Evidence Of Fault Activity Research Articles

Stratigraphic and structural evidence of transpressional Quaternary fault reactivation along the SE Korean Peninsula

Comprehending the nature, extent, and distribution of seismogenic structures, along with their seismogenic potential to induce destructive earthquakes in low seismic strain regions, holds significant socio-economic significance. Analyzing historical and paleoearthquakes becomes essential to understanding the influencing factors controlling the origin of earthquakes in intraplate regions, such as the Korean Peninsula. Based on current knowledge, the seismic pattern within the intraplate region, particularly along the Korean Peninsula, exhibits greater heterogeneity. This observation is drawn from historical seismic records, instrumentally detected seismic patterns, and paleoseismological analyses. Comprehensive paleoseismological studies play a crucial role in providing new evidence for fault activity, and hence they are an important contribution to the understanding of the seismic and structural evolution of faults. Existing paleoseismic investigations have predominantly focused on southeastern Korea, primarily along the Yangsan or Ulsan faults, with less attention given to other faults in the southeastern part of the Korean Peninsula. In the ongoing Korean Active Fault Mapping Project, this study specifically identifies a fault trace approximately 5.5–7 km long along the Ulsan-Dongnae Fault system named as Seokgye fault, named after the locality. Detailed paleoseismic investigations were carried out along the Seokgye fault. The fault presents a clear example of fault reactivation under the present compressional tectonic setting with a paleoearthquake during the late Pleistocene (∼121 ± 6 ka). Based on the length of the fault traced and observed displacement in the trench, Seokgye fault is capable of generating an earthquake of magnitude similar to the 2016 Gyeongju earthquake (Mw 5.8). This research enhances our understanding of the ongoing tectonic processes and Quaternary activities of fault systems in the southeastern Korean peninsula. Additionally, it contributes valuable insights for local-scale seismic hazard analysis in the area.

Evidence for fault activity during accumulation of the Furongian Chaomidian Formation (Shandong Province, China)

The Late Cambrian (Furongian) Chaomidian Formation accumulated in an epeiric sea that covered a large part of the North China Plate and extended from China to Korea. The depositional environment of the formation is commonly considered to have been affected by storms that broke up numerous limestone layers, but that was tectonically quiet. It is here argued, however, that some features of the formation – more in particular the many dozens of breccia layers and the occurrence of slid-down limestone blocks that are embedded in autochthonous oolites – can be explained satisfactorily only if some significant fault activity took place during its accumulation. The faulting may have been due to differential loading and subsidence, but an endogenic origin seems more probable. This implies that the structural history of the study area in Shandong Province may need re-consideration.

Detailed tectonic geomorphology of the Dras fault zone, NW Himalaya

<abstract> <p>Our recent mapping of the Dras fault zone in the NW Himalaya has answered one of the most anticipated searches in recent times where strike-slip faulting was expected from the geodetic studies. Therefore, the discovery of the fault is a leap towards the understanding of the causes of active faulting in the region, and how the plate tectonic convergence between India and Eurasia is compensated in the interior portions of the Himalayan collision zone, and what does that imply about the overall convergence budget and the associated earthquake hazards. The present work is an extended version of our previous studies on the mapping of the Dras fault zone, and we show details that were either not available or briefly touched. We have used the 30 m shuttle radar topography to map the tectonic geomorphological features that includes the fault scarps, deflected drainage, triangular facets, ridge crests, faulted Quaternary landforms and so on. The results show that oblique strike-slip faulting is active in the suture zone, which suggests that the active crustal deformation is actively compensated in the interior portions of the orogen, and it is not just restricted to the frontal portions. The Dras fault is a major fault that we have interpreted either as a south dipping oblique backthrust or an oblique north dipping normal fault. The fieldwork was conducted in Leh, but it did not reveal any evidence for active faulting, and the fieldwork in the Dras region was not possible because of the politically sensitive nature of border regions where fieldwork is always an uphill task.</p> </abstract>

Geomorphological evidence of active faulting in low seismicity regions - examples from the Valley of Lakes, southern Mongolia

