Active faults of Alaska

<p>Active faults are characterized by creation/destruction of secondary (tectonic) permeability in response to a continuous interplay between deformation and fluid pressure fluctuations during the seismic cycle. The study of the paleofluid circulation in fault rocks can thus provide insights into the hydraulic and mechanical behavior of the seismogenic crust.</p><p>This work integrates data from field geology with geochemical and geochronological constraints to understand the spatio-temporal evolution of the paleofluid circulation in the Mount Morrone Fault System (MMFS), a ~25 km-long tectonic structure activated during the extensional Quaternary phase of the central Apennines (Italy). The MMFS cuts through a Mesozoic-Cenozoic multilayer carbonate succession for a cumulative stratigraphic offset of about 2 km. Fluvio-lacustrine and slope deposits (Middle-Late Pleistocene) occur at its hanging wall and are variably involved by faulting. The MMFS is currently classified as a silent seismic fault, with an estimated Mw= 6.5-7.0 potential magnitude and recurrence time at 2.4 ka for an expected earthquake.</p><p>The structural survey focused on the western strand of the MMFS cutting through a succession of Sinemurian dolomitized limestones. A composite network of NW-SE-striking, SW-dipping fault surfaces defines the structural architecture of the MMFS in the study outcrops, with high angle (dip > 55°) faults that systematically cut and displace medium-to-low angle (dip in the order of 30°-50°) faults. Both fault systems are characterized by dominant dip-slip movement and normal kinematics. Lenses of cm-thick cataclasites often occur along the slip surfaces. Cataclasites are made by sub-angular to sub-rounded carbonate clasts (up to 1 cm-wide) dispersed in a very fine-grained matrix. Layers of cm-thick carbonate concretions occur associated with the cataclasites, testifying for pulses of fluid discharge along the fault surface during the tectonic activity of the MMFS. Microstructural investigations document that: (i) carbonate concretions show an internal texture of fibrous vein having fiber growth direction roughly perpendicular to the vein wall, and (ii) the basal portions of the carbonate concretions are fractured and incorporated within the underlying cataclasites through the deposition of a new calcite cement. The geochemical (δ<sup>13</sup>C and δ<sup>18</sup>O stable isotope) analyses on selected samples attest for a progressive chemical shift of the mineralizing fluid from marine (in host rock and in cataclasites) to meteoric waters (in carbonate concretions). The U-Th dating of carbonate concretions and calcite slickenfibers constrains the fault-controlled fluid circulation to the Middle Pleistocene, with ages spanning from 270 to 180 ka. Significantly, the dating of carbonate concretions documents a 12-kyr cyclicity of the fluid infiltration in the fault zone.</p><p>The development of the secondary permeability in the MMFS thus corresponds to a combination of faulting and tensile fracturing, in response to a cyclic increasing of the shear stress and the pore pressure during the seismic cycle. The polyphasic deformation system of the MMFS constitutes a record of fault activation and reactivation episodes that could contribute to define the recurrence model of seismic events on regional-scale faults.</p>

Seismic reflection profiling across the seismogenic fault of the 1995 Kobe earthquake, southwestern Japan

