Physical and stochastic models of earthquake clustering   总被引：4，自引：2，他引：4  

Rodolfo Console  Maura Murru  Flaminia Catalli 《Tectonophysics》2006,417(1-2):141

The phenomenon of earthquake clustering, i.e., the increase of occurrence probability for seismic events close in space and time to other previous earthquakes, has been modeled both by statistical and physical processes.From a statistical viewpoint the so-called epidemic model (ETAS) introduced by Ogata in 1988 and its variations have become fairly well known in the seismological community. Tests on real seismicity and comparison with a plain time-independent Poissonian model through likelihood-based methods have reliably proved their validity.On the other hand, in the last decade many papers have been published on the so-called Coulomb stress change principle, based on the theory of elasticity, showing qualitatively that an increase of the Coulomb stress in a given area is usually associated with an increase of seismic activity. More specifically, the rate-and-state theory developed by Dieterich in the ′90s has been able to give a physical justification to the phenomenon known as Omori law. According to this law, a mainshock is followed by a series of aftershocks whose frequency decreases in time as an inverse power law.In this study we give an outline of the above-mentioned stochastic and physical models, and build up an approach by which these models can be merged in a single algorithm and statistically tested. The application to the seismicity of Japan from 1970 to 2003 shows that the new model incorporating the physical concept of the rate-and-state theory performs not worse than the purely stochastic model with two free parameters only. The numerical results obtained in these applications are related to physical characters of the model as the stress change produced by an earthquake close to its edges and to the A and σ parameters of the rate-and-state constitutive law.  相似文献   

Spin state of ferric iron in MgSiO3 perovskite and its effect on elastic properties     

Krystle Catalli  Sang-Heon Shim  Vitali B. Prakapenka  Jiyong Zhao  Wolfgang Sturhahn  Paul Chow  Yuming Xiao  Haozhe Liu  Hyunchae Cynn  William J. Evans 《Earth and Planetary Science Letters》2010,289(1-2):68-75

Recent studies have indicated that a significant amount of iron in MgSiO₃ perovskite (Pv) is Fe³⁺ (Fe³⁺/ΣFe = 10–60%) due to crystal chemistry effects at high pressure (P) and that Fe³⁺ is more likely than Fe²⁺ to undergo a high-spin (HS) to low-spin (LS) transition in Pv in the mantle. We have measured synchrotron Mössbauer spectroscopy (SMS), X-ray emission spectroscopy (XES), and X-ray diffraction (XRD) of Pv with all iron in Fe³⁺ in the laser-heated diamond-anvil cell to over 100 GPa. Fe³⁺ increases the anisotropy of the Pv unit cell, whereas Fe²⁺ decreases it. In Pv synthesized above 50 GPa, Fe³⁺ enters into both the dodecahedral (A) and octahedral (B) sites approximately equally, suggesting charge coupled substitution. Combining SMS and XES, we found that the LS population in the B site gradually increases with pressure up to 50–60 GPa where all Fe³⁺ in the B site becomes LS, while Fe³⁺ in the A site remains HS to at least 136 GPa. Fe³⁺ makes Pv more compressible than Mg-endmember below 50 GPa because of the gradual spin transition in the B site together with lattice compression. The completion of the spin transition at 50–60 GPa increases bulk modulus with no associated change in density. This elasticity change can be a useful seismic probe for investigating compositional heterogeneities associated with Fe³⁺.  相似文献   

A high pressure infrared spectroscopic study of PbCO3-cerussite: constraints on the structure of the post-aragonite phase     

K. Catalli  J. Santillán  Q. Williams 《Physics and Chemistry of Minerals》2005,32(5-6):412-417

We have measured the infrared spectrum of aragonite-structured PbCO₃-cerussite to 41 GPa at 300 K in the diamond anvil cell. We observed a phase transition from an orthorhombic to a trigonal structure beginning at ~15 GPa, manifested by a splitting of the ν₂-out-of-plane bending vibration and a broadening and dramatic decrease in amplitude of the ν₁-symmetric stretching vibration of the carbonate group. While the locations of the ν₁-symmetric stretching and ν₄-in-plane bending bands are similar between the low- and high-pressure phases, their mode shifts and peak shapes change markedly near the transition. In particular, the ν₁ symmetric stretch has an essentially zero pressure shift in the high pressure phase, and its dramatically enhanced peak width indicates that it may be symmetry forbidden. The decreased mode shifts of the carbonate vibrations after the phase transition suggest that the carbonate group is less compressible in the new structure. The spectral changes observed are consistent with a small, trigonal unit cell, with space group ${P\bar{3}{1c}}$ and two formula units, instead of a previously proposed orthorhombic cell with sixteen formula units. This structure is identical to that of the high-pressure phase of BaCO₃, and likely CaCO₃ as well. Our results thus indicate that the post-aragonite, high-pressure phase of divalent-cation carbonates may be a comparatively high-symmetry trigonal structure.  相似文献