Geomorphological evidence of active faulting in low seismicity regions - examples from the Valley of Lakes, southern Mongolia

Evidence for active faulting in the eastern part of the Gulf of Saros, northern Aegean, from high-resolution seismic data

This study focuses on the determination of the near-surface tectonic features in the eastern part of the Gulf of Saros, a highly active seismic region within the North Anatolian Fault Zone. Approximately 350-km-line high-resolution seismic data were acquired to understand the active tectonic setting of the inner side of the gulf. The Ganos Fault, which generated the 9 August 1912 earthquake (Mw = 7.3) in western Turkey, enters into the Gulf of Saros from the east, cuts the southern margin of the gulf forming a trough which becomes broader and deeper westward. The seismic data reveal that the fault is not made up of a single segment or a pair of border faults bounding the trough. According to the seismic images of the fault segments, however, the emanating earthquake energy will possibly be carried by two different faults; namely the Ganos and Saros segments. These fault segments will be presented first in this paper in detail from new collected seismic data at the inner part of the gulf, and will be used to help a new tectonic model that explains how the Ganos segment controls the northern margin of the trough while the Saros segment controls the central part of the main trough. The latter is responsible from the development of an active basin and it forms the sudden deepening observed on the trough.

Re-evaluating seismic hazard along the southern Longmen Shan, China: Insights from the 1970 Dayi and 2013 Lushan earthquakes

Competing hypotheses have been proposed to explain the seismic hazard (i.e. whether earthquakes with M≥7 occur) of the southern Longmen Shan (LMS). This region did not rupture during the 2008 Mw 7.9 Wenchuan earthquake, but later generated the 2013 Mw 6.6 Lushan earthquake. Currently, the maximum possible earthquake magnitude, its average recurrence interval, and the seismogenic structure of the southern LMS, remain poorly documented. This study aims to re-evaluate seismogenic structures and seismic hazard along the southern LMS. We first describe the sub-surface structural geometry, as well as the total slip and Quaternary activity of the Range Front blind thrust (RFBT), using high-resolution seismic reflection profiles, borehole data, and intensity-derived macroscopic epicenters. This thrust, which generated the 1970 Ms 6.2 Dayi and 2013 Mw 6.6 Lushan earthquakes, extends for >250km along the LMS range front. Integrating new evidence of active faulting and folding and previous quantitative horizontal shortening rate results, we estimate that the Quaternary slip rate of the RFBT is nearly 1mm/yr, with a minimum total slip of 5km since 8–5Ma. Furthermore, we calculate the accumulation rate of seismic moment, 8.04 (±2.09)×1017N·m/yr, for the main active thrusts on the southern LMS, to compare with the moment release rate for earthquakes in the region. When we combine this with the Gutenberg–Richter distribution obtained from historical and instrumental catalogs, we estimate that the potential maximum moment magnitude of an earthquake in the southern LMS is 7.7. Finally, we conclude that the entire southern LMS is capable of generating much larger earthquakes (Mw 7.3–7.7) than seen recently, with an average frequency of once every 1000–1400years. Therefore, our findings confirm that there is potential for large earthquakes in the southern LMS, especially on the RFBT, which extends beneath the densely populated Chengdu Plain.

Active Fault-Related Folding beneath an Alluvial Terrace in the Southern Longmen Shan Range Front, Sichuan Basin, China: Implications for Seismic Hazard

