Quaternary Faults Research Articles

3D-thrust fault pattern control on negative inversion: An analogue modelling perspective on central Italy

During the last decades, central Italy has been struck by severe seismic sequences. Some authors have suggested that inherited thrust faults may have played an important role in controlling the recent-to active extensional deformation in the area, particularly during the 2016 Central Italy seismic sequence. To explore this hypothesis, we performed an analogue modelling study that addressed the structural evolution of a composite, heterogeneous multilayer affected by polyphase deformation. The overall three-dimensional geometry resulting from the modelling consists of a flat-ramp extensional fault system, with flats being localised along the weaker stratigraphic units, and ramps locally reactivating the pre-existing thrust ramps at depth. At shallower levels, deformation can localize at newly-formed short-cut faults depending on the geometry of deeper structures. The experimental results provide further support to the hypothesis of a link between Quaternary normal faults and inherited thrust faults during the 2016 seismic sequences. Specifically, analogue modelling results suggest that the Quaternary fault pattern may be controlled by the interaction between the active stress field and the pre-existing compressional structures. This scenario bears significant implications regarding the empirical relationship between the geometry of surface faulting and the magnitude of earthquakes, with considerable repercussions on seismic risk assessment.

Characterizing strain between rigid crustal blocks in the southern Cascadia forearc: Quaternary faults and folds of the northern Sacramento Valley, California

AbstractTopographic profiles across late Quaternary surfaces in the northern Sacramento Valley (California, USA) show offset and progressive folding on series of active east- and northeast-trending faults and folds. Optically stimulated luminescence ages on deposits draping a warped late Pleistocene river terrace yielded differential incision rates along the Sacramento River and indicate tectonic uplift equal to 0.2 ± 0.1 and 0.6 ± 0.2 mm/yr above the anticline of the Inks Creek fold system and Red Bluff fault, respectively. Uplift rates correspond to a total of 1.3 ± 0.4 mm/yr of north-directed crustal shortening, accounting for all of the geodetically observed contractional strain in the northern Sacramento Valley, but only part of the far-field contraction between the Sierra Nevada–Great Valley and Oregon Coast blocks. These structures define the southern limit of the transpressional transition between the two blocks.

Recent tectonic activity in Central Alborz Mountain, Iran: morphometric analysis and knickpoint identification

Alborz, as part of the Alpine-Himalayan orogeny belt, has been the result of the convergence of the Central Iranian and Eurasian plate since the late Triassic. The study area located in Central Alborz encompasses different Quaternary faults. Thus, the present study aimed to evaluate the effect of faults on river landforms through morphotectonic indices and the causes of knickpoints and knickzones in the Bedrock Rivers in part of Central Alborz. To this end, six morphometric indices such as longitudinal gradient (SL), hierarchical anomaly (Δa), the bifurcation index (R), hypsometric integral and hypsometric curve (Hi-Hc), relative relief (Bh), and basin shape (Bs) were calculated and analyzed in 38 sub-basins of the area. Finally, the area was divided into extremely high, high, medium, and low tectonic activity areas using the relative tectonic activity (IAT). Normalized steepness and concavity indices along with the longitudinal profiles of the streams were obtained using Matlab and Arc GIS software. Based on the findings, the existence of slope-break knickpoints at the mountain piedmont at the outlet of large rivers through active faults demonstrated that most of these landforms were created by movements along the main faults such as Khazar, Nusha, Soheil, Deylaman, Kashachal, representing high tectonic activity in the central and southern parts of the study area. However, the values of these indices were extremely low and indicated low tectonic activity in the northern parts located in the embayment part of the Caspian Sea. Finally, the findings revealed that these classes correspond well to the areas with landforms such as V-shaped and narrow valleys, gorges, deflected and offset streams, deformed Neogene, and Quaternary units that indicate the post-Neogene activity.