<p>One unconventional coal extraction method is in-situ coal conversion. In this process, the coal is gasified in an underground reactor. A crucial issue that should be considered in this approach is the assessment of short and long-term environmental hazards and risks to human health and the environment resulting from potential surface subsidence and fault activation in the presence of complex geological conditions. This research aimed to assess potential environmental impacts associated with a commercial-scale application of in-situ coal conversion in a high coal production area in the Maza-Varalja region in Hungary. The Maza-Varalja region is an environmentally protected forested area. In this research, the numerical modeling of surface subsidence and fault activation was implemented using the finite-volume numerical modeling software FLAC3D. A predictive three-dimensional geomechanical model has been developed using site-specific geological data. The material model is Mohr-Coulomb elastic-plastic. Zero thickness interfaces were employed to address the fault behavior with friction and cohesive characteristics. The in-situ stress was determined by geostatic loading and a horizontal stress factor. The boundary conditions were zero-displacement and positioned sufficiently far from the coal seams to not artificially influence the stress field. The initialized zone stresses were considered using the density of the zones above them and gravity. The horizontal to vertical stresses ratio was determined to be one. A series of sensitivity studies were conducted to address the importance of geologic parameters that have an impact on surface subsidence, fault activation, and pollutant migration to the surface. In order to achieve this, seven variables, including the unit weight, Young’s modulus, Poisson’s ratio, friction angle, cohesion, fault friction, and excavation sequence, were considered. Sixty-six simulations were undertaken and analyzed. The simulation results demonstrate that surface subsidence is affected by the average Young’s modulus of the geological strata and the fault activation to the friction angle of the faults. Also, shallower seams are more likely to produce surface subsidence, while as excavation depth increases, surface subsidence decreases. The model's results have been used to develop an Environmental Hazard and Risk Management toolkit (Tranter et al., 2022) for planning and decision-making processes during in-situ coal conversion to ensure that environmental risks and mitigation actions are clearly quantified and outcomes forecasted. </p>

Permafrost, or perennially frozen ground, covers 9×105km2 or 55% of the landmass of Alaska. The continuous zone of permafrost encompasses the physiographic subdivisions of the Arctic Coastal Plain, the Arctic Foothills, the northern Norton Sound Highlands, and the Brooks Range. The zone of discontinuous permafrost encompasses the physiographic subdivisions of the Interior Alaska Lowlands, the Interior Alaska Highlands, the Alaska Range, the Copper River Plateau, the Kuskokwin Highlands, the southern Norton Sound Highlands, and the Western Alaska Coastal Plains and Deltas (Wahrhaftg, 1965; Pewe, 1975) (see Figure 2.2.1).

Tectonic deformation as manifested by seismicity and active faulting in the Coast Ranges in the vicinity of Lake Berryessa appears to be concentrated along the Green Valley-Cedar Roughs fault trend and to a lesser degree, the Coast Ranges-Sierran block (CRSB) boundary zone. The Green Valley-Cedar Roughs fault trend appears to be a complex, discontinuous or segmented shear zone consisting of multiple faults. Geomorphic evidence of Quaternary displacement exists along many portions of the fault trend with Holocene features and evidence for fault creep occurring along the Green Valley fault. In contrast, no historic earthquakes greater than ML 5 are known to have occurred along the fault trend. Earthquakes relocated in this study from 1970 to 1988 occur in the vicinity of mapped faults; however, the seismicity is discontinuous with a strong tendency to occur in clusters. Also superimposed on the general north-northwest fault trend are north-south epicentral trends not associated with any mapped faults. Focal mechanisms suggest predominantly right-lateral, strike-slip faulting on both north and north-northwest-trending planes. The existence of reverse and normal focal mechanisms also attests to the complex faulting occurring along the Green Valley-Cedar Roughs trend. In general, the geologic and seismogenic characteristics are consistent with the hypothesis that the Green Valley-Cedar Roughs fault trend represents young faulting, possibly related to a newly developing plate boundary east of the San Andreas fault. Earthquakes are confined to the top 12 km of the upper crust. Seismicity within the CRSB boundary zone since 1970 has been generally confined to a sequence in 1978 near Madison with a mainshock of ML 4.2. Thrust/reverse faulting appears to be the source of this activity, consistent with the seismogenic processes observed along other segments of the boundary zone. Only one earthquake has occurred since 1970 in the epicentral area of the 1892 ML 6¾ Vacaville-Winters earthquake. The state of stress in the Lake Berryessa region as exhibited by focal mechanisms appears to be characterized by NE-directed tectonic compression as observed elsewhere away from the San Andreas fault system in northern and central California.

