Tectonic Geomorphology Research Articles

The Late Quaternary dip–slip characteristics of the left-lateral strike-slip Yuanmou fault, the southwestern margin of the north–south seismic belt of China

The North–South Seismic Belt distributed along the eastern margin of the Tibetan Plateau is a regional-scale seismically active zone. The Yuanmou Fault, located at the junction of the North–South Seismic Belt and the Central Yunnan Sub-Block, is an important boundary of earthquakes distribution and topography. Therefore, the studying of the Late Quaternary activity of the Yuanmou Fault is of great significance to understand the regional geodynamic mechanism and its efforts on the regional tectonic activities, seismic distribution and future risk. Based on field observations and analysis of earthquake geology and tectonic geomorphology and the dating results of Quaternary chronology, together with the previous studies, revealed that: (1) the fluvial terrace T1 was cut by the Yuanmou fault on the northern section of Jiangbian, and the most recent earthquake event happened about 7 ka B.P. age on the Jiangbian–Luochuan segment. (2) Based on the offset measurement and dating results of deformed terraces, the horizontal and vertical average slip rate of the Yuanmou fault were determined to be ~ 1.0 mm/year and ~ 0.1 mm/year, respectively. (3) Moreover, the latest activity time of the southern segment of the Yuanmou Fault is late Pleistocene, indicating the segmentation between the northern and southern segments of the Yuanmou Fault. (4) The differential activity intensity and activity ways of the Yuanmou Fault on different segments is probably associated with the change of local stress. Therefore, these findings concerning with seismic activities and activity segmentation of the Yuanmou Fault reveal the complexity of the regional dynamic mechanisms and provide a new insight for exploring regional differences in the tectonic deformation mechanisms of the southeastern margin of the Tibetan Plateau during the Late Cenozoic.

Quaternary Rock Uplift Rates and Their Implications for the Western Flank of the North Anatolian Fault Restraining Bend; Inferences From Fluvial Terrace Ages

AbstractIn the western flank of the North Anatolian Fault restraining bend (i.e., Central Pontides), the Filyos River incises through the uplifting Karabük Range, creating the ~1.7‐km‐deep Filyos River Gorge on the hanging wall of the reverse Karabük Fault. Seven fluvial strath terrace levels are preserved in this gorge. optically stimulated luminescence ages from quartz‐rich sediments of five terrace levels reveal an average long‐term rock uplift rate of 0.45 ± 0.02 mm yr−1 with an unsteady pattern of uplift during the last 542 ± 24 kyr. Uplift rates of 1.52 ± 0.6 and 0.74 ± 0.3 mm yr−1 occurred before 366 ± 19 kyr, followed by lower rates of ~0.1 and 0.31 mm yr−1 through present. These later uplift rates may reflect relatively slower tectonic rates since ~366 kyr, with closer similarity to regional uplift rates of ~0.3 mm yr−1 yielded from the eastern flank of the Central Pontides. The Karabük Range fluvial terraces are near the North Anatolian Fault, meaning pre‐ ~366 kyr uplift rates may be a glimpse of the highest Central Pontides Quaternary rock uplift rates on uplifting hanging wall blocks activated by the restraining bend. When we consider offshore seismic reflection data, the focal mechanism solution of the Bartın Earthquake, onshore structural data, and regional tectonic geomorphology, the western flank of the Central Anatolian Plateau's northern margin is propagating northward as a growing orogenic wedge with a positive flower‐structure geometry.

Tectonic geomorphology and Plio-Quaternary structural evolution of the Tuzgölü fault zone, Turkey: Implications for deformation in the interior of the Central Anatolian Plateau

AbstractSituated within the interior of the Central Anatolian Plateau (Turkey), the 200-km-long Tuzgölü extensional fault zone offers first-order constraints on the timing and pattern of regional deformation and uplift. In this study, we analyze the morphometrics of catchments along the Tuzgölü range-front fault and the parallel, basinward Hamzalı fault using a variety of measured morphometric indicators coupled with regional geomorphic observations and longitudinal profile analysis. In addition, we use field and remote mapping to constrain the geometry of two key marker beds, the Pliocene Kızılkaya ignimbrite and Kışladaǧ limestone, in order to investigate deformation in the footwall of the Tuzgölü fault zone. The marker beds form a broad arch along the footwall of the fault, with greatest cumulative displacement along the central part of the fault zone, suggesting early Pliocene extensional reactivation of the Tuzgölü fault with a typical fault-displacement profile. However, a change in deformation pattern is marked by transient knickpoints along river channels; morphometric indicators sensitive to shorter (1−3 Ma) time scales, including river steepness, basin elongation, and mountain front sinuosity, indicate an overall southeastward increase in footwall uplift rate of the Tuzgölü fault zone, which could reflect block rotation or interaction with the Hasan Dag volcano. Basin asymmetry and basin-fault azimuth measurements indicate north-northwest tilting of footwall catchments, which may be linked to regional tilting across the Central Anatolian Plateau interior. Varying patterns of spatial and temporal deformation along the length of the Tuzgölü fault zone are likely due to the interference of crustal- and lithospheric-scale processes, such as rotation of crustal blocks, extrusion of the Anatolian microplate, crustal heating, gravitational collapse associated with plateau uplift, and mantle-driven vertical displacements.

