Gravity variations and recent geodynamics of the south-western part of the Baikal region

Abstract

Modern methods for determination of gravity values make it possible to obtain measurements with the accuracy up to 10 -9 from g 0 of the normal value (up to 1 microgal = 10 m/sec 2 ). While all the systematic and periodic effects are excluded, a question is raised about stability of the gravity field of the Earth over time. Changes of the altitude (the Earth's radius) with time can be estimated with an accuracy of 0.1 mm by modern space geodetic techniques, such as VLBI method. Our experi ments for evaluation of stability of the gravity values over the past decades are based on the data obtained by Russian and foreign observatories using absolute ballistic laser gravimeters. The results put a limit of 10 -10 per year to changes of the Earth's radius. These estimations can be useful for testing hypotheses in tectonics.Measurements of nontidal variations of gravity (∆g), which were obtained from 1992 to 2012 at the Talaya seismic sta tion (located in the southwestern part of the Baikal region), are interpreted together with GPS observation data. At the Ta laya seismic station, the linear component of gravity variations corresponds to changes in the elevation of this site. The corre lation coefficient is close to the normal value of the vertical gradient of gravity. At this site, coseismic gravity variations at the time of the Kultuk earthquake (27 August 2008, Mw=6.3) were caused by a combined effect of the change of the site's elevation and deformation of the crust. Our estimations of the coseismic effects are consistent with results obtained by mod eling based on the available seismic data.Key words: monitoring of gravity variations, changes in the Earth's radius, rift zone, GPSmonitoring, earthquake.Recommended by V.A. San'kov Citation: Timofeev V. Yu., Kalish Ye.N., Stus' Yu.F., Ardyukov D.G., Arnautov G.P., Smirnov M.G., Timofeev A.V., Nosov D.A., Sizikov I.S., Boiko E.V., Gribanova E.I. 2013. Gravity variations and recent geodynamics of the southwestern part of Baikal region.

Local deformation and rheological parameters by measurements in Talaya station gallery (Baikal region)

“…Estimating the size of the area being representative for tilt observations is complicated due to the following factors: in the area of Talaya Seismic Station, the terrain is strongly dissected; a zone of fracturing strikes along the Talaya stream valley; the Main Sayan fault zone is located 3 km to the north of the station. Based on the recorded tilt variations (from 0.1 to 3 arc-seconds per year) and velocities of vertical movements (according to space geodesy techniques, 1-3 mm per year) [Timofeev et al, 2013], the size of the zone can be estimated from the following ratio of the annual tilt rate:…”

“…Left-lateral shift motion takes place at the Main Sayan fault. According to the available geological data and tectonic models of south-western part of the Baikal rift zone, horizontal displacement rates are from 0.8 to 2.0 mm per year, and displacements are mainly directed to the east [San'kov et al, 1999[San'kov et al, , 2000Calais et al, 2002;Lukhnev et al, 2010;Timofeev et al, 2012Timofeev et al, , 2013.…”

Creating the Kultuk polygon for earthquake prediction: variations of (234U/238U) and 87Sr/86Sr in groundwater from active faults at the western shore of Lake Baikal

“…(соответственно, M W =6.8 и 6.3). Условиям их проявления были посвящены специальные исследования [Radziminovich et al, 2006;Melnikova et al, 2012;Timofeev et al, 2013;и др.]. Эпицентр главного толчка последнего из них (названного Култукским) находился в акватории Байкала, в 40 км к востоку-юго-востоку от пос.…”