The Alps are a dynamic orogen, as evidenced by recent crustal uplift and seismic activity. Earthquakes are primarily occurring along the many pre-existing Neogene faults formed during the Alpine orogeny, making it challenging to predict which faults are being reactivated. Limited geophysical data, low strain rates, high erosion rates, and widespread faulting complicate the detection of active faults in low-strain regions. Currently there is a lack of knowledge about the abundance, architecture, and properties of active faults in the Alps, which is however critical for evaluating the regional seismic hazard.This study adopts an interdisciplinary approach to identify and characterize active faults in the Rawil depression and surrounding areas north of the Rhône-Simplon fault system, located in the southwestern Swiss Alps. A comprehensive seismotectonic description of the region is achieved by combining information from recent high-precision earthquake catalogs derived from relative relocations covering about 40 years, new fault maps using remote sensing and field surveys, updated stress inversion from extended focal mechanism catalogs and paleostress inversion from fault slip data, as well as GNSS data. Results from 3D imaging of active faults at depth, based on the high-precision hypocenter catalogs, reveal that subvertical faults, striking E-W, host most of the present-day earthquakes in the region. This imaging also uncovers previously unknown NW-SE striking active faults potentially contributing to the overall strain distribution in this part of the Alps. Compared to principal stress orientations in the upper crust derived from focal mechanisms, faults striking in both E-W and NW-SE directions appear to be optimally oriented for reactivation in the current stress field. Recent crustal stresses, consistent with the results obtained from paleostress inversion indicating NE/SW-directed transtension, suggest a relatively constant stress regime over the last couple of million years. This implies similarities between exhumed and seismically active faults at depth. The agreement between fault geometries exhumed at the surface and reconstructions of active faults at depth, as determined by hypocenter-based 3D imaging of active faults, support these findings. In conclusion, our study demonstrates that such interdisciplinary studies provide valuable insights into the deformation processes in tectonically active regions, contributing to refined seismic hazard assessments.

BackgroundPleistocene climatic instability had profound and diverse effects on the distribution and abundance of Arctic organisms revealed by variation in phylogeographic patterns documented in extant Arctic populations. To better understand the effects of geography and paleoclimate on Beringian freshwater fishes, we examined genetic variability in the genus Dallia (blackfish: Esociformes: Esocidae). The genus Dallia groups between one and three nominal species of small, cold- and hypoxia-tolerant freshwater fishes restricted entirely in distribution to Beringia from the Yukon River basin near Fairbanks, Alaska westward including the Kuskokwim River basin and low-lying areas of Western Alaska to the Amguema River on the north side of the Chukotka Peninsula and Mechigmen Bay on the south side of the Chukotka Peninsula. The genus has a non-continuous distribution divided by the Bering Strait and the Brooks Range. We examined the distribution of genetic variation across this range to determine the number and location of potential sub-refugia within the greater Beringian refugium as well as the roles of the Bering land bridge, Brooks Range, and large rivers within Beringia in shaping the current distribution of populations of Dallia. Our analyses were based on DNA sequence data from two nuclear gene introns (S7 and RAG1) and two mitochondrial genome fragments from nineteen sampling locations. These data were examined under genetic clustering and coalescent frameworks to identify sub-refugia within the greater Beringia refugium and to infer the demographic history of different populations of Dallia.ResultsWe identified up to five distinct genetic clusters of Dallia. Four of these genetic clusters are present in Alaska: (1) Arctic Coastal Plain genetic cluster found north of the Brooks Range, (2) interior Alaska genetic cluster placed in upstream locations in the Kuskokwim and Yukon river basins, (3) a genetic cluster found on the Seward Peninsula, and (4) a coastal Alaska genetic cluster encompassing downstream Kuskokwim River and Yukon River basin sample locations and samples from Southwest Alaska not in either of these drainages. The Chukotka samples are assigned to their own genetic cluster (5) similar to the coastal Alaska genetic cluster. The clustering and ordination analyses implemented in Discriminant Analysis of Principal Components (DAPC) and STRUCTURE showed mostly concordant groupings and a high degree of differentiation among groups. The groups of sampling locations identified as genetic clusters correspond to geographic areas divided by likely biogeographic barriers including the Brooks Range and the Bering Strait. Estimates of sequence diversity (θ) are highest in the Yukon River and Kuskokwim River drainages near the Bering Sea. We also infer asymmetric migration rates between genetic clusters. The isolation of Dallia on the Arctic Coastal Plain of Alaska is associated with very low estimated migration rates between the coastal Alaska genetic cluster and the Arctic Coastal Plain genetic cluster.ConclusionsOur results support a scenario with multiple aquatic sub-refugia in Beringia during the Pleistocene and the preservation of that structure in extant populations of Dallia. An inferred historical presence of Dallia across the Bering land bridge explains the similarities in the genetic composition of Dallia in West Beringia and western coastal Alaska. In contrast, historic and contemporary isolation across the Brooks Range shaped the distinctiveness of present day Arctic Coastal Plain Dallia. Overall this study uncovered a high degree of genetic structuring among populations of Dallia supporting the idea of multiple Beringian sub-refugia during the Pleistocene and which appears to be maintained to the present due to the strictly freshwater nature and low dispersal ability of this genus.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0413-2) contains supplementary material, which is available to authorized users.