Quantitative assessment of the relative tectonic activity using the analytical hierarchy process in the northwestern margin of the Lut Block, Central Iran

In this study, the analytical hierarchy process (AHP) was used to enhance the accuracy of the results obtained from the geomorphic analysis of tectonic activity. For this purpose, the relative tectonic activity index was computed by applying different and specific weights to each index based on the general geological and structural conditions of the study area. The Kuh-e-Sarhangi Mountain with a NE-SW strike is located in the northern part of the Tabas Block in the Central Iran Plate. The Kuh-e-Sarhangi Fault is considered one of the major faults in Central Iran and shows evidence of Quaternary activity. In this study, in order to evaluate the activity of the faults, six morphotectonic indices were computed and the different conditions which influenced the morphometric factors were considered and analyzed. The relative tectonic activity of Kuh-e-Sarhangi was classified based on the analytical hierarchy process method. These results were confirmed by field studies. The results of this method fitted well with some independently detected Quaternary faults and other reactivated faults in the Kuh-e-Sarhangi Mountain. With a right-lateral movement, some of these faults have caused the displacement of rivers up to 900 m. The dispersal of the high tectonic activity classes based on the AHP method conforms to the post-Neogene activity of the region. The distribution of the classes illustrates that morphotectonic anomalies correspond with the incised alluvial fans and terraces and the bisected and displaced rivers in the study area. Accordingly, the integration of the results of field investigations, satellite images, morphometry, and the AHP method shows a high accordance with the active structures and demonstrates that the study area is tectonically active. This analysis illustrates the recent movements of the Kuh-e-Sarhangi Fault and the activity of the Lut Block due to the convergent movement of the Arabian plate toward Eurasia.

Patterns of recent deformation of the western Maracaibo block, northern Colombia and western Venezuela, based on integration of geomorphic indices with regional geology

The Maracaibo block is a triangular, continental tectonic terrane that includes two isolated Andean ranges of northern Colombia and western Venezuela: the Sierra de Santa Marta Massif (SSMM; maximum elevation 5700 m) in the west and the Perija Range (PR; 3600 m) to the east. The Cesar-Rancheria Basin (CRB) is an intermontane basin that separates the two ranges. To establish patterns of recent deformation of this elevated region and to infer its tectonic mechanism, we have integrated the following results: (1) analysis of 350 stream profiles and calculations of geomorphic indices, including stream length-gradient (SL) index, ratio of valley-floor width to valley height (VF), and hysometric curves for 20 watersheds in both ranges and (2) interpretation of three seismic reflection profiles within the CRB and adjacent areas. We determine that the northeastern part of the SSMM is tectonically quiescent based on its concave stream profiles, low geomorphic indices, and few vertical-step knickpoints. In comparison, we find that the central, southern, and eastern parts of the SSMM show tectonic uplift and recent fault control based on slope-break knickpoints and values in steepness and geomorphic indices with possible additional controls from lithologies of varying erosional resistance. Correlations between steepness, SL indices, slope-break knickpoints, and topographic elevations of the SSMM and central PR all indicate recent deformation of these areas. We use seismic reflection profiles from the eastern part of the CRB to confirm the existence of late Quaternary faulting and folding in these geomorphologically active areas. We propose that active, southeastward shallow (approximately 10°–15°) subduction of the Caribbean plate along the base of the South American continental crust produces active crustal deformation within the southern and eastern SSMM. The central PR and eastern CRB are also being deformed by active strike-slip faults.

Late Pleistocene sedimentary environment and reverse faulting along the Chugaryung Fault in the central Korean Peninsula: a case study on the Cheorwon Basin

The Cheorwon area of South Korea has several records of the Quaternary faulting along the Chugaryung fault system and volcanic activity (Hantangang River Basalt). The most recent faulting event occurred along a segment of the Wangsukcheon fault (ca. 210 ka). In this study, a 5-m-deep trench was examined at the northern end of the Cheorwon Plain. The formation mechanism(s) and characteristics of local sediments as well as the timing of the Quaternary faults observed in the lower sections were analyzed. The sediments are very fine-grained, with a sand content of less than 5%. Soil wedge structures indicate that the sediments were affected by an ice-age environment. Some stratification and our analyses suggest that the sediments were formed on a floodplain. The ages of the sediments range from 150 to 130 ka, based on quartz optically-stimulated luminescence (OSL) dating. The absence of sediments younger than 100 ka is likely attributable to a change to sedimentary environments where erosion processes are dominant, with sediments being removed to the Hantangang River area. Meanwhile, a N-S-striking fault, dipping 30° eastward, cut across the sediments during 140–130 ka. This study provides important information on Quaternary sedimentary environment nearby the Hantangang River area, but also the introduction of the Quaternary fault into Chugaryung fault system, which has been lacking to data.

