Seismic Instruments最新文献

In order to clarify the genesis of liquefaction folds (convolutions) developed at lithological boundaries in lacustrine sediments, such structures in three regions were compared. Folds in each region differ in morphology, composition of sediments, and the vertical gradient of their density and viscosity upon deformation. It is proposed to use the ratio of the widths of syn- and anticlinal folds in the convolution horizon (K_s) to analyze the latter, in which K_s > 1 corresponds to the normal viscosity gradient, and K_s < 1, to its inversion. Convolutions of the Baltic Shield and Yakutia from K_s ≥ 1 are noted in the most liquefied sediments with unstable density stratification (sands-on-silts), which indicates the possibility of their spontaneous formation during lithogenesis. Folds with K_s ≈ 1 are widespread in Yakutia, which indicates their cryogenic genesis. Convolutions in the Tien Shan were formed with stable sediment stratification in terms of density (silts-on-sands); low-fluidized coarse-grained sediments with viscosity inversion were also involved in deformation. These features indicate the seismic initiation of liquefaction processes. The results substantiate the lithogenic genesis of convolutions in lacustrine complexes of the Baltic Shield, cryogenic and lithogenic in Yakutia, and seismogenic in the Tien Shan. It is proposed to determine the scatter of the K_s value in the diagrams for diagnosing the genesis of convolutions. For lithogenic structures, this parameter is shifted to the region with K_s > 1, and for seismites, it is relatively symmetric with respect to K_s = 1.

The article presents a description and the first results of an experiment on deformation-seismic monitoring of the technical condition of a residential building located in a subsidence zone above mine workings. Deformation processes are monitored by hydrostatic leveling. Dynamic monitoring is implemented by controlling the change in the resonance (eigen) frequency using seismological equipment. A description of the hardware and software for the deformation-seismic monitoring subsystems is given. The first results for an 8-month continuous observation period are presented. Conclusions are made about the prospects of this type of monitoring in the event of a threat to the mechanical safety of a protected building. The material is addressed to specialists engaged in solving problems in the inspection and monitoring of the technical condition of buildings and structures.

The characteristics of the attenuation field in the lithosphere of South Asia are considered. Records of local earthquakes, obtained at the NIL station, and ratios of maximum amplitudes of S_n and P_n waves within the distance range of ~300–1900 km are analyzed. About 200 earthquake seismograms were processed in aggregate. It is established that generally lower attenuation is observed in the uppermost mantle beneath the Indian Plate (for the meridional profile directed toward the source zone of large Bhuj earthquake of January 26, 2001, with M_W = 7.7). Considerably higher attenuation corresponds to the regions of Himalayas and, especially, Southern Tibet. It is shown that increased attenuation is observed in the source zone of the recent large Nepal earthquake of April 25, 2015 (M_W = 7.8). Additionally, lower and intermediate attenuation is reported within the source zones of large and great interplate events (M_W = 7.0–8.1), occurred in the Himalayan region in 1897–1930. Conversely, substantially decreased attenuation corresponds to the source zone of the Bhuj intraplate earthquake. These new results are consistent with earlier data, which indicate concentration of mantle fluids below source zones prior to large interplate earthquakes, as well as ascent of fluids into the crust after these events. High attenuation zones are distinguished in the regions of West Himalayas and central Pakistan, where large earthquakes have not occurred for a long time. It is suggested that processes related to the preparation of large seismic events can occur there.

The study of archaeological sites in the area of Mt. Opuk (southeast Crimea) allow us to outline approximately the chronology of seismic events. The revealed deformations of building structures, taken separately, and, moreover, taken together, indicate their seismogenic character. In ancient building structures and cultural layers of archaeological sites in the Mt. Opuk area, numerous ruptures were identified. Fissures found in the ash dump, fading in the layer of the end of the 2nd–3rd century CE are typical seismogenic ruptures. It is possible that this earthquake occurred at the end of the 3rd century. The traces of two earthquakes are found at the Hill A settlement. The first earthquake is reflected in systematic clockwise rotations of the submeridional walls around the vertical axis. The seismic oscillations from this earthquake were directed at an angle to the mentioned walls, along the NNE–SSW axis. The building was preserved and repaired (buttress wall at the northern face of the southern wall of room A). The second earthquake, which was stronger, caused surface rupturing and displacements in the SE part of the building, almost completely destroying it. The time when this room was destroyed dates back to the beginning of the 4th century BCE. Traces of catastrophic destruction are documented in the ruins of a citadel on the upper plateau of Mt. Opuk; the NW tower of the citadel experienced significant deformations; traces of two earthquakes are found in the barracks; the western curtain wall and the citadel wall were severely damaged. Significant seismic deformations were also studied on the so-called eastern defensive wall, which is most likely synchronous with the citadel. The citadel completely ceased to exist in the first half of the 6th century CE, possibly after a strong seismic event, which was the final one in a series of destruction of the ancient Kimmerikon infrastructure. Before the Saltovo-Mayatsk people arrived at the Kerch Peninsula, no traces of human settlements on Mt. Opuk or its vicinity were reported. The traces of two earthquakes are revealed in the manor belonging to the Saltovo-Mayatskii (Khazarian) period of the early medieval time. The first seismic event led to counterclockwise rotation of all submeridional walls of the manor around the vertical axis. This shows that the seismic impact was directed at an angle to these building elements, namely, along the NNW–SSE axis. The building was preserved; only a retaining wall was erected at the southern (outer) face of the eastern wall of the room. The second earthquake was stronger: its intense seismic shaking collapsed both repaired and retaining wall in the southern direction, from where elastic waves arrived. The manor finally perished in the 930s–940s CE. Remarkable traces of strong earthquakes are observed in the topography of Mt. Opuk. According to the collected data, the main rupture on the mountain is seismotectonic in nature; however, the offset value was inte