Offset measurements along active faults based on the structure from motion method – A case study of Gebiling in the Xorkoli section of the Altyn Tagh Fault

This study reconstructs high-precision three-dimensional (3D) surface models using aerial imagery derived from unmanned aerial vehicles (UAVs) with the structure from motion (SfM) method. By combining automatic extraction and manual visual interpretation, the geometry of the active tectonics and offset channels along the fault is obtained. The offsets, caused by the motion of active tectonics, are measured via the retrodeformation of geomorphologic markers. This paper takes the tectonic geomorphology of Gebiling in the Xorkoli section of the Altyn Tagh fault as a case study. After the construction of 3D surface models using the UAV images and the SfM method, a data set of more than 200 offsets is obtained. The results indicate that 11 paleoearthquakes may have ruptured along the Gebiling section of the Altyn-Tagh fault.

Integration of tectonic geomorphology and crustal structure across the active obliquely collisional zone on the island of Hispaniola, northeastern Caribbean

Abstract Active tectonic deformation and seismicity of Hispaniola define a 250 km-wide, oblique collisional zone between the Bahamas, the island arc of Hispaniola and the Caribbean Large Igneous Province (CLIP). To reflect how collision is accommodated within Hispaniola, we calculate river normalized steepness and terrain surface roughness to reveal the areas of the most active uplift within central and western Hispaniola compared to eastern Hispaniola. We use gravity modelling to show thickness variations in the main crustal types in the obliquely convergent zone: (1) 33–45 km-thick arc crust in central and western Hispaniola; (2) 15–25 km-thick oceanic crust beneath the Bahamas north of Hispaniola; (3) 5–8 km-thick Atlantic oceanic crust NE of Hispaniola; and (4) 6–16 km-thick CLIP south of Hispaniola. Intermediate to deep earthquakes beneath eastern Hispaniola indicate active southwestward subduction of normal oceanic crust and northward subduction of the CLIP. We interpret that the west-to-east geomorphological and crustal variations within Hispaniola to be the result of an along-strike transition from crustal shortening without subduction between the Bahamas and arc crust in central and western Hispaniola to subduction of the North American and Caribbean plates beneath eastern Hispaniola. Crustal shortening in central and western Hispaniola produces thrust-fault-bounded basins with sufficient clastic sedimentary infill to produce hydrocarbon maturity.

Himalayan cross faults affect thrust sheet geometry: An example from the Munsiari thrust sheet near the Gish Transverse fault zone, frontal Darjiling Himalaya, India

The Munsiari thrust (MT) sheet is a dominant thrust sheet in the Himalaya and forms the frontal ridge in the Gorubathan recess of the Darjiling Himalaya. The geometry of the MT sheet in the recess was poorly constrained thereby inhibiting the understanding of how the geometry and kinematics of the sheet varied from the Nepal to the Bhutan Himalaya. We present new structural data and infer the deformation mechanisms and the geometry of the MT sheet in the Gorubathan recess in the Darjiling Himalaya to fill this knowledge gap. The MT sheet was dominated by large-scale, overturned antiforms and synforms. The entire MT sheet was later folded to a north-easterly plunging synformal fold with NE-SW axial trend due to the effect of a Himalayan cross fault in the region named the Gish Transverse fault. A new brittle, out-of-sequence and neotectonically active, Phaparkheti thrust, was recognized in the MT sheet. Deformation microstructures indicate that the temperature of deformation in the MT fault zone and the sheet was ~500 °C to 700 °C and ~400 °C, respectively. Our approach of first mapping major and minor structures and then integrating these studies with deformation microstructure and tectonic geomorphology data resulted in an improved understanding of the structural characteristics of the MT sheet in the Darjiling Himalaya. Our study also suggests that there is considerable variation in the geometry and kinematics of frontal thrust sheets along the Himalayan arc that must be studied systematically in the context of Himalayan salients and recesses.

