Description of the Active Faults of Eurasia Database
Principles and methods
A methodology for creating and maintaining of new Active Faults of Eurasia (and Adjacent seas) Database (AFEAD) is presented, which integrated in a single format the material accumulated to date by many researchers, including the authors of the database. It contains more than 20,000 geographically attached objects - faults, fault zones and related structural forms with signs of recent movements in the Late Pleistocene and Holocene.
The scale in which the database is compiled is 1: 500,000. The base demonstration scale is 1: 1,000,000. Each database object is equipped with two types of characteristics (attributes) - justifying and evaluative. Substantiating attributes contain information about objects - their names, data on morphology and kinematics, displacement amplitudes for different periods of time, motion velocities calculated on them, the age of the last recorded signs of activity, seismicity and paleoseismicity, the relationship of objects with crustal earthquake parameters, and other characteristics, as well as information about the sources of information, a list of which is attached to the database.
Evaluation attributes are a system of indices reflecting the kinematics of faults according to typification accepted in structural geology, the rate of speed of the Late Quaternary movements (three gradations) and the degree of reliability of distinguishing the structure as active (four gradations). Indexes allow you to compare objects by any of the attributes in a computer way with each other and with any other types of digitized information using any GIS program.
Thus, the database makes it possible to extract specific information about faults and solve more general problems - thematic mapping, determining the parameters of modern geodynamic processes, assessing seismic and other geodynamic hazards, tectonic development trends at the last, Pliocene-Quaternary, stage of Earth's development. The format for building of proposed database allows for its continuous replenishment and correction with the advent of new information.
Databases represent an important tool for modern scientific research. The unambiguity and uniformity of the presentation of information in the form of a database opens up wide and diverse prospects for the study of geological phenomena (automated processing and a comprehensive analysis of their characteristics).
The main content of the proposed database is active faults - tectonic disturbances, movements along which occurred in the recent past and therefore can be expected in the near future. The reason to believe that shifts in the future are possible are traces of movements in the nearest time interval corresponding to the maximum known repetition period of strong crustal earthquakes, i.e. over the last 30 thousand years [Kozhurin et al., 2008; Trifonov, Kozhurin, 2010]. Since in many areas the shifts of this time are difficult to separate by geological and geomorphological methods from the shifts in the earlier stages of the Late Pleistocene, we consider an active fault along which manifestations of movements during the late Pleistocene and Holocene were recorded, i.e. over the last ~ 130 thousand years [Trifonov, Machette, 1992]. The severity of shifts in the displacements of young landforms and sediments, and sometimes of technogenic structures, is the main search, mapping, and evaluative sign of an active fault. The technique of such studies is described in numerous publications [Wallace, 1968; Sieh, 1978; Trifonov, 1983, 1985; Active tectonics, 1986; Paleoseismology, 1996; Yeats, Sieh, Allen, 1997; Kozhurin, 2004; Trifonov, Kozhurin, 2010; Kozhurin, 2013; and etc.].
The use of the database is twofold: practical (assessment of various kinds of geodynamic hazards, primarily seismic), and theoretical (expanding the possibilities of studying the latest and active tectogenesis). The latter is determined by the fact that database objects (active faults) are, by definition, geologically coeval structures that reflect synchronous tectonic movements. This allows you to compare modern geodynamics and the structure of remote and diverse regions.
In 1996, many years of work, in which more than 70 researchers from 50 countries participated in the International Project II-2 “Map of Large Active Faults of the World” of the International Program “Lithosphere”, led to the creation of an electronic database on active faults of Eurasia, which included information on more than 10,000 faults of a significant part of the Eurasian continent and adjacent waters. Work on the project for the territory of Eurasia was headed by V.G. Trifonov, and in the generalization of the materials presented by the researchers in the form of a database, A.I. Kozhurin, D.M. Bachmanov, G.A. Vostrikov, A.I. Joffe and R.V. Trifonov. This database (DB-96) was an outstanding achievement of geoinformatics both in terms of the methodology of formalizing geological data and the total amount of information contained in it. For the first time, such a voluminous and detailed material was collected on such a vast territory using a unified methodology, which was convenient for comparison with other materials and suitable for comprehensive analysis using various computer processing algorithms.
