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Extensometric researches in Ukraine:methods, instruments, results

A. Nazarevych1, L. Nazarevych2, V. Nasonkin3, O. Boborykina3, 2010

1Carpathian Branch of Institute of Geophysics, National Academy of Sciences of Ukraine, Lvov, Ukrainenazarevych-a@cb-igph.lviv.ua

2Department of seismicity of Carpathian region of Institute of Geophysics,National Academy of Sciences of Ukraine, Lvov, Ukraine

nazarevych.l@gmail.com3Taurichesky National University, Simferopol, AR Crimea, Ukraine

b0b04ka14@mail.ru

Extensometric seismoprognostic researches areconducted in Ukraine for over 20 years. They areconcentrated in the Transcarpathians and theCrimea as the most seismoactive regions of the

country (Figure). In Transcarpathians the quartzextensometers was working [Latynina et al., 1992;1993; Verbytsky et al., 2003; Verbytsky, Naza-revych, 2005; Nazarevych, 2006]. Now works 3 de-

Points of extensometric researches in Ukraine (marked by red triangle): 1 — RGS "Beregove"; 2 — RGS "Koroleve"; Geophy-sical Observatory of TNU (AR Crimea, Sevastopol, Cape Chersonese).

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vices. At different times they were equipped withvarious measuring and recording systems [Latyni-na et al., 1993; Verbytsky et al., 2003; Verbytsky,Nazarevych, 2005; Nazarevych l., Nazarevych A.,1999; 2006]. In parallel in one of the stations forsome time the 2 — axis tiltmeter was worked. Re-cently, we have developed and put into operation inone of quartz extensometers in regime geophysicalstation (RGS) "Beregove" (see Figure) the compu-terized measurement and recording system with anoncontact capacitive sensor of micromoving mea-suring. The system has a primary tool sensitivity10 nm (about 10−9 in relative units) at 2 count persecond and can obtain the sensitivity 1 nm in thesignal accumulation mode (1 count per 10 s). Fortemperature control and accounting of parasitic ther-moelastic deformation of constructions constituentthe system is equipped with a temperature controlchannel with a sensitivity 0.01 °C.

In Crimea on Geophysical observatory (Sevas-topol) of Vernadsky name Taurichesky National Uni-versity the extensometric laser interferometer com-plex was created and works [Shliakhovyj et al.,2007; http://www.tnu.crimea.ua/tnu/str_praz/obser-vatory/index.htm]. The complex consists of 2 equal"shoulder" ("shoulder" length is 5 m) two-ray laserinterferometers of Michelson type with separatedbeams using the frequency-stabilized laser as awavelength standard. Their basic metrological cha-racteristics are following: the sensitivity on strains(ADC LSD unit) — 0.16 nm, the instrumental long-term drift — not more than 2.5×10−8 units per year.There is computer registration, measurements aremade at intervals 4 s. In the same place 2 — axistiltmeter which was created in Poltava gravimetricobservatory of Subbotin name Institute of Geophy-sics of NASU also works.

During the extensometric observations the num-ber of more or less intensive predictive deformationanomalies which accompany the preparation of lo-cal earthquakes was recorded. In Transcarpathiansone of the most intensive was precursor of sensible1989 Vynogradove earthquakes with M=2.9 (I=5.5)

[Nazarevych A., Nazarevych L., 2008; Nazarevych,2010], which was registered in extensometric sta-tion "Muzhiyevo" ("Beregove-1") at the epicentraldistance 23 km. Anomaly started 5 months beforeearthquake and had absolute amplitude 30,8 mkmrelative to trend component (11×10−7 in relative units).In the period of preparation and after earthquake thenature of deformation processes in rock massifs inobservation area was changed: by extensometer d1the average annual compression with value≈10.5×10−7 was changed by expansion with value≈4.1×10−7, by extensometer d2 the average annualcompression with value ≈23×10−7 decreased to≈9.6×10−7. Also we can note that there was a simi-lar nature (expansion) and correlated in time chang-es of deformation (d1) and registered on a nearbypoint of geoacoustic observations acoustic anoma-lies [Nazarevych, 2010].

An example of deformation precursor of theCrimea — Black Sea region earthquake is recor-ded in a distance of about 250 km anomaly, whichaccompanied the preparation of the 07.05.2008earthquake with a magnitude M=4.9, epicentre co-ordinates 45.36°N, 30.92°E and focal depth about10 km. Duration of anomaly was about one and halfmonths, the absolute amplitude relative to trendcomponent was 1,92 mkm (~4×10−7 in relative units).

Comparison of values of recorded deformationanomalies with data of theoretical studies on pro-pagation of deformations from the future earthquakeemerging focal zone [Dobrovolsky, 1991] shows thatregistered anomalies are in value by 10—100 timeshigher than results of theoretical estimations withtaking into account the size of the source [Na-zarevych A., Nazarevych L., 2009] for earthquakesof corresponding energetic class/magnitude. Thereason for this can be features of tectonic structureof these regions lithosphere and the presence hereof horizontal tectonic stresses [Nazarevych L.,Nazarevych A., 2006]. These results indicate thatpotential and prospects of extensometric methodin seismoprognostic monitoring are substantiallygreater than it was consider before.