Seismic history of a bedrock fault scarp using quantitative morphology together with multiple dating methods: A case study of the Luoyunshan piedmont fault, southwestern Shanxi Rift, China

The study of bedrock fault scarps is a useful approach to identify paleo-earthquakes and acquire the faulting history in bedrock areas where traditional trench techniques are not applicable. Here, we report a study on the Luoyunshan piedmont fault (LYSPF), southwestern Shanxi Rift, China. Although several studies have analyzed the LYSPF, its faulting behavior is still under debate. For example, the tectonic geomorphology fails to determine the frequency of past slips and the elapsed time. To address these problems, we investigated two bedrock fault surfaces, Luoyuncun (northern segment) and Weicun (southern segment) using quantitative morphology analyses together with multiple Quaternary dating techniques. Quantitative morphology analysis shows that both bedrock fault surfaces have the characteristics of vertical segmentation. This kind of segmentation indicates that the fault surfaces are exhumed intermittently, likely owing to periodic faulting earthquakes. Therefore, earthquake events can be identified as morphological segments, and the corresponding co-seismic displacement can be determined by the height of these segments. According to the results from the quantitative morphology and dating techniques, four seismic events, with a co-seismic vertical displacement of 0.9 m, 0.82 m, 1.64 to 2.38 m and 2.30 to 2.54 m, on the northern segment occurred during the late Pleistocene, whereas, two seismic events, with a co-seismic vertical displacement of ~1.33 m and 1 to 1.08 m are identified on the southern segment occurred during the Holocene. Combined with the results of knickpoint series and trench techniques of the LYSPF, eight paleo-earthquake events were identified since 45 ka, with an average recurrence interval of 5.8 kyr. The more complete paleo-earthquake sequence also showed the possibility that the variation of the slip rate along the LYSPF depends on the segment, and that the displacement produced by the Linfen M 7½ earthquake of 649 CE has been recorded at the WC fault surface.

Geomorphological analysis of drainage changes in the NE Apennines piedmont area: the case of the middle Tavo River bend (Abruzzo, Central Italy)

ABSTRACT This work presents a tectonic geomorphology analysis of a river bend in the middle Tavo River valley, in the piedmont area of the NE Apennines (Abruzzo Region), between the eastern slope of the chain (Gran Sasso Massif) and the Adriatic coast. The main map (1:15,000 scale) was obtained through a morphometric, geological, and geomorphological analysis, and was composed of four sections including orography and hydrography at basin scale, main map at local scale, geomorphological cross-section and longitudinal profiles, and morphoneotectonic analysis. This study provides a basis for the recognition of morphostructural and morphotectonic features that control the drainage evolution of the Tavo River. Specifically, the study is focused on the Tavo-Saline basin characterized by possible capture processes, and the evolution of the watershed with the Pescara basin. The results from this study can contribute to the understanding of the evolution of the NE Apennines piedmont area since the Middle Pleistocene.

Evidence From High‐Resolution Topography for Multiple Earthquakes on High Slip‐to‐Length Fault Scarps: The Bilila‐Mtakataka Fault, Malawi

AbstractGeomorphological features such as fault scarps and stream knickpoints are indicators of recent fault activity. Determining whether these features formed during a single earthquake or over multiple earthquakes cycles has important implications for the interpretation of the size and frequency of past events. Here, we focus on the Bilila‐Mtakataka fault, Malawi, where the 20 m high fault scarps exceed the height expected from a single earthquake rupture. We use a high‐resolution digital elevation model ( 1 m) to identify complexity in the fault scarp and knickpoints in river profiles. Of 39 selected scarp profiles, 20 showed evidence of either multiscarps or composite scarps, and of the seven selected river and stream profiles, five showed evidence for multiple knickpoints. A near‐uniform distribution of vertical offsets on the subscarps suggests they were formed by separate earthquakes. These independent methods agree that at least two earthquakes have occurred with an average vertical offset per event of 10 and 12 m. This contrasts earlier studies which proposed that this scarp formed during a single event and demonstrates the importance of high‐resolution topographic data for understanding tectonic geomorphology. We use a one‐dimensional diffusion model of scarp degradation to demonstrate how fault splays form multiscarps and estimate the diffusion age of the Bilila‐Mtakataka fault scarp to be m , corresponding to years since formation. We calculate that a continuous rupture would equate to a M earthquake, greater than the largest seismic event previously recorded in East Africa.

