G. G. Kocharyan

Variations in Rupture Zone Stiffness during a Seismic Cycle

The character of variations in the stiffness of the interblock contact at different stages of the stick-slip motion are experimentally estimated for the first time. Some possible consequences of the observed phenomenon are considered. It is shown that at the final stage of the cycle before the dynamic break the shear stiffness of the contact drastically decreases, which can be detected in nature with the help of seismic methods. This effect can serve as a base for the development of new active and passive methods of monitoring of seismically active regions.

Hydrologic response of underground reservoirs to seismic vibrations

The response of the water level in wells to seismic impacts from remote earthquakes and explosions are analyzed. It is shown that in most cases the magnitude of the postseismic change in the water level scales as a square root of the amplitude of the deformation wave. The intensity of persistent changes averages a dynamical deformation of 1–5 cm/μstrain. Noticeable deviations from the mentioned range are possible, depending on the particular structural features of the layer.The possibility of the destruction of poorly permeable barriers, which are formed in the fractures in rocks during precipitation of microparticles, by dynamical pulses is studied in laboratory experiments. It is shown that the fracture’s permeability of the rock may considerably increase even in the range of low-amplitude vibrations which are unlikely to cause a failure of the rock or a growth of the existing cracks in response to the passage of a seismic wave. It is established that the effect may progressively accumulate under the prolonged action of seismic impacts.The change in the number of open cracks and the increase in their effective permeability may bring about fluid migration and variations in pore pressure and, consequently, change the whole range of the local mechanical properties of the rock.

Seismogenic Width of a Fault Zone

High-precision catalogues containing data on the spatial distribution of earthquake sources associated with several fault zones have been processed. The analysis shows a high degree of spatial localization of seismicity. Most of the events are observed in a narrow zone with a characteristic width of about 100 m. This value is a part of a percent of the fault zone length and corresponds to the upper boundary of estimates concerning the effective fault width, which are made on the basis of data on the characteristic parameters of roughness and waviness of rock discontinuities.

Physical meaning of deviation of some parameters from the similarity law in a seismic process

An experimentally substantiated explanation is proposed for recently discovered specific regularities between the time of earthquake preparation and the earthquake scale. It is shown that the observed regularity of the time of earthquake preparation, which grows slowly with the scale as compared with what follows from the relations for the self-similar environment, may be governed by the nonlinear scale dependence of specific stiffness of discontinuities that demonstrates a gradual increase in the effective elastic modulus of fault zones as their typical size grows.

On the evaluation of displacement and deformation in tidal waves according to digital records of STS-2 and KSESh-R seismometers

A procedure for eliciting displacements in tidal waves from seismograms of broadband velocimeters like STS-2 and KSESH-R and the evaluation conversion of these displacements into vertical or volumetric deformation is proposed.

Groundwater level monitoring by precision measurements

The paper presents the results of processing the data on variations of groundwater level in an aquifer opened by a well in a depth interval of 76–115 m. The obtained series are compared with the volume deformation of the aquifer, calculated theoretically using the ETERNA 3.0 tidal analysis program. Two components are detected in the long-period area: the one coherent to the luni-solar tides and the one incoherent to them. It is established that the phase shift between the variations of volume deformation of the aquifer and the corresponding variations of water level in the well depends not only on the stressed-deformed state of the surrounding rock massif, but on the position of the piezometric surface of the aquifer as well. Some peculiarities of the effects of luni-solar tides on variations of groundwater level are considered. The amplitudes of groundwater level and volume deformation of the aquifer, as well as the phase shift between these parameters are estimated for the detected tidal waves. The value of the amplitude factor lies in the range of 0.04–0.058 cm/nanostrain.

The Use of Local Seismic Networks for Identifying the Seismogenic Structure of Faults

We consider a method for identifying the segments of localization of deformation processes within fault zones. The method is based on the results of seismic monitoring at a dense seismic network in California. For the first time, by analyzing the seismogenic structure of several fault zones, we highly accurately located the domains involved in active deformation processes. Three-dimensional reconstructions show that these domains are a set of local segments each having a characteristic size of about 100 m, which is commensurable with the scale of the probable anthropogenic impacts on the geological medium.By the example of a region in the North Caucasus, it is shown that by combining observations at a regional seismic network and at a local group of stations successively arranged at several segments close to the fault zone, it is in principle possible to achieve an accuracy of locating the seismic events, which is sufficient for such reconstructions.