Dobrovolsky I. P. The theory of tectonic earthquakepreparation. — Moscow: IPhE RAS, 1991. — 219 p.(in Russian).

http://www.tnu.crimea.ua/tnu/str_praz/observatory/index.htm (in Russian).

Latynina L. A., Baysarovych I. M., Brymyh L., Varga P.,

Yurkevych O. H. Deformation measurements in theCarpathian-Balkan region // Phys. Earth. — 1993.— � 1. — P. 3—6 (in Russian).

Latynina L. A., Yurkevych O. I., Baysarovych I. M. Theresults of deformation measurements in Berego-vo area // Geophys. J. — 1992. — 14, � 2. — P. 63—67 (in Russian).

References

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Nazarevych L., Nazarevych A. Seismicity and geome-chanics of Ukrainian Carpathians region litho-sphere // Proc. of XYIII-th congress of the Car-pathian-Balkan geological association. September3—6, 2006, Belgrade, Serbia. — Belgrade, 2006.— P. 402—403.

Nazarevych A. Extenzometric research in Beregovoarea in Transcarpathians // Proc. of SSSh. — Lvov,2006. — Volume XVII. Geophysics. — P. 129—139(in Ukrainian).

Nazarevych A. V., Nazarevych L. Ye. Deformation pre-cursors of Carpathian earthquakes: separationmethods and analysis results // Theoretical andapplied aspects of Geoinformatics. — Kiev, 2008.— P. 311—320 (in Ukrainian).

Nazarevych A. V., Nazarevych L. Ye. Scale-energycorrelation ratio for Transcarpathian earthquakessources: some consequences and energetic veri-fication // Theoretical and applied aspects of Geoin-formatics. — Kiev, 2009. — P. 279—298 (in Ukrai-nian).

Nazarevych A. V. Geophysical precursors of somesensible Transcarpathian earthquakes as a reflec-

tion of the formation of focal zones // Theoreticaland applied aspects of Geoinformatics. — Kiev,2010. — P. 274—285 (in Ukrainian).

Nazarevych A., Nazarevych L. Optoelectronic mea-suring channel to quartz extensometer // Geody-namics. — 1999. — � 1(2). — P. 116—120 (inUkrainian).

Shliakhovyj V. P., Tregubenko V. I., Shliakhovyj V. V.,Boborykina O. A., Nasonkin V. A. Some results ofdigital seismic and tidal observations at Cape Cher-sonese (Sevastopol) // Geodynamics. — 2007. —��1(6). — P. 29—36 (in Ukrainian).

Verbytsky T. Z., Gnyp A. R., Malytsky D. V., Nazare-vych A. V., Verbytsky Yu. T., Ignatyshyn V. V., No-votna O. M., Narivna M. I., Yarema I. I. Microseismicand extensometric studies in the Carpathians: re-sults and prospects // Geophys. J. — 2003. — 23,��3. — P. 99—112 (in Ukrainian).

Verbytsky T. Z., Nazarevych A. V. Extensometric andgeoacoustic studies in Transcarpathians // Studiesof modern geodynamics of Ukrainian Carpathians/ Ed. V. I. Starostenko. — Kiev: Nauk. dumka, 2005.— P. 113—131 (in Ukrainian).

Small-scale convection produces sedimentary sequences

S. Nielsen1, K. Petersen1, O. Clausen1, R. Stephenson2, T. Gerya3, 2010

1Aarhus University, Department of Earth Sciences, Denmarksbn@geo.au.dk

kenni@geo.au.dkorc@geo.au.dk

2Geology and Petroleum Geology, School of Geosciences, College of Physical Sciences, MestonBuilding, King’s College, Aberdeen, Scotland

stephenson@abdn.ac.uk3Department of Geosciences, ETH-Zurich, CH-8092 Zurich, Zurich, Switzerland

taras.gerya@erdw.ethz.ch

It is generally acknowledged that heat transferin the sub-lithospheric mantle is dominated by con-vection that maintains an adiabatic temperature gra-dient close to 0.6 K/km. Transfer of the advectedheat to the conductive lithosphere takes place atthe base of the lithosphere, which is maintained ata relatively constant temperature in the vicinity of1300 °C. However, the thermo-mechanical detailsof this highly dynamic boundary condition at thebase of the lithosphere are frequently approximatedby a fixed temperature at the assumed long-termequilibrium depth of the base of the lithosphere (the

plate model). The present contribution investigatesthis approximation. We apply a two-dimensional,numerical, thermo-mechanical model of the lithos-phere and upper mantle [Petersen, 2010] to assesthe effects resulting from a more correct represen-tation of the sub-lithospheric small-scale convec-tion, which is responsible for heat transfer in thesub-lithospheric mantle. Given a particular mantlerheology, our model shows small-scale convection,and converges over time towards a self-consistent,quasi-steady-state with a stable lithosphere, thethickness of which depends on the chosen creep