Bending-moment Faults Research Articles

Multiple Fold Earthquakes Recorded by the Paleoseismic Surface Ruptures of Bending-Moment Faults in the Qiulitage Anticline, South Tianshan, China

Abstract Bending-moment faults (BMFs), as a fundamental type of secondary faulting, are intrinsically linked to the primary causative faults within active thrust-fold belts. When these faults thrust through the ground surface, the resulting geomorphic scarps offer the characteristics of local earthquake recurrence. This information helps to fill a gap left by main faults, which often lack coseismic surface ruptures. The Qiulitage anticline where the 1949 M 7¼ Kuqa earthquake occurred is an active thrust-and-fold belt predominantly governed by blind faults. In addition, several typical BMFs extensively crop out as surface scarps in the front of the mountain. Our research concentrates on the well-developed BMF scarps in this region and seeks to explore the recurrence characteristics of paleoearthquakes, which remain inadequately comprehended. Our study reveals that (1) secondary BMF with high enough magnitude can directly generate coseismic ground ruptures, and (2) the seismic behavior of BMFs exhibits a degree of repeatability, potentially linked to the concurrent movement of various BMFs or the solitary action of a single fault. However, the case study presented in this article also highlights the limitation of fold earthquake research because of the swift attenuation of coseismic fault slip as it approaches the ground surface.

Surface deformation induced by the 2016 Meinong earthquake and its implications to active folds

We present 230 field observations on the location, trending, and displacement vectors of the coseismic surface cracks induced by the 2016 Meinong earthquake in the Guanmiao area, SW Taiwan. Coseismic surface cracks trends from the north to northeast. The coseismic deformed region moved toward the W-WNW. In Guanmiao town, surface cracks were mainly distributed on both limbs of the Guanmiao syncline. The preseismic deformation was also observed along the axial trace of the Guanmiao syncline. These results give clues to high structural activities in SW Taiwan. We argue that Guanmiao syncline is an active fold with both coseismic activity and interseismic creeping, which induced nonnegligible micro-geohazards because of the continual loss. We report a new case of the normal bending-moment fault, the Luosianliao fault, which locates between the Guanmiao syncline and Chungchou anticline. However, the linkage between the shallow Luosianliao fault and the deep-seated causative fault of Guanmiao aftershocks are not known yet. We demonstrate the kinematic process of coseismic surface deformation and argue that the bending-moment fault could provide an opportunity to understand the recurrence interval of folding. The mechanism of earthquake-induced folding amplification through high fluid-pressure rocks may play a critical role in assessing earthquake hazard risks in regions with similar geology to SW Taiwan.

Using fluvial terraces as distributed deformation offset markers: Implications for deformation kinematics of the North Qilian Shan Fault

Knowledge of the kinematics of thrusts is the key to understanding mountain building processes in compressive ranges; however, relatively little attention has been paid to distributed deformation (on-fault and off-fault such as rotation and warping) across a thrust fault. Distributed deformation is widespread along the northern front of the Qilian Shan, in the NE Tibetan Plateau. In the Daciyao River, of the central North Qilian Shan, the East Yumu Shan Fault (EYF) splays into four parallel faults at the piedmont. The Daciyao River flows across the deformation zone and its terrace landform record provides a valuable geomorphic marker for reconstructing the cumulative deformation. Terrace deformation across the fault splays was estimated with measured longitudinal profiles using differential GPS, and the fault slip was reconstructed by applying the trishear model, a widely applied model used to explain the geometry of basement-related structures. At least 10 strath terraces are formed with bedrock bases developed into Neogene red beds along the mountain front. The age of one of the terraces (T8) was constrained by Optically Stimulated Luminescence (OSL) dating of the overlying aeolian loess, which provide a minimum age (68 ka) for the age of terrace abandonment. The survey data and trishear model results suggest that the fault splays are bending-moment faults (BMF), originating from a fault propagation fold. Based on the fault and fold geometry across the EYF, the total vertical slip rate is estimated as 0.9–1.2 mm/yr. Slip rates on the EYF are consistent along-strike during the Late Pleistocene but they are twice as high during the Holocene, indicating a high potential for large earthquakes along this fault. This work also indicates that to calculate accurate total slip rate, terrace heights must be measured outside of the distributed broad zone.

