查看更多>>摘要：Integrated structural/geochmnological studies help unraveling complex brittle deformation histories. We have analysed the structural geological database of brittle faults from the ONKALO (TM) underground facility for spent nuclear fuel in Olkiluoto in southwestern Finland. Based on the structural geological data from eleven representative fault zones, we classify the Olkiluoto brittle structural features into four fault systems, referred to as Fault system I to IV. The classification is based on their structural properties and tectonic history, crosscutting relationships, fault rock mineralogical characterization and 3D modelling. Some constraints on the timing of faulting are provided by K-Ar dates on synkinematic illite from fault gouge samples. Our results show that the bedrock in southwestern Finland experienced numerous brittle deformation phases between ca. 1.75 and 0.9 Ga. N-S strike-slip faults (Fault systems I and II) formed at mid-crustal levels ca. 1.79-1.75 Ga ago in response to NW-SE/NNW-SSE compression soon after the Svecofennian omgeny. Later E-W striking oblique dextral/normal faults (Fault system III) are tentatively associated with the Gothian omgeny 1.6 Ga ago. These three fault systems were reactivated during NE-SW compression ca. 1.3-1.2 Ga ago, coeval with intrusion of a regional swarm of olivine diabase sills. E-W compression at the onset of the Sveconorwegian omgeny ca. 1.1-1.0 Ga ago resulted in the formation of SE dipping low-angle thrust faults (Fault system IV) and the selective reactivation of fault system II and III. Overall E-W extension during the collapse of the Sveconorwegian orogen ca. 0.97-0.87 Ga ago caused the localised reactivation of fault systems III and IV. Our research approach, which is integral to the siting process of repositories for spent nuclear fuel, demonstrates that the basement in southwestern Finland experienced repeated reactivation since the Mesoproterozoic, suggesting that future deformation localization is likely to be also accommodated by reactivation of existing brittle structures rather than formation of new faults.
Peron-Pinvidic, GwennAkermoen, TorLeivestad, Lars Ivar
15页
查看更多>>摘要：The Norwegian Continental Shelf is one of the worlds most used laboratories to study rifting processes and rifted margin architecture. Available datasets are dense, various and of good quality. However, since the full basement is rarely imaged, major questions remain unanswered regarding the structural details and nature of rocks at depth. The Geoex MCG Regional Deep Imaging 2019 (RDI19) dataset presents - for the first time - a series of regional long-offset seismic reflection profiles, of high resolution and deep imaging (16 s-twtt). The dataset offers an unprecedented imaging of the entire margin architecture including deep basement units, Moho and upper mantle - from the proximal margin to the outer margin. This contribution introduces the dataset and proposes an interpretation accompanied by gravity modelling experiments. Focus is set on the identification and seismic facies characteristics of the top basement and Moho core envelopes to discuss the dip and lateral variability of the various basement/crustal units. Basic gravity models are used to develop a discussion on the possible nature of the acoustic basement in the distal margin (crust, magma, mantle, combinations). Based on the observations and interpretation, an updated map of the More and Wring margin structural domains is proposed and discussed.
查看更多>>摘要：The origin and development of the Black Sea Basin (BSB) remain controversial. In this study, we determined the main tectonic features of the BSB using satellite gravity, heat flow, and seismological data. Positive gravity anomalies are observed in the arc region due to high-density material, while negative gravity anomalies are seen in the trench region owing to the mass deficiency and sediments. The trench region has a relatively low heat flow anomalies along the Black Sea coasts. The Moho depth increases from 18.11 km in the Eastern Black Sea Basin (EBSB) to 51.83 km in the Eastern Anatolia Plateau (EAP) with an average of 34.13 +/- 6.15 km. The lithosphere thickness changed between 78.48 km beneath Anatolia and 120.57 km below the EBSB with an average of 99.17 +/- 8.17 km. The low heat flow and Moho temperature values indicate that the lithosphere is strong and cold beneath the BSB. The numerical results, therefore, provide evidence for southward subduction of the Tethys oceanic lithosphere below the Anatolian plate during the late Mesozoic-Cenozoic. Considering all geophysical and geological data, we conclude that the Black Sea Basin represents a relict basin, rather than a back-arc basin.
