Tectonic Plates in Northeast Asia: GPS Evidence

1. Tectonic Plates in Northeast Asia: GPS Evidence Grigory M. Steblov1, Mikhail G. Kogan2 Contributed: Nikolai F. Vasilenko3 Vasily Y. Levin4 Robert W. King5 Thomas A. Herring5, Christopher H. Scholz2, Roland Bürgmann6 Dmitry I. Frolov7 1 RDAAC/Geophysical Service RAS, Moscow, Russia 2 Lamont-Doherty Earth Observatory of Columbia University, USA 3 IMGG FEB RAS, Yuzhno-Sakhalinsk, Russia 4 KOMSP Geophysical Service RAS, Petropavlovsk, Russia 5 MIT, Cambridge, MA, USA 6 University of California Berkeley, USA 7 Institute of Physics and Technology RAS, St Petersburg, Russia Northeast Russia Tectonics Workshop

2. Plate Scenarios for East Asia • Geometry of the Eurasia – North America plate boundary in east Asia has been discussed since the 1970s, with varying interpretations of diffuse seismic belts in Siberia and marginal seas. GPS observationsinSiberiain 1996-2004,combined with global observations, place crucial constraints on the plate scenario for east Asia. Northeast Russia Tectonics Workshop

3. Network used in Solution GPS2004.9 • GPS2004.9 is a global solution with a focus on sampling the stations in Siberia. These stations represent both EUR and NAM. Epochs span 1996-2004.9 Northeast Russia Tectonics Workshop

4. Subset Sampling Stable Plate Interior • Plates EUR, NAM, and PAC are sampled from three sources of GPS data: • Continuous and survey mode observations in eastern Russia under project RUSEG since 1995 • Continuous observations of the IGS Network • Continuous observations in western Pacific under project WING [Kato et al., 1998]. Northeast Russia Tectonics Workshop

5. Origin Translation Rate and Reference Frames • We evaluate the reference frame (RF) origin translation rate from GPS data themselves for both components: • Along spin axis • Across spin axis • As a result, the solution is independent of any conventional RF. Northeast Russia Tectonics Workshop

6. Relative Motion EUR-NAM: Continuous Stations • By comparing velocities relative to EUR Northeast Russia Tectonics Workshop

7. Relative Motion EUR-NAM: Continuous Stations • By comparing velocities relative to EUR and to NAM, we conclude that east Siberia to the east of the Cherskiy Range belongs to NAM. This geometry was hypothesized for three decades but never proven. Northeast Russia Tectonics Workshop

8. Relative Motion EUR-NAM: Regional Surveys • Our scenario is further confirmed by regional GPS surveys. Compare velocities over the Cherskiy Range, in Chukotka, and northern Kamchatka • relative to EUR Northeast Russia Tectonics Workshop

9. Relative Motion EUR-NAM: Regional Surveys • Our scenario is further confirmed by regional GPS surveys. Compare velocities over the Cherskiy Range, in Chukotka, and northern Kamchatka: • and relative to NAM Northeast Russia Tectonics Workshop

10. Relative Motion EUR-NAM: Regional Surveys • Convergence rate EUR-NAM is higher in Sakhalin than in Siberia for geometrical reasons. • Sakhalin is a complex, seismically highly active deformation zone jammed between EUR and NAM. • Predominant deformation style in Sakhalin is transpression, with the compressional component more conspicuous than the strike-slip. NAM EUR Northeast Russia Tectonics Workshop

11. Amurian Microplate? • From GPS evidence, the region attributed to “AMU” is, in fact, a mozaic of: • Zone of distributed deformation in east China • Southern margin of Siberian craton • Baikal Rift zone • EUR-NAM plate boundary in Sakhalin GPS Velocity Solutions: Steblov et al. [GRL, 2003]; Rotated and Translated to Steblov et al.: Zhang et al. [Geology, 2004]; Calais et al. [JGR, 2003] Northeast Russia Tectonics Workshop

