Active Fault Map Research Articles

Localization and characterization of the southern Ulsan fault (UF) using geo-electrical imaging: Implication for seismic hazard assessment in an urbanized area

In seismic hazard assessment, subsurface geophysical surveying has gained popularity in recent years towards fault mapping and determining seismic deformation parameters such as fault offset, recurrence, and depth of fault, locating proper trench sites based on the subsurface information. In the present study, electrical resistivity tomography (ERT) was used to (1) locate the trace of the southern segment of the Ulsan fault, (2) to test the applicability of ERT techniques for active fault mapping in a close to the highly urbanized and complex geological environment with a slow tectonic activity. We have applied the ERT technique at five sites. At one place, we used the Wenner array, Schlumberger array, Dipole-Dipole array, and Seismic-profiling techniques to know which method provides a better result in complex geological conditions like Korea. Out of these methods, the Dipole-Dipole array provided high-resolution results and was used for the other two sites. The ERT result shows high and low resistivity zones interpreted as bedrock (mainly Tertiary and Cretaceous formations) and coarse fluvial sediment layer, respectively. The maximum vertical displacement recorded along the fault varies from 6 m to 12 m. Based on the ERT results, two trenches were excavated to directly investigate the deformation pattern associated with the southern segment of the Ulsan fault. The ERT and trench survey results support that the southern Ulsan fault has slipped multiple times since Quaternary. Using this multi-approach, ~5 km long active fault map was prepared for the southern Ulsan Fault. It is found from this study that the integrated approach is highly beneficial where contrasting sub-lithological units exist in terms of their physical properties, even though human activity or the ongoing urbanization process has modified the surface morphology. This study argues for judicious use of ERT techniques to delineate the shallow subsurface geology across various active faults in the Korean peninsula and similar tectonic settings.

A reappraisal of active faults in central-east Iran (Kerman province)

Fault lineaments are the main input data in earthquake engineering and seismology studies. This study presents a digitally-based active fault map of the Kerman region in central-east Iran which experienced several devastating earthquakes on poorly exposed and/or not identified active faults. Using Landsat 8 data, we have carried out the image-based procedures of fault mapping, which include applying the contrast stretching technique, the principal component analysis, the color composite technique, the spectral rationing, and creating the false-color composite images. Besides, we have cross-checked the resulting map with the geological maps provided by the Geological Survey of Iran to decrease the associated uncertainties. The resulting map includes 123 fault segments, still, a part of which has been expressed in the previously compiled active-fault maps of Iran. Indeed, the new one is mapping the poorly exposed active faults, so-called secondary faults, which are able to produce strong events. These faults are primarily associated with poorly defined areas that accommodate low levels of seismicity; however, sporadic strong events are likely to occur. It has also been investigated that these kinds of faults are seismogenic and are able to produce destructive events. In total, the outcome of this study can also be jointed with seismic studies for investigating parts of the earthquake activity in central-east Iran, in particular for the fault-based approaches in impending earthquake-resistant buildings.

Joint‐Rupture Pattern and Newly Generated Structure of Fault Intersections on the Northern Margin of the Linhe Basin, Northwestern Ordos Block, China

AbstractThe activity of major active faults around the Ordos Block is of great interest to seismologists, as at least fourM ≥ 8 earthquakes have been recorded. However, the Linhe Basin, which has the thickest Cenozoic sediments, has no record of large earthquakes. Does this basin have the structural conditions required for large earthquakes? The northern boundary fault of the Linhe Basin is composed of the NE‐striking Langshan piedmont fault (LPF), E‐W‐striking western section of the Seertengshan piedmont fault (WSPF), and NW‐striking eastern section of the Seertengshan piedmont fault (ESPF). Based on large‐scale active fault mapping, this article analyzes data from 23 trenches, using an unmanned aerial vehicle to measure the faulted landform, and combines these data with Quaternary dating methods to acquire the paleoearthquake sequences of the LPF, WSPF, and ESPF. Furthermore, this article explores their rupture modes and discusses the structural evolution of two intersection points. Through paleoseismic comparison, seven trenches revealed historical earthquakes from 7 BC, with a common magnitude ofM8.1. The trenches also revealed seven paleoseismic events since the Holocene, which conformed to the periodic model with a period of 1.37 ± 0.11 ka. The elapsed time since the latest event (2.0 ka) has exceeded the earthquake recurrence period; thus, the area is currently at risk of anM7.4–8.0 earthquake. The NE‐striking LPF and E‐W‐striking WSPF are connected by two left‐stepping small fault segments. The E‐W‐striking WSPF and NW‐striking ESPF are connected by a large triangular relay ramp.