查看更多>>摘要：The seismicity in the north-eastern fringe of the Indian Plate in the Eastern Himalayan Syntaxis (Tidding-Tuting Suture) and adjoining areas have been studied by analyzing the earthquake data recorded by the local broadband seismograph network as well as reviewed catalog data of the International Seismological Center. The study reveals that the region is seismically active up to similar to 40 km depth. In contrast, the seismicity in the Indo-Burma Ranges (IBR) is observed up to a depth of similar to 200 km suggesting the active subduction process of the Indian plate beneath the IBR. This study suggests that the subduction process terminates north of similar to 27(0) N Latitude and the indentation process of the rigid Indian plate into south-east Asia predominantly controls the seismicity north of the IBR. The seismicity and its linkage with the existing tectonic features are critically examined in the Lohit Valley and Mishmi Hills regions. Source mechanisms of 10 earthquakes (3.5 <= M <= 4.2) are evaluated with the help of the waveform inversion technique. The results of the source mechanism study reveal that the closely spaced Mishmi, Tidding, and Lohit faults are steeply dipping thrust sheets that accommodate the large crustal shortening owing to the indentation process and clockwise rotation tectonics. The Walong fault is characterized by strike-slip motion which helps to facilitate the clock-wise rotation of crustal material around the syntaxis. Significant strain partitioning is anticipated from the variation of pressure (P) axes orientations indicating the effect of complex syntaxial tectonics.
查看更多>>摘要：Recent studies of anthmpogenic seismicity have improved our understanding of the causal relationships between earthquakes and industrial activity. Whether larger-magnitude earthquakes can be triggered and how human injection and production of fluids interact with active faults remain poorly understood. The 2017 Mw 6.5 Leyte earthquake nucleated at a depth close to the production zone and within 2 km of an actively producing geothermal field in Philippines. Here we use satellite radar data to constrain the pre-earthquake ground deformation across the field and the Leyte fault and to determine the coseismic source parameters. From consideration of regional historical seismicity and fluid extraction model constrained by fluid injection and extraction rates, we find evidence suggesting that the mainshock is directly associated with the geothermal production efforts. Our findings demonstrate that the extraction of geothermal power close to active fault zones is capable of triggering damaging earthquakes, a hazard that was previously underappreciated
Rae, Auriol S. P.Kenkmann, ThomasPadmanabha, VivekPoelchau, Michael H....
15页
查看更多>>摘要：Brittle deformation at high strain rates results in intense fragmentation and rock pulverisation. For rocks, the critical strain rate at which this behaviour occurs is similar to 10(2) s(-1). The mechanical properties of rocks at these strain rates can also be very different from their quasi-static properties. Deformation of rocks at these strain rates can occur during fault rupture, landslide events, and meteorite impacts. In this study, we present the results of high strain rate mechanical tests to determine the characteristic strain rate for rate-dependent brittle failure, and the fragment size and shape distributions that result from failure at these conditions. We investigated sandstone, quartzite, limestone, and marble and considered whether the fragment characteristics can be used as diagnostic indicators of loading conditions during brittle failure. We find that the characteristic strain rates, where the dynamic strength is twice the quasi-static strength, range between similar to 150 and 300 s(-1) for rate-dependent brittle failure in the investigated lithologies. Furthermore, we use our results to demonstrate an empirical inverse power-law relationship between fragment size and strain rate for dynamic failure under uniaxial compression. On the other hand, we show that fragment shape is independent of strain rate under dynamic uniaxial loading.
查看更多>>摘要：Historically, devastating major earthquakes have occurred frequently in the peripheral zones of the Ordos Block. Thus, identifying possible locations of future catastrophic earthquakes in these regions is urgent both in the scientific community and in the public. For this purpose, we at first compute strain rates by means of GPS vectors and b-value from seismicity, then obtain geodetic earthquake potential. The calculation results show that high strain rates are mainly distributed in the peripheral zones of the Ordos Block with very small deformation in the interior of the Block, in good agreement with geology and seismicity. Based on seismic potential, considering historical and modern seismicity, and neotectonic structures together, we conclude that the west end of the Weihe Graben, southwest corner of the Ordos, is the most likely earthquake-prone area in future. Secondary risk regions for future strong earthquakes are located on the intersection between the Haiyuan fault and Liupanshan fault in the eastern Tibet, in the Yinchuan Graben and southwest of Hohhot around the Ordos Block. Therefore, this work may be significant for predicting earthquake risk and assessment of seismic hazard.