New insights into the effect of the quaternary fault activity on river knickpoints in the Central Alborz (Iran)

This study examines the knickpoints in a region to provide new insights for assessing the Tectonically Formed Knickpoints (TFKs). In this paper, we have used a quantitative method to recognize TFKs using two different river steepness methods; the stream gradient (Gd) and the normalized steepness index (kSn). Analysis of the extracted TFKs with the longitudinal profile, logarithm slope-area plots, and natural logarithm gradient-distance plots suggests that these knickpoints correlate with the active segments of faults. In addition, evaluation of the TFKs indicates that the different length and height of the TFKs can be related to the different features of each fault. The investigation of TFKs was implemented in the Central Alborz located at the southern margin of the Caspian Basin in northern Iran which is a part of an active deformation region of the Arabian and Eurasian plate collision zone. The investigation of TFKs suggests that the Quaternary faults’ activities are related to the recent tectonic activity in the northern flank of the Central Alborz as well as the central part of the Central Alborz which is consistent with Global Positioning System (GPS) studies and increased uplift rate. The results are in agreement with field observations in terms of geomorphic features and geology.

Proterozoic–Paleozoic Sedimentary Rocks and Mesozoic–Cenozoic Landscapes of the Cape Mountains Across the Kango Complex Reveal ‘More Gaps Than Record’ from Rodinia and Gondwana to Africa

The Kango (Cango) region flanks the northern margins of the Klein Karoo and the Cape Mountains across the Western Cape Province of South Africa. It preserves a condensed Proterozoic–Paleozoic stratigraphy exposed via a Mesozoic–Cenozoic morphology with a present Alpine-like topography. Its rocks and landscapes have been repeatedly mapped and documented for the past 150 years. Over the last 25 years, we remapped and dated a central-eastern section of this region. The subvertically bedded and cleaved rocks reveal an 8–10 km thick stratigraphy covering more than 700 million years between ca. 1200 and 500 Ma with several unconformities and disconformities. At ca. 252 Ma, during the Cape orogeny, this Kango Complex was deformed along thrusts and sub-isoclinal folds producing steeply dipping phyllites and slates. It was uplifted by 3–5 km during the Kalahari epeirogeny between 140 and 60 Ma while eroding at ca. 100–200 m/m.y. (120–80 Ma). During the Cenozoic, the rate of uplift decreased by an order of magnitude and today is ca. 0.4–0.7 m/m.y. across steep slopes and canyons in contrast to the Himalayas where erosion rates are about hundred times faster. A recent publication about this central-eastern section of the Kango region disputes the existence of regional isoclinal folds and suggests that deposition of the oldest sedimentary successions, including carbonate rocks of the Cango Caves (limestone-marble with enigmatic microfossils) was simple, continuous and restricted to between ca. 700 and 500 Ma, decreasing earlier estimates of the stratigraphic age range by 60–80%. Similarly, recent interpretations of the complex landscapes link the northern contact between the Kango and Table Mountain rock sequences to Quaternary faults. We present a new geological database, mapped between 1:500 and 1:10,000 scales, and twelve stratigraphic sections with younging directions linked to structural and isotopic data that support repetitions along regional isoclinal folds and thrust zones of the Kango sequences during the Permo–Triassic Cape orogeny, and geomorphic data that link the origin of its landscapes to weathering and erosion during the Cretaceous–Cenozoic Kalahari epeirogeny. During its evolution, the Kango Basin directly flanked both Grenvillian and Pan-African Mountain systems. But, at an average sedimentation rate of ca. 1 mm/70 years (0.014 mm/year) and with present low erosion rates (0.005 mm/year), there is likely more time missing than preserved of the tectono-erosion across these different regions of Rodinia and Gondwana before Africa emerged. To further evaluate the geodynamic significance of these time gaps requires more field mapping linked to new transdisciplinary geosciences.