Growth of bending-moment faults due to progressive folding: Insights from sandbox models and paleoseismological implications

Bending moment normal faults (BMF) form during outer-arc extension of a folding layer. These faults, observed in contractional and extensional tectonic environments, can represent the only tectonic features potentially available for paleoseismological investigations (i.e., trenching) in order to date the movement of deeper structures. Yet, the reliability of BMF as a paleoseismological feature is debated in terms of its potential to continuously record coseismic deformation and their relationship with progressive flexure.We made use of analogue modeling in order to explore a simple model of progressive orthogonal flexure and the development of BMF. We collected data on mode of BMF inception and growth by analyzing time-series of cross section deformation, measuring dip-parallel BMF displacement profiles, and constructing a three-dimensional model of fault architecture by slicing of the experiment.Our results point to a model of BMF development typical of mechanically constrained faults, where limits on self-similar growth of faults is imposed once a maturity stage of displacement accumulation is attained. The BMF can accumulate displacement until the structure reaches a maturity stage when further slip is inhibited. This could result in an incomplete paleoseismological record of further fold movements. However, this fault stage can be recognized by the D-shaped displacement profile, typical of mature BMF. A simple two-dimensional constant-area balancing model is proposed, allowing us to derive incremental changes in flexuring, given the area of the collapsed sector with BMF and the thickness of the faulted layer. These results support the use of BMF as a paleoseismological proxy for deeper structures.

The role of pre-existing discontinuities in the development of extensional faults: An analog modeling perspective

Several mountainous regions are currently affected by syn- or post-orogenic active extension. We investigate how a newly-formed normal fault interacts with structures inherited from a previous contractional phase. To this end, we use analog models that adopt an innovative technique for performing a precut that mimics such inherited structures into a clay layer; this clay layer is laid on top of a master fault simulated by two rigid blocks sliding along an inclined plane. We carry out six experiments with variously oriented precuts and compare the results with those obtained in a reference isotropic experiment. All other conditions are identical for all seven realizations. Fault evolution is monitored by taking closely-spaced snapshots analyzed through the Digital Image Correlation method. We find that the upward propagation of the normal fault can be either accelerated or decelerated depending on the presence of a precut and its orientation. Such precuts can also promote or inhibit the formation of bending-moment faults. These interactions between master fault and precut also affect the shape of the fault-related syncline–anticline pair.

Antislope scarps, gravitational spreading, and tectonic faulting in the western Yakutat microplate, south coastal Alaska

Mountain ridges in the western Yakutat microplate are riddled with swarms of antislope scarps and troughs. These landforms were previously interpreted as gravity failures (sackungen), but if partly or wholly tectonic (flexural slip or bending moment faults), they represent part of the strain budget from ongoing plate collision. To determine scarp origin, we mapped landforms, bedrock structure, and trenched scarps at Kushtaka Mountain and south of Martin Lake. The Kushtaka scarps paralleled west-dipping coal and sandstone beds in the Tertiary Kultieth Formation, and were spaced 35–60 m apart with heights of 1–4 m. Structural and paleosol relationships in a 6-m-long, 1.3-m-deep trench indicate the scarp was produced by Holocene creep on a normal fault underlying the scarp. The Kushtaka scarps thus represent toppling-style slip on bedding-plane faults in the eastern limb of a syncline, as the fold “unfolds” due to gravitational spreading. The Martin Lake scarps are more complex and include downslope-facing landslide scarps, upslope-facing flexural toppling scarps, and an oblique-slip tectonic scarp. A 2-m-deep trench across the WNW-trending tectonic scarp exposed the underlying bedrock fault plane with slickensides raking only 17°–20°, indicating mainly left-lateral slip on a sinistral-normal fault. In contrast, swarms of ENE-trending antislope scarps showed normal-oblique (dextral) slip. The two scarp sets may form a conjugate pair that simultaneously accommodates left-lateral tectonic slip and NNE-directed gravitational spreading. Our results, plus those recently published by [Li et al. (2010)][1], show that most antislope scarps in the western Yakutat microplate are formed by normal slip on bedding-plane faults that dip into the mountain, and represent gravitational spreading expressed as toppling-style failure or “unfolding” of strata on fold limbs. Conversely, the sinistral-oblique slip fault at Martin Lake is one in a family of east-trending faults accommodating accretion of the Yakutat microplate into the cuspate syntaxis of the Alaskan plate margin. [1]: #ref-14

