Electronic geothermal atlases of Asian Russia

Albert D.Duchkov ,Michael Zheleznjak ,Ludmila S.Sokolova

1.Trofimuk Institute of Petroleum Geology and Geophysics,Siberian Branch of the Russian Academy of Sciences,Novosibirsk 630090,Russia

2.Melnikov Permafrost Institute,Siberian Branch of the Russian Academy of Science,Yakutsk,677010,Russia

1 Introduction

Thermal parameters of the crust,including measured and predicted temperatures and heat flow,as well as depths to permafrost and gas hydrate stability zones,are of special interest for geoscientists who study the Earth’s interior.However,geothermal data are often restricted to unpublished technical reports or poorly accessible dispersed publications.This lends special importance to synthesis of geothermal data published periodically as catalogs or maps.

TheGeothermal Atlas of Europe(Hurtiget al.,1992) was the first work of this kind created in the 1980s–early 1990s to synthesize geothermal evidence from European Russia in a catalog for heat flow maps(q) and temperatures (T) at depths of 0.5,1.0,2.0,3.0,and 5.0 km.Similar work for Siberia and the Russian Far East began about the same time and resulted in heat flow catalogs (Veselov and Lipina,1982;Duchkov,1985) and maps of the USSR and all of northern Eurasia(Smirnovet al.,1986;Gordienko and Moiseenko,1991).The information collected in those years was later used for the electronic GAS completed generally by 2000,and was designed to continue theGeothermal Atlas of Europeto the east.It consists of color-coded maps of the Siberian territories (lacking Russian Far East)showing heat flow and temperature variations by contour lines.They are digital colored maps created in the ARC/INFO system,which can be viewed on screen or printed.TheGAS (1995–2000) is currently available at the website of the Trofimuk Institute of Petroleum Geology and Geophysics in Novosibirsk(www.ipgg.sbras.ru/ru/institute/structure/geophysics/natural-fields),and its CD-ROM copies have been forwarded to numerous institutions.

At present,the following stage of work (2009–2012)has been completed covering the entire Asian Russia,including the marginal seas.

2 Data catalogs

The presented new GASRFE adds heat flow and temperature estimates for the Far East territory to the wealth of data collected for the GAS.

The database includes heat flow determinations at 2,300 terrestrial stations (from thermal logs of two or three boreholes at each site) and about 2,000 shallow measurements of bottom sediments in marginal seas and in Lake Baikal.It is noteworthy that almost allqvalues have been obtained by independent measurements of temperatures in boreholes and thermal conductivity of core samples.Most of the catalogued data are heat flows estimated from rather accurate temperature logs in boreholes of different depths (from few hundreds of meters to 4.5–5.0 km),as well as less accurate logs collected by survey enterprises.The geothermal coverage of Asian Russia is very uneven,the measurements being especially few in the northern and eastern areas.