Incipient evolution of the Eastern California shear zone through the transpressional zone of the San Bernardino Mountains and San Gorgonio Pass, California

AbstractThe nature of the connection between the Eastern California shear zone (ECSZ) and the San Andreas fault (SAF) in southern California (western United States) is not well understood. Northwest of San Gorgonio Pass, strands of the ECSZ may be migrating south and west into the convergent zone of the San Bernardino Mountains (SBM) as it is advected to the southeast via the SAF. Using high-resolution topography and field mapping, this study aims to test whether diffuse faults within the SBM represent a nascent connection between the ECSZ and the SAF. Topographic resolution of ≤1 m was achieved using both lidar and unmanned aerial vehicle surveys along two Quaternary strike-slip faults. The Lone Valley fault enters the SBM from the north and may form an along-strike continuation of the Helendale fault. We find that its geomorphic expression is obscured where it crosses Quaternary alluvium, however, suggesting that it may have a low rate of yet-undetermined activity. The Lake Peak fault is located farther south and cuts through the high topography of the San Gorgonio massif and may merge with strands of the SAF system. We find that this fault clearly cuts Quaternary glacial deposits, although the magnitude of offset is difficult to assess. Based on our interpretation of geomorphic features, we propose that the Lake Peak fault has predominantly dextral or oblique-dextral motion, possibly with a slip rate that is comparable to the low rates observed along other strands of the ECSZ (i.e., ≤1 mm/yr). Comparing the geomorphic expressions of these faults is difficult, however, given that the erosive nature of the mountainous landscape in the SBM may obscure evidence of active faulting. Based on these observations, as well as the occurrence of other diffuse faults in the region, we suggest that dextral strain is overprinting the actively convergent zone of the SBM, thereby creating a throughgoing connection between the ECSZ and the SAF west of San Gorgonio Pass.

Interpretation of lineaments and faults near Summerville, South Carolina, USA, using LiDAR data: implications for the cause of the 1886 Charleston, South Carolina, earthquake

LiDAR (light detection and ranging) data acquired near Summerville, South Carolina, reveal numerous lineaments trending in various directions across the Middleton Place-Summerville seismic zone (MPSSZ) and surrounding area. These lineaments are defined by linear depressions and stream valleys that are developed within late Eocene to Holocene marine, marginal marine, and fluvial sediments of the Atlantic Coastal Plain. The 40-kmlong, ENE-WSW-oriented Deer Park lineament coincides with the Woodstock epicenter of the 1886 Charleston earthquake, suggesting that the main shock may have occurred along a fault associated with this lineament. The proximity of the 17-km-long, ENE-WSW-oriented Middleton Place lineament to the Middleton Place epicenter suggests that it too may have ruptured in 1886. Several E-W-oriented topographic scarps are also located near the area of modern seismicity, including the 3- to 5-km-long, south-facing McChune and Summerwood scarps. The McChune scarp is aligned with the E-W-trending portion of the Summerville scarp to the west, suggesting that both scarps may be from uplift to the north along the same fault. The McChune scarp and the Otranto and Middleton Place lineaments coincide with faults interpreted from previously acquired seismic-reflection profiles, suggesting that these features are surface expressions of Quaternary faults. Other lineaments east of the MPSSZ are associated with Neogene structural domes, indicating that the interpreted faults along these lineaments have been active during the late Cenozoic. The LiDAR data also revealed a ~350-m dextral offset of a middle Pleistocene beach ridge along the Woodstock fault and a ~20-km-long, NW-SE-oriented lineament to the east (Canterhilllineament) that appears to be the surface expression of the Charleston fault.

