Seismic Instruments最新文献

A brief analysis of different regulations for determining seismic loads based on the spectral theory shows that they have much in common but, at the same time, contain numerous amendments and clarifications for assessing true seismic effects. The calculation of seismic loads for one and the same conditions according to the regulations used in different countries produces significantly different results. According to the authors, there is a real possibility of creating common international regulations by refining and supplementing the existing ones. Apparently, the most promising regulations are European Standards EN 1998-2004/2012. The principle of calculation according to EN is more natural because seismic actions are actually transmitted to structures through a foundation. In addition, this approach allows consideration of a number of factors that affect the degree of seismic effects (ultimate shear resistance of soils, pressure on foundation soils, foundation−soil contact area, seismic beam tilt, etc.). An attempt is also made to assess the factors that impede the acceleration of building foundations during strong earthquakes.

Automated assessment of felt reports in accordance with the regionalized DYFI questionaries were implemented on mobile applications and messengers of the seismological service eqalert.ru. The new tool was tested on Sakhalin Island, which is considered as an active crustal region. We have developed a regression relationship between the peak ground acceleration and the community internet intensity for the studied area. The community internet intensity calculated from a large number of felt reports has a variance comparable to those given from a prediction equation of the physically based ground motion parameters. The given approach is considered as a state-of-art tool for the rapid collecting and assessment of macroseismic data. It may be used both with the weighted average method for generating high-quality shaking maps immediately following the felt earthquake. It is also a good way to involve the population in ground shaking measures.

This paper reports the first estimates of the characteristics of radiation and propagation of seismic waves in the Ural region obtained by modeling the accelerograms of recorded local earthquakes. The obtained source parameters are similar to those of the Caucasian region, while the seismic wave propagation characteristics are similar to those of the Baikal rift zone. A somewhat increased duration of strong motion in the Ural region can obviously be explained by a fractured structure of the Ural Mountains. The ground motion prediction equations (GMPEs) proposed by the Global Earthquake Model (GEM) project for the Ural region correspond to the platform regions with a stable continental seismicity, while the obtained characteristics of radiation and propagation of seismic waves in the Ural region correspond to the seismically active regions with a crustal seismicity. The comparison of the amplitudes of acceleration response spectra of the strongest earthquake recorded in the region with the estimates obtained by using the GMPEs has revealed a considerable excess of the estimates over the observed spectral amplitudes. Hence, the recommendations of the GEM should not be used in their original form, without correction factors, and it is necessary to develop the regional GMPEs for the purposes of seismic hazard analysis.

This paper presents the results of a detailed study of two relatively strong seismic events, occurred on November, 22, 2016 (М_W = 5.0) and April 3, 2017 (М_W = 4.8) at the northeastern flank of the Baikal rift zone in the areas of the South Muya and Kalar ranges. Both the events were followed by weak aftershocks (N = 178–539, К_р ≤ 11.0), whose epicenters were densely distributed over an area. The seismic moment tensors and hypocentral depths of the mainshocks were calculated from surface wave amplitude spectra. It has been shown that their sources were formed under the influence of the subhorizontal SE–NW extension and the subhorizontal or inclined NE–SW compression. Both the earthquakes were followed by noticeable macroseismic effects at epicentral distances up to 500 km. In the area of the Baikal−Amur Railway, their shaking intensity was IV–V MSK-64. The results obtained can be used in continuous seismic monitoring at the northeastern flank of the Baikal rift zone and can contribute to an objective seismic hazard assessment of the study area.

This study considers the hardware and methodological possibilities for increasing the information content of seismological observations in the epicentral zone of a platform earthquake without obvious surface manifestations. It is shown that the microseismic background analysis conducted during the installation of several seismic stations is efficient for both identifying the source location and refining the geodynamic features of the environment in the epicentral zone. The results of the coherent-time analysis of recordings at the three-component registration made to identify endogenous microcracks hidden by microseismic noise are presented. Their power, number, and azimuths are calculated. The possibility of using an autostructural function for the time series of a stream of micropulses at long-term recording of microseisms is shown to identify the self-organization of crustal blocks by similarities in their geodynamics. The requirements for the seismic equipment necessary for the observations are discussed.

The data on seismic activations (SAs) in Italy, Greece, and Turkey for the 17th–19th centuries are analyzed to clarify the common patterns of SA occurrence in the different seismically active regions associated with similar geodynamic conditions. The time clustering of strong earthquakes (М ≥ 5.6, I ≥ IX) in Italy, Greece, and Turkey in the 17th–19th centuries has made it possible to identify a number of SAs of various durations both in each country and in the whole region. However, the revealed recurrences are extremely uneven in the time range, the number of earthquakes, and the intervals between the individual SAs. Italy is recorded to have had 12 SAs; the 17th and 18th centuries are characterized by the maximum seismic activity, declining gradually by the 19th century. Nine and eight SAs were detected in Greece and Turkey, respectively, with seismic activity increasing strongly in these countries in the 19th century. The periods of common seismic activation for the entire region are also defined: 1658–1680, 1694–1743, 1766–1791, and 1846–1867.

We present the results of very high-resolution seismic profiling (VHR) and underwater electrical resistivity tomography (ERT) measurements in the Petrozavodsk Bay of Lake Onega, which were carried out to research the structure of Quaternary sediments. According to the VHR, five seismic sequences were identified during the seismic stratigraphy analysis, and a three-layer geoelectric section was obtained using ERT. The next step was an accomplishment of 2D ERT inversion based on reflectors from the VHR data. The joint interpretation of geophysical data was completed on the basis of comparative and cluster analyses with reference to the well and known geological data. During the research new information was obtained about the physical properties of the bottom sediments. The results indicate the need to apply such an approach to the interpretation of geophysical data and the prospects for the joint application of VHR and ERT acquisitions.

A method is proposed for calculating scalar products of pairs of seismic events that are closest in time to isolate sequences of epicenters of crustal earthquakes (chains) connected in space and time. To verify the developed methodology, the model and real catalogs of earthquakes of the Garm region in Tajikistan are compared. The efficiency of the proposed algorithm is shown. Based on the totality of the results of the allocation of chains, the issues that complicate the detection of the mentioned structures in the general case are considered. In the process of applying the created program to the real catalog of earthquakes of the Garm region, the existence of four pairwise orthogonal prevailing directions in their orientation was established. There were also some changes in the time of the predominant role of the selected strike of chains of earthquake epicenters. It is possible that these changes may reflect some elements of the dynamics of the seismic process in the Garm region.