Geologic Evidence for Surface Rupture Associated with the 1847 M 7.4 Zenkoji Earthquake at Dannohara, Nagano City, Japan

Abstract The 1847 M 7.4 Zenkoji, Japan, earthquake was caused by movement of the west-dipping, western margin reverse-fault zone of the Nagano basin (WFZNB) and produced surface ruptures reported in Japanese historical documents. Despite previous studies to assess fault activity of the WFZNB, our trench excavation at Dannohara, Nagano City, exposed near-surface fault structures associated with the Zenkoji earthquake for the first time and provided geologic evidence for three earlier paleoseismic events. Three core samples 10–15 m long defined a hanging-wall anticline beneath the trench. Although the primary fault was not observed, the revealed subsidiary features enabled us to discuss surface rupture morphology and its repetition patterns. We suggest that: (1) the east-dipping reverse faults exposed on the trench walls and the hanging-wall anticline are developed above a west-dipping blind reverse fault; (2) the east-dipping normal faults represent bending-moment faults at the crest of the hanging-wall anticline; (3) the exposed east-dipping faults slipped during the Zenkoji earthquake to produce elongated linear rise scarps described in historical documents; (4) the hanging-wall anticline grew during the earthquake to generate uplifted lands as reported in historical documents; and (5) faulting similar to that during the Zenkoji earthquake also occurred during the penultimate earthquake. We propose preliminary but better constraints on timing of the third and fourth latest faulting events, and a tentative and maximum recurrence interval of 800–1000 years for the WFZNB. To better understand reverse-fault rupture patterns for appropriate evaluation of seismic hazard, historical surface ruptures should be studied in more detail.

Evidence for coupled reverse and normal active faulting in W Iberia: The Vidigueira–Moura and Alqueva faults (SE Portugal)

The Vidigueira–Moura fault (VMF) is a 65 km long, E–W trending, N dipping reverse left-lateral late Variscan structure located in SE Portugal (W Iberia), which has been reactivated during the Cenozoic with reverse right-lateral slip. It is intersected by, and interferes with the NE–SW trending Alentejo–Plasencia fault. East of this intersection, for a length of 40 km the VMF borders an intracratonic tectonic basin on its northern side, thrusting Paleozoic schists, meta-volcanics and granites, on the north, over Cenozoic continental sediments preserved in the basin, on the south. West of the faults intersection, evidence of Cenozoic reactivation is scarce. In the eastern sector, Plio-Quaternary VMF reactivation is indicated by geomorphologic, stratigraphic, and structural data, showing reverse movement with a right-lateral strike-slip component, in response to a NW–SE trending compressive stress. An average vertical displacement rate of 0.06 to 0.08 mm/yr since late Pliocene (roughly the last 2.5 Ma) is estimated. The Alqueva fault (AF) is a subparallel, northward dipping, 7.5 km long anastomosing fault zone that affects Palaeozoic basement rocks, and is located 2.5 km north and on the hanging block of the VMF. The AF is also a reverse left-lateral late Variscan structure, which has been reactivated during the Tertiary with reverse right-lateral slip; however, Plio-Quaternary reactivation was normal left-lateral, as shown by abundant kinematical criteria (slickensides) and geomorphic evidence. It shows an average displacement rate of 0.02 mm/yr for the vertical component of movement in the approximately last 2.5 Ma. It is proposed that the normal displacements on the AF result from tangential longitudinal strain on the upthrown block of the VMF above a convex ramp of this main reverse structure. According to this model of faults interaction, the AF is interpreted to work as a bending-moment fault sited above the VMF thrust ramp. Consequently, it is expected that the displacements on the AF increase towards the topographic surface with the increase in the imposed extension, declining downwards until they vanish above or at the VMF ramp. In order to constrain the proposed scheme, numerical modeling was performed, aiming at the reproduction of the present topography across the faults using different geodynamic models and fault geometries and displacements.