Post-LGM faulting in Central Europe: LiDAR detection of the >50 km-long Sub-Tatra fault, Western Carpathians

The increasing availability of high-resolution LiDAR data reveals surprisingly strong topographic evidence of late Quaternary faulting in some intraplate regions characterized by weak recent tectonic activity. For the first time, we present evidence of a >50 km-long post-Last Glacial Maximum (LGM) tectonic rupture along the southern margin of the Tatra Mountains (Slovakia) in the highest part of the Carpathian Mountains. Using a high-resolution 1 × 1 m LiDAR DEM, we recognize that the normal, range-bounding Sub-Tatra fault (STF) and its eastward branch, the Ružbachy fault (RBF), offset late Quaternary glacial moraines, alluvial fans and colluvial slopes. The fault zone morphology is dominated by a nearly continuous, southward-facing, up to ~18 m-high main scarp locally accompanied by antithetic fault scarps and hanging wall grabens. Similar offsets of pre-LGM and LGM deposits and the absence of fault scarps within Holocene alluvium suggest that the STF and RBF were active for a relatively short time interval between ~18 ka and the Holocene. Using the vertical separation of dated LGM moraine crests, we estimate that the minimum average postglacial slip rates along the STF and RBF varied from ~0.1–0.3 mm/year, i.e., rates one order of magnitude higher than those reported for other faults in Central Europe. Additionally, deep-seated landslides and the presence of large rock avalanches along the fault suggest possible postglacial high-magnitude earthquake(s) producing coseismic rupture of the STF and RBF. We conclude that 1) southern range-bounding faults of the Tatra Mountains are the longest (>50 km) and only documented post-LGM ruptures revealing extensive offset of late Quaternary deposits in the Western Carpathians and 2) relatively small along-strike variations in postglacial offset mimic the long-term exhumation trends and imply “en block” uplift of the southern margin of the Tatra Mountains with the highest displacement along the east STF.

Revisiting the slip rate of Quaternary faults in the Iberian Chain, NE Spain. Geomorphic and seismic-hazard implications

The seismogenic potential of active faults for seismic hazard analyses are typically constrained using slip rates. These parameters, derived from numerically dated Quaternary deposits and landforms, have a critical impact on seismic hazard estimates with relevant societal and economic implications. Recently published geomorphological and paleoseismic investigations on active normal faults in the intraplate Iberian Chain (Spain), based on OSL ages from a now closed commercial laboratory, indicate anomalously high slip rates and paleoearthquake frequencies and extremely high fluvial incision rates. Parameters derived from those numerical ages have been used for seismic hazard assessments at critical facilities. This work revisits the chronology of Quaternary deposits associated with several faults applying various geochronological methods: Electro Spin Resonance (ESR), AMS Radiocarbon, Optically Stimulated Luminescence (OSL) and U-series dating. The totality of the new numerical ages is markedly different from the previously published OSL ages. The thirteen new ESR, OSL and U-series ages are systematically between three and six times older than the previous OSL ages. These data strongly suggest that previous ages overestimate the activity of the faults and seismic hazard in the region. The lack of validity of the revisited OSL analyses is attributed to inadequate dating procedures. Slip rates calculated with the new numerical ages are consistent with the slip rates estimated using Pliocene markers in the Iberian Chain and the slip rates published for other normal faults in eastern Spain. The new geochronological data also indicate reasonable fluvial incision rates, comparable with those estimated in nearby regions. The findings presented in this work have also implications for other Quaternary geomorphological studies in Spain based on potentially non-valid OSL ages.

경북 포항 냉수리 제4기 단층물질과 미구조에 기록된 동지진성 미끌림 흔적

경북 포항 냉수리 제4기 단층물질과 미구조에 기록된 동지진성 미끌림 흔적

Exhumation history of the north-central Shanxi Rift, North China, revealed by low-temperature thermochronology

