Although volcano-tectonic (VT) earthquakes often occur in response to magma intrusion, it is rare for them to have magnitudes larger than similar to M4. On 24 May 2007, two shallow M4+ earthquakes occurred beneath the upper part of the east rift zone of Kilauea Volcano, Hawai'i. An integrated analysis of geodetic, seismic, and field data, together with Coulomb stress modeling, demonstrates that the earthquakes occurred due to strike-slip motion on pre-existing faults that bound Kilauea Caldera to the southeast and that the pressurization of Kilauea's summit magma system may have been sufficient to promote faulting. For the first time, we infer a plausible origin to generate rare moderate-magnitude VTs at Kilauea by reactivation of suitably oriented pre-existing caldera-bounding faults. Rare moderate-to large-magnitude VTs at Kilauea and other volcanoes can therefore result from reactivation of existing fault planes due to stresses induced by magmatic processes.

The ''excess'' of siderophile elements in Earth's mantle is a long-standing problem in understanding the evolution of Earth. Determination of the partitioning behavior of tungsten and molybdenum between liquid metal and silicate melt at high pressure and temperature shows that partition coefficients (D-metal/silicate) vary by two orders of magnitude depending on whether metal segregated from a basaltic or peridotitic melt. This compositional dependence is likely a response to changes in the degree of polymerization of the silicate melt caused by compositional variations of the network-modifying cations Mg2+ and Fe2+. Silicate melt compositional effects on partition coefficients for siderophile elements are potentially more important than the effects of high pressure and temperature.

Synchrotron infrared measurements were conducted on a self-doped La(x)MnO(3-delta) (x similar to 0.8) film. From these measurements we determined the conductivity and the temperature dependence of the effective number of carriers. While the metal-insulator transition temperature (T(MI)) and the magnetic ordering temperature (T(C)) approximately coincide, the onset of the change in the free carrier density occurs at a significantly lower temperature (similar to 45 K below). This suggests that local distortions exist below T(MI) and T(C) which trap the e(g) conduction electrons. These regions with local distortions constitute an insulating phase which persists for temperatures significantly below T(MI) and T(C).

Telica Volcano, Nicaragua, is a persistently restless volcano with daily seismicity rates that can vary by orders of magnitude without apparent connection to eruptive activity. Low-frequency (LF) events are dominant and peaks in seismicity rate show little correlation with eruptive episodes, presenting a challenge for seismic monitoring and eruption forecasting. A short period seismic station (TELN) has been operated on Telica's summit since 1993, and in 2010 the installation of a six-station broadband seismic and eleven-station continuous GPS network (the TESAND network) was completed to document in detail the seismic characteristics of a persistently restless volcano. Between our study period of November 2009 and May 2013, over 400,000 events were detected at the TESAND summit station (TBTN), with daily event rates ranging from 5 to 1400. We present spectral analyses and classifications of -200,000 events recorded by the TESAND network between April 2010 and March 2013, and earthquake locations for a sub-set of events between July 2010 and February 2012. In 2011 Telica erupted in a series of phreatic vulcanian explosions. Six months before the 2011 eruption, we observe a sudden decrease in LF events concurrent with a swarm of high-frequency (HF) events, followed by a decline in overall event rates, which reached a minimum at the eruption onset. We observe repeated periods of high and low seismicity rates and suggest these changes in seismicity represent repeated transitions between open-system and closed-system degassing. We suggest that these short- and long-term transitions between open to closed-system degassing form part of a long-term pattern of stable vs. unstable phases at Telica. Stable phases are characterised by steady high-rate seismicity and represent stable open-system degassing, whereas unstable phases are characterised by highly variable seismicity rates and represent repeated transitions from open to closed-system degassing, where the system is unable to sustain steady open-system degassing. These observations have implications for seismic monitoring at persistently restless volcanoes as the recognition of unstable seismic phases may indicate the open-system degassing process cannot be sustained and explosions are likely. (C) 2014 The Authors. Published by Elsevier B.V.