Updated historical earthquake catalog of İzmir region (western Anatolia) and its importance for the determination of seismogenic source

Although destructive earthquakes have not occurred in the instrumental period except for the 30 October 2020 Samos earthquake (Mw = 6.6), the records show that there were significant earthquakes that caused great destruction in İzmir and its surroundings in the historical period. However, it is not yet clear which faults are causative for these earthquakes affecting İzmir and its surroundings. For this purpose, it has been attempted to determine new geological, seismological and environmental data by examining a large number of original sources, records and old international earthquake catalogs, other than the existing national catalogs used in seismicity studies in Turkey. In this context, a new local and updated historical earthquake catalog was prepared for İzmir and its immediate vicinity. The data obtained from the records show that the maximum intensity of some destructive historical earthquakes in the İzmir region was X. This means that the active faults in İzmir and its immediate vicinity have the potential to generate earthquakes of up Mw = 7.1 in the future. Details on historical earthquakes strengthen the possibility that these earthquakes may have been generated by active faults located near the İzmir city settlement. The isoseismic maps created for the first time using historical data, point out that the highest seismic intensity in the 178, 1688 and 1778 A.D. earthquakes caused destruction in the İzmir city center and nearby settlements indicate that they were concentrated at a relatively small area in the Bay of İzmir, and tectonically in the hanging-wall of the İzmir Fault. In the most likely scenario, all these damages observed may be attributed to the western segment of the İzmir Fault (Balcova segment) since it was defined as the only seismic source around the İzmir Bay in the updated active fault map of Turkey, of course, these data should be verified by performing detailed paleoseismological studies.

Active fault mapping in the onshore northern Banda Arc, Indonesia: Implications for active tectonics and seismic potential

The northern Banda Arc accommodates some portion of the left-lateral slip due to the Pacific plate’s rapid westward movement relative to the Australian plate. The region is seismically active and has experienced several damaging earthquakes. However, the active tectonics of the northern Banda Arc is poorly understood. We mapped and described the tectonic geomorphic features in the northern Banda Arc using 3D anaglyph images, constructed from the Indonesian Digital Elevation Model (DEMNAS) ~8 m resolution. We combined our interpretation with seismicity data, published structural maps, and geodetic measurements to discuss the active tectonics of the northern Banda Arc and its seismic hazard. In north Seram, geomorphic features such as uplifted marine terraces, fault scarps, and wind gaps on a ridge represent active thrust-faulting activity. The Kawa and Bobot faults are the major left-lateral strike-slip faults in central and east Seram and are characterized by linear valleys, offset rivers, beheaded rivers, pressure ridges, and shutter ridges. Numerous active faults cut uplifted marine terraces in Amahai, Ambon, and surrounding islands. Some active faults bound intramountain depressions in central Buru. Our analysis suggests that active faults in the study area likely to accommodate the convergence of the northern Banda Arc and the Bird’s Head of Papua in an east-northeast direction. We suggest that active faults in the region can produce ≥ Mw 6.4 earthquakes. The 34-km-long Ambon fault may cause a devastating earthquake as it traverses Ambon City, the capital of Maluku Province.

Assessing the accuracy of combined DEM-based lineament mapping and the normalised SL-index as a tool for active fault mapping

Satellite image-based lineament mapping in combination with the normalised Stream Length Gradient Index (SL/K-index) is one of the most widely used methods to identify active faults in areas where other verification methods, such as faulted strata, geophysical subsurface data, or seismic activity in the upper crust, are unavailable, and to classify their degree of activity. The accuracy of this approach, however, has not yet been assessed rigorously. We assess its accuracy by comparing the results against 27 thrust fault segments that were identified from six seismic reflection profiles with a total length of 340 km. Over 106,000 SL/K points were calculated from 815 river profiles on basis of the SRTM v.3.0 DEM. Standard deviations (SD) of < -2SD (class 1) to > +2SD (class 5) were calculated from the lognormalised SL/K data and five SL/K classes were made and assigned to the nearby lineaments. A comparison with the fault segments from the seismic profiles showed a good coincidence between the presence of knickpoints, SL/K classes 4 and 5 and to a lesser extent class 3. Lineaments with SL/K classes 1 and 2 never corresponded to actual faults. We identified seven master thrusts of which three are very active to highly active, likely older, structures with important amounts of accumulated slip. The other thrusts are probably younger faults with relatively little accumulated slip, yet they are also active to highly active faults. Minor strike-slip faults were identified as very active to highly active structures. Published slip rates shows that at least some of the SL/K class 4 faults experience slip rates of ~1 to ~4 mm a−1 and the SL/K class 5 strike-slip faults may experience slip rates as high as one metre over the course of several months. Most active faults occur where the basal evaporite layer is abnormally thick.

