Chen Gu

The postspinel boundary in pyrolitic compositions determined in the laser-heated diamond anvil cell

In situ multianvil press (MAP) studies have reported that the depth and the Clapeyron slope of the postspinel boundary are significantly less than those of the 660 km discontinuity inferred from seismic studies. These results have raised questions about whether the postspinel transition is associated with the discontinuity. We determined the postspinel transition in pyrolitic compositions in the laser-heated diamond anvil cell (LHDAC) combined with in situ synchrotron X-ray diffraction. The Clapeyron slope was determined to be −2.5 ± 0.4MPa/K and did not vary significantly with compositions and used pressure scales. Using Pt scales, our data indicate that the postspinel transition occurs in pyrolitic compositions at 23.6–24.5GPa (1850K). The transition pressure and slope are consistent with the depth and topography of the 660 km discontinuity. Our data reveal that inaccuracy in pressure scales alone cannot explain the discrepancy and technical differences between MAP and LHDAC contribute significantly to the discrepancy.

Electronic structure of iron in magnesium silicate glasses at high pressure

[1]xa0A recent study attributed the source of an iron partitioning change between silicate melt and minerals at deep mantle conditions to a high-spin to low-spin change in iron, which was found in a Fe-diluted Mg-silicate glass at a similar pressure. We conducted X-ray emission spectroscopy and nuclear forward scattering on iron-rich Mg-silicate glasses at high pressure and 300xa0K in the diamond-anvil cell: Al-free glass up to 135xa0GPa and Al-bearing glass up to 93xa0GPa. In both glasses, the spin moment decreases gradually from 1xa0bar and does not reach a complete low-spin state even at the peak pressures of this study. The gradual change may be due to the existence of diverse coordination environments for iron in the glasses and continuous structural adjustment of the disordered system with pressure. If the result can be extrapolated to iron in mantle melts, the small, gradual changes in the spin state of iron may not be the dominant factor explaining the reported sudden change in the partitioning behavior of iron between silicate melt and minerals at lower-mantle pressures.

Source Mechanism Study of Local Earthquakes in Kuwait

ABSTRACT Historically, Kuwait has relatively low seismicity; however, in recent years the Kuwait National Seismic Network (KNSN) has detected a significant number of local earthquakes. In 2015, two earthquakes— M w xa04.5 on 21 March 2015 and M w xa04.1 on 18 August 2015—were recorded by the KNSN and were widely felt across Kuwait. Most earthquakes happen in two areas close to the northern and southern oil/gas fields. The earthquakes are generally small ( M w

Ground Motion in Kuwait from Regional and Local Earthquakes: Potential Effects on Tall Buildings

In recent years, the construction of tall buildings has been increasing in many countries, including Kuwait and other Gulf states. These tall buildings are especially sensitive to ground shaking due to long period seismic surface waves. Although Kuwait is relatively aseismic, it has been affected by large (Mwu2009>u20096) regional earthquakes in the Zagros Fold-Thrust Belt (ZFTB). Accurate ground motion prediction for large earthquakes is important to assess the seismic hazard to tall buildings. In this study, we first analyze the observed ground motions due to two earthquakes widely felt in Kuwait: the 08/18/2014 Mw 6.2 earthquake, 360xa0km NNE of Kuwait City, and the 11/12/2017 Mw 7.3 earthquake, 642xa0km NNE of Kuwait City. The peak spectral displacement periods of the ground motion from the 08/18/2014 Mw 6.2 earthquake matched well with the ambient vibration spectra of the tallest building—the Al-Hamra Tower. We calculate the ground motions from potential regional and local earthquakes. We use a velocity model obtained by matching the observed seismograms of the 2014 and 2017 earthquakes. We calculate ground motions in Kuwait due to a regional Mwu2009=u20097.5 earthquake, and a local Mwu2009=u20095.0 earthquakes. Our study shows that a significant source of seismic hazard to tall buildings in Kuwait comes from the regional tectonic earthquakes. However, local earthquakes have the potential to generate high peak ground accelerations (~u200998xa0cm/s2) close to their epicenters.