain at its steep southern limb and the flat-lying hinterland farther north at the flat limb. The sharp northern margin of the Ganos Mountain coincides closely with the monoclinal axis. The strike of the bedding, and the minor and regional fold axes in the Eocene turbidites in Ganos Mountain are parallel to the trace of the Ganos Fault indicating that these structures, as well as the morphology, have formed by shortening perpendicular to the North Anatolian Fault. The monoclinal structure of Ganos Mountain implies that the North Anatolian Fault dips under this mountain at 50°, and this ramp terminates at a decollement at a calculated depth of ∼8 km. East of this fault bend, the northward dip of the North Anatolian Fault is maintained but it has a normal dip-slip component. This has led to the formation of an asymmetric half-graben, the Tekirdağ Basin in the western Sea of Marmara, containing a thickness of up to 2.5 km of Pliocene to Recent syn-transform sediments. As the Ganos uplift is translated eastwards from the transpressional to the transtensional zone, it undergoes subsidence by southward tilting. However, a morphological relic of the Ganos uplift is maintained as the steep northern submarine slope of the Tekirdağ Basin. The minimum of 3.5 km of fault-normal shortening in the Ganos Mountain, and the minimum of 40 km eastward translation of the Ganos uplift indicate that the present fault geometry has existed for at least the last 2 million years.

The Gubbio normal fault (Central Italy): geometry, displacement distribution and tectonic evolution

Normal faults within orogenic belts can be pre-, syn- or post-orogenic features. We studied the Gubbio normal fault (central Italy), which is an example of a pre-orogenic fault reactivated in a post-orogenic stage. The Gubbio Fault is a 22-km-long fault bordering a Quaternary basin and part of an active faults system in the Umbria–Marche region (Central Italy). The interpretation of a set of seismic profiles enables us to reconstruct the fault geometry in detail and to measure displacement and throw distributions along the fault strike. Seismic data indicate that the Gubbio Fault represents an example of multiple reactivation: at least a portion of the fault was active in the Miocene and only a part of the total displacement was achieved in the Quaternary. The reconstruction of the fault geometry at depth shows that the fault is characterised by listric geometry. The fault is also characterised by a bend along strike and structure contours show that this geometry is maintained at depth. As the fault is commonly addressed as presently active, the maximum fault dimensions are correlated to the maximum expected earthquake, and the presence of the fault bend is discussed as a possible barrier to seismic ruptures propagation.

Finite Element Analysis of Fault Bend Influence on Stick-Slip Instability along an Intra-Plate Fault

Earthquakes have been recognized as resulting from stick-slip frictional instabilities along the faults between deformable rocks. A three-dimensional finite-element code for modeling the nonlinear frictional contact behaviors between deformable bodies with the node-to-point contact element strategy has been developed and applied here to investigate the fault geometry influence on the nucleation and development process of the stick-slip instability along an intra-plate fault through a typical fault bend model, which has a pre-cut fault that is artificially bent by an angle of 5.6° at the fault center. The numerical results demonstrate that the geometry of the fault significantly affects nucleation, termination and restart of the stick-slip instability along the intra-plate fault, and all these instability phenomena can be well simulated using the current finite-element algorithm.

Dépliage 3-D des anticlinaux bordant le synclinal fermé de la vallée des Ponts, Jura central, Suisse

The Ponts valley syncline is a closed basin within the Neuchâtel Jura fold and thrust belt. This syncline, apparently uplifted to an altitude of around 1000m is closed in the SW by an anticline with an oblique WNW-ESE direction. The 3-D geometry of the entire structure is examined and unfolded in detail. This syncline is filled with an unexpectedly thick series (~400m) of Tertiairy Molasse, as revealed by the CS-AMT (controlled source audio-magneto-telluric) and a reflexion seismic line. The latter also documents internal compressional structures within the well layered upper freshwater Molasse series. The 3-D configuration of the top Malm limestones has been constructed for the entire area based on new detailed geologic and structural mapping, hundreds of dip measurements, as well as geophysical data. The Malm marker bed displays three distinct types of structures: 1) Thrust faults with shallow dips, vergent to the NW and/or SE that are associated with folds interpreted as fault bend folds; 2) high angle inverse faults, mostly with a SE vergence are interpreted as inverted normal faults, inherited from a modest Oligo-Miocene extensional phase in a NW-SE direction; and 3) tear faults with a dominant N-S direction, probably inherited from an Oligocene extensional phase in association with the opening of the Rhine and Bresse grabens. Tear faults accommodate important lateral changes in fold geometry during the Late Miocene main folding-and-thrusting phase. All deformations are easily explained in an entirely thin-skinned fashion, taking place above a thick detachment horizon within Triassic evaporite series.