查看更多>>摘要：To take advantage of complementary strengths of earthquake body wave data and surface wave data from both earthquake and ambient noise sources, we have jointly used them to determine a high-resolution 3D Vs model of the lithosphere in South China by the joint inversion algorithm of Zhang et al. (2014). For body wave data, we assembled P- and S-wave arrival times for 40,028 earthquakes during the period of 2008/10-2018/06 recorded by 676 stations in South China. For surface wave dispersion dataset, it includes Rayleigh wave phase velocity maps at periods of 8-70 s and group velocity maps at periods of 8-50 s from Shen et al. (2016). Due to the complementary strengths of the two data types, the resolution of the jointly inverted Vs model has improved compared to the separately inverted models. The joint inversion model can also fit both data types at a similar level compared to separate inversions. In comparison with previous models, the new velocity model better delineates the sedimentary basins in the shallow crust and high velocity root in the lithosphere beneath the Sichuan basin, as well as better resolves the velocity variations between western and eastern Yangtze craton, thin lithosphere beneath eastern Yangtze craton and Cathaysia block, and helps us to better understand the mechanism of the lithosphere thinning. From the correlation between high velocity anomalies in the middle crust and the distribution of Neoprotemzoic basalt samples, we propose the amalgamation suture between the Yangtze craton and Cathaysia block is along the eastern segment of the Jiangshan-Shaoxing fault and the west margin of the Jiangnan orogen volcanic rocks. Our new joint inversion model is useful for constructing a community velocity model and for better understanding the complex tectonics of the South China block.
查看更多>>摘要：The central Indian Ocean Basin (CIOB) comprises numerous tectonic elements related to the early-mid Cretaceous Antarctica-India rifting and subsequent formation of the Indian Ocean. A protracted rift-drift journey of the Indian plate was accompanied with frequent interactions between concurrent mantle plumes and spreading centres. In 2015, we acquired similar to 420-km long wide-angle reflection and refraction seismic profile in the CIOB south off Sri Lanka, which lies in close proximity to the Indian Ocean Geoid Low. Our primary aim is to decipher crustal and uppermost mantle structure variations with an emphasis on prior tectonics. Two dimensional traveltime tomographic inversion complemented by potential field modelling yields sub-surface velocity-interface structures of the CIOB. Results demonstrate presence of an anomalously thick crust (similar to 14 km) underneath the Comorin ridge, which gradually thins out in the east towards the centre of the geoidal low. We observe distinct evidence for an anomolously high velocity lower crust (velocities greater than 7 km/s across a similar to 160 km wide region) west of 79(0) E longitude. However, crust to the east of this point appears to be normal oceanic type. We attribute the lateral diversity in the crustal type to possible magmatic underplating beneath the Comorin ridge. We interpret that the concurrent plume-ridge interaction during the late Cretaceous India-Madagascar break-up may have caused this crustal underplating. These findings have significant implications towards better understanding of plume-ridge interaction processes along various passive margins as well as precise reconstruction of India-Madagascar dispersal.
查看更多>>摘要：A shear zone developed in the Teshima granite in the Ryoke metamorphic belt of Japan contains isolated K-feldspar inclusions showing various shapes within deformed host quartz grains. We present a shape-change model for isolated K-feldspar inclusions, which is a mathematical equation that considers stress, inclusion size, temperature, and the duration of deformation. To calculate the shape-change pattern (i.e., the aspect ratio and size of inclusions) with respect to deformation duration using the model, we used values for deformation temperature (similar to 500-600 degrees C) and paleo-stress (90 +/- 10 MPa) estimated from deformed quartz microstructures within the shear zone. Shape-change patterns were obtained by calculating the model at the estimated range of temperatures with an interval of 25 degrees C and at the estimated paleo-stress. Shape-change patterns were subsequently corrected by compensating for the effect of post-deformation annealing during exhumation of the shear zone. Deformation duration was estimated by identifying the shape-change pattern calculated by the model that most closely corresponded to the observed shape-change pattern for the shear zone and considering the cooling rate of the Ryoke belt. The resultant deformation duration of the shear zone is estimated as 16,500-8400 yr under conditions of T = 550 degrees C and sigma = 90 +/- 10 MPa. Shear strain in the shear zone is calculated as 50-260 by multiplying the shear strain rate by the deformation duration.
NSTL
Elsevier