The West Siberian plate has been the best documented,with temperatures measured in several thousands of boreholes with depths of 3–4 km and heat flows determined at 1,400 sites.The thermal field of the Siberian craton and the Verkhoyansk-Kolyma orogeny remains poorly constrained:500–600 geothermal boreholes,1–3 km deep,at 310 heat flow sites.In the highlands of southern Siberia (Altai-Sayan fold area,Baikal rift zone,and Transbaikalia),heat flow has been determined at 250 sites using data from 400 to 500 boreholes of 300 to 500 m average depths;the logged boreholes were deeper than 2 km only in intermountain basins (e.g.,Kuznetsk,Minusa).Evidence from the mountain systems (e.g.,Gorny Altai,Sayans,South-Muya Range,Udokan) is sporadic.Poor land coverage of the Baikal rift system has been somehow compensated by high-resolution studies in Lake Baikal,where heat flow through the lake bottom was estimated at about 800 stations from bottom sediment temperatures measured at 2–5 m below the water-sediment interface with probes similar to marine heat flow instruments (Fotiadi,1987;Duchkovet al.,1999).The reliability of shallow measurements has been validated by heat flow estimates inferred from acoustic depths to the methane stability zone and from temperature logs of underwater boreholes.Within the onshore Far East area (from Chukchi to Primorie,Sakhalin Island,and the Kuriles),heat flow has been determined at 320 sites from logs of 600–700 boreholes within 1 km deep on average (Gornovet al.,2009).Seafloor sediments in the Pacific marginal seas have been better studied:about 1,100 heat flow determinations,mainly from shallow temperature and thermal conductivity measurements with marine probes(Veselov,2000).Several tens of near-shoreqestimates have been obtained using temperatures measured in underwater boreholes.Offshoreqdeterminations are from the Bering (43 stations),Okhotsk (580),and Japan(367) seas and the Pacific Ocean around the Kuriles(110 stations).The catalog contains nearly fiftyqdeterminations from the Arctic seas east of Novaya Zemlya,mostly based on bottom sediment measurements under shallow measurements,as well as nineqestimates from temperature logs in island boreholes.

In addition to heat flow data,there are about 2,300 deep temperature measurements (the deeper the fewer)and predictions for depths of 0.5,1,2,3,and 5 km.Temperatures at 3 to 5 km below the surface were predicted using extrapolation of temperature logs,forward modeling with the thermal conductivity equation,and empiricalq–Tcorrelation relationships.

The catalog additionally reports the depths to the permafrost base ("zero" isotherm) at 550 sites,as well as locations of gas hydrates in bottom sediments discovered at present only within Lake Baikal.

3 The structure of the new electronic atlas

The data were inputted,pre-processed,and shared(Dobretsovet al.,2007) using web service technologies like Web Map,Web Feature,and Web Coverage Services designed by the Open GIS Consortium(OGC),an international non-profit organization.The geo-information system is based on the map service with a large-capacity disk store of about 40 terabytes,run by the Siberian Branch of the Russian Academy of Sciences to store various cartographic data and publish it at websites,also providing access to related attribute information.

The system maintains the Google Mercator projection allowing imaging the Atlas over the whole territory without additional software means.The software platform and database are repeatedly updated.The contributors have permanent access to the tabulated data open for updating.The information is displayed in appropriate styles.All parameters (physiographic data,heat flow,temperatures at different depths,depths to the permafrost base and gas hydrate data) are assigned to geothermal layers,in which the amount and locations of data are shown with symbols,and parameter variations are color-coded.

4 Maps of geothermal parameters

The contributors presented their regional geothermal data in spreadsheets of different formats.After processing,the point data were exported to shape files brought together into a singleArcGisproject and complemented with other input maps,such as river network,urban territories,frontiers,and the coordinate grid(ESRT–Asia North Equidistant Conic coordinates).

It is noteworthy that there are different ways of mapping heat flow and temperature.Most often the parameter values are presented as dots at locations ofqandTmeasurements and contour lines showing their spatial variations (Smirnovet al.,1986;Gordienko and Moiseenko,1991;Hurtiget al.,1992).Less frequently,special symbols are used for geothermal stations,with their shapes or colors indicative ofqorTmagnitudes and no contour lines are drawn (HFMESA,1997;Podgornykh and Khutorskoi,1997);otherwise,both symbols and contour lines are used in some cases(Blackwell and Steele,1992).

The maps of the GASRFE display data (heat flow,deep temperatures,and depths to permafrost base)symbolically as color-coded dots.The color scale records changes at every 20 mW/m2in heat flow maps,at every 5–20 °С in the temperature map,and only at 250 m in the permafrost map.

After the necessary procedures had been completed,Russian and English versions of the GASRFE(2009–2012) was published on the internet at http://maps.nrcgit.ru/geoterm/.Fragments of some maps of the Atlas are presented in figures 1–3.

