Ergodicity and Earthquake Catalogs: Forecast Testing and Resulting Implications

Recently the equilibrium property of ergodicity was identified in an earthquake fault system (Tiampo et al., Phys. Rev. Lett. 91, 238501, 2003; Phys. Rev. E 75, 066107, 2007). Ergodicity in this context not only requires that the system is stationary for these networks at the applicable spatial and temporal scales, but also implies that they are in a state of metastable equilibrium, one in which the ensemble averages can be substituted for temporal averages when studying their behavior in space and time. In this work we show that this property can be used to identify those regions of parameter space which are stationary when applied to the seismicity of two naturally-occurring earthquake fault networks. We apply this measure to one particular seismicity-based forecasting tool, the Pattern Informatics index (Tiampo et al., Europhys. Lett. 60, 481–487, 2002; Rundle et al., Proc. National Acad. Sci., U.S.A., Suppl. 1, 99, 2463, 2002), in order to test the hypothesis that the identification of ergodic regions can be used to improve and optimize forecasts that rely on historic seismicity catalogs. We also apply the same measure to synthetic catalogs in order to better understand the physical process that affects this accuracy. We show that, in particular, ergodic regions defined by magnitude and time period provide more reliable forecasts of future events in both natural and synthetic catalogs, and that these improvements can be directly related to specific features or properties of the catalogs that impact the behavior of their spatial and temporal statistics.     

Energetic Particle Acceleration and Propagation in Strong CME-Less Flares

Flares and coronal mass ejections (CMEs) contribute to the acceleration and propagation of solar energetic particles (SEP) detected in the interplanetary space, but the exact roles of these phenomena are yet to be understood. We examine two types of energetic particle tracers related with 15 CME-less flares that emit bright soft X-ray bursts (GOES X class): radio emission of flare-accelerated electrons and in situ measurements of energetic electrons and protons near 1 AU. The CME-less flares are found to be vigorous accelerators of microwave-emitting electrons, which remain confined in low coronal structures. This is shown by unusually steep low-frequency microwave spectra and by lack of radio emission from the middle and high corona, including dm?–?m wave type IV continua and metre-to-hectometre type III bursts. The confinement of the particles accelerated in CME-less flares agrees with the magnetic field configuration of these events inferred by others. Two events produced isolated metric type II bursts revealing coronal shock waves. None of the seven flares in the western hemisphere was followed by enhanced particle fluxes in the GOES detectors, but one, which was accompanied by a type II burst, caused a weak SEP event detected at SoHO and ACE. Three of the CME-less flares were followed within some hours by SEP-associated flares from the same active region. These SEP-producing events were clearly distinct from the CME-less ones by their association with fast and broad CMEs, dm?–?m wave radio emission, and intense DH type III bursts. We conclude that radio emission at decimetre and longer waves is a reliable indication that flare-accelerated particles have access to the high corona and interplanetary space. The absence of such emission can be used as a signal that no SEP event is to be expected despite the occurrence of a strong soft X-ray burst.     

Atmospheric nitrogen inputs into the North Sea: effect on productivity

The ANICE (Atmospheric Nitrogen Inputs into the Coastal Ecosystem) project addressed the atmospheric deposition of nitrogen to the North Sea, with emphasis on coastal effects. ANICE focused on quantifying the deposition of inorganic nitrogen compounds to the North Sea and the governing processes. An overview of the results from modelling and experimental efforts is presented. They serve to identify the role of the atmosphere as a source of biologically essential chemical species to the marine biota. Data from the Weybourne Atmospheric Observatory (UK) are used to evaluate the effect of short episodes with very high atmospheric nitrogen concentrations. One such episode resulted in an average deposition of 0.8 mmol N m⁻² day⁻¹, which has the potential to promote primary productivity of 5.3 mmol C m⁻² day⁻¹. This value is compared to long-term effects determined from model results. The total calculated atmospheric deposition to the North Sea in 1999 is 948 kg N km⁻¹, i.e. 0.19 mmol N m⁻² day⁻¹ which has the potential to promote primary productivity of 1.2 mmol C m⁻² day⁻¹. Detailed results for August 1999 show strong gradients across the North Sea due to adjacent areas where emissions of NO_x and NH₃ are among the highest in Europe. The average atmospheric deposition to the southern part of the North Sea in August 1999 could potentially promote primary production of 2.0 mmol C m⁻² day⁻¹, i.e. 5.5% of the total production at this time of the year in this area of the North Sea. For the entire study area the atmospheric contribution to the primary production per m² is about two-third of this value. Most of the deposition occurs during short periods with high atmospheric concentrations. This atmospheric nitrogen is almost entirely anthropogenic in origin and thus represents a human-induced perturbation of the ecosystem.     