Delineation of tectonically active zones in the Island Belt Uplift region, Kachchh Basin, western India: A geomorphic and geodetic approach

In the present study, we have identified the tectonically active zones along the Island Belt Uplift (IBU), an upthrown block of E-W trending Island Belt Fault (IBF). Major and minor transverse faults have segmented the IBU into four sub-uplifts, viz. Pachham Uplift (PU), Khadir Uplift (KU), Bela Uplift (BU), and Chorar Uplift (CU) from west to east, respectively. The work includes geodetic and morphotectonic analysis of the IBU region. The Normalized Steepness Index (Ksn) analysis was performed supported by swath profiling to mark the tectonic activity variations along and across the strike of the IBF in the IBU region. Further, the Ksn contour map was prepared by using a power-law function of slope (S) of the longitudinal profiles of the river, concavity index (ө), and upstream area (A), which is an integral part of the Stream Power Incision Model (SPIM). The Ksn analysis suggests that the maximum amount of tectonic activity is restricted along the northern escarpment of the IBU, which falls in the vicinity of IBF and it's associated longitudinal and transverse faults. Based on the results of Ksn analysis, we have marked the tectonically active zones in the IBU region, which shows that amongst four sub-uplifts, the PU and BU were found most active (Zone-I), the KU expresses moderate activity (Zone-II), while CU demonstrated to be least active (Zone-III). The results were also confirmed by documentation of active tectono-geomorphic features like strath terraces, river offsets, straight fault scarps, triangular facets, linear valleys, fault ridges, Quaternary upwarps, laterally displaced crests and alluvial fans within the IBU. The active deformation pattern calculated using the Global Positioning System (GPS) data-set from 2009–2019 along IBU reveal maximum deformation rate of ∼2.5 ± 0.5 mm/yr in the PU, ∼2.0 ± 0.5 mm/yr in the BU while, the KU shows the deformation rate of ∼1.2 ± 0.5 mm/yr, which coincides well with the results of Ksn. The Ksn analysis results were also validated by comparing them with existing Gradient Length Anomaly (GLA) and Differential Interferometric Synthetic Aperture Radar (DInSAR) data. The ongoing tectonic activity in the study area is also manifested by the occurrence of moderate seismic activities in the identified active zones. The active tectono-geomorphic features and fault scarp geometry were analyzed and compared with the existing experimental models of basement fault and overlying sedimentary covers, which allow us to understand the nature of fault components of IBF. The analysis reveals that the IBF has been influenced by both dip-slip and strike-slip fault components of motion, which can be further confirmed by geophysical analysis. The results of Ksn analysis and field evidence were merged to prepare Active Fault Map of the IBU region that can be implemented for future seismic hazard assessment.

Database of Active Faults in Slovenia: Compiling a New Active Fault Database at the Junction Between the Alps, the Dinarides and the Pannonian Basin Tectonic Domains

We present the compilation of a new database of active faults in Slovenia, aiming at introducing geological data for the first time as input for a new national seismic hazard model. The area at the junction of the Alps, the Dinarides, and the Pannonian Basin is moderately seismically active. About a dozen Mw &amp;gt; 5.5 earthquakes have occurred across the national territory in the last millennium, four of which in the instrumental era. The relative paucity of major earthquakes and low to moderate fault slip rates necessitate the use of geologic input for a more representative assessment of seismic hazard. Active fault identification is complicated by complex regional structural setting due to overprinting of different tectonic phases. Additionally, overall high rates of erosion, denudation and slope mass movement processes with rates up to several orders of magnitude larger than fault slip rates obscure the surface definition of faults and traces of activity, making fault parametrization difficult. The presented database includes active, probably active and potentially active faults with trace lengths &amp;gt;5 km, systematically compiled and cataloged from a vast and highly heterogeneous dataset. Input data was mined from published papers, reports, studies, maps, unpublished reports and data from the Geological Survey of Slovenia archives and dedicated studies. All faults in the database are fully parametrized with spatial, geometric, kinematic and activity data with parameter descriptors including data origin and data quality for full traceability of input data. The input dataset was compiled through an extended questionnaire and a set of criteria into a homogenous database. The final database includes 96 faults with 240 segments and is optimized for maximum compatibility with other current maps of active faults at national and EU levels. It is by far the most detailed and advanced map of active faults in Slovenia.

