E. P. Timoshkina

Joint Inversion of the Differential Satellite Interferometry and GPS Data: a Case Study of Altai (Chuia) Earthquake of September 27, 2003

Based on the data of differential satellite interferometry, the field of displacements of the Earth’s surface in the line-of-sight direction is determined for the region of the Altai Earthquake that struck on September 27, 2003. The displacements are estimated for unforested areas of Chuia and the Kurai depressions, and for a part of their mountainous surroundings. In that part of the region where unwrapping of the data was possible, the amplitude of displacements amounts up to 150 cm for Chuia and 100 cm for the Kurai depressions. In order to locate the surface of the seismic rupture and to find the field of displacements on this surface, the method for the combined inversion of the displacements data, provided by satellite interferometry (the present work) and geodesy [Gol’din et al., 2005], is suggested and applied. The admissible range of the parameters of the rupture was specified from the seismology and seismotectonics data.The combined use of geodetic and satellite interferometry data makes the solution of the inverse problem more stable and yields a seismic momentum estimate, which is consistent with the seismological determinations. We discuss the possible contributions of various postseismic processes; in particular, based on analyzing the energy of the aftershocks, we assess the contribution of the postseismic creep to the displacements, determined from the interferometry and geodesy data, for different coseismic and postseismic time intervals.

Some problems of landslide monitoring using satellite radar imagery with different wavelengths: Case study of two landslides in the region of Greater Sochi

The problems of processing and interpreting the data provided by radar satellite interferometry for the conditions of landslides covered by vegetation are analyzed in two case studies of landslides in the Northern Caucasus in the region of Kepsha and Mamaika villages in the vicinity of the railway tunnels. The estimates of the displacement fields are obtained by the method of persistent scatterers using the StaMPS program package. The five-year experience of landslide monitoring shows that in the unfavorable conditions of satellite radar interferometry, proper selection of the strategy of satellite image processing is vital. In the present paper, we discuss, in particular, the crop selection, the selection of the master image, reference area, and digital elevation model. For the landslide located in the sparsely populated region near Kepsha village, we used the data from the ascending and descending tracks of the long-wavelength ALOS and shorter-wavelength ENVISAT satellites. For the landslide in the region of Mamaika village with a large number of different buildings serving as good scatterers for radar signals, we used the images from the ENVISAT and from TerraSAR satellite, which transmits even shorter waves. The average line-of-sight (LOS) displacement velocities VLOS for the landslide near Kepsha village measure at most 10 mm per annum, which means that this landslide has remained stable at least since 2004. The landslide in Mamaika village is significantly more active. The average LOS displacement velocities in the active part of this landslide attain 60 mm per annum. The artificial corner reflector installed on the segment of the landslide where natural scatterers of radar signal are absent made it possible to estimate the LOS displacement velocity on this segment of the slope at 49 mm per annum.

Comparative study of temporal variations in the earth’s gravity field using GRACE gravity models in the regions of three recent giant earthquakes

Comparative analysis of coseismic and postseismic variations of the Earth’s gravity field is carried for the regions of three giant earthquakes (Andaman-Sumatra, December 26, 2004, magnitude Mw = 9.1; Maule-Chile, February 27, 2010, Mw = 8.8, and Tohoku-Oki, March 11, 2011, Mw = 9.0) with the use of GRACE satellite data. Within the resolution of GRACE models, the coseismic changes of gravity caused by these seismic events manifest themselves by large negative anomalies located in the rear of the subduction zone. The real data are compared with the synthetic anomalies calculated from the rupture surface models based on different kinds of ground measurements. It is shown that the difference between the gravity anomalies corresponding to different rupture surface models exceeds the uncertainties of the GRACE data. There-fore, the coseismic gravity anomalies are at least suitable for rejecting part of the models that are equivalent in the ground data. Within the first few months after the Andaman-Sumatra earthquake, a positive gravity anomaly started to grow above the deep trench. This anomaly rapidly captured the area of the back-arc basin and largely compensated the negative coseismic anomaly. The processes of viscoelastic stress relaxation do not fully allow for these rapid changes of gravity. According to the calculations, even with a sufficiently low viscosity of the upper mantle, relaxation only covers about a half of the observed change of the field. In order to explain the remaining temporal variations, we suggested the process of downdip propagation of the coseismic rupture surface. The feasibility of such a process was supported by numerical simulations. The sum of the gravity anomalies caused by this process and the anomaly generated by the processes of viscoelastic relaxation accounts well for the observed changes of the gravity field in the region of the earthquake. The similar postseismic changes of gravity were also detected for the region of the Tohoku-Oki earthquake. Just as in the case discussed above, this earthquake was also followed by a rapid growth of a positive postseismic anomaly, which partially counterbalanced the negative coseismic anomaly. The time variations of the gravity field in the region of the Maule-Chile earthquake differ from the pattern of changes observed in the island arcs described above. The postseismic gravity variations are in this case concentrated in a narrower band above the deep trench and shelf, and they do not spread over the continental territory, where the negative coseismic anomaly is located. These discrepancies reflect the difference in the geodynamical settings of the studied earthquakes.