The names and affiliations of the editors,compilers,contributors,and active users of theAtlasare listed in the title page.The first page contains theHeat Flow Mapand a list of layers which enables opening other maps.

Management and navigation in the maps are the same as inGoogle Earth,with options for zooming(panel on the left),selecting and unselecting layers(from a list),and retrieving attributed information(with a mouse click on the respective item).The attributes are data from the main catalog:heat flow,measured and predicted temperatures at depths of 0.5,1,2,3,and 5 km,and the depths to the permafrost base.Editor of geothermal pointshas been specially designed to allow input of additional data from archive reports (historic background,references,selected text,figures,or tables).As further development,theAtlasis expected to include data from territories adjacent to Asian Russia.

Figure 1 Fragment of the electronic publication of the heat flow map of Siberia and the Far East on the Internet (WEB publication)

Analysis of heat flow and temperature distributions for the territory in question is contained in numerous publications (Fotiadi,1987;Duchkovet al.,1999;Veselov,2000;Gornovet al.,2009).Briefly,we note that the thermal regime of Siberia and Far East hinterlands is determined by features of geological structures and development of the regions.Most of this territory is occupied by two broad platforms (West-Siberian and Siberian),markedly different in the thermal regime(Figure 1).Heat flow in the West-Siberian plate averages 55–60 mW/m2,sometimes rising to 70–80 mW/m2.The Siberian platform is characterized by a predominance of low heat flow values in the order of 30–40 mW/m2.From the south and east the platforms are framed by mountain-folded areas with heat flow anomalies (to 70–80 mW/m2) which are formed mainly under the influence of mantle heat sources (asthenosphere projections or mantle diapirs).

Analysis of temperature distributions shows that temperature conditions in the five-kilometer upper layer of rocks are mainly determined by the heat flow magnitude.Accordingly,the highest temperatures are observed in the earth crust of West-Siberian plate and in the mountain-folded areas (Figure 2).In the northern areas and at depths of up to 1.5–1.7 km,there exists perennial cooling effect of a permafrost zone.

Geocryological studies have shown that the permafrost in Siberia was developed mostly during the Late Pleistocene,during the epoch of Sartanian glaciation (30–20 thousand years ago) (Kondratievaet al.,1993).During this period,the southern border permafrost extended to 48°N–49°N,while at present permafrost area is essentially reduced (Figure 3).In Western Siberia,the southern border of permafrost was displaced to the north up to 60oN.In the southern part of the plate (south 65oN–66°N) permafrost top has been degraded,with only isolated blocks of relict permafrost.In Eastern Siberia,permafrost thickness has been reduced.The permafrost reaches the greatest thickness (to 1.3 km) in Yakutiya (central part of Siberia) (Duchkov and Balobaev,2001;Duchkov,2006)and is the most cooled block of lithosphere in Northern Eurasia.In other areas of Siberia and Far East permafrost thickness does not exceed 400–600 m.

Figure 2 Fragment of the electronic publication of temperature map at a depth of 3 km in Siberia and the Far East on the Internet (WEB publication)

Figure 3 Fragment of the electronic publication of low boundary cryolithozone map in Siberia and the Far East on the Internet (WEB publication)

5 Conclusions

1) The GASRFE (2009–2012) has been compiled and published on the Internet.It provides access to an exhaustive database on the Asian part of Russia collected over the past fifty years.

2) TheAtlasand the database it contains can be used for heat flow zoning,assessment of permafrost and gas hydrate resources,and for any other applications that need geothermal data.

3) Work on theAtlascontinues:updated maps,improved interface,selective addition of archive data,and geothermal evidence from the neighbor countries is being processed.

The Project VIII.70.2.3 of IPGG SB RAS and Project 7.1 of Department of Earth Sciences of Russian Academy of Sciences (Program 7) were supported this work.The authors are grateful to Dobretsov NN,Veselov OV,Gornov PY for their assistance in the project.

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