We propose a model for the generation of average MORBs based on phase relations in the CaO-MgO-Al2O3-SiO2-CO2 system at pressures from 3 to 7 GPa and in the CaO-MgO-Al2O3-SiO2-Na2O-FeO (CMASNF) system at pressures from similar to0.9 to 1.5 GPa. The MELT seismic tomography (Forsyth et al., 2000) across the East Pacific Rise shows the largest amount of melt centered at similar to30-km depth and lesser amounts at greater depths. An average mantle adiabat with a model-system potential temperature (T-P) of 1310degreesC is used that is consistent with this result. In the mantle, additional minor components would lower solidus temperatures similar to50degreesC, which would lower T-P of the adiabat for average MORBs to similar to1260degreesC. The model involves generation of carbonatitic melts and melts that are transitional between carbonatite and kimberlite at very small melt fractions (<0.2%) in the low-velocity zone at pressures of similar to2.6 to 7 GPa in the CMAS-CO2 system, roughly the pressure range of the PREM low-velocity zone. These small-volume, low-viscosity melts are mixed with much larger volumes of basaltic melt generated at the plagioclase-spinel lherzolite transition in the pressure range of similar to0.9 to 1.5 GPa.

We observe the appearance of a phonon near the lock-in temperature in orthorhombic REMnO3 (RE denotes rare earth) (RE: Lu and Ho) and anomalous phonon hardening in orthorhombic LuMnO3. The anomalous phonon occurs at the onset of spontaneous polarization. No such changes were found in incommensurate orthorhombic DyMnO3. These observations directly reveal different electric polarization mechanisms in the E-type and incommensurate-type orthorhombic REMnO3. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3533022]

Seismic anisotropy, measured through shear wave splitting (SWS) analysis, can be indicative of the state of stress in Earth's crust. Changes in SWS at Kilauea Volcano, Hawai'i, associated with the onset of summit eruptive activity in 2008 hint at the potential of the technique for tracking volcanic activity. To use SWS observations as a monitoring tool, however, it is important to understand the cause of seismic anisotropy at the volcano throughout the eruptive cycle. To address this need, we analyzed SWS results from across Kilauea in combination with macroscopic surface structures (mapped fractures, faults, and fissures) and stress orientations inferred from fault plane solutions. Seismic anisotropy seems to be due to pervasive aligned structures in most regions of the volcano. The upper East and Southwest Rift Zones, however, show a bimodality in stress and SWS, suggesting a stress discontinuity with depth, perhaps related to magma conduits that trend obliquely to the dominant structure. Other areas in and around Kilauea Caldera display principal stresses of similar magnitudes, indicating that small stress perturbations can rotate the maximum horizontal compressive stress direction by up to 90 degrees. In these locations, static structures generally control SWS, but dynamic conditions due to magmatic activity can override the structural control. Monitoring of SWS may therefore provide important signs of impending volcanism.

[1] We have determined the postspinel transformation boundary in Mg2SiO4 by combining quench technique with in situ pressure measurements, using multiple internal pressure standards including Au, MgO, and Pt. The experimentally determined boundary is in general agreement with previous in situ measurements in which the Au scale of Anderson et al. [1989] was used to calculate pressure: Using this pressure scale, it occurs at significantly lower pressures compared to that corresponding to the 660-km seismic discontinuity. In this study, we also report new experimental data on the transformation boundary determined using MgO as an internal standard. The results show that the transition boundary is located at pressures close to the 660-km discontinuity using the MgO pressure scale of Speziale et al. [2001] and can be represented by a linear equation, P(GPa) = 25.12 - 0.0013T(degreesC). The Clapeyron slope for the postspinel transition boundary is precisely determined and is significantly less negative than previous estimates. Our results, based on the MgO pressure scale, support the conventional hypothesis that the postspinel transformation is responsible for the observed 660-km seismic discontinuity.

Structural changes in RMnO3 (R = Y, Ho, Lu) under high pressure were examined by synchrotron x-ray diffraction methods at room temperature. Compression occurs more readily in the ab plane than along the c axis. With increased pressure, a pressure-induced hexagonal to orthorhombic phase transition was observed starting at similar to 22 GPa for Lu(Y)MnO3. When the pressure is increased to 35 GPa, a small volume fraction of Lu(Y)MnO3 is converted to the orthorhombic phase and the orthorhombic phase is maintained on pressure release. High-pressure infrared absorption spectroscopy and Mn K-edge near-edge x-ray absorption spectroscopy confirm that the hexagonal P6(3)cm structure is stable below similar to 20 GPa and the environment around the Mn ion is not changed. Shifts in the unoccupied p-band density of states with pressure are observed in the Mn K-edge spectra. A schematic pressure-temperature phase diagram is given for the small ion RMnO3 system.