Microwave diagnostics of energetic electrons in flares

Electrons accelerated during solar flares are revealed by their electromagnetic radiation in different spectral ranges, emitted at different heights in the solar atmosphere. The observational analysis points to a common and continuous injection of particles. Based on this result, a quantitative investigation of the hard X-ray and microwave emissions observed during the 29 June, 1980 flare at 11: 40 UT has been performed. This is the first modelisation that takes into account both the inhomogeneity of the microwave source region and the dynamical evolution of the electron population. First results of our model computations demonstrate that during the most energetic phase of the event both hard X-rays and microwaves are described by electron populations resulting from the same injection function, and that the total numbers of electrons required for both emissions are compatible. Account for the inhomogeneity of the microwave source is shown to be a necessary condition for the interpretation of observed spectra.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985.     

Lunar materials: Their mineralogy,petrology and chemistry

The manned Apollo 11, 12, 14 and 15 and the automated Luna 16 lunar missions have provided us with lunar rock and regolith (soil) samples from a number of geologically distinct sites. The mare regions were sampled by Apollo 11, 12 and Luna 16, whereas Apollo 14 landed on a terrain with more relief, the Fra Mauro Formation which represents an ejecta blanket from the Imbrian Basin, and Apollo 15 touched down near the lunar highlands. The samples collected consist of a mixture, mainly of basalt, breccia and regolith (soil-particulate matter, generally < 1 cm in size). The basalts show considerable variation in texture, mineralogy and chemistry and probably represent fragments from various parts of relatively thin and extensive lava flows in the maria. The breccias represent regolith material which was indurated to varying degrees by impact events. The regolith is a product of the breakdown, again by impact, of coherent rock masses of basalt and breccia.     

Constraints on the composition of the Venus atmosphere from microwave measurements near 1.35 cm wavelength

The determination of the brightness temperature of Venus near 1.35 cm wavelength is reviewed. The observed brightness temperature is compared with models for the microwave emission based on the physical and chemical structure of the atmosphere as obtained from spacecraft. Upper limits are set on the concentrations of microwave-absorbing minor constituents. In particular, upper limits are determined for SO₂ (180 ppm) and H₂O (0.3%) for a mixing-ratio profile that is uniformly mixed up to the cloud bottom at 50 km and is rapidly depleted ($\text{scale height}\text{? 1}\text{km}\text{)}$ at higher altitudes. The total optical depth of the cloud region at or above 50 km is <0.17 at 1.35 cm wavelength. The SO₂ upper limit is only in marginal agreement with the spacecraft results, and it may be that the latter have been overestimated, or that the distribution of SO₂ is more complex than given by the uniform mixing model.     

Al depth profile in Apollo 15 drill core

Cosmic-ray-produced²⁶Al (t_1/2 = 7.05 × 10⁵ years) has been measured in the Apollo 15 long core (surface to 390 g/cm²—218 cm) for study of galactic cosmic ray production profiles, using accelerator mass spectrometry. The results are in general accord with non-destructive counting data obtained earlier, but systematically lower, and significantly higher precision. From this experiment the half-attenuation length for²⁶Al production can be calculated to be 122 g/cm² (150–400 g/cm² region) after normalizing the data to average chemical composition. The⁵³Mn (t_1/2 = 3.7 × 10⁶ years) production profile in deep cores was also compiled to date. The half-attenuation length for⁵³Mn production was calculated to be 123 g/cm² (150–400 g/cm² region).     

