Crack damage stress as a composite function of porosity and elastic matrix stiffness in dolomites and limestones

Twenty-five uniaxial compression tests were performed to determine stress at onset of dilation, referred to herein as “the crack damage stress,” in heterogeneous dolomites and limestones. A simplified model for crack damage stress (σ_cd) is developed here using porosity, elastic modulus, Poisson's ratio and three empirical coefficients. The model shows that when porosity decreases and elastic modulus increases, σ_cd rapidly increases and approaches its maximum value. On the other hand, when porosity increases and elastic modulus decreases, σ_cd rapidly decreases and approaches its minimum value. The proposed model is validated for six heterogeneous limestone and dolomite formations which are widely distributed in Israel.     

Localization of mining-induced horizontal fractures along rock layer interfaces in overburden: field measurements and prediction

The locations of mining-induced horizontal fractures along rock interfaces in the overburden of Donetsk Coal Basin were identified using an original experimental device. The device traps methane from horizontal fracture zone (100–fold coal seam thickness) over an active longwall mining excavation. Presence or absence of horizontal fractures along rock layer interfaces is correlated with physical characteristics of the overburden, such as thickness, uniaxial compressive strength of overburden rock layers, location of rock layer interfaces and thickness of extracted coal seams. As a result, a combined criterion based on these physical characteristics is proposed to predict the presence of overburden horizontal fracturing in coal mine operations.     

Calibration of the ART-XC mirror modules at MSFC

The Astronomical Röntgen Telescope X-ray Concentrator (ART-XC) is a hard X-ray telescope with energy response up to 30 keV, to be launched on board the Spectrum Röntgen Gamma (SRG) spacecraft in 2018. ART-XC consists of seven identical co-aligned mirror modules. Each mirror assembly is coupled with a CdTe double-sided strip (DSS) focal-plane detector. Eight X-ray mirror modules (seven flight and one spare units) for ART-XC were developed and fabricated at the Marshall Space Flight Center (MSFC), NASA, USA. We present results of testing procedures performed with an X-ray beam facility at MSFC to calibrate the point spread function (PSF) of the mirror modules. The shape of the PSF was measured with a high-resolution CCD camera installed in the focal plane with defocusing of 7 mm, as required by the ART-XC design. For each module, we performed a parametrization of the PSF at various angular distances Θ. We used a King function to approximate the radial profile of the near on-axis PSF (Θ < 9 arcmin) and an ellipse fitting procedure to describe the morphology of the far off-axis angular response (9 < Θ < 24 arcmin). We found a good agreement between the seven ART-XC flight mirror modules at the level of 10%. The on-axis angular resolution of the ART-XC optics varies between 27 and 33 arcsec (half-power diameter), except for the spare module.     

Seismicity and crustal deformation preceding the January 1996 eruptions at Karymsky Volcanic Center,Kamchatka

Two explosive eruptions occurred on 2 January 1996 at Karymsky Volcanic Center (KVC) in Kamchatka, Russia: the first, dacitic, from the central vent of Karymsky volcano, and the second, several hours later, from Karymskoye lake in the caldera of Akademia Nauk volcano. The main significance of the 1996 volcanic events in KVC was the phreatomagmatic eruption in Karymskoye lake, which was the first eruption in this lake in historical time, and was a basaltic eruption at the acidic volcanic center. The volcanic events were associated with the 1 January Ms 6.7 (Mw 7.1) earthquake that occurred at a distance of about 9–17 km southeast from the volcanoes just before the eruptions. We study the long-term (1972–1995) and short-term (1–2 January 1996) characteristics of crustal deformations and seismicity before the double eruptive event in KVC. The 1972–1995 crustal deformation was homogeneous and characterized by a gradual extension with a steady velocity. The seismic activity in 1972–1995 developed at the depth interval from 0 to 20 km below the Akademia Nauk volcano and spread to the southeast along a regional fault. The seismic activity in January 1996 began with a short sequence of very shallow microearthquakes (M ~0) beneath Karymsky volcano. Then seismic events sharply increased in magnitude (up to mb 4.9) and moved along the regional fault to the southeast, culminating in the Ms 6.7 earthquake. Its aftershocks were located to the southeast and northwest from the main shock, filling the space between the two active volcanoes and the ancient basaltic volcano of Zhupanovsky Vostryaki. The eruption in Karymskoye lake began during the aftershock sequence. We consider that the Ms 6.7 earthquake opened the passageway for basic magma located below Zhupanovsky Vostryaki volcano that fed the eruption in Karymskoye lake.     

Seismic quantification of the explosions that destroyed the dome of Volcán de Colima, Mexico, in July–August 2003

In July–August 2003, the andesitic lava dome at Volcán de Colima, México, was destroyed by a sequence of explosions that replaced the 2×10⁶ m³ dome with a crater 200 m across and 30 m deep. The two strongest explosions occurred on July 17 and August 28. The initial low-frequency impulses that they produced, which were recorded on broadband seismic records, allowed an estimation of the counter forces of the initiating process as being equal to 0.3×10¹¹ N and 1×10¹¹ N for the July and August events, respectively. The seismic characteristics follow the Nishimura-Hamaguchi scaling law for volcanic explosions, reflecting self-similarity in the processes initiating explosive events. The results also show that counter forces can discriminate between the sizes of explosive eruptions that are assigned the same magnitude by conventional methods of classification such as the Volcanic Explosivity Index. The increasing use of broadband seismometers may therefore provide the basis for using counter forces to determine the magnitude of explosive eruptions.     

Application of laser strainmenters to the study of earthquake physics

The paper considers possibilities of applying laser strainmeters for the study of earthquake physics. One of laser strainmeters is described. A high efficiency of using the laser strainmeters for the study of earthquakes and their precursors is shown. In records of the spaced laser strainmeters, anomalous deformations propagating from the east to the west with the speed comparable with that of migration of earthquakes were found.     

Microbial Processes in Stratified Lake Doroninskoe(Transbaikal Region)

正In recent decades,meromictic ponds attract the attention of researchers in different directions,because here the character of the physical,chemical and biological processes differ from those of typical mixing waters(Kuznetsov,1970;Hutchinson,1969).In Transbaikalia widely distributed soda and salt lakes with different salinity.Notable among them is Lake Doroninskoye,which has a pronounced stratification for a