SEISMICITY of KAZAKHSTAN and ADJACENT TERRITORIES in 2015

In 2015, the seismic monitoring in Kazakhstan was conducted by two Organizations: Seismological Experience-Methodical Expedition of the Ministry of Education and Science of the Republic of Kazakhstan (SEME), and the Republican State Enterprise Institute of Geophysical Research of the Ministry of Energy of the Republic of Kazakhstan (IGR). The paper presents detailed information on seismic observation networks. The joint catalogue based on the data of two organizations was compiled. It includes 489 earthquakes having energy class KR=6.6–12.2. The largest earthquake occurred on January 20, 2015 near the Semipalatinsk Test Site. The earthquake had magnitude MPVA=5.3, energy class KR=12.2, and was felt in a range of Kazakhstan settlements.

Organization of the stationary seismological observations point

The Institute of Geophysics of the NASU organizes and carries out continuous regional and local seismic observations on the territory of Ukraine. The article presents a universal modern model of seismic activity monitoring process, which is used in most international seismological agencies (USGS, EMSC, NEIC) and describes a typical stationary point of seismological observations of the National Seismological Network of the Institute of Geophysics of NAS of Ukraine. Seismological network of observations is a complex of systems consisting of stationary seismological points of registration of seismic waves, the distributed system of transfer and collecting of the seismological information, and also the center of operative processing of the data arriving from data registration points. The process of conducting regime seismological observations of local and remote seismic events on the territory of Ukraine and adjacent regions is described. Some important aspects of the need for comprehensive processing of registered events to identify local earthquakes and assess the current activity of tectonic structures in Ukraine are presented. The seismological network of the National Seismological Center of the Institute of Geophysics of the National Academy of Sciences of Ukraine is represented by a small number of stationary observation points: «Kiev-IRIS», «MI02-Poltava», «MI03-Skvyra», «MI04-Dnipro», «MI05-Stepanivka», «MI07-Mykolaiv», «ODS-Odesa», «MIU-Kryvyi Rih», and «MI06-Kremenchug». This number of seismological observation points does not actually provide seismic observation data to the central, eastern and southern parts of the territory of Ukraine and does not allow to reliably determine the level and quantitative characteristics of its seismic hazard. The seismic recorder Guralp CMG-40T manufactured by the British company GURALP SYSTEMS LIMITED is offered as optimal for the conditions and financial realities of Ukraine when organizing a stationary seismic observation point. It is proposed to use the seismological processing package SeisComP, which works on the SeedLink protocol, which is the basis of the data collection system by the Internet. This software product is the de facto world standard in the field of seismological data processing.

Hydrogeochemical characteristics and genesis of Seismic observation wells in Shandong Province

Hydrogeochemical characteristics, controlling factors, and recharge sources of the seismic observation wells in Shandong Province were investigated by analyzing cation and anion concentrations, hydrogen and oxygen isotopes in well water. A total of 17 water samples in seismic observation wells were collected on April 25-29, 2018. The results show that temperatures of seismic observation wells were in the range of 14.8 to 52.1°C, and the values of δD and δ 18 O ranged from -72.4‰ to -37.9‰ and from -9.4‰ to -4.3‰, respectively. Using C.A. ЩукаЛев’s classification method, the water samples of 17 seismic observation wells were classified into 7 types: Cl·SO 4 -Na·Ca, SO 4 -Na, Cl-Na, HCO 3 -Na·Ca, HCO 3 -Mg·Na·Ca, HCO 3 -Na and HCO 3 -Mg·Ca·Na. The results indicate that the hydrogeochemical characteristics of 17 seismic observation wells, with a certain spatial distribution pattern, are affected by several factors, such as the tectonic, topography, stratigraphy, hydrology and meteorology. The analyses of ratio coefficients, Schooller diagram, hydrogen and oxygen isotopes compositions, Giggenbach and Gibbs diagram suggest that the atmospheric precipitation is the main recharge source of 17 observation wells. The recharge sources of deep lateral runoff and sedimentation water, moreover, play a significant role in some seismic observation wells. Combined with the amount of precipitation, the distance from recharge areas, the closure degree of observation wells and the stage of water-rock reactions, the development directions of faulting and topography control the directions of groundwater recharge, runoff and discharge, which make hydrogeochemical characteristics represent complex spatial distribution rules.

An Optimum 2D Seismic-Wavefield Reconstruction in Densely and Nonuniformly Distributed Stations: The Metropolitan Seismic Observation Network in Japan

We propose an optimization method for applying the seismic-wave gradiometry (SWG) method to a dense seismic station network consisting of nonuniformly distributed seismographs. As a nonuniformly distributed station array, we consider the station layout of the Metropolitan Seismic Observation Network (MeSO-net) operated in and around the Tokyo metropolitan area, Japan. In this study, thereby, we numerically investigate optimum shapes of weighting functions, which control the spatial weights of individual stations when estimating waveforms at any grid points in the SWG method, to reconstruct seismic wavefields propagating in the MeSO-net. The functions with isotropic spatial weights are found to be appropriate for wavefield reconstructions with seismic waves incoming from practically all directions, even for nonuniformly distributed stations. The reproducibility of the wavefields is greatly improved by changing the shapes of the spatial weights reflecting density of the stations. Further plausible wavefield reconstructions are made by considering the propagation directions of the seismic waves. In these cases, if the weight of a contribution for a wavefield reconstruction is larger at far stations with a direction perpendicular to the wave propagation direction, then the reproducibility of the waveforms is significantly increased. In addition, the spatial gradients of the amplitudes are well reproduced by the optimized SWG method even though the optimization only focused on the amplitudes. Therefore, our proposed optimization scheme can be used to accurately estimate seismic wavefields in a nonuniformly distributed station array. Actually, the weighting functions optimized in this study succeeded to reconstruct the seismic wavefield of a shallow crustal earthquake that occurred around the Tokyo metropolitan area, based on the observed seismograms obtained by the MeSO-net.