Diachronous Tibetan Plateau landscape evolution derived from lava field geomorphology

Abstract Evolution of the Tibetan Plateau is important for understanding continental tectonics because of the plateau’s exceptional elevation (∼5 km above sea level) and crustal thickness (∼70 km). Patterns of long-term landscape evolution can constrain tectonic processes, but have been hard to quantify, in contrast to established data sets for strain, exhumation, and paleo-elevation. This study analyzes the relief of the bases and tops of 17 Cenozoic lava fields on the central and northern Tibetan Plateau. Analyzed fields have typical lateral dimensions of tens of kilometers, and so have an appropriate scale for interpreting tectonic geomorphology. Fourteen of the fields have not been deformed since eruption. One field is cut by normal faults; two others are gently folded, with limb dips <6°. Relief of the bases and tops of the fields is comparable to that of modern, internally drained parts of the plateau, and distinctly lower than that of externally drained regions. The lavas preserve a record of underlying low-relief bedrock landscapes at the time they were erupted, which have undergone little change since. There is an overlap in each area between younger published low-temperature thermochronology ages and the age of the oldest eruption in each area, here interpreted as the transition between the end of significant (>3 km) exhumation and plateau landscape development. This diachronous process took place between ∼32.5°N and ∼36.5°N and between ca. 40 Ma and ca. 10 Ma, advancing northwards at a long-term rate of ∼15 km/m.y. Results are consistent with incremental northward growth of the plateau, rather than a stepwise evolution or synchronous uplift.

Along-strike variations in recent tectonic activity in the Santander Massif: New insights on landscape evolution in the Northern Andes

The integration of drainage analysis and topographic metrics provides excellent tools to assess the Quaternary tectonic activity modeling landscape evolution in evolving orogens. Furthermore, detecting active structures through the geomorphological analysis of landscapes helps to identify potentially seismogenic structures that could impact the socio-economic conditions in developing countries. Therefore, this paper presents a tectonic geomorphology study conducted on the Santander Massif (SM, Colombian Eastern Cordillera) and surrounding areas. The SM has structures with reported Quaternary activity such as the Bucaramanga, Morro Negro-Las Mercedes, and Chitagá faults, which summed to a poorly-constrained paleosismological history with significant shallow events is the prime incentive of this work. Our study is based on the acquisition of topographic data through swath profiles, local relief, slope variability, filtered topography, minimum bulk erosion, which along with geomorphic indices like the normalized concavity steepness (ksn), the hypsometric integral (HI), the ratio valley floor width to valley height (Vf) and normalized river profiles provided new insights on the recent landscape evolution in this part of the Northern Andes.We compared published apatite fission tracks (AFT) data for the study area with the uplift pattern deciphered from the geomorphic indices to detect the consistency in exhumation and denudation processes both in the long and short-term. Consequently, the central SM, as well as the faulted block between the Bucaramanga and Guamalito faults, evidence a highly-incised landscape with local relief values exceeding the 1500 m, then, responding with a sharp incision to recent surface uplift. Interestingly, this uplift pattern in central SM matches with published AFT data and is related to Neogene exhumation events controlled by secondary structures like the Suratá Fault. We attribute this exhumation event, and accelerated denudation rates within the SM, to the influence exerted by the “collision” between the SM and the Pamplona Indenter, leading to the unroofing of basement rocks at the deformation front (e.g., the Vetas High) and the topographic building of the range.For the upthrown block (hanging wall) of the Bucaramanga Fault, the occurrence of poorly-graded river profiles with an average concavity factor of 12.01, as well as irregular hypsometric curves with convex lower reaches, reinforce the hypothesis that late Cenozoic topographic rejuvenation in the SM was also forced by the tectonic activity of the Bucaramanga Fault. We expect empirical uplift rates >0.08 mm/yr (very high to high tectonic activity) for the mountain front encompassed between La Esperanza and Bucaramanga localities. We state this assumption since the mountain front delimited by the structure mentioned above is quite straight, it preserves remarkable morphostructural features and displays V-shaped valleys with an average Vf index of 0.38. This uplift rate is in good agreement with recent thermochronological exhumation rates (0.1 to > 0.3 mm/yr) published by Siravo et al. (2019).Higher uplift rates associated with the Bucaramanga Fault were also constrained with the erosion proxy index, i.e., the ksn index. High ksn values (above 128) were observed following a linear pattern, which in turn seems controlled by the main trace of the Bucaramanga Fault. For instance, the river system draining the western piedmont of the SM, near Aguachica, records slope-break knickpoints that we interpret as evidence of an incisional wave migrating upstream and adjusting a late Neogene uplift event associated with the Bucaramanga Fault. Conversely, the northern SM presents variable tectonic activity with the inner part, east of the Guamalito Fault, presenting low tectonic activity with little surface uplift and dominant strike-slip kinematics. We recognize the Ocaña-Ábrego zone as a relict landscape with well-preserved non-consolidated deposits that may record the initial exhumation and denudational pulses of the SM during the Andean Orogeny.

