M. V. Rodkin

Archaeoseismological studies and structural position of the medieval earthquakes in the South of the Issyk-Kul depression (Tien Shan)

We carried out archaeoseismological studies in the Southern Issyk-Kul region (Kyrgyz Tien Shan) and obtained radiocarbon datings of the collected samples. These data suggest that the sources of strong earthquakes have occurred in this territory in the 11th and (probably) 16th centuries. These earthquakes had magnitude M ≥ 7 and seismic intensity of at least I ≥ 9. The sources of these earthquakes were associated with the local adyr (piedmont) faults—components of the Pre-Terskei border fault. Our results demonstrate considerable underestimation of the seismic hazard for the South Issyk-Kul region in the latest Seismic Zoning Map of Kyrgyz Republic (2012), which should be taken into account in the construction of the new seismic zoning map for Kyrgyzstan.

Fuzzy logic algorithms in the analysis of electrotelluric data with reference to monitoring of volcanic activity

The expert processing of monitoring data of large networks on hazardous natural phenomena becomes increasingly more complicated due to an increase in the initial data flow. An approach alternative to the visual recognition of signals is proposed. A number of recognition algorithms and results of their application to the analysis of geoelectric potential monitoring data are discussed. Data of monitoring La Fournaise Volcano (Réunion Island) obtained in the vicinity of the intense volcanic eruption of 1988 are used. The obtained results show that these algorithms are capable of recognizing anomalous segments of records and discriminating between several types of anomalies presumably associated with the effects of various physical factors (heavy atmospheric precipitation, hydrothermal processes, and so on). The algorithms proposed in this work can be used both for the automation of expert work in operating monitoring systems and in investigations aimed at the identification of typical morphologic sequences in time series of data of various origins.

Estimation of the probability of strongest seismic disasters based on the extreme value theory

This paper presents the review of the experience in applying the approach based on the limiting distributions of the extreme value theory (the generalized Pareto distribution, GPS, and generalized extreme value distribution, GEV) for deriving the distributions of maximal magnitudes and related ground accelerations from the earthquakes on the future time intervals of a given duration. The results of analyzing the global and regional earthquake catalogs and the ground peak accelerations during the earthquakes are described. It is shown that the magnitude of the strongest possible earthquake Mmax (and analogous characteristics for other types of data), which is often used in seismic risk assessment, is potentially unstable. We suggest a stable alternative for Mmax in the form of quantiles Qq(τ) of the maximal possible earthquake, which could occur during the future time interval of length τ. The quantity of the characteristic maximal event Mc, which has been introduced in our previous publications, is another helpful robust scalar parameter. All the cases of approximation of the tails of empirical distributions, which were studied in our works, turned out to be finite (bounded); however, the rightmost point of these distributions, Mmax, is often poorly detectable and unstable. Therefore, the Mmax parameter has a low practical value.

The evolution of the stress state in Southern California based on the geomechanical model and current seismicity

A three-dimensional geomechanical model of Southern California, which includes the mountain topography, fault tectonics, and main structural boundaries (the top of the lower crust and the Moho), is developed. The main stress state of the model is determined by the own weight of the rocks and by the horizontal tectonic motions identified from the GPS observations. The model enables tracking the changes which occur in the stress-strain state of the crust due to the evolution of the seismic process. As the input data, the model uses the current seismicity and treats each earthquake as a new defect in the Earth’s crust which brings about the redistribution of strains, elastic energy density, and yield stress of the crust. Monitoring the variations in the stress state of the crust and lithosphere arising in response to the seismic process shows that the model is suitable for forecasting the enhancement in seismic activity of the region and delineating the earthquake-prone areas with a reasonable probability on a given time interval.

The instability of the Mmax parameter and an alternative to its using

The work presents statistical methods for estimating the distribution parameters of rare, strong earthquakes. Using the two main theorems of extreme value theory (EVT), the distribution of T-maximum (the maximum magnitude over the time period T). Two methods for estimating the parameters of this distribution are proposed using the Generalized Pareto Distribution (GPD) and the General Extreme Value Distribution (GEV). In addition, the that allow the determination of the distribution of the T-maximum for an arbitrary value of T are proposed. The approach being used clarifies the nature of the instability of the widely accepted M max parameter. In the work, instead of unstable values of the M max parameter, the robust parameter QT(q), the q level quantile for the distribution of the T-maximum, is proposed to be used. The described method has been applied to the Harvard Catalogue of Seismic Moments of 1977–2006 and to the Magnitude Catalogue for Fennoscandia in 1900–2005. Moreover, the estimates of parameters of the corresponding GPD and GEV distributions, in particular, the most interesting shape parameter and the values of the Mmax and QT(q) parameters are given.

