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This work presents the results of complex gravity observation performed at Shults Cape, Gamov peninsula (42.58°N, 131.15°E), Russia. Absolute laser gravimeter GABL type and Scintrex type relative gravimeter were used for measurement. To investigate the accuracy of tidal corrections we compared the observed tidal parameters of the main tidal waves O1 and M2 with modeled ones computed from 6 different ocean tidal models: CSR4, FES02, FES04, GOT00, NAO99 and TPX06. After discussion a theoretical model based on TPX06 ocean tides model and DDW99 non hydrostatic body tides model was used for tidal correction of absolute gravity data. Preliminary estimate of gravity effect induced by the Tohoku-Oki earthquake of11 March 2011Mw = 9.0 at Primorye territory (Russia) was found to be 5.1 ± 2.0 μGal. Co-seismic crustal displacements revealed by GPS data at Far EastRussiacontinental coast are also investigated.** **Volumetric dilatation of this area is observed at +1.7 × 10^{-8} level.

Joint project to measure gravity change associated with tidal and earthquake’s effect using absolute and relative gravimeters was started at 2010 year. Well-known coseismic effects in gravity and in displacement field distributed on big territory for the earthquake of Mw ≥ 9. GPS measured displacement jump at 1 cm level was registered at 1500 km from epicenter of Sumatran earthquake 27.12.2004, M > 9 [1,2]. Gravity effect at 15 µGal level was measured by GRACE method at 1000 km distance. The Tohoku-Oki earthquake of 11 March 2011 Mw = 9.0 description is presented in many articles [3-8]. We tried to measure co-seismic gravity effect at south part of Primorye territory (Russia) at 1000 km distance from the epicenter. Some GPS results measured during last years at Far East Russia continental coast are also investigated. List of points for observation is presented at

Gravity observation started on 2010. Absolute gravimeter GABL [

For the main tidal waves we determine the amplitude A and the phase difference α, i.e. the vector A(A, α), with respect to the astronomical tide of amplitude A_{th} (_{th} [_{th}

Points marked by^{*} from work [

δ_{DDW}, 0) computed from the DDW99 non-hydrostatic inelastic model [_{m}(A_{m}, α_{m}) is given as

The modeled amplitude factor δ_{m} is simply given by the ratio A_{m}/A_{th}.

The tidal loading vector L, which takes into account the direct attraction of the water masses, the flexion of the ground and the associated change of potential, is generally evaluated by performing a convolution integral between the ocean tide models and the load Green’s function computed by Farrell [

The corrected tidal factors are defined as

We built also the residual vector defined as (see

The accuracy of the absolute gravity determination depends strongly on the precision of the tidal correction. The Trans-Siberian tidal gravity profile [^{2} on the Siberian territory.

The situation is more delicate at Shults Cape which is located directly on the coast. The resolution of the grid being at the best of 10 km, the ocean tides models do not follow accurately the coast line and the precision of the numerical evaluation is degraded.

Tidal gravity records remain thus important to try to determine experimentally the tidal parameters, at least in the diurnal (D) and semidiurnal (SD) tides. However long records are required to reach the suitable precision of 0.2% (5 nm/s^{2}) and we have only two summer records of 3month each. Our precision is only of 0.5% in amplitude and 0.25 in phase (

A more detailed comparison is given in

For the while our gravity tides predictions remain thus based on the modelled tidal factors. For absolute gravity measurements the modelling of the long period (LP) tides is very important. It is the reason why we used only the three ocean tides models including the LP tides: NAO99 (0.5˚ × 0.5˚), TPX06 (0.25˚ × 0.25˚) and FES04 (0.125˚ × 0.125˚). ^{2}. It is the expected precision of the gravity tides prediction at Shults Cape.

Finally we used the theoretical model based on TPX06 ocean tides model and DDW99 non hydrostatic body tides model for station Shults Cape and computed tides with Tamura potential for absolute gravity correction.

Absolute gravimeter situated at Shults Cape station is presented at

Absolute gravity observations were performed during two periods: 23-30 October 2010 and 15-30 August 2011. Mean square error of measurements series was 1-2 microgal. Gravity value increased by 5.1 microgal during this period including 11 March 2011 earthquake.

Original and published results [

are presented in

GPS measured horizontal displacement jump (5 - 8 cm) was registered at 1000 km from epicenter of Sumatran earthquake 27.12.2004, M > 9 [

You can see on

(BRIA, DUKI, HURM, UKTR) and 15 - 20 days at ZMEY base station by two receivers TRIMBLE4700 type with MICROCENTERED antennas. We used hard benchmarks to monument the network (

Horizontal velocity relative to YSSK permanent station for the period 2003-2006 is shown on

Connection gravity variation with height change may be described as:

where: g-vertical gradient of gravity g, normal value −3.08 × 10^{−6 m/s2}; DZ(t)—height change, ξ—error.

Subduction of Primorye region (Shults Cape) was induced by Tohoku-Oki Megathrust. Preliminary result

gravity change 5.1 microgal means 17 mm subsidence of crust surface. A vertical subsidence of 8 mm was Registered at ZMEY point by GPS method. It is not clear if it is regional or local. From other side, if we have deformation of a medium, the associated variation of g is given by:

where: k—gravity constant, ρ—density of a medium, ε_{vol}_{.} —volumetric strain jump, H—thickness of a layer (earth crust or lithosphere).

Strain measurements in two orthogonal directions on

the flat surface can be used to calculate areal, volumetric, and vertical strain. For an isotropic medium we get:

where, ν is Poisson coefficient.

Level of regional deformation can be estimated by GPS results (^{−}^{8} for EW KULD-VANB line. For orthogonal NS DUKI-ARTM line we have +1.7 × 10^{−}^{8}. We may estimate Volumetric dilatation at +1.7 × 10^{−}^{8} level (Poisson coefficient ν = 0.25). Gravity changes for lithosphere thickness (50 km, 100 km and 150 km) will be −0.1 microgal, −0.2 microgal and −0.3 microgal (ρ = 3.5 × 10^{3} kg/m^{3}). It is negligible with respect to subsidence effect. Observed gravity variation is connected only with height change or with tectonic plate level down.

Now gravity observation is continued at Shults Cape station. Microg LaCoste&Romberg (gPhone, n111) gravimeter is used for the registration of tidal variation (