Imprints of Himalayan thrust tectonics on the Quaternary piedmont sediments of the Neora–Jaldhaka Valley, Darjeeling–Sikkim Sub-Himalayas, India

Geological mapping in the Neora–Jaldhaka Valley of the Darjeeling–Sikkim Sub-Himalayan foothill region reveals the presence of discontinuous strands of tectonically active Quaternary thrust faults. The zones of active faulting coincide with occurrences of deeply incised piedmont deposits and river terraces along an E–W trending corridor. In order of younging, the successive Quaternary thrust faults delineated are the Gorubathan, Matiali and Chalsa thrusts. Unequivocal geological evidence of surface-rupture faulting, however, is noted only along the Gorubathan thrust where the Precambrian Daling Group of rocks is thrust over the Quaternary piedmont sediments along a low northerly-dipping plane. The presence of deformational features in the Quaternary sediments such as anticlines, bending moment faults and back-tilting of both the piedmont and the incising river terraces along active fault scarps are interpreted to signify the presence of north-dipping blind thrusts below the Matiali and Chalsa scarps. Radiocarbon dates of organic-rich clay components indicate that the Gorubathan thrust post-dated 33,875 ± 550 Ybp and the lower bound age of the Chalsa thrust is 22,030 ± 130 Ybp. Successive foreland-ward development of these active strands and the increasing spacing between the successive thrust traces are interpreted to be due to foreland-propagating blind thrusts of the Himalayan FTB (Fold and Thrust Belt) in the Sub-Himalayan terrain. Evidences of backthrust movement are also presented along the Thaljhora North fault. The segmented and variable geometry of these thrusts imply that the MFT (Main Frontal Thrust) is still in its early stage of growth and the lateral linkages between the active fault-strands are yet to be established.

Newly found Tunglo Active Fault System in the fold and thrust belt in northwestern Taiwan deduced from deformed terraces and its tectonic significance

We found active faults in the fold and thrust belt between Tunglo town and the Tachia River in northwestern Taiwan. The surface rupture occurred in 1999 and 1935 nearby the study area, but no historical surface rupture is recorded in this area, suggesting that the seismic energy has been accumulated during the recent time. Deformed fluvial terraces aid in understanding late Quaternary tectonics in this tectonically active area. This area contains newly identified faults that we group as the Tunglo Fault System, which formed after the area's oldest fluvial terrace and appears at least 16 km long in roughly N–S orientation. Its progressive deformations are all recorded in associated terraces developed during the middle to late Quaternary. In the north, the system consists of two subparallel active faults, the Tunglo Fault and Tunglo East Fault, striking N–S and facing each other from opposite sides of the northward flowing Hsihu River, whose course may be controlled by interactions of above-mentioned two active faults. The northern part of the Tunglo Fault, to the west of the river, is a reverse fault with upthrown side on the west; conversely the Tunglo East Fault, to the east, is also a reverse fault, but with upthrown side on the east. Both faults are marked by a flexural scarp or eastward tilting of fluvial terraces. Considering a Quaternary syncline lies subparallel to the east of this fault system, the Tunglo Fault might be originated as a bending moment fault and the Tunglo East Fault as a flexural slip fault. However, they have developed as obvious reverse faults, which have progressive deformation under E–W compressive stress field of Taiwan. Farther south, a west-facing high scarp, the Tunglo South Fault, strikes NNE–SSW, oblique to the region's E–W direction of compression. Probably due to the strain partitioning, the Tunglo South Fault generates en echelon, elongated ridges and swales to accommodate right-lateral strike–slip displacement. Other structures in the area include eastward-striking portion of the Sanyi Fault, which has no evidence for late Quaternary surface rupture on this fault; perhaps slip on this part of Sanyi Fault ceased when the Tunglo Fault System became active.

