Microseismic field affected by local geological heterogeneities and microseismic sounding of the medium

Abstract

Seismic hazard assessment with the use of an integrated approach is discussed on the case of the left bank of the Angara river in Irkutsk, Russia. Potential earthquake focal zones have been identified in the study area. A brief overview of fault tectonics, seismology and seismogeology of the study area is presented. The map of the epicenters of local earthquakes and the map of active faults in the study area show the magnitudes of potential seismic events in the potential earthquake focal zones. The methodology of instrumental measurements and the methods of seismic hazard assessment are considered in detail. Calculations are based on the data obtained by the instrumental methods of seismic microzoning. Theoretical seismic effects on typical ground conditions are calculated, and the estimations are obtained with reference to maximum accelerations for predicted strong earthquakes. Estimated are potential seismic effects of probable strong earthquakes on the foundations of structures in the study area. Based on the estimations, an initial signal is formed (taking into account the potential earthquake focal zones, their parameters and the spectral composition of vibrations corresponding to the local earthquakes), and a required set of seismic models is developed in order to quantify the parameters of soil motions that may take place in the event of a strong earthquake. The experimental methods provided the data on the seismic properties of the reference and investigated soils, the propagation rates of seismic waves in such soils, and the pattern of microseism levels, as required for a valid estimation of seismic effect parameters by the seismic rigidity method and the microseism technique. Currently, both methods are by far the most effective in determining the seismic hazard of the territories. Statistical analysis was carried out using the calculations and the simulation data to more clearly determine the scatter of the results obtained. The seismic hazard of the study area is assessed based on the results of this study.

Application of Surface-Wave Methods for Seismic Site Characterization

“…This is the case for Rayleigh wave field sounding near the scattering heterogeneities (e.g., cavities) of wavelengths of the same or smaller size (Gorbatikov and Tsukanov 2011). Gorbatikov et al (2008) suggested that, in this situation, monitoring lateral variations of ambient vibration average relative amplitudes can be considered as useful exploration tool to detect localized bodies. Numerical simulations and field experiences support this suggestion (Gorbatikov and Tsukanov 2011).…”

New data on the deep structure of the Northern Vent of the Great Tolbachik Fissure Eruption (1975–1976)

“…The usage of digital wide band registration of seis mic signals and development of principally innovative technology for estimation of the parameters of geolog ical features, namely, low frequency microseismic sounding [3,4], made it possible to initiate develop ment of a deep structure model in the GTFE region at the modern level, to specify the previously obtained results, and to reveal new peculiar features of the erup tion.…”

“…It should be noted that the applied method of microseismic sounding [3,4] does not require explo sive sources for its implementation, existence of local seismicity, or extended synchronized seismic networks with numerous sensors. In comparison with the exist ing seismic technologies, providing obtainment of detailed deep structure, this method is characterized by low costs, high efficiency, and environmental safety.…”

“…well as by simulations [3,4]. According to the results of numerical simulations [4], the horizontal resolution of the method (that is, the distance between heteroge neities required for their distinguishability) is esti mated as ~25% of the length of the sounding wave, or, respectively, ~50% of the depth of occurrence of the geological feature.…”

“…In order to understand the deep structure under the NV GTFE, low frequency microseismic sounding [3,4] was applied, which is based on the data on spa tial spectral variations of the natural microseismic field. In the world the most recognized mechanisms of generation of low frequency microseisms are swash action and pressure variations directly affecting the ground surface or by a water layer on the bottom of water areas with subsequent distribution over the con tinent.…”