The possibility of complex studying for the geological environment during seismic-ecological monitoring in areas of increased environmental danger

Актуальность настоящей статьи состоит в том, чтобы показать возможность при проведении локального сейсмо-экологического мониторинга (ЛСЭМ) получать не только двумерное, но и трехмерное представление о глубинном и скоростном строении изучаемого объекта, а также анализировать трехмерные модели показателей напряженного состояния геологической среды во времени. ЛСЭМ проводится на ограниченных территориях с целью оценки степени экологической безопасности и уменьшения риска опасных природных явлений на этапе наблюдения при строительстве и эксплуатации объектов особой важности, таких как ГЭС, АЭС, объектов недропользования, а также мегаполисов. Цель работы. Цель настоящей статьи показать результаты трехмерного комплексного изучения среды с помощью локального сейсмо-экологического мониторинга на реальных объектах для районов Балаковской АЭС и Московского мегаполиса. Методы исследования. По кинематике обменных волн PS от далеких землетрясений получены данные о рельефе глубинных границ и скоростном строении изучаемых регионов. Построены трехмерные модели глубинного и скоростного строения. По энергии обменных волн от далеких землетрясений оценены показатель анизотропности g и показатель напряженного состояния среды S для разных уровней глубин и разных временных интервалов наблюдения в районе планируемой Тверской АЭС. Результаты исследований. Построены трехмерные модели показателя анизотропности g. Полученные трехмерные модели показателя анизотропности g и оценка показателя S позволили выявить аномалии показателя g, усиление и исчезновение этих аномалий в пространстве и во времени, а также выявить влияние далекого катастрофического землетрясения из района Аляски на изменение значений геодинамических показателей. Сделан вывод, что при проведении локального сейсмо-экологического мониторинга (ЛСЭМ) в разных районах исследования имеется возможность построить трехмерные модели глубинного и скоростного строения исследуемого региона, а также изучить распределение геодинамических показателей анизотропности g и напряженного состояния S в разных диапазонах глубин и для разных временных интервалов, и как результат, построить трехмерные модели, характеризующие напряженное состояние региона во времени. The relevance of this article is to show the possibility of obtaining not only a two-dimensional, but also a three-dimensional idea about the depth and speed structure of the object during researching by local seismic-ecological monitoring (LSEM), as well as to analyze three-dimensional models of indicators of the stress state of the geological environment over time. LSEM is carried out in limited areas in order to assess the degree of environmental safety and reduce the risk of natural hazards at the stage of observation during the construction and operation of facilities of special importance, such as hydroelectric power stations, nuclear power plants, subsoil use facilities, as well as megalopolis. Aim. The purpose of this article is to show the results of a three-dimensional complex study of the environment using local seismic -ecological monitoring at real objects for the Balakovo NPP region and the Moscow megalopolis. Methods. Based on the kinematics of the converted waves PS from distant earthquakes, data were obtained on the relief of deep borders and the speed structure of the studied regions. Three-dimensional models of deep and speed structure were built. Based on the energy of converted waves from distant earthquakes, the anisotropostig indicator gand the stress state indicator of medium S for different depth levels and different time observation intervals for the area of the planned Tver NPP were estimated. Results. Three-dimensional models of the anisotropy indicator gare built. The obtained three-dimensional models of the anisotropy indicator g. and the assessment of the indicator S revealed the anomalies of the indicator g., the amplification and disappearance of these anomalies in space and in time, as well as the influence of a distant catastrophic earthquake from the Alaska region on the change in the values of geodynamic indicators. It was concluded that when conducting local seismic-ecological monitoring (LSEM) in different study areas, it is possible to build three-dimensional models of the depth and speed structure of the studied region, as well as to study the distribution of geodynamic indicators of anisotropy of g. and stress state S in different depth ranges and for different time observation intervals, and as a result, to build three-dimensional models characterizing the stressed state of the region in time.

