Remote detection of aftershock activity as a new method of seismic monitoring

A weak seismic event with body wave magnitude 2.1 was detected near the epicenter of an underground explosion conducted by the Democratic People’s Republic of Korea (DPRK) on September 9, 2016. The event occurred approximately two days after the test. Using the method of waveform cross-correlation, two array stations of the International Monitoring System (IMS), USRK and KSRS, recorded the arrival of P _n waves. At the same time, this event was not recorded during the standard automatic processing at the International Data Center. The location and other characteristics of this weak event indicate that it is likely to have been an aftershock of the preceding explosion. Based on the successful automatic detection and construction of the event, we conducted an extended investigation, which consisted in searching for secondary seismic phases at the nearest stations that do not belong to the International Monitoring System. The final solution, which is based on waveform cross-correlation, includes stations MDJ (China) and SEHB (Republic of Korea), the aftershock epicenter is located at ~2 km northwest of the epicenter of the DPRK test.     

Equation of state of Fe3+-bearing phase-X

We investigated the high-pressure behaviour of Fe³⁺-bearing hydrous phase-X, (K_1.307Na_0.015)(Mg_1.504Fe _0.373 ³⁺ Al_0.053Ti _0.004 ⁴⁺ )Si₂O₇H_0.36, up to 34?GPa at room temperature by synchrotron X-ray powder diffraction. The lattice parameters behave anisotropically, with the [001] direction stiffer than [100]. In the 10^?4 to 22?GPa pressure range, the axial bulk moduli are K _0a ?=?112(3) GPa and K′?=?4, and K _0c ?=?158(2) GPa and K′?=?4, and the anisotropy of the lattice parameters is β_0c :β_0a ?=?0.71:1. The cell volumes are fitted by a second-order Birch–Murnaghan equation of state giving a bulk modulus of K ₀?=?127(1) GPa and K′?=?4 in the same pressure range. After 22?GPa, a discontinuity in volume and lattice parameters can be recognized. Sample did not become amorphous up to 34?GPa. The coupled substitution K?+?Mg?=?[]?+?Fe³⁺ has only a limited influence on the bulk modulus and structural stability of phase-X.     

Biogenic contribution of minor elements to organic matter of recent lacustrine sapropels (Lake Kirek as example)

An approximate biogenic contribution of minor elements to sapropel of Lake Kirek in West Siberia is estimated using the “model of direct inheritance” of their composition in plankton by OM of bottom sediments (Yudovich and Ketris, 1990). It is shown that the lifetime accumulation of P, Br, and Zn in copepod zooplankton of Lake Kirek notably affects the concentration of these elements in sapropelic mud (biogenic contribution is approximately 95–53%). The biogenic share of other elements in these sediments is substantially lower: approximately 30% for Sr and Ba; 26–16% for Ca, Pb, Cd, Cu, K, Mg, and Cr; and no more than 5% for As, Co, Fe, Ni, Ti, Y, and Mo.     

Comparison of Synchrotron Radiation X-Ray Fluorescence with Conventional Techniques for the Analysis of Sedimentary Samples

A comparison is made of elemental analyses of sediment samples (lake bottom sediments and sediments from the petroliferous Bazhenovka Formation) by five competitive methods (synchrotron radiation X-ray fluorescence (SR-XRF), INAA, ICP-MS, AAS and traditional XRF). The object of this study was to identify the most suitable analytical techniques for applications in sedimentary geochemistry. Advantages and shortcomings of the five techniques were considered with respect to applications related to studies of palaeo-climate changes recorded in sedimentary cores from Lake Baikal and the geochemical stratigraphy of the Bazhenovka Formation, which is rich in organic material. We have concluded that SR-XRF was the best technique for producing extensive analytical data series, from the point of view of its speed, ease of application, cost, non-destructive nature and sensitivity, which allowed for the simultaneous determination of more than twenty elements of geochemical interest in small samples of sediments. An additional benefit of the method was demonstrated when used for the independent certification of geological reference materials. International reference samples BIL-1 and SDO-1 were certified by means of this method without use of reference materials. Analyses were based on the physics of the theory of energy transport.     

Multi-Wavelength Synchrotron Radiation XRF Determination of U and Th in Sedimentary Cores from Lake Baikal

A new technique for the determination of uranium and thorium in lacustrine sediments is based on non-destructive synchrotron radiation X-ray fluorescence analysis (SR-XRF) of sediment samples using monochromatic beams of different energies as excitation sources, with the recording and subsequent iterative processing of the X-ray fluorescence spectra. The technique has a multielement capability and enables fast, simultaneous analysis of a few tens of elements. The proposed SR-XRF technique was tested against INAA and ICP-MS methods and showed a number of advantages with a generally good correlation of results by the three methods. Uranium and Th profiles have been measured at a time resolution of 2 kyr in a drill core (BDP-96) from Lake Baikal bottom sediments deposited between 780 and 40 kyr B P. During this time span, peaks in the U and U/Th concentration marked warm climates. Oscillations of U and U/Th in Baikal bottom sediments during the Brunhes chron reflect climate-induced global change in the volume of polar ice, controlled by long-term cyclicity of the Earths orbital parameters. The response of these warm periods is similar to that observed earlier in shorter cores that span the two last interglacials (220-0 kyr BP).     

Chromium solubility in anhydrous Phase B

The crystal structure and chemical composition of a crystal of (Mg_14?x Cr _x )(Si_5?x Cr _x )O₂₄ (x ≈ 0.30) anhydrous Phase B (Anh-B) synthesized in the model system MgCr₂O₄–Mg₂SiO₄ at 12 GPa and 1600 °C have been investigated. The compound was found to be orthorhombic, space group Pmcb, with lattice parameters a = 5.900(1), b = 14.218(2), c = 10.029(2) Å, V = 841.3(2) Å³ and Z = 2. The structure was refined to R ₁ = 0.065 using 1492 independent reflections. Chromium was found to substitute for both Mg at the M3 site (with a mean bond distance of 2.145 Å) and Si at the octahedral Si1 site (mean bond distance: 1.856 Å), according to the reaction Mg²⁺ + Si⁴⁺ = 2Cr³⁺. Such substitutions cause a reduction in the volume of the M3 site and an increase in the volume of the Si-dominant octahedron with respect to the values typically observed for pure Anh-B and Fe²⁺-bearing Anh-B. Taking into account that Cr³⁺ is not expected to be Jahn–Teller active, it appears that both the Cr³⁺–for–Mg and Cr³⁺–for–Si substitutions in the Anh-B structure decrease the distortion of the octahedra. Electron microprobe analysis gave the Mg_13.66(8)Si_4.70(6)Cr_0.62(4)O₂₄ stoichiometry for the studied phase. The successful synthesis of this phase provides new information for the possible mineral assemblages occurring in the Earth’s deep upper mantle and shed new light on the so-called X discontinuity that has been observed at 275–345 km depth in several subcontinental and subduction zone environments.     

The Chelyabinsk Meteorite as a multiple source of acoustic and seismic waves

Shock waves and impact of the Chelyabinsk Meteorite fragments on the ground initiated various waves in the atmosphere and the earth. Three different sources of seismic and infrasound waves were found by arrival time and azimuth of seismic and infrasound waves recorded by the International Monitoring System.