Updated Segmentation Model and Cummulative Offset Measurement of the Aceh Segment of the Sumatran Fault System in West Sumatra, Indonesia

Sumatran fault in western Indonesia is one of the largest strike-slip fault in the world. The fault was formed as a result of the slip partitioning of the oblique convergence between the Indo-Australian and Eurasian plate along the Sunda trench. The right-lateral movement of the fault is accomodated by 19 fault segments that dissects the entire Sumatra island. We study the Aceh fault segment, which is located at the northernmost parts of the fault. The Aceh fault segment spans 250 km long passing through three districts: West Aceh, Pidie Jaya, and Aceh Besar and is affecting a total of ~546.143 population in the area. The current segmentation model assumes that Aceh fault segment acts as a single fault segment, which would generate closer to a M8 earthquake. This estimation is inconsistent with the ~M6-7 historical earthquake data. We conduct a detailed active fault mapping using the ~8 m resolution digital elevation model of DEMNAS and the sub-m DEM data from UAV-based photogrammetry to resolve the segmentation model of this fault. Our study indicate that the Aceh fault segment can be divided into 8 subsegments: Beutong, Kuala Tripa, Geumpang, Mane, Tangse, Jantho, Indrapuri, and Pulo Aceh. The fault kinematics identified in the field is consistent with right-lateral faulting. We measured cumulative displacement of geomorphic features (channels and ridges) ranging from 12.7 to 1931 m at some area. Findings of our study provide better estimation of the fault geometry and the maximum magnitude of potential earthquake along the Aceh fault segment as well as recommendation of prospective sliprate study sites. These informations are important for the development of seismic hazard analysis of the area.

Cost-effective Baseline Studies for Induced Seismicity Monitoring Related to CO2 Storage Site Preparation

Induced seismicity has been identified as one of the key showstoppers for the safety of geological CO2 storage sites. The selection procedure for adequate storage sites therefore needs to include the assessment of the seismic hazard. Such studies include the mapping of active seismic faults and understanding their maximum magnitude potential. In addition, the injection and related pore pressure changes will result in stress field changes in, around and outside of the reservoir. These stress field changes can reach several kilometres outside of the field and have the potential to trigger seismicity on faults that are critically stressed, i.e. close to failure. To better assess the stress field conditions in certain regions, knowledge on the seismic activity of regional faults is important. This is generally conducted by recording a baseline of the seismicity. Having established such baseline seismicity, subsequent changes in the seismicity level can be rapidly identified during continuous monitoring. Hence, seismicity that is induced or triggered due to the injection, can be separated from the baseline seismic activity and evaluated accordingly. Based on the location, strength, mechanism and pattern of the seismicity, an estimate of both the short-term and long-term hazard can provide a decision basis on how to proceed with an injection programme. The establishing of a stable baseline-seismicity-estimate may require many years of recording within the area of interest, given a sufficiently dense deployment of seismometers. How long the actual recording time should last is dependent on the earthquake activity in the region and on the expected magnitude range that the baseline should cover. Ideally, a dense network of sensors can be deployed directly above the anticipated storage site, with sensors in shallow boreholes. In most cases of offshore CO2 storage, the deployment of a network of seismometers or geophones above the target storage site with the sole purpose of establishing a baseline is economically prohibitive. The main costs for such an offshore deployment are related to the shipping and sensor deployment, and different solutions for power consumption, which need to be properly evaluated. There is a variety of sea-floor sensors available, ranging from industry standard 4C geophones to broad-band Ocean Bottom Seismometers. Deployment methods also vary from rope installation to free-fall and pop-up to ROV operated installation. Noise from seismic interferences (shooting), platform noise and vessels also need to be considered, along with fishery/trawling routes and other offshore infrastructure. Consequently, a method to establish the baseline seismicity from land would be preferable. A very cost-effective, alternative approach to monitoring seismicity from far distances is the use of seismic arrays. By placing a number of seismometers in a certain spatial pattern, this technology takes advantage of the local coherency of the seismic wavefield while simultaneously reducing the noise. This methodology is well-known to and applied in the Comprehensive Nuclear-Test-Ban Treaty Organization, where seismic arrays are used for global monitoring. This technology is especially useful if a deployment of sensors close-by or above an area of interest is not possible. For offshore CO2 storage sites, the only cost-effective long-term installation would be onshore, which must take into account the distance to the target region, anthropogenic noise sources, property rights and other borders. To demonstrate this technology, a temporary seismic array has been installed on the Norwegian coastline with the sensor setup evaluated for both its ability for noise reduction and signal improvement. Together with single sensors along the coastline, this temporary array installation is analysed in terms of its detection capabilities and thus ability for providing an adequate seismicity baseline. Ultimately, such an array can easily be converted into a permanent installation and hence provide a continuous record of the seismic activity throughout the CO2 injection period and during the post-injection phase. The first results from a small sub-set of sensors provide encouraging results towards improved detection capabilities.