Tectonic geomorphology of the Aras drainage basin (NW Iran): Implications for the recent activity of the Aras fault zone

Complex geology and tectonics of the NW Iran, the Caucasus region, and Eastern Turkey, are responsible for the present‐day landscapes of the region. The Aras drainage basin located in Iran, Azerbaijan and Armenia borders, provides an appropriate geographical environment for systematically studying the landforms produced or modified by active tectonic processes. Several morphometric indices were calculated for 114 sub‐basins to assess relative tectonic activity levels. Results were evaluated using two different methods; Index of Active Tectonics (IAT) and Analytical Hierarchy Process (AHP) methods. IAT results show that 2% of the sub‐basins belong to very high, 25% to high, 46% to moderate and 27% to low tectonic activity classes. AHP results, display that 12% of the sub‐basins belong to very high, 25% to high, 43% to moderate, and 20% to low tectonic activity classes. Results of both methods show approximate consistency and indicate that the tectonic activity along the Aras drainage basin is moderate to high and decreases from southwest to the northwest which is probably due to terminating fault branches in young unconsolidated deposits or strain partitioning processes. The major fault zones (e.g., Aras, Pambak–Sevan–Sunik, Akera, and Moghan fault zones) include areas with very high and high tectonic activity classes. Accordingly, the uplift rates have been estimated as >0.5 mm/yr for central and western parts, whereas the uplift rates are relatively less in the eastern part (<0.5 mm/yr). The Aras fault zone includes five active structural segments that the main Aras and Horadiz segments of them show relatively higher tectonic activity.

Detailed volcanic and tectonic morphology of Nakadomari Hill in the southern Okinawa Trough

Nakadomari Hill is an unexplored edifice in the southern Okinawa Trough back-arc basin where crustal extension by continental rifting occurs and few submarine eruptions associated with back-arc volcanism have been mapped in detail. High-resolution bathymetric mapping with an autonomous underwater vehicle (AUV) reveals that Nakadomari Hill is a submarine volcanic complex with recent lava flow eruptions. The high-resolution (2 m) bathymetry shows striking contrast between rugged terrain in the central area and the adjacent smooth terrain. The cone-shaped features in the rugged terrain are covered by ropey fabric with high acoustic reflectivity and are devoid of tectonic deformation, thus they are interpreted to be relatively younger lava domes. The cone-shaped features in the smooth terrain show low reflectivity and are dissected by ENE–WSW trending tectonic lineaments, suggesting they were formed during older volcanism. Nakadomari Hill developed through multi-stage eruptions before and after back-arc rifting and faulting. The ropey and curtain-folded morphology with high acoustic reflectivity are interpreted to be a field of lava flows and they are relatively young. The area considered to be lava flows is estimated to be over 13 km2, showing that eruptions in the southern Okinawa Trough have been extensive. An active volcanic system is supported by indicators of high-temperature hydrothermal venting. Hydrothermal plumes with concurrent sharp temperature increases of up to 0.17 °C were present even at the vehicle altitude of ~100 m above the bottom. The alignment of volcanic cone-shaped features at Nakadomari Hill is in the NNW–SSE direction which is clearly different from the orientation of local rifting (ENE–WSW). At a larger scale, the volcanic edifices west of Kume Island from the arc to back-arc are also aligned roughly in the NNW–SSE direction and they are sub-parallel to a major tectonic structure in the arc, the Kerama Gap. The agreement of the local volcanic and tectonic trends implies that magmatic focusing may have taken place along the tectonic structures of the Kerama gap and in turn caused the extensive back-arc volcanism in this area.