Constraints on the Neogene–Quaternary Geodynamics of the Southern Urals: Comparative Study of Neotectonic Data and Results of Strength and Strain Modeling Along the URSEIS Profile

Much geological and geomorphologic evidence indicates that the modern topography of the Southern Urals has been formed during the Neogene-Quaternary due to superposition of, (1) NW-SE compression and asymmetric uplift of the area as a whole, and (2) more vigorous transpressive uplift of the Central and Western Uralian blocks in the Late Pliocene-Quaternary. Strength modeling based on data on the deep structure, temperature and composition of the crust revealed that the Western and Central Uralian blocks are characterized by low total strength. Numerical strain modeling showed that vertical Neogene-Quaternary movements of the area can be a consequence of intraplate compression, maximum deformation being concentrated in weak blocks. The model predicts different deformational style in the upper and lower parts of inhomogeneous Uralide crust: the zone of maximum deformation at the top of the crust occurs in the Main Uralian fault zone while, in the lower crust, it is shifted 70 km to the west, where a vertical Moho offset (the so-called Makarovo fault) is located. Thus, this fault could have developed (or at least been sufficiently renewed) during Neogene-Quaternary.

Why the sacramento delta area differs from other parts of the great valley: numerical modeling of thermal structure and thermal subsidence of forearc basins

Data on present-day heat flow, subsidence history, and paleotemperature for the Sacramento Delta region, California, have been employed to constrain a numerical model of tectonic subsidence and thermal evolution of forearc basins. The model assumes an oceanic basement with an initial thermal profile dependent on its age subjected to refrigeration caused by a subducting slab. Subsidence in the Sacramento Delta region appears to be close to that expected for a forearc basin underlain by normal oceanic lithosphere of age 150 Ma, demonstrating that effects from both the initial thermal profile and the subduction process are necessary and sufficient. Subsidence at the eastern and northern borders of the Sacramento Valley is considerably less, approximating subsidence expected from the dynamics of the subduction zone alone. These results, together with other geophysical data, show that Sacramento Delta lithosphere, being thinner and having undergone deeper subsidence, must differ from lithosphere of the transitional type under other parts of the Sacramento Valley. Thermal modeling allows evaluation of the rheological properties of the lithosphere. Strength diagrams based on our thermal model show that, even under relatively slow deformation (10−17 s−1), the upper part of the delta crystalline crust (down to 20–22 km) can fail in brittle fashion, which is in agreement with deeper earthquake occurrence. Hypocentral depths of earthquakes under the Sacramento Delta region extend to nearly 20 km, whereas, in the Coast Ranges to the west, depths are typically less than 12–15 km. The greater width of the seismogenic zone in this area raises the possibility that, for fault segments of comparable length, earthquakes of somewhat greater magnitude might occur than in the Coast Ranges to the west.

Formation of the orogen-foredeep system: A geodynamic model and comparison with the data of the northern Forecaucasus

The disturbance of mechanical and thermal equilibria in the upper shell of the Earth as a result of mantle or local within-plate processes related to periodic tectonic activity gives rise to the formation of convective flows in the low-viscosity asthenosphere. These flows affect the lithosphere and create domains of subsidence and uplift, which can continue to develop long after the cessation of active periods. If the density of the lithosphere does not decrease with depth, then small-scale flows increase uplift in zones of compression of the continental lithosphere and create domains of extension at their margins. In our opinion, small-scale convection is the main geodynamic factor that forms foredeeps. The results of detailed numerical modeling of foredeep formation at the margins of adjoining orogens are presented in the current paper. In order to set the initial conditions for the stage of continental collision, the precollision stages of the foldbelt evolution are considered, including the stage of trough formation on the thinned continental crust or on the oceanic lithosphere and the stage of sedimentary basin formation; depending on the degree of extension, this can be an inner sea or a passive continental margin. Such initial conditions were used in modeling of the compression stage (continental collision), when the orogen-foredeep system is formed. The parameters of the model and the tectonic processes are chosen so as to bring the results of numerical computation in line with the data on the Greater Caucasus and northern Forecaucasus, including the thickness of the crustal layers and sedimentary cover, structure of the foredeeps, rate of tectonic subsidence, heat flow, etc. Comparison of the numerical modeling results with the formation history of the Caucasus foredeeps confirms that the first stage of regional compression of the Greater Caucasus took place before the deposition of the Maikop sediments. At least three compression stages followed: 16.6–15.8 Ma (Tarchanian), 14.3–12.3 Ma (Konkian-early Sarmatian), and 7.0–5.2 Ma (Pontian). The next stage of regional compression is apparently occurring at present.

