Seismic Study of an Oceanic Ridge Earthquake Swarm in the Gulf of California

Detailed seismic investigation of an unusually intense earthquake swarm which occurred in the northern Gulf of California during March 1969 has provided new information about seismic processes which occur on actively spreading oceanic ridges and has placed some constraints on the elastic wave velocities beneath them. Activity during this swarm was similar to that of a foreshock-mainshock-aftershock sequence, but with a ‘mainshock’ composed of over 70 events with magnitudes between 4 and 5.5 occurring in a 6-hr period about a day after swarm activity was initiated. ‘Aftershocks’, including many events greater than magnitude 5, continued for over two weeks. Near-source travel-time data indicate all sources located are within 5–10 km of each other and that hypocentres are confined to the upper crust. Teleseismic P-delays for rays travelling beneath this ridge may be interpreted in terms of an upper mantle with compressional velocities 5–10 per cent less than normal mantle to a depth of 200 km. Average apparent stresses for all swarm events studied are very similar, show no consistent pattern as a function of time, and are close to values obtained from other ridges. The focal mechanism solution shows a large component of normal faulting. An apparent non-orthogonality of nodal planes common to this mechanism solution and to normal faulting events on other ridges disappears when the indicated low upper mantle velocities beneath the source are taken into account. A survey of recent seismicity (post 1962) in the northern Gulf suggests seismic coupling across about 200 km between adjacent inferred spreading ridge segments. Surface waves from these Gulf Swarm earthquakes have amplitudes from one to two orders of magnitude greater than Northern Baja California events with similar short period body wave excitation

Why national health research systems matter

Some of the most outstanding problems in Computer Science (e.g. access to heterogeneous information sources, use of different e-commerce standards, ontology translation, etc.) are often approached through the identification of ontology mappings. A manual mapping generation slows down, or even makes unfeasible, the solution of particular cases of the aforementioned problems via ontology mappings. Some algorithms and formal models for partial tasks of automatic generation of mappings have been proposed. However, an integrated system to solve this problem is still missing. In this paper, we present AMON, a platform for automatic ontology mapping generation. First of all, we show the general structure. Then, we describe the current version of the system, including the ontology in which it is based, the similarity measures that it uses, the access to external sources, etc

Variations in rotational barriers of allyl and benzyl cations, anions, and radicals

High accuracy quantum chemical calculations show that the barriers to rotation of a CH2 group in the allyl cation, radical, and anion are 33, 14, and 21 kcal/mol, respectively. The benzyl cation, radical, and anion have barriers of 45, 11, and 24 kcal/mol, respectively. These barrier heights are related to the magnitude of the delocalization stabilization of each fully conjugated system. This paper addresses the question of why these rotational barriers, which at the Hückel level of theory are independent of the number of nonbonding electrons in allyl and benzyl, are in fact calculated to be factors that are of 2.4 and 4.1 higher in the cations and 1.5 and 1.9 higher in the anions than in the radicals. We also investigate why the barrier to rotation is higher for benzyl than for allyl in the cations and in the anions. Only in the radicals is the barrier for benzyl lower than that for allyl, as Hückel theory predicts should be the case. These fundamental questions in electronic structure theory, which have not been addressed previously, are related to differences in electron–electron repulsions in the conjugated and nonconjugated systems, which depend on the number of nonbonding electrons