Abstract The devastating 2008 M w 7.9 Wenchuan earthquake, China, demonstrates that the central and northern parts of the Longmen Shan are currently active. Evidence for active faulting and folding in the southern Longmen Shan, however, remains poorly documented. In this paper, we define the structural geometry, fault kinematics, and seismic hazard of the Qiongxi thrust fault system (QTF) along the southern Longmen Shan range front by integrating deep and shallow seismic‐reflection data and geomorphic observations. The QTF is a 50 km long, north–south‐trending set of faults and associated folds that exhibit geomorphic evidence of Quaternary surface deformation. Geomorphic observations and seismic‐reflection data reveal that these faults dip steeply to the east and merge at depth with a blind, west‐dipping thrust ramp. The trend and reverse sense of slip along the QTF indicates that the structure accommodates east–west crustal shortening. Based on uplift of stratigraphic horizons across the fault zone, we define a Late Pliocene–to–Early Pleistocene fault slip rate of 0.2–0.3 mm/yr and a Middle Pleistocene–to–present rate of 0.4–1.2 mm/yr on the west‐dipping thrust ramp. This ramp soles to a basal detachment in the Triassic section at a depth of 4.5–5.5 km. To the west, this detachment steps down onto a blind, northwest‐dipping thrust termed the Range Front thrust. A rupture of the QTF in combination with the Range Front thrust could generate an M w 7.8 earthquake with average displacement of 5.7 m. This type of earthquake source poses significant hazards to the adjacent, highly populated Sichuan basin. Online Material: Figures detailing cross sections and 3D surfaces, additional reflection profiles, and dating information.

Late Pleistocene and Holocene Faulting in the Western Truckee Basin North of Truckee, California

Evidence for active faulting in the Truckee Basin, north of Lake Tahoe, is observed in a meadow containing a scarp and small closed depression. Shallow, hand‐dug trenches show offset marsh stratigraphy of Holocene age. Lithostratigraphy descriptions and radiocarbon dates indicate the meadow was a marsh during the late Quaternary that was abruptly infilled with the deposition of the ∼7000 yr B.P. Tsoyawata tephra (Mt. Mazama). The tephra is offset up to 80 cm across a narrow, sub‐vertical, north–south‐striking fault zone. Additional offset of 30 cm occurred across the same structure during the late Pleistocene. Our study provides direct stratigraphic evidence for at least one surface‐faulting event during the Holocene, and another in the late Pleistocene, within the Truckee fault zone and provides new constraints on seismic sources capable of significant ground rupture and/or shaking in the greater Reno–Tahoe–Truckee area.

New geophysical and geological evidence for the present day southernmost active deformational front of the Rif thrust-and-fold belt and the oceanic accretionary prism of Cadiz: the Dhar Doum–Lalla Zahra fault, Northwestern Atlantic Coastal Morocco

Combining the results from field observations, high resolution 2D-electric resistivity and high resolution seismic refraction tomography, we have found new evidence for active faulting in the Dhar Doum area, northwestern Atlantic coast of Morocco. Qualitative interpretation of the inverted resistivity and seismic refraction data reveals the presence of two thrust faults that cut the topographic surface and displace the most recent sedimentary deposits. Furthermore, one of these seismically imaged faults strongly correlates with the Dhar Doum–Lalla Zahra fault. The steepening at the surface and the flattening with depth of this fault are likely to indicate an important strike-slip component associated with a major reverse component. If extended offshore to the west, the Dhar Doum fault could be a continuation of the southernmost deformational front of the Cadiz oceanic accretionary prism. Therefore, this structure is very likely to represent the actual active southern deformational front of the oceanic accretionary prism, as well as that of the Rif fold-and-thrust belt. The southward thickening of the growth strata composing the uppermost dune system and the occurrence of Plio-Quaternary conglomerates north of the Dhar Doum–Lalla Zahra fault suggest that the neotectonic activity may have started by the end of the Pliocene and have continued to the present as indicated by the folding-and-faulting of the most recent sedimentary deposits and the presence of high scarps. The identification of active faulting in the study area that may have a profound influence on seismic hazard analysis of the whole Rif foredeep basin.