An inventory of the available surficial data on active faults in Italy has been compiled by gathering all the available information on peninsular Italy (project by CNR, National Group for the Defense against Earthquakes), the central-eastern Alps and the Po Plain (EC ‘PALEOSIS’ project). Such information has been summarised in maps (reporting surficial expressions of faults with length L≥11 km) and in a table where fault parameters relevant for seismic hazard assessment (e.g. slip rates, recurrence intervals for surface faulting events, etc..) have been reported. Based on the geological characteristics of the Italian territory, a fault has been considered as active if it shows evidence of Late Pleistocene-Holocene displacements. Active faults in Italy are distributed throughout the entire Apennine chain, in the Sicilian and Calabrian regions and in some Alpine sectors, but knowledge is not homogeneously distributed through the territory. The largest amount of data is related to the central Apennines. In contrast, fault geometries and parameters are less well defined in the southern Apennines, Sicily and Calabria, where investigations have started more recently. Knowledge is sparse in the northern Apeninnes, where data necessary to define fault parameters are lacking and also the chronology of the activity has to be considered cautiously. Abundant blind faulting in the Po Plain hinders the detection of active faults by means of the classical surficial investigations and therefore the present knowledge is limited to the Mantova fault. Blind faults and the peculiar recent geological history of the Alpine areas, which is strongly conditioned by the erosional and depositional activity during and after the last glacial maximum, also hinder the identification of active faults in the central-eastern Alps. Some faults in this Alpine sector are believed to be active, but data on their segmentation are still missing. Available information indicates that Italian active faults are usually characterised by slip rates lower than 1 mm/yr. Recurrence intervals for surface faulting events are longer than 1,000 years in the central and southern Apennines. This review on the Italian active faults represents the first step to produce a map of the major seismic sources in Italy, which in turn will result from the merge of surficial data with seismological and geological subsurficial data. The available knowledge gathered in this paper indicates those areas where data are presently sparse. It should be, therefore, possible to better plan future geomorphological and paleoseismological investigations.

The Dongbielieke Fault, an active fault that originated during the Holocene, is located at a key position in the West Junggar orogenic belt. The total length of NE-striking the fault is 120 km. Since the Late Quaternary, continuous activity on the Dongbielieke Fault has caused clear left-lateral dislocations at all morphological units along it, and a continuous linear steep ridge has formed on the eastern side of the Tacheng Basin. Using high-resolution UAV images and differential GPS to depict and measure the strike-slip dislocations at each river terrace level, it was found that the maximum left-lateral dislocations in the T5, T4, and T2 terraces are 30.7 m, 12.0 m, and 8.7 m, respectively. In addition, based on the geomorphic ages from optically stimulated luminescence analyses, we have limited the sliding rate of different terraces on the Dongbielieke Fault. The average left-lateral strike-slip rate since the late Quaternary of the Dongbielieke Fault is 0.91 ± 0.18 mm/a. Combining the GPS rates for North Tianshan with those for the Tacheng Basin, it is believed that the three large NE-trending strike-slip faults (Daerbute, Tuoli, and Dongbielieke faults) absorb a large amount of residual deformation in the area. This would allow the faults to maintain a higher left-lateral slip rate. In summary, analysis of surface faulting, Quaternary geology, seismicity, and measurements of Holocene morphology suggests that the Dongbielieke Fault is an active strike-slip fault with high seismic risk. However, it is unlikely that this fault could generate an earthquake of magnitude greater than 7.5. Our data do not allow for discussion of a more complex seismic cycle.