12. GPS and Geologic Plate Models We found a significant discrepancy between geologic (NUVEL-1A) and geodetic relative plate motions for almost all plate pairs that were analyzed. • For EUR-NAM, a comparison of GPS with NUVEL-1A shows • More rapid opening in North Atlantic • More rapid EUR-NAM convergence in east Asia Northeast Russia Tectonics Workshop

13. Motion of Siberia vs Europe ? • There are small, at a 1 mm/yr level, coherent plate-residual station velocities in Eurasia. They may reflect, if confirmed, a small relative motion of Europe and Siberia which were separate continents prior to collision along the Urals orogeny (in the Devonian). Northeast Russia Tectonics Workshop

14. Motion of Siberia vs Europe ? • EUR-NAM rotation pole is displaced to NW if GPS in Europe only is used [Steblov et al., 2003]. • Both NUVEL1-A and revised geologic plate model [Calais et al., 2003] give the pole location significantly different from GPS. Northeast Russia Tectonics Workshop

15. Conclusions • GPS observations in east Siberia, combined with global observations collected in 1995-2003, place constraints on the geometry and motion of Eurasian, North American, and Pacific plates in east Asia. • From GPS evidence, easternmost Siberia to the E of the Cherskiy Range, including Chukotka and Kamchatka, belongs to the North American plate. The data do not invoke the presence of microplates here. • GPS hints at a slight relative motion of Europe with respect to Siberia <2 mm/yr. Northeast Russia Tectonics Workshop

16. Origin Translation Rate and Reference Frames • Geodetic solution yields well-constrained interstation baselines Dij and their rates-of-change dDij/dt but not yet station velocities. • The solution matrix is free to rotate and and “almost free” to translate (it is rank-deficient). • Can we map dDij/dtinto station velocities on several plates simultaneously? • Yes, if the origin of reference frame has zero translation rate. Northeast Russia Tectonics Workshop

17. Origin Translation Rate and Reference Frames • We evaluate the origin translation rate (OTR) from GPS data themselves for both components: • Along spin axis Northeast Russia Tectonics Workshop

18. Processing of GPS2004.0 • At all steps of processing except the last, station positions were loosely constrained. • Definition of the Reference Frame is made consistently at the end in order to tightly constrain the solution for positions, velocities, and plate model. Northeast Russia Tectonics Workshop

19. Origin Translation Rate and Reference Frames • For GPS2004.0, origin translation rate is determined uniquely, regardless of the reference frame used. • Rotation rates differ significantly; however, they cannot not affect relative plate rotation vectors. • GPS2004.0 differs from ITRF2000_rfwg in origin translation rate by less than 0.5 mm/yr. Northeast Russia Tectonics Workshop

20. Discrepancy: GPS-Geology NNR • For all plates, GPS rms plate-residual velocities are much smaller than GPS-geologic differences. Northeast Russia Tectonics Workshop

21. Origin Translation Rate and Reference Frames • A remarkable property of our solution: it does NOT depend on a choice of Reference Frame (RF). • 2 quite different RF were tested: • ITRF2000 • A priori station velocities set to 0 • Relative plate rotation vectors are identical in both cases. Northeast Russia Tectonics Workshop

22. Micro-plates in east Asia ? • GPS arguments for AMU were based on biased velocity of the single reference station (Tsukuba). • RMS “plate-residual” velocity for AMU is as high as 2.5 mm/yr! Northeast Russia Tectonics Workshop

23. Motion of Siberia vs Europe ? • All estimates dominated by stations in Europe agree in more north-westerly location of pole EUR-NAM. • Geologic plate models determine relative velocity of EUR and NAM mostly from marine magnetic anomalies in north Atlantic and in the Arctic. This is the motion of Europe relative NAM. Northeast Russia Tectonics Workshop

24. Micro-plates in east Asia ? • South Northeast Russia Tectonics Workshop