Quaternary reactivation of the Kern Canyon fault system, southern Sierra Nevada, California

The Kern Canyon fault, the longest fault in the southern Sierra Nevada, is an active structure and has been reactivated at discrete times over the past ~100 m.y. in response to changing lithospheric stresses. After initiation as a Cretaceous transpressional structure, the Kern Canyon fault transitioned into a dextral strike-slip shear zone that remained active as it was exhumed into the brittle regime during regional Late Cretaceous uplift of the Sierra Nevada batholith. The Kern Canyon fault was reactivated during Miocene regional extension as part of a transfer zone between two differentially extending domains in the southern Sierra Nevada. Subsequent normal displacement along the fault began in Pliocene time. New evidence for fault activity, which continued into late Quaternary time, includes its current geomorphic expression as a series of meters-high, west-side-up scarps that crop out discontinuously along the fault’s 130-km length. Relocated focal mechanisms of modern earthquakes confirm ongoing normal faulting, and geodetic measure ments suggest that the Sierra Nevada is uplifting relative to the adjacent valleys. This evidence for recent activity overturns a long-held view that the Kern Canyon fault has been in active for more than 3.5 m.y. Its reactivation indicates that deformation repeatedly localized along a pre existing crustal weakness, a Cretaceous shear zone. We propose that a system of inter related normal faults, including the Kern Canyon fault, is responding to mantle lithosphere removal beneath the southern Sierra Nevada region. The location of the active Kern Canyon fault within the Sierra Nevada–Great Valley microplate indicates that deformation is occurring within the microplate.

Fault-controlled alpine topography in Norway

Abstract: Alpine topography in Norway is largely fault-controlled. Linear and asymmetric ranges developed in the footwalls of normal faults that were reactivated after the main phase of Mesozoic rifting, but prior to the Late Cenozoic glaciations. Stark geomorphological contrasts developed across the faults, reflecting differential glacial exploitation of the pre-glacial drainage pattern. Alpine topography developed preferentially in the footwalls. Triangular facets mark the traces of the most recently active faults. At the base of deeply incised, alpine range-front escarpments, the best-exposed faults display metres-thick fault-rock successions and record multiple phases of fault movement. Juxtaposition of Precambrian and Caledonian basement rocks with Jurassic or Cretaceous sedimentary rocks provides evidence for fault activity in or after the Mesozoic for some of the faults. Late Cretaceous or younger reactivation is indicated by jumps in apatite fission-track apparent ages across the faults, and interferometric synthetic aperture radar and earthquake data attest to normal faulting at the present day. Two of the areas described host anomalous clusters of rockslides that may relate to tectonic activity. The most distinct landscape-forming faults in western Scandinavia were probably active in the Cenozoic, and imposed asymmetric landscape patterns from the scale of single mountain ranges to the whole of Scandinavia.

Geomorphic signatures of recent normal fault activity versus geological evidence of inactivity: Case studies from the central Apennines (Italy)

We have here analysed two normal faults of the central Apennines, one that affects the south-western slopes of the Montagna dei Fiori–Montagna di Campli relief, and the other that is located along the south-western border of the Leonessa intermontane depression. Through this analysis, we aim to better understand the reliability of geomorphic features, such as the fresh exposure of fault planes along bedrock scarps as certain evidence of active faulting in the Apennines, and to define the Quaternary kinematic history of these tectonic structures. The experience gathered from these two case studies suggests that the so-called ‘geomorphic signature’ of recent fault activity must be supported by wider geomorphologic and geologic investigations, such as the identification of displaced deposits and landforms not older than the Late Pleistocene, and/or an accurate definition of the slope instabilities. Our observations indicate that the fault planes studied are exposed exclusively because of the occurrence of non-tectonic processes, i.e. differential erosion and gravitational phenomena that have affected the portions of the slopes that are located in the hanging wall sectors. The geological evidence we have collected indicates that the Montagna dei Fiori–Montagna di Campli fault was probably not active during the whole of the Quaternary, while the tectonic activity of the Leonessa fault ceased (or strongly reduced) at least during the Late Pleistocene, and probably since the Middle Pleistocene. The present lack of activity of these tectonic structures suggests that the fault activation for high magnitude earthquakes that produce surface faulting is improbable (i.e. M > 5.5–6.0, with reference to the Apennines, according to Michetti et al. [Michetti, A.M., Brunamonte, F., Serva, L., Vittori, E. (1996), Trench investigations of the 1915 Fucino earthquake fault scarps (Abruzzo, Central Italy): geological evidence of large historical events, J. Geoph. Res., 101, 5921–5936; Michetti, A.M., Ferreli, L., Esposito, E., Porfido, S., Blumetti, A.M., Vittori, E., Serva, L., Roberts, G.P. (2000), Ground effects during the September 9, 1998, Mw = 5.6, Lauria earthquake and the seismic potential of the aseismic Pollino region in Southern Italy. Seis. Res. Letts. 71, 31–46]). If, according to the current view, the shifting of the intra-Apennine extension towards the Adriatic sectors is still active, the Montagna dei Fiori–Montagna di Campli fault might be involved in active extensional deformation in the future.