During the 2016 Kumamoto earthquake, surface fault ruptures appeared not only along the well-known active Futagawa-Hinagu fault but also in the urbanized area of Mashiki Town, where no active faults have previously been identified. This chapter describes the distribution of the earthquake faults in Mashiki Town and evaluates their relationship with tectonic landforms and building damage based on Suzuki et al. (2018). We conclude that: (1) The earthquake faults were continuous for at least 5 km from the main trace of the Futagawa fault; (2) The fault diverged from east to west but maintains the total amount of displacement of approximately 70 cm; (3) The earthquake fault locations coincided with those of tectonic landforms, and (4) building damage tended to be severe near the earthquake fault.Keywords2016 Kumamoto earthquakeEarthquake faultActive faultBuilding damage

Drained thaw lake basin recovery on the western Arctic Coastal Plain of Alaska using high-resolution digital elevation models and remote sensing imagery

Based on results of the supplementary feasibility study geological and geotechnical investigation of some hydropower project about the active fault, which is partly buried by thick quaternary soil and partly exposed fault that triggered the earthquake ( M7.6 ) of Kashmir in 2005, Comprehensive methods such as geological mapping, drilling, borehole TV, acoustic wave test and testing on-site, are applied, it ascertains location, strike (orientation and dips), width of affected band, approximate depth, properties and integrity of the rocks within the active fault, developing trend and distribution range of the active fault. Interrelations of different methods and advantages or disadvantages are discussed and analyzed, at the same time, key points, difficulties and working procedures during the geological and geotechnical investigations are summarized, lot of data, results and figures are offered and analyzed,these methods and procedures can be mirrored and inferred in the future similar project.

Regional crustal shortening in northern Yukon and northeastern Alaska occurred episodically from the latest Cretaceous to the late Miocene, with a major culmination occurring in the Paleocene to middle Eocene, and a secondary culmination in the late Miocene. Structural trends are predominantly north to northeastward in northern Yukon and adjacent east-central Alaska, and generally east-west along the Brooks Range. The early Tertiary trend is strongly arcuate in the Beaufort fold belt and adjacent onshore areas. The continuity of structures southward from the Beaufort Sea region through northern Yukon and east-central Alaska supports the interpretation that the structures north of 65°N form a single orogenic entity. The Beaufort Sea region is 1000 km from the nearest plate margin. Northward shortening across Arctic Alaska and the northern Canadian cordillera reflects the convergent component of Kula (later, Pacific)–North America interactions throughout the Tertiary. North-to northeast-trending structures of latest Cretaceous to early Tertiary age in northern Yukon and east-central Alaska accommodate shortening of 180–240 km, and reflect Eurasia–North America convergence. The strongly arcuate offshore Beaufort fold belt and similar structures in adjacent northernmost Yukon and northeast Alaska were formed by the complex interplay of three factors: shortening of northern Yukon between Arctic Alaska and the craton to produce a north-trending orogenic welt; northward displacements propagated from the Kula plate margin; and local boundary conditions imposed by lithology and crustal structure, which aided lateral escape of the deforming supracrustal succession northward into the Beaufort Sea. In central Alaska, any kinematic linkage between the Kaltag fault in the west and the Tintina fault of the northern cordillera is more complex than was previously assumed. A new regional tectonic reconstruction of northern Yukon-Alaska quantifies the tectonic shortening in central Alaska south of the Kaltag and Tintina faults in an area where tectonic shortening is difficult to quantify due to complex geology. Complex deformation accommodated by folding, thrust and strike-slip faulting, and/or tectonic rotations accounts for an estimated 460 km of crustal shortening, approximately equivalent in magnitude to the total Tintina fault displacement of at least 450 km. The foreland of the Brooks Range, the Beaufort fold belt, and the northern cordillera contain proven petroleum basins. This regional synthesis validates a model of orogenic shortening for the Beaufort fold belt and provides a unifying tectonic setting for oil and gas plays throughout the region. The latest Cretaceous–Tertiary structural evolution of the Brooks Range, Beaufort, and northern Yukon fold belts is a case study of the temporally and kinematically complex far-field deformation arising from the convergence of four major tectonic plates.