We present new apatite U-Th-Sm/He (AHe; n = 51), apatite fission track data (AFT; n = 12), and zircon U-Th/He (ZHe; n = 8) data for two elevation transects in the north-central Shanxi Rift, North China. Low-temperature thermochronologic data combined with forward and inverse time-temperature history models reveal a Precambrian to Quaternary thermal history characterized by: (1) cooling to <∼50°C during the Proterozoic, consistent with the development of a regional unconformity above Neoarchean–Paleoproterozoic cratonic basement rocks; (2) reheating to <∼180°C due to sediment burial during the Paleozoic to Mesozoic; (3) cooling at a rate >3.5°C/Ma during the Late Jurassic to earliest Cretaceous Yanshanian orogeny; (4) a possible ca. 120-90 Ma reheating event due to elevated geothermal gradients and/or local sediment burial; (5) Late Cretaceous (ca. 110-65 Ma) cooling contemporaneous with regional extension in eastern Asia and denudation of the paleo-Taihangshan highlands; and finally, (6) post ca. 10 Ma cooling associated with extension in the Shanxi Rift. AFT dates from the deepest exhumed structural positions of the sampled footwall blocks are mostly >65 Ma and AHe dates tend to be highly dispersed within samples. AFT inverse and AHe forward model results indicate that samples were at temperatures of <∼75°C by ca. 70 Ma. Despite the early Cenozoic and older AFT and AHe dates, metamict zircon grains with high effective uranium (eU >∼750 ppm) yield young ZHe dates of ca. 13-9 Ma, consistent with Late Miocene exhumation. We argue for the onset of latest cooling by ca. 10 Ma based on these ZHe dates; however, the precise timing for the onset of rifting remains uncertain. The results further suggest that Late Miocene–Quaternary extension in the north-central Shanxi Rift is responsible for ≤∼2.5 km of exhumation, such that published Quaternary extension and fault throw rates are significantly (>100%) higher than long-term rates inferred from the thermochronologic data.

Surface rupture geomorphology and vertical slip rates constrained by terraces along the Wulashan piedmont fault in the Hetao Basin, China

The Wulashan piedmont fault is a typical normal fault in the northern Ordos Block and has exhibited intense activity since the Late Pleistocene. It is located among the Ordos Block, Alashan Block, Yanshan Block and North China Block and between the NE expansion of the Tibetan Plateau and the subduction of the Pacific Plate. This area is important as a key location to study the remote effects of the Tibetan Plateau NE expansion. Historical M 8 earthquakes in 7 BCE and 849 CE occurred near this fault and thus the fault poses a potential earthquake threat but has received little research attention. We observed the surface ruptures, measured the heights of terraces created by fault offsets, excavated trenches and used optically stimulated luminescence (OSL) dating of samples to study the late Quaternary fault activity. This study shows that the fault is divided into three segments. Three levels of terraces were produced by movement on the fault. The T1 terrace formed at approximately 10 ka, the T2 terrace formed between 30 and 40 ka, and the T3 terrace formed between 40 and 50 ka. Based on the average terrace heights along the fault, we calculate that the vertical fault slip rates have been approximately 1.12–1.34 mm/a in the Holocene and 2.2–2.28 mm/a since 50 ka. Our analysis shows that the Daqingshan piedmont fault has the highest vertical slip rate, the Wulashan piedmont fault has an intermediate slip rate and the Sertengshan piedmont fault has the lowest vertical slip rate. The area between the Wulashan and Daqingshan piedmont faults readily accumulates seismic stress and represents a potential future earthquake site. Trenches provide visible evidence of vertical rupture and slip movement in subsurface profiles, revealing six events on the Gongmiaozi segment since 25 ka and 14 events on the Baotou segment since 120 ka. The analysis shows that the Ordos peripheral fault system formed due to the subduction of the Pacific Plate. The northward expansion of the Tibetan Plateau and the movement of the Ordos Block have caused fault activity in the northern part of the Hetao Basin since the Late Pleistocene. The modern tectonic stress field and the upwelling of asthenospheric material east of the Hetao fault zone have resulted in an increase in the slip rate on the Hetao fault zone from west to east.