New Data on the Olyutorskii Earthquake Acquired via SAR Interferometry

A coseismic displacement field based on SAR interferometry data was determined for the area of the April 20, 2006 Olyutorskii earthquake. The resulting image shows displacements toward the satellite (“uplifts”) to the northwest of the surface rupture area where the epicenters of most aftershocks lie. The displacement- affected area extends as far as the Vyvenka–Vatyna tectonic suture. We have developed a model for the rupture surface that is in agreement with the hypothesis of A.V. Lander and T.K. Pinegina stating that the largest displacements occurred along a fault northwest of the surface rupture zone; the fault dips southeast and is not exposed. The slip on the fault is close to a pure thrust type. These results furnish another confirmation of the fact that advanced satellite technologies can provide important additional information on the dynamics of seismic regions, especially where the existing observing networks are sparse.

Large-Scale Aseismic Creep in the Areas of the Strong Earthquakes Revealed from the GRACE Data on the Time Variations of the Earth’s Gravity Field

The refinement of the accuracy and resolution of the monthly global gravity field models from the GRACE satellite mission, together with the accumulation of more than a decade-long series of these models, enabled us to reveal the processes that occur in the regions of large (Mw≥8) earthquakes that have not been studied previously. The previous research into the time variations of the gravity field in the regions of the giant earthquakes, such as the seismic catastrophes in Sumatra (2004) and Chile (2010), and the Tohoku mega earthquake in Japan (2011), covered the coseismic gravity jump followed by the long postseismic changes reaching almost the same amplitude. The coseismic gravity jumps resulting from the lower-magnitude events are almost unnoticeable. However, we have established a long steady growth of gravity anomalies after a number of such earthquakes. For instance, in the regions of the subduction earthquakes, the growth of the positive gravity anomaly above the oceanic trench was revealed after two events with magnitudes Mw=8.5 in the Sumatra region (the Nias earthquake of March 2005 and the Bengkulu event of September 2007 near the southern termination of Sumatra Island), after the earthquake with Mw=8.5 on Hokkaido in September 2007, a doublet Simushir earthquake with the magnitudes Mw = 8.3 and 8.1 in the Kuriles in November 2006 and January 2007, and after the earthquake off the Samoa Island in September 2009 (Mw=8.1). The steady changes in the gravity field have also been recorded after the earthquake in the Sichuan region (May 2008, Mw = 8.0) and after the doublet event with magnitudes 8.6 and 8.2, which occurred in the Wharton Basin of the Indian Ocean on April 11, 2012. The detailed analysis of the growth of the positive anomaly in gravity after the Simushir earthquake of November 2006 is presented. The growth started a few months after the event synchronously with the seismic activation on the downdip extension of the coseismically ruptured fault plane zone. The data demonstrating the increasing depth of the aftershocks since March 2007 and the approximately simultaneous change in the direction and average velocity of the horizontal surface displacements at the sites of the regional GPS network indicate that this earthquake induced postseismic displacements in a huge area extending to depths below 100 km. The total displacement since the beginning of the growth of the gravity anomaly up to July 2012 is estimated at 3.0 m in the upper part of the plate’s contact and 1.5 m in the lower part up to a depth of 100 km. With allowance for the size of the region captured by the deformations, the released total energy is equivalent to the earthquake with the magnitude Mw = 8.5. In our opinion, the growth of the gravity anomaly in these regions indicates a large-scale aseismic creep over the areas much more extensive than the source zone of the earthquake. These processes have not been previously revealed by the ground-based techniques. Hence, the time series of the GRACE gravity models are an important source of the new data about the locations and evolution of the locked segments of the subduction zones and their seismic potential.

A postseismic process in the area of the Simushir 11/2006 Earthquake recovered by the GRACE data

The GRACE data make it possible to detect the areas where the earthquakes initiate postseismic creep in regions much larger than the focal area. This information is important for estimation of the seismic potential and position of the locked segments in the subduction zones.

The combination of methods for analyzing the amplitude and phase of satellite radar images for the estimation of displacements on landslide-affected slopes

The efficiency of combining methods for analyzing the amplitude and phase of radar images from the ENVISAT, ALOS, and TerraSAR-X satellites is shown based on a case study of a landslide in Baranovka Settlement, Greater Sochi. The offset tracking method in the amplitude field of the reflected radar signal allowed us to define the contour of the area where the landslide occurred in the night between January 23 and 24, 2012 and to estimate the displacements in different parts of the landslide body. The maximum displacement was 7.5 ± 1 m. The displacements prior to the landslide from January 22, 2007 until September 17, 2010, as obtained from the ALOS satellite by the persistent scatterer method, demonstrate seasonal autumn–winter accelerations. The time series of displacements from the ENVISAT satellite shows that from November 29, 2010 until July 27, 2011 the displacement rates in the line-of-sight direction vLOS were relatively small (21 mm/yr), but in the period from September 25, 2011 to December 24, 2011 the slide rate increased to 50 mm/yr. As obtained by the TerraSAR-X satellite, the slide rate vLOS after landsliding in the period from February 17, 2012 to March 10, 2012, reached 30 mm/month, but after June 6, 2012 it decelerated to 2–3 mm/month. Similar slide rates were also obtained for the same periods based on differential interferograms.