ALOS 30 DSMアナグリフ画像を用いたイランの活断層マッピング（予報）

ALOS 30 DSMアナグリフ画像を用いたイランの活断層マッピング（予報）

ALOS 30 DSMアナグリフ画像を用いたトルコの活断層マッピング

ALOS 30 DSMアナグリフ画像を用いたトルコの活断層マッピング

Rupture models and viscoelastic stress changes of three Mw ~ 6.3 earthquakes along the southern front of the Qilian Mountains, northeastern Tibetan plateau

Around the southern front of the Qilian Mountains, three Mw 6.3 strong earthquakes have occurred since 2003. The distances between the epicenters of these events range from 18 to 46 km. By collecting available datasets, including broadband waveforms, coseismic surface geodetic measurements and active fault mapping results, we invert rupture models for these strong earthquakes with a finite fault model approach in elastic half space. Constrained by these detailed rupture models, we then build a three-dimensional finite element model to calculate Coulomb stress change due to the coseismic displacement and postseismic viscoelastic relaxation. Combined with an effective friction coefficient of 0.2–0.8 and variable rheological characteristics, numerical results show that following the 2003 event, the Coulomb stress change along the 2008 rupture segment was positive with magnitudes between 1.8 × 103 Pa and 2.2 × 103 Pa. Among the stresses, the postseismic viscoelastic relaxation contributed 10.7% ~ 23.3%. Just prior to the occurrence of the 2009 earthquake, the total changes of the Coulomb stress around its hypocenter reached 2.71 × 104– 3.72 × 104 Pa, to which the 2003 event and the 2008 event contributed approximately 7 × 102– 1.5 × 103 Pa (2.58% ~ 4.03%) and 2.64 × 104– 3.57 × 104 Pa (95.97% ~ 97.42%), respectively. We believe that other postseismic behaviors, including afterslip and poroelastic rebound, could also yield extra changes in the Coulomb stress, which probably further enhance the triggering effect among the sequential earthquakes. The numerical results also show that the increased stress around the hypocenters of latter two events was mainly determined by the positive shear stress. After the three strong earthquakes, the Coulomb stress on some active faults increased and is still increasing, suggesting that great attention should be paid to the potential earthquake hazards in this region.

Spatial Distribution of Rn, CO2, Hg, and H2 Concentrations in Soil Gas Across a Thrust Fault in Xinjiang, China

Spatial distribution characteristics and origin of soil gases were discussed in this study. We also examine the correlation between the spatial variation of soil gases and fault activity, based on the measurements of Rn, Hg, H2, and CO2 concentrations in the eastern segment of the BLT fault zone in the southern Tianshan Mountains, Xinjiang, China. The results show that the Rn and CO2 concentrations on the hanging wall were higher than those near the fault zone and on the footwall of the fault. Moreover, the Hg and H2 concentrations on the footwall were also higher than those near the fault and on the hanging wall of the fault. The main factors affecting the variations in soil gas spatial distribution were gaseous origin structure of the crust, fault activity, fault fracture degree, stratigraphic lithology, and the cover layer. The results of active structural fault mapping show that the BLT fault has been active since the Late Quaternary and the thrust has broken the fault surface. Under the influence of tectonic compressive stress, the tension zone was formed on the hanging wall of the fault and fractures were developed. This result is consistent with the characteristics of soil gas concentrations measured in this study, indicating that the concentrations of Rn, Hg, H2, and CO2 are closely related to the fault activity. These findings can be applied to identify seismic precursors from gas monitoring data of the studied area.