Iran has long been known as one of the most seismically active areas of the world, and it frequently suffers destructive and catastrophic earthquakes that cause heavy loss of human life and widespread damage. The Alborz region in the northern part of Iran is an active EW trending mountain belt of 100 km wide and 600 km long. The Alborz range is bounded by the Talesh Mountains to the west and the Kopet Dagh Mountains to the east and consists of several sedimentary and volcanic layers of Cambrian to Eocene ages that were deformed during the late Cenozoic collision. Several active faults affect the central Alborz. The main active faults are the North Tehran and Mosha faults. The Mosha fault is one of the major active faults in the central Alborz as shown by its strong historical seismicity and its clear morphological signature. Situated in the vicinity of Tehran city, this 150-km-long N100° E trending fault represents an important potential seismic source. For earthquake monitoring and possible future prediction/precursory purposes, a test site has been established in the Alborz mountain region. The proximity to the capital of Iran with its high population density, low frequency but high magnitude earthquake occurrence, and active faults with their historical earthquake events have been considered as the main criteria for this selection. In addition, within the test site, there are hot springs and deep water wells that can be used for physico-chemical and radon gas analysis for earthquake precursory studies. The present activities include magnetic measurements; application of methodology for identification of seismogenic nodes for earthquakes of M ≥ 6.0 in the Alborz region developed by International Institute of Earthquake Prediction Theory and Mathematical Geophysics, IIEPT RAS, Russian Academy of Science, Moscow (IIEPTM a feasibility study using a dense seismic network for identification of future locations of seismic monitoring stations and application of short-term prediction of medium- and large-size earthquakes is based on Markov and extended self-similarity analysis of seismic data. The establishment of the test site is ongoing, and the methodology has been selected based on the IASPEI evaluation report on the most important precursors with installation of (i) a local dense seismic network consisting of 25 short-period seismometers, (ii) a GPS network consisting of eight instruments with 70 stations, (iii) magnetic network with four instruments, and (iv) radon gas and a physico-chemical study on the springs and deep water wells.

Ordinary General Meeting 9 December 1970 at 5.00 p.m. This meeting was devoted to a presentation by staff of The British Petroleum Company Ltd, on Alaskan exploration and the development of the Prudhoe Bay Oilfield. 1. The general geology of northern Alaska By R. Stoneley. Alaska is a country of over half-a-million square miles. It can be divided into three major geological-physiographical provinces: southern Alaska formed of the arcuate Pacific Mountain System (the Aleutian-Alaska and Coastal Ranges, separated by depressions), central or interior Alaska which is the counterpart of the inter-montane plateaux of the western United States, and northern Alaska, the extension of the Rocky Mountain System and Interior Plains. Northern Alaska, on which attention was focussed in the lecture, includes the Brooks Range, the Arctic Foothills and the treeless tundra of the Arctic Coastal Plain or Slope, in all an area of about 125000 square miles. The Brooks Range is a continuous chain of mountains composed of Palaeozoic and early Mesozoic sedimentary rocks which in the western and central part are thrust northwards over the Mesozoic rocks of the foothills. The Arctic foothills are underlain by a very thick succession of Cretaceous flysch and molasse which in the southern part show complex fold and thrust structures comparable with the foothills structures of the Canadian Rockies. In the northern foothills the Cretaceous beds exposed at the surface are folded into a series of long, narrow anticlines and broader synclines which for the most part die out at depth in a