HomeLGPSMain scientific results

Main results (over the 5 last years)

  • Print
  • E-mail

In the foothills of the Northern Tien Shan, southern of Bishkek, according to GPS data, zones of increased values ​​of deformation rate of the Rarth's crust were identified, these zones are located on segments of active faults (2019).

Based on the data of long-term measurements of points in Bishkek local GPS network, an averaged tensor field of horizontal strain rate is constructed. At most calculation points, the main shortening axes have a meridional direction and values ​​in the order of 10 -7 year-1. Shortening maxima are accompanied by rotation of axial strike in the northeast direction to 25 °, and an increase in values ​​on the perpendicular axes of elongation. The coincidence of such zones of suspended deformations with the paths of active discontinuities suggests the presence of segmented left-side shifts against the general background of reverse faults, and the possibility of accumulation of stresses with their subsequent discharge through earthquakes.

1

Figure 4.1. The average tensor field of the horizontal deformation rate based on the data of long-term measurements of the Bishkek local GPS network points (blue rhombuses). Red arrows are the main axis of shortening, blue arrows are the axis of elongation. Brown lines - active faults

At the geodetic sites of Bishkek Geodynamic Proving Ground (Northern Tien Shan) along the active fault zone, 4 types of pulsed deformation events were revealed according to linear-angular measurements (2018).

Weekly measurements of 44 baseline lengths (BL) at 3 geodetic sites spaced 5–13 km along the active fault zone revealed the presence of elastic deformation events (10–4–10–5) with length variations from the first mm to 4 cm: 1 ) isotropic in terms of short-period (6–7 days) synchronous maximum elongations of all BLs at all sites; 2) lengthening of BL of the north direction and shortening of BL of the east direction for 3-4 months: for all directions, the extremes of changes in the lengths of the BL are shifted to the end of the event, in the latitudinal direction there is a delay of 1–3 weeks; 3) BL extensions in the north direction and insignificant BL extensions in the east direction for 4–5 months: in all directions, the extrema of the BL length changes are shifted to the beginning of events; 4) the change in lengths on individual baselines in only one of the directions in the plan.

2

Figure 4.2. Variations in the lengths of the shortest and mutually perpendicular (N – S and B – W) BLs of the Almaly site according to linear-angular measurements with reflection of the main types of pulsed deformation events

On the territory of the Bishkek Geodynamic Proving Ground (Northern Tien Shan), a spatial and temporal relationship was recorded between the manifestation of local earthquakes and variations in the deformational environment of the earth's crust (2017).

The results of linear-angular and GPS observations, in comparison with seismicity and focal mechanisms, made it possible to assess the geodynamic situation during a local earthquake of energy class 10. A few days before the earthquake, GPS data showed a subsidence in this area of ​​the Earth's surface with an amplitude of up to 20 mm. In the period 5 days before and 2 days after the event, an average increase of 8 mm in lengths of lines crossing the Shamsinsky fault was noted by ~ 2 km from the earthquake source according to light-ranging measurements. Such an increase in the fault width corresponds to variation of ~ 7 MPa in the tectonic stresses acting in the fault zone.

3

Figure 4.3. The scheme of study area with sites location (points and their numbers) of linear-angle observations POLYGON, KENTOR AND ALMALY (1), GPS measurement IATA, IAT3, POL2, CHUM points (2), sensing stations using the method of establishing a field in the far zone (3 ), the focal mechanism of the earthquake source (4). Lines are active faults

Anisotropic (with respect to the cardinal points) elastic deformations with regular periodicity (2016) were revealed within the Bishkek Geodynamic Proving Ground.

On the geodetic site, according to GPS observations for the baseline IAT1-3 (north-south) and IAT3-5 (east-west), the presence of repeating elastic deformations with a periodicity of ~ 1 year was established. On average, the beginning of deformation events occurs in December and the end in May, with a cycle duration of 4-5 months. In the northward direction, ~ 300 m regularly show elongation cycles (up to 22 mm or 7.3 × 10-5). In the eastward direction by ~ 360 m, as a rule, with a delay of events of 20-30 days, shortening (up to 16 mm or 4.3 × 10-5) is noted.

4

Figure 4.4. Graphs of variations in the lengths of baselines combined with wavelet spectrograms (Haar, MatLab). Upper - for the line IAT1-3 (compare long. 301486.4 mm, S-S); lower - for the IAT3-5 line (cf. length 360335.6 mm, B-W). Low-frequency deformations with maximum amplitudes in the spectrograms are shown by vertical contrasting dividing lines between the light and dark regions. The larger the deformation value is, the higher is the contrast between the color gamut change

With general consistency in the distribution of the total horizontal strain rate by GPS and seismological data on the territory of the Central Tien Shan, a block of the Earth's crust with elevated and potentially dangerous strain rate gradients has been identified (2015).

For a large area of ​ KNET seismological network, a high degree of positive correlation is noted in the distribution of the total horizontal strain (dilatancy) rate according to surface GPS observations and seismological data (depth 5-20 km) for 1998-2014. measurements. An exception is the central region of the study area (Dzhumgal-Too mountains), where lower surface velocity upper dilatancy (according to GPS data) and higher strain rates in the lower seismically active horizon are recorded. The revealed differences in the distribution of deformation for the near-surface part and with depth (up to 5 km) indicate the energy-saturated and potentially dangerous volume of the Earth's crust, in terms of the manifestation of seismic events and discontinuous disturbances.

Distribution of the total horizontal strain rate (colored ovals) for 1998-2014. observations in the Central Tien Shan: the upper - according to near-surface GPS observations, blue diamonds - GPS points; bottom — according to seismological data, black dots — earthquakes with solutions to focal mechanisms (5–20 km deep).

5

Figure 4.5. Distribution of the total horizontal strain rate (colored ovals) for 1998-2014. observations in the Central Tien Shan: the upper - according to near-surface GPS observations, blue diamonds - GPS points; bottom — according to seismological data, black dots — earthquakes with solutions to focal mechanisms (5–20 km deep).

 

Photogallery

Geographic location

40 km. from Bishkek