Mapping of active major faults in the Mamasa and surrounding areas using satellite gravity data and topographic features

The mapping of active faults in Indonesia, especially in areas near the city center is very important to determine the building code. Mamasa Regency, West Sulawesi is one of the areas that have active faults, has not been mapped well in the 2017 seismic hazard book, which is a guidebook in creating building codes in Indonesia. A total of 762 earthquakes occurred in this area from November to December 2018. This study aims to map active faults associated with the source of these earthquakes. TOPEX satellite gravity data were processed to obtain the Complete Bouguer Anomaly. The residual and regional gravity values were separated using a Gaussian filter to identify the lineation of the fault and the existing fracture zone. The multiscale second vertical derivative was also implemented to identify and characterize the fault. Topographic contour mapping was carried out to confirm the presence of fault on the surface as well as to observe the direction of fault movement. We used seven focal mechanism data from Global CMT to support the interpretation result of gravity and topographic data. The result, the main fault is a sinistral strike-slip fault with N164E strike orientation. This strike-slip fault has two sides. The movement of the strike-slip fault on these two sides causes a pull-apart which results in normal faults in the pull zone between the two faults.

Mapping of active and presumed active faults in Afghanistan by interpretation of 1-arcsecond SRTM anaglyph images

Afghanistan is a tectonically complex zone developed as a result of the collision between the Eurasian plate and the Indian plate to the southeast and the Arabian plate to the south. The active tectonics of the country is distinguished by a wide zone of crustal deformation. There is no large-scale active fault map in Afghanistan, which is essential for seismic hazard mitigation. I, therefore, mapped active and presumed active faults mainly based on interpretation of 1-arcsecond SRTM anaglyph images and shaded relief map. The map reveals that there are significant active faults across the country. In consideration based on the available data and geomorphic criteria, 22 faults are considered seismically active. The result from the mapping represents that three dominant types of structures (left-lateral strike-slip, right-lateral strike-slip, and thrust faults) characterized the interior of Afghanistan. Then the active fault map was combined with earthquake catalog data to interpret the seismic hazard and define earthquake sources based on focal mechanisms and distribution of earthquakes. To contribute to the understanding of seismic hazard, the paper outlines regions with similar neotectonic constraints and observations of type and age of faults that generate background seismicity. I delineated four seismic source zones: (1) east-northeastern, (2) Afghanistan-North Pamir, (3) Northern Afghanistan platform, and (4) middle and southwestern Afghanistan. The east-northeastern seismic zone is the most seismically active and has more crustal earthquakes in the country. This zone is cut by large active and potentially active faults, and Chaman fault is the most significant left-lateral fault that produced five historical surface ruptures.

Seismotectonics of Malatya Fault, Eastern Turkey

AbstractTurkey is located in a seismically active region with a complex tectonic history. In order to perform seismic risk assessment precisely, major fault zones (North Anatolian Fault Zone and East Anatolian Fault Zone) that are well defined are monitored continuously. It is a widely known fact that intraplate settings, such as Anatolian Plate, in which devastating earthquakes may occur, need to be observed densely. In this study, we investigate the seismotectonics of Malatya Fault within the Malatya Ovacık Fault Zone (MOFZ), which is one of the major agents responsible for internal deformation acting on Anatolian Plate. Recent geological and paleoseismological studies underline the necessity of comprehending the seismicity and latency of a major earthquake in this fault zone.We applied traditional techniques to investigate data of such a region. Earthquakes that occured in the vicinity of Malatya Fault between the years 2011 and mid-2019 are employed in a detailed analysis. The results of this study are constrained by the distribution of sensor networks in the region, yet allowing to define an active structure which is not included in the active fault map of Turkey, therefore, making a significant contribution to seismic hazard estimation.

Active faults of the Kerch’s Peninsula: new results

In the paper there are results of a recent study of the active faults in the Kerch Peninsula. There was compiled a Map of Active Faults - sources of the strong earthquakes occurred in Late Holocene. The map is a regional seismotectonic model of strong earthquake sources - detailed basis for a spatial prognosis of the seismic hazard. Results of the study show that the Kerch Peninsula demonstrates signs of the classical morphostructures, and a morphology of the modern peninsula contours is caused by the large active fault zones.

Active Faults in the Kerch Peninsula: New Results

This paper reports recently obtained research data on active faults in the Kerch Peninsula. The compiled Map of Active Faults demonstrates foci of Late Holocene strong earthquakes. This map is a regional seismotectonic model of strong earthquake foci, and a detailed basis for prediction of spatial seismic hazards. According to the research results, the Kerch Peninsula is characterized by the features of classical morphostructures, while the morphology of recent peninsula contours is caused by large active fault zones.

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.