Using original sources of information is an important requirement in historical seismology. Modern technologies make it much easier to access old papers and other, before hardly accessible archive materials. The new possibilities lead to publications in which previously studied historical earthquakes are revised. Such is this publication. The main aim is to present newly found macroseismic information on the 1802 deep Carpathian earthquake from original sources and assess its magnitude based on this data. Assessment of magnitude using a macroseismic field equation specially developed for deep Carpathian earthquakes is characterized by a larger error than that calculated using the equation for crustal earthquakes. However, the specially developed equation is better balanced for entire epicentral distances in the near and far zones, in the sense that the magnitude and its error are practically the same, being calculated separately for the near and far zones. Application of the macroseismic field equation to crustal earthquakes leads to significant differences in these assessments.

The article compares the results and estimation of the application conditions of seismic microzoning (SMZ) by numerical and instrumental methods for sites characterized by relatively small horizontal heterogeneity of the structure and properties of the soil strata. The results of applying the instrumental method for recording microseisms (Nakamura method) and calculation methods the of seismic stiffness and spectral transfer functions for SMZ of Oktyabrsky Island in Kaliningrad, Kaliningrad oblast were investigated. It is shown that the used SMZ methods yielded consistent results, differing mainly in the degree of detail and completeness of information. The results of the instrumental method for recording microseisms are characterized by the greatest detail and contain the most complete real, rather than model-calculated, frequency response of the expected seismic shaking. It is concluded that for weakly seismic areas with layered soil strata rather similar in structure to a horizontally homogeneous model, the choice of SMZ methods should be substantiated by the degree of importance of structures projected on the territory and, therefore, by the necessary amount of information on the frequency response of the expected vibrations and required site distribution details in seismic intensity increments.

We have conducted a complex of archaeoseismological works in the ancient town of Myrmekion, which belonged to the Bosporan Kingdom (Crimea). Numerous instances of destruction and deformation of buildings were revealed in archeological excavations: ruptures displacing walls, significant tilt of entire walls of the buildings, and rotations of wall fragments and individual stones around the vertical axis. This deformation complex indicates their seismogenic origin. We have revealed traces of a few strong earthquakes (three to five during the first millennium BCE and two during the first centuries CE). For some, we were able to reveal the directions of maximum seismic oscillations. The intensity of the seismic oscillations were I₀ ≤ IX. The obtained data could serve for more reliable seismic hazard assessment for the Crimean Peninsula, as well as for assessment of the contribution of natural disasters to the development of civilization.

To solve the problem of antiseismic strengthening, the integer macroseismic intensity of a building is insufficient, because this intensity cannot describe the seismic hazard of a territory. For this, it is necessary to establish the peak ground accelerations and estimate their statistical parameters. The paper constructs the probability density function of the peak ground acceleration for a building site. The basic data for such construction are the shaking of the territory, the peak ground acceleration values on a seismic scale, and the hypothesis on the distribution of peak ground accelerations according to Weibull’s law for the conditions under which the earthquake has occurred. The peak ground acceleration values are taken in accordance with the new seismic scale developed by F.F. Aptikaev. Shaking of the territory was taken in accordance with the traditional linear dependence of the recurrence macroseismic intensity logarithm. Limiting oneself to integer intensity values leads to a polyextremal distribution of peak ground accelerations with peaks at integer intensity values, since it is assumed that there are no earthquakes with intermediate intensities. A peculiarity of the research is construction of the probability density function of peak ground accelerations without using the discrete macroseismic earthquake intensity, but its continuous calculated value, replacing summation over discrete intensity values with the corresponding integration. As a result, a monotonically decreasing distribution density function is obtained, which, in a first approximation, can be described as exponential distribution.

The aim of the work is the substantiate the development of a GNSS deformation monitoring network at the site of the underground research laboratory, for estimating the safety of underground isolation of radioactive waste in the Nizhne-Kansk massif. The article overviews the international experience of GNSS observations of recent crustal movements in the vicinities of underground research laboratories location (Switzerland, Finland, Sweden). The general information and main results of research works during 2010–2020 in the Nizhne-Kansk geodynamic test area are described. The article presents the prospects for extending the geodetic network in connection with the start of construction of the underground research laboratory. Based on the Delaunay triangulation we have analyzed the triangular finite elements of the existing and planned geodetic network. It is shown that the location of new points will significantly affect the geometry of the network. As a result, the number of near-equilateral triangles in the network will increase, which has a positive effect on increasing the accuracy in determining deformations of the Earth’s surface when processing geodetic measurements.

The development of a structural-parametric approach to constructing analytical approximations is considered. Within the framework of the new method, which includes modified S-approximations and determination of the integral curves of the vector field, a method is proposed for finding the analytic continuation of the field in the case of profile (route) geophysical measurements. The results of a mathematical experiment using real data on an anomalous gravitational field from data of marine areal gravimetric and airborne gravimetric route surveys are presented. It is shown that the proposed analysis algorithm is promising for finding analytic continuations of geopotential fields within a certain neighborhood of the measurement profile when a sufficient volume of areal data is lacking.