The age of the Roter Kamm impact crater,Namibia: Constraints from 40Ar-39Ar,K-Ar,Rb-Sr,fission track,and 10Be-26Al studies

Abstract The well-preserved 2.5 km diameter Roter Kamm impact crater is located in the Namib desert in Namibia. The impact has occurred in Precambrian granitic and granodioritic orthogneisses of the 1200–900 Ma old Namaqualand Metamorphic Complex which were partly covered by Gariep metasediments; the granites are invaded by quartz veins and quartz-feldspar-pegmatites. Previous geological field evidence suggested a crater age of about 5–10 Ma. In order to constrain this age, we selected a set of basement rocks (granites, granodiorites) exposed at the crater rim and studied the Rb-Sr, K-Ar, ⁴⁰Ar-³⁹Ar, and ¹⁰Be-²⁶Al isotopic systems as well as apatite fission track ages of these samples. The Rb-Sr isotopic systematics confirm the derivation of these samples from the Namaqualand basement (age about 1.29 Ga), which underwent Damaran orogenesis at about 650 Ma. No basement rocks with Rb-Sr ages younger than about 410 Ma were identified. The K-Ar ages of pseudotachylite and melt breccia samples show that these samples are dominated by incompletely degassed fragments of basement rocks, with some retaining their original metamorphic ages of about 470 Ma. The apatite fission track ages range from 20–28 Ma, which may be interpreted as an extension of the 25 Ma Burdigalian peneplanation event, or as incomplete resetting of the apatite fission tracks during the impact event. The ¹⁰Be and ²⁶Al exposure age of a quartz sample isolated from a quartz-pegmatite was found to be 150 ka; it is likely that the exposure of the sample began after material covering it had been removed by erosion 150 ka ago. Two glassy fractions extracted from a rim granite were dated by ⁴⁰Ar-³⁹Ar analysis. One sample gives practically a plateau age of 3.7 ± 0.3 Ma, while the other gives a minimum age of 3.6 Ma. The best available age estimate for the Roter Kamm crater is therefore 3.7 ± 0.3 Ma.     

Solar Energetic Particles and Associated EIT Disturbances in Solar Cycle 23

We explore the link between solar energetic particles (SEPs) observed at 1 AU and large-scale disturbances propagating in the solar corona, named after the Extreme ultraviolet Imaging Telescope (EIT) as EIT waves, which trace the lateral expansion of a coronal mass ejection (CME). A comprehensive search for SOHO/EIT waves was carried out for 179 SEP events during Solar Cycle 23 (1997?–?2006). 87 % of the SEP events were found to be accompanied by EIT waves. In order to test if the EIT waves play a role in the SEP acceleration, we compared their extrapolated arrival time at the footpoint of the Parker spiral with the particle onset in the 26 eastern SEP events that had no direct magnetic connection to the Earth. We find that the onset of proton events was generally consistent with this scenario. However, in a number of cases the first near-relativistic electrons were detected too early. Furthermore, the electrons had in general only weakly anisotropic pitch-angle distributions. This poses a problem for the idea that the SEPs were accelerated by the EIT wave or in any other spatially confined region in the low corona. The presence of weak electron anisotropies in SEP events from the eastern hemisphere suggests that transport processes in interplanetary space, including cross-field diffusion, play a role in giving the SEPs access to a broad range of helio-longitudes.     

The Viking biological experiments on Mars

The essential findings of the three biological experiments aboard the two Viking Mars landers are reviewed and compared. All three of the experiments yielded significant data in repeated tests of Martian surface samples. Some of the results are consistent with a biological interpretation, although there are serious reservations in accepting this conclusion. Most of the findings, however, are inconsistent with a biological basis. The combined data suggest the presence of several classes of oxidants on Mars and these would account for the most of the observations. An explanation for the apparent small synthesis of organic matter in the pyrolytic release experiment remains obscure.