Geometric tests and their application to fault-related folds in Kuqa

For brittle rock deformation, there are two main types of fault-related folds found in foreland thrust belts, i.e. fault-bend folds and fault-propagation folds. The predicted angular function for the quantitative geometric relationships between fault shapes and fold shapes in fault-bend folds and fault-propagation folds have been tested in seismic profiles; i.e. Deep Bashijiqike, Tugeerming, Kashangtokai, East Qiulitage, Deep East Qiulitage and Yakelike fault bend anticlines and Bashijiqike, Yiqikelike and South Yiqikelike fault propagation anticlines in the Kuqa rejuvenated foreland thrust belt. Test results for the transformation from seismic-time section into seismic-depth section using the seismic velocity spectrum can be used to identify whether the interpreted structures are reasonable. With geometric analysis and testing of the subsurface structures, it is possible to predict the existence of the fault-bend folds and fault-propagation folds in the Kuqa area. This study provides convincing proof that the Kuqa basin is a rejuvenated foreland basin.

Crustal scale geometry of the Zagros fold–thrust belt, Iran

Balanced cross-sections across the Zagros fold–thrust belt in Iran are used to analyze the geometry of deformation within the sedimentary cover rocks, and to test the hypothesis of basement involved thrusting throughout the fold–thrust belt. Although the Zagros deformation front is a relatively rectilinear feature, the sinuous map-view morphology of the mountain front is a result of a 6 km structural step in the regional elevation of the Asmari Limestone that produces a pronounced step in topography termed the ‘mountain front flexure’. Although the height of the mountain front flexure is sufficient to permit basement fault–bend folds at the front of the Lorestan and Fars regions, the taper of the orogen, low percentage of shortening, and consistent structural elevation from the mountain front flexure to the hinterland suggest that Lorestan and Fars segments of the fold and thrust belt are completely detached on lower Cambrian salt and that basement-involved thrusting occurs only in the hinterland of the orogen. Mass balance constraints necessitate that detachment folds throughout the fold–thrust belt are cored by faults that branch from the basal detachment. The steep dips of these faults and their depth within the lower Paleozoic sedimentary rocks can account for recorded earthquakes. This suggests that the ∼11±4-km-deep earthquakes throughout the fold–thrust belt may be nucleating within sedimentary rocks rather than in the basement as previously proposed. Total shortening in the Zagros fold–thrust belt is 70±20 km, which corresponds to ∼20% shortening of the Arabian block.

Balanced sections and the propagation of décollement: A Jura perspective

The propagation of thrusting is an important problem in tectonics that is usually approached by forward (kinematical) modeling of balanced sections. Although modeling techniques are similar in most foreland fold‐thrust belts, it turns out that in the Jura, there are modeling problems that require modifications of widely used techniques. In particular, attention is called to the role of model constraints that complement the set of observational constraints in order to fully define the model. In the eastern Jura, such model constraints may be inferred from the regional geology, which shows a peculiar noncoaxial relation between thrusts and subsequent folds. This relation implies changes in the direction of translation and the mode of deformation in the course of the propagation of décollement. These changes are conjectured to be the result of a change in partial decoupling between the thin‐skinned fold‐thrust system (nappe) and the obliquely subducted foreland. As a particularly instructive case in point, a cross section through the Weissenstein range is discussed. A two‐step forward (kinematical) model is proposed that uses both local observational constraints as well as model constraints inferred from regional data. As a first step, a fault bend fold is generated in the hanging wall of a thrust of 1500 m shortening. As a second step, this structure is transferred by flexural slip into the actual fold observed at the surface. This requires an additional 1600 m of shortening and leads to folding of the original thrust. Thereafter, the footwall is deformed so as to respect the constraint that this deformation must fit into the space defined by the folded thrust as the upper boundary and the décollement surface as the lower boundary, and that, in addition, should be confined to the area immediately below the fold. In modeling the footwall deformation a mix of balancing methods is used: fault propagation folds for the competent intervals of the stratigraphic column and area balancing for the incompetent ones. Further propagation of décollement into the foreland is made possible by the folding process, which is dominated by a sort of kinking and which is the main contribution to structural elevation and hence to producing a sort of critical taper of the moving thin‐skinned wedge.

The Three-Dimensional Dynamics of a Nonplanar Thrust Fault

Advances in computational methodology have made it possible to ex- plore the dynamics of earthquake rupture on nonplanar faults. Using a method that allows geometrical flexibility, we simulate in three dimensions the dynamics of a fault that has an abrupt change in dip with depth. Using a homogeneous prestress on both fault segments, we find that while the resultant final stress field is strongly influenced by the fault bend, the fault slip and low-frequency ground motion are relatively insensitive to the pure dynamic effects of the nonplanar fault. The ground velocity from the nonplanar fault is qualitatively quite similar to that of a planar fault with the same dip angle as the nonplanar fault's shallow segment. As the effects of multiple earthquakes accumulate on this fault, stress concentrations at the fault bend are compounded, but the effect of the free surface on the stress appears to approach a steady state. The results of this study imply that for the prediction of peak ground motion from faults that intersect the surface of the Earth, a bend in the fault at depth may not be a significant factor. The very long term effects of the fault bend are not fully determined, but could lead to complexity in the rupture and slip process in future events.