Implications of differences in thermodynamic conditions for the seismic process

Variations in characteristics of the seismic process are considered under various thermodynamic conditions. In addition to the usual parameters, differences between hypocenter depths obtained from seismic moment solutions and ordinary hypocentral determinations are considered. Two different tendencies are shown to prevail in source parameter variations for events that occur above and below 80–100 km. The first tendency apparently corresponds to variations in the parameters of ordinary crustal earthquakes with increasing pressure. The second tendency is supposedly associated with the prevalence of specific deep mechanisms of seismogenesis. Distinctions in the dynamics of earthquakes developing downward and toward the surface are examined and accounted for by a low density fluid phase present in earthquake sources. The localization of deep earthquakes at certain depths and specific features of deep seismogenesis are discussed. Such features are related to the role of transformations in the material of subducting plates in the occurrence of deep earthquakes. The problem of genesis of deep earthquakes is discussed.

Specific Features of the Seismic Regime in the Lithosphere: Manifestations of the Deep Aqueous Fluid Action

We considered the seismic regime in the upper 70–100 km of the lithosphere and identified the layers (at depths of about 10, 20–30, and 60–80 km) characterized by relatively reduced effective strength and increased seismicity. The existence of such layers is related to changes in the regime of fluid-rock interaction, namely, to the characteristic depths of a jump-like decrease in the effective permeability of rocks and an increase in the spatial homogeneity of a fluid-rock system.

Nonparametric methods in studies of the seismic regime

The application of nonparametric statistical methods to the estimation of some characteristics of the seismicity regime is considered. Emphasis is placed on the behavior of the distribution tail (i.e., the distribution of the strongest events). The methods described do not use any assumptions concerning the distribution function. Confidence intervals are derived for the magnitude distribution function and for the Poisson intensity of the flow of seismic events. The probability that a previously recorded maximum magnitude will be exceeded during some future time interval T and the confidence interval of this probability are estimated. The distribution of the time to the nearest event exceeding the last maximum (to the nearest record) is derived. The nonparametric approach is most effective if the type of empirical data parameterization is unknown or there are grounds for doubting its adequacy.

Strong Paleoearthquakes along the Aksuu Border Fault according to the Results of Dating the Offset Terrace Complex of the Chon-Aksuu River, Northern Tien Shan

The study and radiocarbon dating of the low alluvial terraces of the Chon-Aksuu River, in the Northern Issyk-Kul region, which were broken by the Kebin (Kemin) earthquake of 1911 (Ms = 8.2, Io = 10 to 11), are carried out. The obtained radiocarbon dated ages refer to the second half of the Holocene. Since that time, at least eight strong earthquakes took place along this (Chon-Aksuu) segment of the Aksuu border fault. Three seismic events, including the earthquake of 1911 occurred in the second millennium A.D. This outburst of seismic energy was preceded by two millennia of seismic quiescence, which set in after another pulse of seismic activation. The latter lasted for 1.5 millennia and included five strong earthquakes. The recurrence period of seismic events during the activations is 300–600 years. Hence, the seismic regime along the Chon–Aksuu segment of the Aksuu border fault in the second half of the Holocene was a succession of two seismic activations, each with a duration of 1.0–1.5 ka, which were separated by a 2-ka interval of seismic quiescence. Therefore, the absolute datings of the river terraces of different ages which have been broken by a seismogenic rupture can serve as a reliable source of information about the age of the strong earthquakes that occurred along the seismogenic fault.

Study of ore deposits by the dynamic systems investigation methods: 1. Calculation of the correlation dimension

The method for calculating the fractal correlation dimension is applied for analyzing the data on the locations of large and extralarge ore deposits. The approach implemented in this study differs by a few of important points from that commonly used, e.g., in the calculations of the correlation dimension for a set of the epicenters (hypocenters) of the earthquakes. Firstly, we demonstrate the possibility and advisability of obtaining different dimension estimates for different spatial scales. Such a separation turned out to be useful in distinguishing between the regularities in the location of ore deposits on the scale of an ore cluster, ore province, and entire continent. Secondly, we introduce a new notion, a mixed correlation dimension, and use it for different types of the objects (e.g., Au and Ag). The standard formula for calculating the correlation dimension is trivially generalized on this case. It is shown that the values of the correlation dimension can be lower and higher than the dimension of the hosting medium. The cases when the correlation dimension is higher than that of the hosting medium are interpreted as a “mutual repulsion” of the deposits of the two mentioned types. In contrast, the small correlation dimensions indicate that the deposits of the corresponding types tend to have spatially close locations. The calculations are conducted for the spherical Earth. The method is applied to the data on the large and extralarge world-class ore deposits from the Largest Mineral Deposits of the World (LMDs) geoinformation system (GIS). Different patterns of the studied behavior are illustrated by the model examples.