Striking differences in lithospheric structure between the north- and south-western Alps: insights from receiver functions along the Cifalps profiles and a new Vs model

<p>The CIFALPS receiver-function (RF) profile in the southwestern Alps provided the first seismological evidence of continental subduction in the Alps, with the detection of waves converted on the European Moho at 75-80 km depth beneath the western edge of the Po basin (Zhao et al., 2015). To complement the CIFALPS profile and enhance our knowledge of the lithospheric structure of the Western Alps, we installed CIFALPS2, a temporary network of 55 broadband seismic stations that operated for ~14 months (2018-2019) across the North-Western Alps (Zhao et al., 2018). The CIFALPS2 line runs from the Eastern Massif Central to the Ligurian coast, across the Mont-Blanc and Gran Paradiso massifs and the Ligurian Alps. Seismic stations were installed along a quasi-linear profile with a spacing of 7-10 km.</p><p>We will show 2 receiver-function CCP (common-conversion point) depth-migrated sections along the CIFALPS2 profile, the first one across the Alps, and the second one across the Ligurian Alps and the Po basin. The time-to-depth migration of RF data is based on the new 3-D Vs model of the Greater Alpine region derived by Nouibat et al. (2021) using transdimensional ambient noise tomography on a large dataset including the AlpArray seismic network. Depth sections across the Vs model are also useful for interpreting the RF CCP sections as they have striking similarities.</p><p>The images of the lithospheric structure of the NW Alps along CIFALPS2 are surprisingly different from those of the SW Alps along CIFALPS. The deepest P-to-S converted phases on the European Moho are detected at 60-65 km depth beneath the Ivrea-Verbano zone, that is 15 km less than on CIFALPS. The negative polarity converted phase interpreted as the base of the Ivrea body mantle flake on the CIFALPS section is still visible on CIFALPS2, but with a lower amplitude. The RF section confirms the existence of a jump of the European Moho of ~10 km amplitude in less than 10 km distance, which is located within a few km from the western boundary of the Mont Blanc external crystalline massif. All these observations are confirmed by the Vs model that also displays a less deep continental subduction than on CIFALPS, weaker S-wave velocities in the Ivrea body wedge, and the jump of the European Moho.</p><p>The Moho beneath the Ligurian Alps is detected at 25-30 km depth both on the RF and on the Vs depth sections. Moving northwards, this Ligurian Moho is separated from the Adriatic Moho by a puzzling S-dipping set of P-to-S converted waves with negative polarity. The crust of the Ligurian Alps is characterized by a set of north-dipping negative-polarity converted waves at 10 to 20 km depth beneath the Valosio massif, which is a small internal crystalline massif of (U)HP metamorphic rocks located north of Voltri. The similarity of this set of negative-polarity conversions to the one observed beneath the Dora Maira massif on the CIFALPS profile suggests that it may be a relic of the Alpine structure overprinted by the opening of the Ligurian sea.</p>

Joint inversion of converted and surface waves for characterization of geothermal fields

<p>Joint inversion of surfaces and teleseismic converted waves is commonly used to retrieve seismic structures beneath a seismic station. Currently, this approach is routinely applied at global and regional scale to probe the structures of the mantle and the lower-crust. However, the difficulty to retrieve reliable converted waves at high frequencies (> 1 Hz) makes challenging to apply this technique to resolve structures at shallow depths (<20 km). Here we explore the feasibility of using a trans-dimensional Bayesian scheme based on a reversible jump Markov Chains Monte Carlo method, to resolve shallow structure at local scale. We use phase and group velocity dispersion curves for Love and Rayleigh waves, from 0.5 to 10 s and tele-seismic converted waves in a distance range from 30<sup>o</sup> to 95<sup>o</sup>. We explore the ability of different approaches to retrieve high frequency converted phases that will be used in the framework of the Bayesian inversion. We present preliminary tests of the reliability of the method and applications to experimental data collected in the super-hot geothermal field of Los Humeros, México. This work is performed in the framework of the Mexican European consortium GeMex (Cooperation in Geothermal energy research Europe-Mexico, PT5.2 N: 267084 funded by CONACyT-SENER: S0019, 2015-04, and Horizon 2020, grant agreement No. 727550).</p>

On parameterization in monoclinic media with a horizontal symmetry plane

I have derived accurate anisotropy parameters for a monoclinic anisotropy model with a horizontal symmetry plane based on normal moveout (NMO) ellipses for P-, S1-, S2-, and converted waves. The NMO velocity ellipse is also defined for all types of converted waves. The parameters are defined in the phase domain and compared with existing approximate monoclinic anisotropy parameters. These parameters are evaluated for two benchmark models consisting of two nonorthogonal fracture sets embedded into a transversely isotropic medium with a vertical symmetry axis. The dependence of monoclinic parameters on the azimuth angle between the fracture sets is analyzed. Being linearized with respect to fracture weaknesses, the monoclinic anisotropy parameters can be decomposed into sine functions of double and quartic azimuth angle between the fracture sets with the weights given by the stiffness coefficients of the background model. The discrimination between the fracture parameters computed from a given set of monoclinic parameters is dependent on the background model and controlled by the azimuth angle between the fracture sets.