Tectonic geomorphology and late Quaternary deformation on the Ragged Mountain fault, Yakutat microplate, south coastal Alaska

The 33 km-long Ragged Mountain fault (RMF) forms the northwestern corner of the Yakutat Terrane, which is colliding with the North American plate in south coastal Alaska at ∼5.5cm/yr. The fault zone contains three types of scarps in a zone up to 175m wide: (1) antislope scarps on the lower range front, (2) a sinuous thrust scarp at the toe of the range front, and (3) a swarm of flexural-slip scarps on the footwall. Trenches across the first two scarp types reveal evidence for two Holocene surface ruptures, plus several late Pleistocene ruptures. In the antislope scarp trench, ruptures occurred at 0.5–3.9 ka; slightly younger than 8.3 ka; and at 18.1–21.8 ka (recurrence intervals 4.4–8 kyr and 9.8–13.3 kyr). Displacements per event ranged from 15 to 40cm. In the thrust trench ruptures are dated at 2.8–5.9 ka; 5.9–17.2 ka, and 17.2–44.9 ka (mean recurrence intervals 7.2 kyr and 19.5 kyr). Displacements per event ranged from 26 to 77cm. We interpret the thrust fault as the primary seismogenic structure, and its largest trench displacement (77cm) equates to the average displacement expected for a 33 km-long reverse rupture. The flexural-slip scarp, in contrast, was rapidly formed ca. 4 ka but its sag pond sediments have continued to slowly fold up to present. The southern third of the fault is dominated by large gravitational failures of the range front (as large as 2.5km wide, 0.6-0.7km long, and 200–250m thick), which head in a linear, 40 m-deep range-crest trough filled with lakes, a classic expression of deep-seated gravitational slope deformation.

Rapid Late Quaternary Slip, Repeated Prehistoric Earthquake Rupture, and Widespread Landsliding Associated With the Karakudzhur Thrust, Central Kyrgyz Tien Shan

AbstractField studies have shown that active faulting in the SW Tien Shan is distributed across a series of E‐W reverse faults along the range fronts and within basin interiors, with summed shortening rates that are consistent with GPS measurements. In contrast, few field studies have been undertaken to determine the distribution, and the average slip rates, of faults in the central and eastern parts of the Tien Shan. In this paper we use remote and field‐based observations to characterize the active faulting and tectonic geomorphology of the Karakudzhur Basin in the central Tien Shan of Kyrgyzstan. We use radiocarbon, luminescence, and uranium series dating to provide ages on three fluvial terraces that are vertically displaced across the basin‐bounding reverse fault and estimate fault slip rates using a 20°S dipping fault exposure. We find that the fault has a slip‐rate of ∼2.4–5.9 mm/year averaged over the Holocene, indicating that it accommodates a major part of the shortening measured by GPS. In contrast to the relatively uniform distribution of N‐S shortening in the SW Tien Shan, significant shortening may instead be concentrated at present on a few active faults in the northern part of the central Tien Shan. The fresh geomorphic expression of the Karakudzhur fault suggests that it has ruptured in recent prehistory in a large‐magnitude Mw ≥ 7 earthquake. From palaeoseismic trenching we show that two significant surface rupturing earthquakes have occurred since ~2.4 ka. The most recent earthquake was potentially accompanied by widespread landsliding and faulting in the surrounding highlands.

Plate boundary localization, slip-rates and rupture segmentation of the Queen Charlotte Fault based on submarine tectonic geomorphology

Linking fault behavior over many earthquake cycles to individual earthquake behavior is a primary goal in tectonic geomorphology, particularly across an entire plate boundary. Here, we examine the 1150-km-long, right-lateral Queen Charlotte-Fairweather fault system using comprehensive multibeam bathymetry data acquired along the Queen Charlotte Fault (QCF) offshore southeastern Alaska and western British Columbia. Fine-scale analysis of tectonic geomorphology allowed us to identify and reconstruct 184 strike-slip piercing points over a 630 km stretch of the QCF. Age constraints from glacial recession and offshore sedimentation patterns yield a consistent slip-rate of ∼50–57 mm/yr since ∼17–12 ka, the fastest rate for a continent-ocean strike-slip fault on Earth. These slip-rates equal or exceed estimates of Pacific-North America (PA-NA) relative motion from global plate reconstructions, indicating that PA-NA motion is highly localized. The QCF cuts the seafloor along a narrow and unusually straight trace for its entire length and multiple fault traces are observed only at local step-overs. The geometry and behavior of the QCF over many earthquake cycles is simple and typical of mature faults with relatively homogeneous stress fields. Since the QCF is the primary PA-NA plate boundary, we used the trace of the QCF to define the small circle path for relative plate motion and computed the associated Euler pole. Predicted along-strike obliquity variations based on the new pole agree with observed tectonic geomorphology and suggest that previous global plate reconstructions overestimated the degree of oblique convergence along the QCF. We also find that subtle, long-wavelength (75–150 km) bends and discrete step-overs appear to define the endpoints of M>7 earthquakes, suggesting that obliquity and resultant fault geometry may control rupture segmentation and asperity development. Lastly, the agreement between predicted obliquity and tectonic geomorphology along the entire length of QCF compelled a reevaluation of regional tectonic models. In the north, the eastern Yakatat Terrane appears to be translating northwest with the Pacific plate, and slip transferred from the QCF to the Fairweather Fault results in ∼20 mm/yr of convergence along the southern St. Elias mountains. In the south, we predict a reduced rate of convergence along the QCF west of Haida Gwaii (∼5–6 mm/yr of shortening, on average) relative to previous studies. Our results support a model for transpression and strike-slip partitioning along the edge of a hot and weak Pacific Plate, leading to crustal thickening and growth of the Queen Charlotte Terrace to the west of Haida Gwaii.