Quantifying rates of “rifting while drifting” in the southern Gulf of California: The role of the southern Baja California microplate and its eastern boundary zone

AbstractThe southern Baja California (Mexico) microplate has been rapidly moving away from the North America plate since ca. 12 Ma. This relative motion toward the northwest developed an oblique-divergent plate boundary that formed the Gulf of California. The rift-drift hypothesis postulates that when a continent ruptures and seafloor spreading commences, rifting on the plate margins ceases, and the margins start to drift, subside, and accumulate postrift sediments, eventually becoming a passive margin. In contrast to this hypothesis, the southern part of the Baja California microplate (BCM), and in particular its actively deforming eastern boundary zone, has continued significant rifting for millions of years after seafloor spreading initiated within the southern Gulf of California at 6–2.5 Ma. This is a process we call “rifting-while-drifting.” Global positioning system (GPS)–based data collected from 1998 to 2011 show relative motion across the eastern boundary zone up to ∼2–3.2 mm/yr with respect to a stable BCM. Furthermore, the velocity directions are compatible with normal faulting across the eastern boundary zone nearly perpendicular to the trend of the plate boundary at the latitude of La Paz and therefore a highly strain partitioned domain. North of 25°N latitude up to the Loreto area, there is a domain with no strain partitioning, and northwest-directed transtensional deformation dominates. From long-term geologic and paleoseismology studies, late Quaternary faulting rates are equal to or less than the GPS-derived rates, while geologic rates older than 1–2 Ma are commonly much higher. We suggest that the “rifting-while-drifting” process may be caused by the large topographic relief across the BCM margin, which created a significant gradient in gravitational potential energy that helps in driving continued relatively slow faulting. The relief was inherited from the much faster faulting of the BCM eastern boundary zone before plate motions largely localized along the modern transform–spreading centers in the axis of the Gulf of California. The low sediment flux from the small drainages and arid climate on the southern Baja California Peninsula result in the maintenance of underfilled to starved basins, and the relatively slow late Quaternary active faulting promotes continued topographic relief over millions of years.

Sequential modelling of the 2016 Central Italy earthquake cluster using multisource satellite observations and quantitative assessment of Coulomb stress change

SUMMARYA sequence of earthquake events consisting of three large shocks occurred in Central Italy from August to October in 2016 with the duration of almost 2 months. The preliminary study on the seismic mechanism suggests that the sequence of events is the result from the activity of the SW dipping Mt Bove–Mt Vettore–Mt Gorzano normal fault system. For investigation and understanding of the coseismic faulting of the seismogenic fault alignment, we collect a set of comprehensive satellite observations including the Sentinel-1A, ALOS-2/PALSAR-2 and GPS data to map the coseismic surface deformation and estimate the source models in this study. The derived faulting model for the first Amatrice event is characterized by two distinct slip asperities suggesting that it is a predominantly normal dip-slip motion with slight strike-slip component. The second event, Visso earthquake is almost a purely normal rupture. The third Norcia event is dominated by the normal dip-slip rupture of the seismogenic fault, and has propagated up to the ground with significant slip. The three faulting models are then utilized to quantify the Coulomb failure stress (CFS) change over the seismic zone. First, the CFS change on the subsequent two seismogenic faults of the earthquake sequence is estimated, and the derived positive CFS change induced by the preceding earthquakes suggests that the early events have positive effects on triggering the subsequent seismicity. We then explore the response relation of the aftershocks including 961 events with magnitudes larger than M 3.0 to the CFS change over the seismic zone. It suggests that the rupture pattern of the aftershocks is similar to the major shocks with predominantly normal dip-slip. To assess the risk of the future seismic hazard, we analyse quantitatively the spatial distribution of aftershock occurrence and CFS transfer at the seismogenic depth, indicating that the ruptures of the three major shocks do partly release the accumulated strain on the associated fault alignment as well as the dense aftershock, but the CFS increase zone with few aftershocks in the southwest of the eastern Quaternary fault alignment of Central Italy poses the potential of further rupture. In particular, the distribution of aftershock migration also suggests that the north extension of the Mt Bove fault is the potential zone with rupture risk.

