Vol 55, No 2 (2019)

The necessary conditions for development and successful implementation of a digital seismic logger “Ermak-5” are considered. A short review of similar technical solutions for modern seismological monitoring systems is given, and qualitative comparative analysis is fulfilled. Technical and operational requirements for development of the logger are substantiated. The results of laboratory and field experiments are reported for confirmation of key specifications of this device. The special attention is paid to conformity of the amplitude–frequency characteristics of the logger to reference analogues. Different types of seismometers were used for comparative testing. Description of hardware–software implementation of the flexible power management system of the logger is given. It helps to decrease power consumption to about 300 mW when the recording is made through six channels. The logger can be used for long-term recording with autonomous power supply sources. The core of time in the logger is developed on the basis of special algorithms to reach technological maximum for inner clock synchronization accuracy using the GPS/GLONNAS systems (hundreds of nanoseconds) and NTP-services (dozens of microseconds). Details of time synchronization algorithms are examined, and a description of experimental laboratory and field setup for time synchronization accuracy is given. The LCD screen of the logger is very important for effective operation. Information about time, some logger parameters, and waveform in different modes appears at the display. The experience of implementation at different seismic monitoring facilities is generalized, and it is taken into account in the revision process of the logger project.

In this paper, we developed algorithms for multichannel processing of seismic array records that allow detecting signals of weak seismic events observed against the background of natural seismic noise. The algorithm for detecting signals of weak seismic events is based on the coherence assessment of longitudinal waves (P-waves) recorded by a small aperture array. The advantage of this algorithm over the known single-channel short/long term averaging (STA/LTA) detector is the ability to detect time intervals of P-waves at a signal-to-noise ratio (SNR) less than unity. Based on the time intervals of the array records with the registered coherence measure values that ​​exceed a certain threshold, the apparent slowness vector is estimated by using the phase bimforming algorithm that is robust to noise (Zhang et al., 2008; Kushnir and Varypaev, 2017). The developed algorithms of multichannel processing were tested using real seismic records of a small aperture array installed in the Kursk Magnetic Anomaly area near the mine workings for iron ore extraction. Signals of both strong (underground industrial explosions) and weak seismic events were detected for 20 h of seismic recording. In some cases, seismic events were shown to have a complex source mechanism. Using the Capon filter (Capon, 1969), for weak seismic events, P-waves with a duration not exceeding 0.2 s and a temporal shape similar to the known function of a Ricker pulse (Bording, 1996) are found to have resemblance.

The spatial pattern of diurnal variations in the temporal sequence of relatively strong earthquakes in the Garm Research Area in Tajikistan for 1955–1991 has been investigated. The earthquakes that occurred in the daytime and at night, as well as the value characterizing their difference, have been mapped separately. The differences in diurnal seismicity variations in a few local zones have been discussed. Compact areas with major daytime seismic events presumably related to quarry explosions have been identified. They are located far beyond the Garm Research Area at a considerable distance from the network of seismic stations. The sources of man-induced seismic events have not been found within the Garm Research Area. The identified large connected areas combine the cells dominated either by day or night earthquakes.

The seismic coda waves attenuation characteristic in the western Tien Shan region were studied. The short-period coda waves of the local earthquakes, recorded by the frequency-selective seismic stations in 1960–1984, and digital seismogram data of 150 earthquakes that had been occurring in the western Tien Shan region since 2005 until 2017, recorded at the AAK station (KNET network), were analyzed. The attenuation field is represented by the zones (blocks) having high Q-factor and being close to isometric in plan and by the linear zones of strong attenuation (weakened zones), which coincide with faults. It was revealed that the structure of attenuation field agrees with the structure of S-wave velocity field and the velocity anomalies of P-waves: low-velocity anomalies correspond to low-Q zones. The most expressed conducting zones, revealed from magnetotelluric data, coincided with the low-Q zones, indicating their significant fluid saturation. Sources of the strongest earthquakes with K > 16.0 were confined to the zones of maximum attenuation contrast, to the boundaries of blocks and weakened zones, where the mobility of blocks was determined by reduced viscosity of low-Q layers and small thickness of high-Q ones. The relationship between the features of seismic processes and spatial inhomogeneities of the attenuation field in the background of variations in the Earth’s rotation speed was also considered.

The article is an attempt to trace the seismic regime (temporal recurrence and grouping of strong earthquakes) in the central and southern Apennines during the historical period, beginning from the 13th century. The special attention is paid to consideration of seismic events of 2009–2017 in Italy in the context of the spatiotemporal regularities of the regional strong seismicity in the past. The analysis of data on historical and modern seismic catalogs enabled to identify eight seismic activations within the central and southern Apennines since the 15th century. These are both general activations, covering the central and southern Apennines, and those that occurred only within the central or predominantly southern Apennines. The identified activations included from three to seven strong earthquakes and continued from 3 to 20 (?) years. The last activation of 1997–2017 is characterized by concentration of seismic events (with no extreme values of magnitudes and intensity) only in the central Apennines and by considerable duration. The role of historical sources (in this case, the Saint Petersburg Vedomosti newspaper) in reconstructing a more complete timeline of past seismicity is emphasized.

This paper considers some aspects of the development of continuous automated systems for monitoring objects with slowly varying parameters using deformation monitoring as an example. Most attention is paid to a number of difficulties in software development at the stage of debugging and testing caused by the low rate of change of monitored variables. It is shown that these problems can be solved based on the methods used in discrete-event simulation. For this purpose, we have developed our own modeling system in the form of a Python-language library focused on solving monitoring problems. The library was used in the autonomous operation of the deformation monitoring system based on the complex of geophysical sensors SNMK Strazh.