Frequency-dependent Shear-wave Q Models for the Crust of China and Surrounding Regions

— Starting with fundamental-mode Rayleigh-wave attenuation coefficient values (_R) predicted by previously determined frequency-independent models of shear-wave Q (Q), we have obtained frequency-dependent Q models that explain measured values of _R as well as of Lg coda Q and its frequency dependence at 1 Hz (Q_o and , respectively) for China and some adjacent regions. The process combines trial-and-error selection of a model for the depth distribution of the frequency dependence parameter () for Q with a formal inversion for the depth distribution of Q at 1 Hz. Fifteen of the derived models have depth distributions of that are constant, or nearly constant, between the surface and a depth of 30 km. distributions that vary with depth in the upper 30 km are necessary to explain the remaining seven models. values for the depth-independent models vary between 0.4 and 0.7 everywhere except in the western portion of the Tibetan Plateau where they range between about 0.1 and 0.3 for three paths. These low values lie in a region where Q_Lg and crustal Q are very low and suggest that they should also be low for high-frequency propagation. The models in which varies with depth all show a decrease in that value ranging between 0.55 and 0.8 in the upper 15 km of the crust and (with two exceptions where =0.0) between 0.3 and 0.55 in the depth range 15–30 km. The distribution of values between 0.6 and 0.8 (the higher part of the range) in the upper crust indicates that high-frequency waves will propagate most efficiently, relative to low-frequency waves, in a band that includes, and strikes north-northeastward from the path between event 212/97 and KMI to the path between event 180/95 and station HIA in the north.Acknowledgement. We thank Lianli Cong for providing his code for plotting crustal Q models and Robert Herrmann for writing the mode summation code for computing Lg synthetics used in this study. Our work benefited from helpful discussions with Jack Xie at Lamont-Doherty Earth Observatory of Columbia University. This research was sponsored by the Defense Threat Reduction Agency Contract No. DTRA-01-00-C-0213.     

Limb darkening in the solar ultraviolet

New photoelectric limb-darkening data are given for 38 of the windows in the UV solar spectrum in which Houtgast has supplied absolute energy measurements. The region, 4000 Å to 3000 Å, is marked by unaccounted opacity. Results are given also for 13 longer wavelengths. The measurements are fully corrected for atmospheric seeing and scattering. The corrected drift curves exhibit a quasi-periodic character suggestive of the supergranulation.     

Issue indivisibility and territorial claims*

Early research on contentious issues in world politics suggested that there is an important distinction between largely tangible and largely intangible issues. Tangible issues are thought to be easier to resolve, while intangible issues can fester for long periods of time through fruitless negotiations and repeated armed conflict. Research on territorial issues has suggested that many territorial claims are driven by both tangible and intangible concerns, though, which complicates the analysis of issue tangibility. The authors argue that territorial issues with greater intangible salience (e.g. historical possessions, important homelands, sacred sites, identity ties) should be harder to resolve peacefully and should produce more frequent and severe militarized conflict. Empirical analyses of 191 territorial claims in the Americas and Western Europe (1816–2001) provide mixed support for these expectations. Territorial claims with high intangible salience are significantly more likely to experience militarized disputes and wars. Surprisingly, though, states are much more likely to strike peaceful agreements with their adversaries over territories that are valued for intangible reasons. *This research was supported by National Science Foundation grants SES-0079421 and SES-0214447.     

Cassini at Titan: the story so far

Cassini's first year examining Saturn and its moons has uncovered many surprises, not least on the enigmatic moon Titan. Nick Teanby reviews the progress made and discusses prospects for the future.