For DB-96, a data recording format was developed that combines the ability to fix a large number of parameters, compact presentation of information, and a clear algorithm for formalizing the initial information. Data on each object constituted a separate block of text consisting of a series of lines with the values of its parameters and a series of lines with the coordinates of the nodes of the fault line. Each line of parameters began with a numerical marker denoting the property of the object whose value was given in this line. Recording in this format was suitable for software processing for each individual parameter. On the basis of DB-96, a map of active faults of Eurasia at a scale of 1: 5000000 [Trifonov, 1997, 2004] and maps and a catalog of active faults of the central segments of the Alpine-Himalayan belt [Trifonov et al., 2002] were built. DB-96 and seismotectonic materials created using it were used to create the Set of General Seismic Zoning Maps of the Russian Federation OSR-97 [Ulomov, Shumilina, 1999].
At the same time, DB-96 had drawbacks due to both the technical capabilities of that time and the uneven exploration of active faults. Thus, the detail of the display, the accuracy of geographic location and the general style of data presentation were significantly different in different regions, which made it difficult to compare them. Due to the formal superposition of materials of different authors on each other, unrealistic relationships and articulations of objects appeared in places, for example, their mutual intersections. A complex system for recording fault attributes required users to know a large number of conditional markers and created problems when objects were grouped according to the desired properties and software data processing. A large proportion of faults was not provided with reliable data to substantiate the values of key parameters, and the different completeness of the characteristics of different regions often created a false impression of their different tectonic activity. The age of the last movements was often not convincingly justified and was assigned according to the results of decoding of low-resolution space images. As a result, faults with Pliocene-Early Quaternary last movements were included in DB-96, and these structures were not clearly separated from the really active ones. The values of the parameters were assigned to extended objects, although accurate and reliable data were available only for their short sections. In some regions, the same parameters were unreasonably assigned to a series of faults; in others, excessive detail and verbosity of characteristics made it difficult to compare objects.
After the creation of DB-96, a lot of new data appeared on active faults, including in the form of a variety of cartographic materials. Among them there are regional and generalizing works published in the form of paper maps or electronic databases. These are maps of Italy [Galadini et al., 2001], Turkey [Emre et al., 2013], Syria [Trifonov et al., 2012], Iran [Hessami et al., 2003], Philippines [Distribution of Active Faults, 2008 ], Thailand [Kosuwan et al., 2006], as well as databases for Southern Europe [Basili et al., 2013], the Iberian Peninsula [Garcia-Mayordomo et al., 2012], France [Jomard et al., 2017] , Afghanistan [Ruleman et al., 2007], Eastern Siberia [Lunina, 2016], the Tibetan-Himalayan region [Taylor, Yin, 2009] and others.
Each of these materials contains valuable information, however, they are compiled according to different methods and in different formats, have different accuracy of displaying objects, different number and meaning of fixed parameters, differ in the understanding of the term “active fault” and, as a result, are difficult to compare. Maps and databases are often limited by state borders or by dictated by production needs frameworks that cut geotectonic elements. This does not allow us to perceive and evaluate them as integral structures in the context of a wider geodynamic situation. Many new materials have the same drawbacks as the DB-96: errors in the topographic location of objects; heterogeneous detail of their image, which interferes with the holistic perception of the system of active structures; incomplete characterization of faults without justification of key parameters or links to data sources where they are given; Assigning the same parameters to series of objects unjustified extrapolation of parameters to the entire length of an extended object. All this complicates the comparison of data, creates difficulties for its software processing.
The accumulation of new information and ideas about the active tectonics of Eurasia required a comprehensive presentation of the total amount of acquired knowledge, both contained in DB-96, and acquired later, i.e. creating a new database of active tectonic disturbances (hereinafter AFEAD), where all available information would be rethought from a common perspective and presented in a single recording system. This system should be user-friendly and allow the ability to quickly compare data by key parameters and combine them with other types of digitized information. The database should be a continuously updated and refined geographic information system that integrates all materials related to active tectonics according to a single method, regardless of what the methods were, the detail and reliability of the materials, and the theoretical views of their authors.
The principles for compiling the database should be the geodynamic integrity of the subject of study; methodological homogeneity of processing included information; the continuity of the process of addition and refinement of the material; the complexity of the material obtained based on the results of all studies of active tectonics. The database should become a means of accumulation and regular updating of data on active faults, the reliability of which would increase as a result of the consistent integration of new information into the database; to combine, within the framework of a unified methodology for the selection and presentation of data, heterogeneous and geographically dispersed information on active tectonics; create geoinformation material that reflects the active tectonics of the Eurasian Plate and its frames as an integrated system.
The database of active faults AFEAD that meets the above requirements was created on the basis of the DB-96 using the ArcGIS software package. The recording format and the database parameter system are substantially modified. Methods have been developed for its replenishment with new materials, their editing and interpretation to ensure the unity of the parameter system and recording format of objects. Additional aspects of active tectonics were revealed, which made it possible to more fully represent the accumulated material and determine the places for further research.
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