Contribution to crustal strain accumulation of minor faults: a case study across the Niigata\u2013Kobe Tectonic Zone, Japan

Recent global navigation satellite system (GNSS) data for the Japanese Islands have revealed a high-strain-rate region suggesting the existence of a region of broad-scale crustal deformation. The Niigata–Kobe Tectonic Zone (NKTZ), which is the high-strain-rate zone in central Japan, shows a short-term dextral strain rate of ~ 12 mm/year. The total slip rate of the Quaternary fault zones in the NKTZ has been estimated as ~ 6.7 mm/year, accounting for just over half the short-term strain rate of the zone. However, this slip rate underestimates the total slip rate on faults within the NKTZ owing to possible distributed deformation on minor faults. This study quantifies the slip rate attributable to these other faults in the southeastern-central NKTZ and reveals the unique deformation structure across the high-strain-rate zone, which comprises a Quaternary fault core, a Quaternary fault damage zone, an incipient brittle shear zone (active background), and an inactive background. The spatial characteristics of the incipient brittle shear zone can be explained in terms of fault density, which increases toward the central NKTZ. Minor faults located > 500 m from major Quaternary faults but within the NKTZ have sense of shear consistent with that of the major faults. In contrast, minor faults outside of the NKTZ show sense of shear that differ from the dextral displacement of the high-strain-rate zone and do not contribute to the slip rate of the zone. The total slip rate of minor faults in the southeastern-central NKTZ is estimated to be 0.46–2.88 mm/year (roughly equal to a major Quaternary fault in the zone), which implies 4–24% of crustal strain is stored in the active background.

Assessment of seismic sources and capable faults through hierarchic tectonic criteria: implications for seismic hazard in the Levant

Abstract. We present a methodology for mapping faults that constitute a potential hazard to structures, with an emphasis on ground shake hazards and on surface rupture nearby critical facilities such as dams and nuclear power plants. The methodology categorises faults by hierarchic seismo-tectonic criteria, which are designed according to the degree of certainty for recent activity and the accessibility of the information within a given region. First, the instrumental seismicity is statistically processed to obtain the gridded seismicity of the earthquake density and the seismic moment density parameters. Their spatial distribution reveals the zones of the seismic sources, within the examined period. We combine these results with geodetic and pre-instrumental slip rates, historical earthquake data, geological maps and aerial photography to define and categorise faults that are likely to generate significant earthquakes (M≥6.0). Their mapping is fundamental for seismo-tectonic modelling and for probabilistic seismic hazard analyses (PSHAs). In addition, for surface rupture hazard, we create a database and a map of Quaternary capable faults by developing criteria according to the regional stratigraphy and the tectonic configuration. The relationship between seismicity, slip dynamics and fault activity through time is an intrinsic result of our analysis that allows revealing the dynamic of the deformation in the region. The presented methodology expands the ability to differentiate between subgroups for planning or maintenance of different constructions or for research aims, and it can be applied in other regions.

Electrical resistivity imaging of active faults in palaeoseismology: case studies from Karachi Arc, southern Kirthar Fold Belt, Pakistan

ABSTRACT Electric resistivity tomography (ERT) is applied across active concealed faults to confirm the subsurface manifestation and lateral extension of capable faults in Karachi Arc, southern Kirthar Fold Belt, Pakistan. During palaeoseismological investigations, active faults and movements along them are identified using electrical resistivity imaging and trenching. The electrical resistivity images present the general structure of the investigated area, with the possibility of tracking the fault in the subsurface. The verification of faults and comparison of ERT profiles with the excavated trench logs confirmed the success of ERT. The results of ERT and trenching in three major parts of Karachi Arc show: (i) the southern inner part of the arc was inactive in Late Quaternary time, where the Sona Fault did not experience any recent movement; (ii) Kirthar and Khud faults in the northwestern part of the study area are active but do not extend into the southern Karachi Arc; and (iii) the frontal part of Karachi Arc is characterised by Quaternary faulting of limited strike length with a moderate rate of seismic activity. Based on the Karachi Arc case studies, ERT is found to be a reliable geophysical technique for studying near-surface geological structures, subsurface lithological mapping and fault characterisation.