Mapping the geology of the 2016 Central Italy earthquake fault (Mt. Vettore – Mt. Bove fault, Sibillini Mts.): geological details on the Cupi – Ussita and Mt. Bove – Mt. Porche segments and overall pattern of coseismic surface faulting

We present the results of a field survey performed in the centralnorthern portion of the Mt. Vettore – Mt. Bove normal fault(VBF), reactivated during the 2016 central Italy earthquake sequence (24 August, Mw 6.0; 26 October Mw5.4 and Mw 5.9; 30 October Mw 6.5). The field survey was carried out by means of digital mapping techniques, and traditional methods on 1:10,000-scale topographic maps. The field work had two main aims: 1) to detail the geology of the central-northern VBF, and to constrain the segmentation and displacement distribution of the entire VBF system; and 2) to map in detail the ruptures of the 26 and 30 October events, filling in the gaps left by previous studies, and provide constraints on the coseismic parameters of the 2016 earthquakes.The results are summarized in a composite geological map, organized in 8 frames showing: the structural architecture in map view of the VBF system (frames 1 and 2); 1:25,000-scale geological maps of the Cupi-Ussita (frame 3) and Mt. Bove – Mt. Porche (frame 4) sectors of the VBF; twelve 1:25,000-scale geological sections for computing the geological displacements (frame 5); a summary of the coseismic parameters of the 2016 earthquakes (diagrams of net displacement, throw and opening; Surface Rupture Length, SRL; Maximum Displacement, MD and Average Displacement, AD) (frame 6); a comparison of the 2016 coseismic parameters with normal faulting earthquakes occurred globally (frame 7); and a computation of the morphological displacement (post-Last Glacial Maximum, LGM) across the VBF, a comparison among geological, morphological and coseismic displacements, and a quantification of the tectonic back-tilting in the area of maximum coseismic displacement (frame 8). Some implications are discussed in this accompanying note, such as the role of fault segmentation deduced from structural geology and tectonic geomorphology in controlling the coseismic displacement, the role of back-tilting in amplifying the coseismic displacement and the limits of empirical regressionsin predicting the relations between rupture parameters and Mw in case of segmented normal faults.

Holocene paleoearthquakes on the Tianqiaogou-Huangyangchuan fault in the northeastern boundary fault system of the Tibetan Plateau

Rupture behavior, one of the quantitative features of active fault, is fundamental for understanding crustal deformation mechanisms and assessing regional seismic risk. The 120-km-long Tianqiaogou-Huangyangchuan Fault (THF) is an important branch fault of the Qilian-Haiyuan Fault System (QHFS), the main boundary fault zone at the emerging northeastern margin of the Tibetan Plateau. Mismatching with the fast strike-slip rate, there is no M ≥ 5 earthquake recorded along the THF. To obtain more precise information of the rupture behaviors along the boundary structure, we conducted a 1:50,000 active fault mapping and paleoearthquake trenching on the THF. Two trenches respectively illustrates at least 3 rupture events combining the radiocarbon dating and the OxCal modeling. According to the overlap of their age ranges and the analysis on completeness of the sedimentary records, it is determined at least 5 paleoearthquakes occurred along the THF in the Holocene with respective age ranges of 485 ± 675 BCE, 2085 ± 295 BCE, 5590 ± 1090 BCE, 7910 ± 970 BCE, and 9975 ± 955 BCE and moment magnitudes estimated to be 7.3–7.4. Meanwhile, the detailed investigations on paleoseismology and tectonic geomorphology show the THF was not involved into the seismogenic structure of the nearby 1927 Gulang M8 earthquake. The Monte Carlo statistical analysis of these paleoearthquakes yields a mean recurrence interval of 2.4 ± 0.3 ka, illustrating a strong activity of the THF that accords with its slip rates and an important role as a tectonic boundary accommodating the eastward extruding of the northeastern Tibet relative to the Gobi Alashan block. Moreover, based on its strong activity and long elapsed time of at least 1.7 ka, we propose the THF is another seismic gap with a potential of M ≥ 7 earthquakes similar to the Tianzhu gap near the triple junction in the QHFS, showing a high seismic risk along the THF and in this region.