Three‐stage massive gravitational collapse of the emergent imbricate frontal wedge, Hikurangi Subduction Zone, New Zealand

A large‐scale east‐facing Quaternary gravitational collapse is affecting the otherwise thrust‐faulted terrain of coastal southern Hawke's Bay on the east coast of North Island of New Zealand, involving an area >30 km long and up to 6 km inland from the coast, but also extending offshore. The western limit of the collapse structure onshore is represented by a footwall escarpment forming the eastern margin of the Maraetotara Plateau (av. elevation 500 m a.s.l.). To the east of this escarpment, the disposition of the Pliocene Te Aute Limestone within a complex extensional zone reflects numerous northeast‐southwest‐trending normal faults (some Holocene active) with the development of horst and graben, fault‐angle depressions, synclinal folds, fissured zones, and large parasitic landslides. Listric normal faulting is reflected by the back‐tilting of large blocks up to several kilometres in length, near the centre of the gravitational collapse. Horizontal extension across the gravitational collapse domain is calculated at between 15 and 20%. West of the footwall escarpment, the Maraetotara Plateau defines a separate structural domain with horizontal extension of between 2 and 5%, inferred to be related to bending moment faults driven by regional arching accompanying uplift. A fundamental contrast exists between active extensional structures onshore and the mainly contractional structures (asymmetrical anticlines, reverse and thrust faults) offshore. A tectonically driven model involving underplating of trench fill best explains the large‐scale gravitational collapse of this part of the emergent imbricate frontal wedge of the Hikurangi Subduction Zone margin.

High-Resolution Seismic Imaging of Quaternary Faulting on the Crittenden County Fault Zone, New Madrid Seismic Zone, Northeastern Arkansas

Other| May 01, 1995 High-Resolution Seismic Imaging of Quaternary Faulting on the Crittenden County Fault Zone, New Madrid Seismic Zone, Northeastern Arkansas Robert A. Williams; Robert A. Williams U.S. Geological Survey Denver Federal Center Box 25046, MS 966 Denver, CO 80225 (R. A. W., D. L. C.) Search for other works by this author on: GSW Google Scholar Eugene A. Luzietti; Eugene A. Luzietti Chevron USA 935 Gravier St. New Orleans, LA 70112 (E. A. L.) Search for other works by this author on: GSW Google Scholar David L. Carver David L. Carver Search for other works by this author on: GSW Google Scholar Seismological Research Letters (1995) 66 (3): 42–57. https://doi.org/10.1785/gssrl.66.3.42 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Robert A. Williams, Eugene A. Luzietti, David L. Carver; High-Resolution Seismic Imaging of Quaternary Faulting on the Crittenden County Fault Zone, New Madrid Seismic Zone, Northeastern Arkansas. Seismological Research Letters 1995;; 66 (3): 42–57. doi: https://doi.org/10.1785/gssrl.66.3.42 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search Abstract The Crittenden County fault zone (CCFZ), located about 25 km northwest of Memphis, Tennessee, is a potential source of damaging earthquakes. To determine if geologically recent movement on the CCFZ has displaced Quaternary deposits, we acquired three very high-resolution compressional-wave seismic-reflection profiles across surface projections of faults that were observed on coincident *Mini-Sosie and Vibroseis seismic-reflection profiles. We used a 12-gauge shotgun and 5 kg weight drop as an energy source, with 100-Hz geophones spaced at 1.83 m and 0.25 m intervals, respectively. Reflections on the data are interpreted to be the Quaternary-Eocene (QE) unconformity whose depth varies between 40-50 m, a clay/sand interface whose depth varies between 25-40 m, and a reflection at 6-7 m depth (H reflector), which is probably a Holocene deposit.On one shotgun profile, the QE unconformity is deformed with about 5 m of relief and is faulted about 2 m, both down-to-the-west. On the second shotgun profile, the QE unconformity appears to be only faulted with about 1 m of throw. The amount of displacement on the QE unconformity is duplicated in the overlying clay/sand reflector on both shotgun profiles and the H reflector appears to be offset about 1 m down-to-the-west about 15 m west of the QE unconformity fault location on the shotgun profile. This fault appears to be a rootless, second-order feature that cannot be traced directly to the underlying main reverse fault. We interpret the down-to-the-west deformation on these reflections, which is opposite to the dominant flexure of underlying Paleozoic, Cretaceous, and Tertiary rocks to be caused by a bending-moment fault that formed in response to the monoclinal bulge caused by the subjacent main reverse fault. The deformation at and above the QE unconformity suggests that the CCFZ has been active during the latest Quaternary and may be a possible source of earthquakes. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Structural Relations and Earthquake Hazards of the Crittenden County Fault Zone, Northeastern Arkansas

