Frictional behavior of oceanic transform faults and its influence on earthquake characteristics

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): B04315, doi:10.1029/2011JB009025.We use a three-dimensional strike-slip fault model in the framework of rate and state-dependent friction to investigate earthquake behavior and scaling relations on oceanic transform faults (OTFs). Gabbro friction data under hydrothermal conditions are mapped onto OTFs using temperatures from (1) a half-space cooling model, and (2) a thermal model that incorporates a visco-plastic rheology, non-Newtonian viscous flow and the effects of shear heating and hydrothermal circulation. Without introducing small-scale frictional heterogeneities on the fault, our model predicts that an OTF segment can transition between seismic and aseismic slip over many earthquake cycles, consistent with the multimode hypothesis for OTF ruptures. The average seismic coupling coefficient χ is strongly dependent on the ratio of seismogenic zone width W to earthquake nucleation size h*; χ increases by four orders of magnitude as W/h* increases from ∼1 to 2. Specifically, the average χ = 0.15 ± 0.05 derived from global OTF earthquake catalogs can be reached at W/h* ≈ 1.2–1.7. Further, in all simulations the area of the largest earthquake rupture is less than the total seismogenic area and we predict a deficiency of large earthquakes on long transforms, which is also consistent with observations. To match these observations over this narrow range of W/h* requires an increase in the characteristic slip distance dc as the seismogenic zone becomes wider and normal stress is higher on long transforms. Earthquake magnitude and distribution on the Gofar and Romanche transforms are better predicted by simulations using the visco-plastic model than the half-space cooling model.This work was supported by NSF-EAR award 1015221, NSF-OCE award 1061203, and a J. Lamar Worzel Assistant Scientist Fund to Y. Liu at WHOI.2012-10-2

Absolute CO number densities measured using TALIF in a non-thermal plasma environment

\u3cp\u3eWe report first measurements of time-resolved absolute CO number densities and rotational temperatures in a non-thermal CO \u3csub\u3e2\u3c/sub\u3e plasma environment using TALIF with a nanosecond pulsed laser. Two-photon excitation spectra from the B \u3csup\u3e1\u3c/sup\u3eΣ+(v′ = 0) ← X \u3csup\u3e1\u3c/sup\u3e Σ+ (v″ = 0) Q-branch are recorded and fitted to extract rotational temperatures. Absolute number densities are determined from the frequency-integrated excitation spectrum. The plasma under investigation is a pulsed glow discharge operated at a frequency of 60 Hz with an plasma-on time of 5 ms per plasma cycle, 50 mA plasma current and a pressure of 6.67 mbar. CO number densities range from (2.6 ± 0.6) × 10 \u3csup\u3e22\u3c/sup\u3e m \u3csup\u3e-3\u3c/sup\u3e to (1.2 ± 0.3) × 10 \u3csup\u3e22\u3c/sup\u3e m \u3csup\u3e-3\u3c/sup\u3e, while rotational temperatures range from 370 ± 40 K to 700 ± 70 K at the beginning and end of the plasma-on phase, respectively. Our results show fair agreement with literature data. \u3c/p\u3

Absolute CO number densities measured using TALIF in a non-thermal plasma environment

We report first measurements of time-resolved absolute CO number densities and rotational temperatures in a non-thermal CO 2 plasma environment using TALIF with a nanosecond pulsed laser. Two-photon excitation spectra from the B 1Σ+(v′ = 0) ← X 1 Σ+ (v″ = 0) Q-branch are recorded and fitted to extract rotational temperatures. Absolute number densities are determined from the frequency-integrated excitation spectrum. The plasma under investigation is a pulsed glow discharge operated at a frequency of 60 Hz with an plasma-on time of 5 ms per plasma cycle, 50 mA plasma current and a pressure of 6.67 mbar. CO number densities range from (2.6 ± 0.6) × 10 22 m -3 to (1.2 ± 0.3) × 10 22 m -3, while rotational temperatures range from 370 ± 40 K to 700 ± 70 K at the beginning and end of the plasma-on phase, respectively. Our results show fair agreement with literature data

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Vibrational kinetics of CO2 in non-thermal plasma

During the presentation I will discuss the development of two diagnostics to increase our current level of understanding of the vibrational kinetics within CO2 discharges, with the intention to ultimately contribute to a controlled and efficient dissociation process. The diagnostic techniques are (1) time resolved in situ Fourier transform infrared (FTIR) spectroscopy and (2) spatiotemporally resolved in situ rotational Raman spectroscopy. Both techniques are used to obtain information about the rovibrational density distributions in the electronic ground state of CO2 in a pulsed glow discharge. During the active part of the plasma pulse a clear non-equilibrium is observed between the rotational and the ν3, and the (ν1, ν2) and ν3 vibrational density distributions. The results provide ample experimental foundation to expand our knowledge on CO2 vibrations and dissociation, especially through comparison with numerical models. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 81339

Measuring vibrational excitation of CO<SUB>2</SUB> in a pulsed glow discharge

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A rotational Raman study under non-thermal conditions in a pulsed CO<SUB>2</SUB> glow discharge

International audienceThe implementation of in situ rotational Raman spectroscopy is realized for a pulsed glow discharge in CO2 in the mbar range and is used to study the rotational temperature and molecular number densities of CO2, CO, and O2. The polarizability anisotropy of these molecules is required for extracting number densities from the recorded spectra and is determined for incident photons of 532 nm. The spatiotemporally-resolved measurements are performed in the same reactor and at equal discharge conditions (510 ms onoff cycle, 50 mA plasma current, 6.7 mbar pressure) as in recently published work employing in situ Fourier transform infrared (FTIR) spectroscopy. The rotational temperature ranges from 394 to 809 K from start to end of the discharge pulse and is constant over the length of the reactor. The discharge is demonstrated to be spatially uniform in gas composition, with a CO2 conversion factor of 0.15 ± 0.02. Rotational temperatures and molecular composition agree well with the FTIR results, while the spatial uniformity confirms the assumption made for the FTIR analysis of a homogeneous medium over the line-of-sight of absorption. Furthermore, the rotational Raman spectra of CO2 are related to vibrational temperatures through the vibrationally averaged nuclear spin degeneracy, which is expressed in the intensity ratio between even and odd numbered Raman peaks. The elevation of the odd averaged degeneracy above thermal conditions agrees well with the elevation of vibrational temperatures of CO2, acquired in the FTIR study

Spatiotemporally resolved rotational Raman spectroscopy in a pulsed CO<SUB>2</SUB> glow discharge

International audienc