Review of geological and seismotectonic investigations related to 1998 Mw5.6 and 2004 Mw5.2 earthquakes in Krn Mountains

A review of geological and seismotectonic investigations conducted in the two decades after the 12 April 1998 earthquake in Krn Mountains, according to its magnitude the strongest earthquake in Slovenia in the 20th century, is given. Many of these studies have wider scientific meaning than expected from the size of the earthquake. This was the first case in Slovenia that a strong earthquake was undoubtedly related to a particular fault. Seismotectonic studies of seismogenic Ravne fault revealed that it is an actively propagating strike-slip fault growing by interaction of individual right stepping fault segments and breaching of local transtensional step-over zones. Airborne laser scanning (LiDAR) of Idrija and Ravne faults, which resulted in high resolution bare earth digital elevation model, was in 2005 for the first time used to study surface expression of an active fault in Europe. Among the primary characteristics of the 1998 earthquake were extensive environmental effects expressed mainly as massive rockfalls. They were systematically documented and evaluated for intensity assessment using European Macroseismic Scale (EMS-98) and Environmental Seismic Intensity (ESI) scale introduced in 2007, because application of the data on damage to buildings was limited in sparsely populated high mountains epicentral area. These studies were pioneering due to novelty of both intensity scales, indicating their strong points and weaknesses. Large variations in damage to buildings in the upper Soča valley at similar epicentral distances pointed to strong site effects due to very heterogeneous glacial and fluvial deposits in sedimentary basins and valleys. Therefore, different seismic microzonation maps were prepared to evaluate the influence of soft sediments on seismic ground motion. Conducted studies fostered development of several earthquake geology research methods in Slovenia as tectonic geomorphology, evaluation of environmental seismic effects and seismotectonics. They had positive impact also on the university education in the fields of geophysics, seismology and structural geology.

Tectonic geomorphology and structural architecture of eastern Sulaiman Fold Thrust Belt (SFTB) and adjacent Sulaiman Foredeep (SF), northwest Pakistan

This investigation combines a number of datasets to provide an enhanced and improved tectono-geomorphological framework with which to identify new possible structural lineaments in northwest Pakistan. The dataset includes satellite images and geographic information system (GIS) methods. The present study was carried out using the USGS ASTER DEM (30 m), Landsat 8 (OLI/TIRS) and surface field geology of the study area. Different band combinations, directional filters and principle component analysis (PCA) methods were used to identify the major structural styles and tectonic geomorphological pattern. The panchromatic band (Band-8) was applied to the Landsat 8 satellite images in order to increase the spatial resolution from 30 m to 15 m which aided in the investigation and comparative analysis of tectonic geomorphology and structural styles. Drainage patterns of Zindapir Anticline (ZA), Sakhi Sarwar (SS), Sulaiman Foredeep (SF) and Kingri Fault (KF) areas were generated using Strahler order of streams. The results suggested a combination of the dendritic network with a minor component of trellis pattern for ZP and SF areas, hence proposing a combined structural and stratigraphic/lithological control, whereas the KF area indicated an element of a rectangular pattern suggesting a more structural influence in the western part in comparison to the eastern region. The presence of water gaps (WaGs) and active drainage network indicate lateral growth and propagation directions of the ZP and SS frontal anticlines following the Paleocene Epoch. The geomorphic evidence coupled with satellite data show that the SFTB is tectonically active along with the adjacent SF. The stream courses are deflected or guided due to active folds and tectonics in the area characterized by the distinct fluvial erosional pattern on the flanks/limbs of ZA. Evidence from the study suggests that compressional deformation, uplift and erosion played a significant role in the shaping of the structural and depositional architecture of the basin. It is proposed that the deformation in the SFTB during the late Paleogene is related to the Indian-Eurasian oblique collision, while the subsequent late Tertiary collision of Indian Plate with the Afghan Block (an accreted part of southern Eurasia) further ensued compressive deformation. The results from this study elucidate the possible models proposed for this compressional regime with prevailing wrenching by presenting new data. The findings from this research reveal new tectono-geomorphological features and lineaments in the area that were not documented previously.