Abstract A preliminary interpretation of about 135 km of seismic-reflection data provides new information on the structural relations between the the Crittenden County fault zone and the subjacent rift-bounding faults along the southeastern margin of the Reelfoot rift in the New Madrid seismic zone. On the reflection data, the rift boundary is marked by a 4- to 8-km-wide zone of incoherent reflected energy and disrupted reflectors in the lower part of the well-stratified, lower Paleozoic sedimentary rocks and in the underlying Precambrian crystalline basement. In places, the zone of disrupted reflectors extends into the upper part of the Paleozoic rocks, and, on some lines, disrupted reflectors and distinct faults are present in the Upper Cretaceous and Tertiary rocks of the Mississippi Embayment. The Crittenden County fault zone is interpreted as a northwest-dipping, high-angle reverse fault with an up-to-the-northwest throw, which is opposite to the net structural relief in the subjacent graben. The fault zone is at least 32 km long and coincides with the rift margin in southwestern Crittenden County, but to the northeast, it diverges away from the aeromagnetically defined margin of the rift by almost 4 km. Most faults in the Crittenden County fault zone are apparently ancient rift-bounding normal faults that were reactivated with a significant amount of reverse slip during the Mesozoic and Cenozoic. On the basis of its apparent connection with the rift-bounding faults, the evidence of its long history of recurrent movement, and its orientation with respect to the modern stress field, the Crittenden County fault zone might be considered to potentially generate major earthquakes. In contrast, the possibility that the Crittenden County fault zone could be a bending-moment fault argues against it being extremely hazardous. Precambrian crystalline basement interpreted on the profiles is commonly deeper than magnetic basement by as much as 2.5 km. This discrepancy between shallow magnetic basement and deeper crystalline basement could be explained by the presence of igneous intrusions in the Paleozoic strata immediately above Precambrian basement.

Vertical displacement rates on Quaternary faults, Wanganui Basin

Abstract Wave-cut platforms of late Quaternary marine terraces between Hawera and Marton in Wanganui Basin are vertically displaced by several faults. The faults are probably high-angle normal, and strike generally northeast. Of the four faults that are known to displace surfaces of different age, two show increasing displacements with increasing age, and two show no change with age. Fault traces typically consist of discontinuous, subparallel scarps, up to 1.5 km long and up to several metres high. Some scarps display a left stepping, en echelon pattern, consistent with a component of dextral horizontal movement, though horizontal displacement of terrace risers isnotevident. Average rates of vertical movement on the faults vary between 0.02 and 0.2 mm/yr, much less than rates of vertical and horizontal movement documented for many other faults in New Zealand. One fault, the Nukumaru Fault, shows a constant rate of vertical movement averaging 0.07 mm/yr for the last 2.2 million years. The faults are tentatively interpreted as bending-moment faults, associated with folding.