Geophysical Survey

About: Geophysical Survey is a facility organization based out in Obninsk, Russia. It is known for research contribution in the topics: Geology & Fault (geology). The organization has 308 authors who have published 256 publications receiving 3067 citations. The organization is also known as: Federal State Institution of Science Geophysical Survey of the Siberian Branch of the Russian Academy of Sciences.

The 1998 Bovec-Krn mountain (Slovenia) earthquake sequence

Abstract: We study the 1998 Bovec-Krn mountain (Slovenia) earthquake sequence by combining hypocenters relocation, strong motion inversion, digital elevation modelling and field geology. The main shock (Ms=5.7), a 12 km right lateral strike-slip event on the Dinaric fault system, occurred on a sub-vertical fault plane. The rupture, confined between 3 and 9 km depth, with no evidence of surface faulting, propagated bilaterally within two structural barriers. The northwestern barrier is at the junction between Dinaric and Alpine structures where there is a sharp change in the geometry of faulting. The southeastern barrier is within the Dinaric system and its surface expression corresponds to the Tolminka-spring perched basin, a 1 km restraining step-over. At this site, the Bovec-Krn earthquake-fault overlaps with a 30 km strike-slip fault segment that is free of aftershocks and could be undergoing an increase of stress. This fault system represents the northern branch of the Idrija right-lateral fault.

Feeding volcanoes of the Kluchevskoy group from the results of local earthquake tomography

Abstract: [1] We present a seismic model of the area beneath the Kluchevskoy volcano group (Kamchatka, Russia) based on the tomographic inversion of more than 66000 P and S arrival times from more than 5000 local earthquakes that occurred in 2004 and that were recorded by 17 permanent stations. Below a depth of 25 km beneath the Kluchevskoy volcano, we observed a very strong anomaly in the Vp/Vs ratio that reached as high as 2.2. This is a probable indicator of the presence of partially molten material with a composition corresponding to deeper mantle layers. The upper part of this anomaly at a depth of 25–30 km coincides with a cluster of strong seismicity that can be explained by strong mechanical stresses in the lowermost crust due to magma ascension, water release and/or phase transitions. In the crust, we observed regular seismicity clusters that link the mantle anomaly with the Kluchevskoy volcano and most likely indicate the paths of magma migration. Between depths of 8 and 13 km, we see several patterns of high Vp/Vs ratios, interpreted as intermediate-depth magma storages. Directly below the Kluchevskoy volcano, we observed a shallow body of high Vp/Vs, which probably represents the activated magma chamber just beneath the volcano cone, which erupted in the beginning of 2005. The existence of three levels of magma storage, based on results of local earthquake tomography, may explain the variety of the lava composition and eruption regimes in different volcanoes of the Kluchevskoy group.

Natural and human-induced sinkhole hazards in Saudi Arabia: distribution, investigation, causes and impacts

Abstract: Approximately 60 % of the 2,150,000 km2 area of Saudi Arabia is underlain by soluble sediments (carbonate and evaporite rock formations, salt diapirs, sabkha deposits). Despite its hyper-arid climate, a wide variety of recent sinkholes have been reported in numerous areas, involving significant property losses. Human activities, most notably groundwater extraction, have induced unstable conditions on pre-existing cavities. This work provides an overview of the sinkhole hazard in Saudi Arabia, a scarcely explored topic. It identifies the main karst formations and the distribution of the most problematic sinkhole areas, illustrated through several case studies covering the wide spectrum of subsidence mechanisms. Some of the main investigation methods are presented through selected examples, including remote sensing, trenching and geophysics. Based on the available data, the main causal factors are identified and further actions that should be undertaken to better assess and manage the risk are discussed.

Deep Structure and Past Kinematics of Accreted Terranes

Abstract: An “accreted terrane” is simply a block of light crust that has been added to a continental margin during the collision of lithospheric plates. At subduction zones, terranes might be seamounts, continental slivers, ophiolites, deep-sea fans, or old volcanic arcs that have been swept from the under riding plate, like packages falling into a basket at the end of a conveyor belt. Accretion also occurs by oblique slip along transform-fault boundaries. Some terranes are exotic, whereas others might be native crust that has been dislodged by rifting or lateral faulting, then transported to a new location. Geologists have been writing about accreted terranes for many years, but only during the last decade has the concept been tested in detail by geophysical methods. For example, paleomagnetic studies in the Cordillera of western North America have revealed discordant paleolatitudes, implying that some terranes have moved thousands of kilometers relative to the craton. In some cases, paleomagnetic discordance is in tune with marked contrasts in fossil assemblages or stratigraphic mismatches that suggest large-scale offsets across fault zones. In others, paleolatitude shifts derived from paleomagnetism have exceeded displacements inferred from geologic mapping, prompting close scrutiny of the geologic and paleomagnetic evidence.