Duplicate Measurements After Nine Years Support a Non-tectonic Origin for Displacement of Shot Holes in West Texas

Meinardus et al. (1993) conducted a geologic evaluation of the Downie roadcut on U.S. Highway 285, 14.6 km (9 miles) north of Sanderson in Terrell County, TX. The roadcut was constructed in 1965. The exposures in the roadcut exhibited offset shot holes with an updip component on the massive limestone of the Santa Elena Formation exposed on the roadcut walls. The total displacement across three bedding planes in the limestone along which the shot holes were offset was approximately 73 cm. The offset shot holes have been interpreted by Bolden (1991) as evidence of active faulting in west Texas. The interpretation by Bolden (1991) implied an annualized total displacement of about 2.5 cm/year. The purpose of the geologic evaluation by Meinardus et al. (1993) was to determine whether active faulting was occurring and whether the structural style invoked by Bolden (1991) as the cause of the active faulting was present. Evidence of active or recent faulting is important in the environmental and regulatory context because state and federal location standards for many types of waste management facilities explicitly address faults and standoff distances from active faults (e.g., 30 TAC 335.204; 40 CFR 264.18). Meinardus et al. (1993) concluded that active faulting was unlikely, that the offset shot holes were caused by blasting effects, and that the structural style and fracture patterns exposed in the roadcut did not support the Reidel shear system postulated by Bolden (1991). Meinardus et al. (1993) made two sets of displacement measurements over 9 months in 1992 and concluded that there was no measurable displacement across the planes of interest during this time frame. The permanent benchmarks established in the rock offer the opportunity for subsequent displacement measurements over a much longer time period. The offset measurements reported in this Technical Note were made in …

Strike-Slip-Influenced Sedimentation in Norfolk Basin, Southeastern Massachusetts: ABSTRACT

Pennsylvanian coarse-grained fluvial sedimentation in the Norfolk basin of southeastern Massachusetts occurred in a tectonically active environment, possible related to sinistral strike-slip motion on faults west of the basin. Detailed measured sections reveal an overall upward-fining succession, with humid alluvial fan facies and braided stream sub-facies with associated overbank/flood-plain deposits. The humid alluvial fan contains massive bedded, clast supported conglomerates with infiltrated sandstone and siltstone. Fluvial dominance during deposition is indicated by frequent upward-fining cycles, lack of evidence of debris flow, and clast rounding and imbrication. The braided stream sub-facies is distinguished by a reduction in bed thickness and clast size (maximum clast size = 5 cm), and commonly contains upward-fining cycles. Although trough cross-bedding angles are low throughout the basin, low angle (< 10°) troughs upslope grade into distal very low angle (< 5°) troughs to plane beds, indicating lesser channel incision and greater sheetflood conditions downslope. The overbank/flood-plain deposits include plane laminated siltstone and claystone with common desiccation cracks. Evidence for active faulting during deposition includes: mismatch of detrital grain mineralogy with adjacent source terrains; soft sediment boudinage; mixtures of fresh and altered feldspar; and rapid lateral and vertical facies changes. Provenance studies suggest a source area for many of the sediments might be metabasalts and marbles of the Blackstone Series of northern Rhode Island. If correct, these results support paleomagnetic and other regional studies suggesting sinistral strike-slip motion may have formed the Carboniferous basins of Massachusetts and Rhode Island. End_of_Article - Last_Page 460------------