Tectonic contraction across Los Angeles after removal of groundwater pumping effects

After the 1987 Whittier Narrows and 1994 Northridge earthquakes revealed that blind thrust faults represent a significant threat to metropolitan Los Angeles, a network of 250 continuously recording global positioning system (GPS) stations was deployed to monitor displacements associated with deep slip on both blind and surface faults. Here we augment this GPS data with interferometric synthetic aperture radar imagery to take into account the deformation associated with groundwater pumping and strike-slip faulting. After removing these non-tectonic signals, we are left with 4.4 mm yr-1 of uniaxial contraction across the Los Angeles basin, oriented N 36 degrees E (perpendicular to the major strike-slip faults in the area). This indicates that the contraction is primarily accommodated on thrust faults rather than on the northeast-trending strike-slip faults. We have found that widespread groundwater and oil pumping obscures and in some cases mimics the tectonic signals expected from the blind thrust faults. In the 40-km-long Santa Ana basin, groundwater withdrawal and re-injection produces 12 mm yr-1 of long-term subsidence, accompanied by an unprecedented seasonal oscillation of 55 mm in the vertical direction and 7 mm horizontally.     

Einfluss von Streptomycin und von Tetracyclinen auf die Entwicklung keimender Samen

Summary Euler (1947) andM. L. Stein (1953) had observed that germinating seeds of barley, rye, wheat and other grasses are colourless when exposed to solutions containing more than 0.2% of streptomycin or dihydrostreptomycin. These plants are not inhibited in growth. The chlorophyll already formed is not destroyed by streptomycin.The present authors describe the bleaching effect on germinating seeds of chlortetracycline and tetracycline. These antibiotics inhibit or reduce the formation of chlorophyll in germinating seeds but the authors could not obtain this inhibition without toxic effects (reduced growth). Contrary to streptomycin, the tetracyclines are not able to precipitate nucleic acids and nucleoproteins.     

Mesozoic origin for West Indian insectivores

The highly endangered solenodons, endemic to Cuba (Solenodon cubanus) and Hispaniola (S. paradoxus), comprise the only two surviving species of West Indian insectivores. Combined gene sequences (13.9 kilobases) from S. paradoxus established that solenodons diverged from other eulipotyphlan insectivores 76 million years ago in the Cretaceous period, which is consistent with vicariance, though also compatible with dispersal. A sequence of 1.6 kilobases of mitochondrial DNA from S. cubanus indicated a deep divergence of 25 million years versus the congeneric S. paradoxus, which is consistent with vicariant origins as tectonic forces separated Cuba and Hispaniola. Efforts to prevent extinction of the two surviving solenodon species would conserve an entire lineage as old or older than many mammalian orders.     

Netrin-1-mediated axon outgrowth requires deleted in colorectal cancer-dependent MAPK activation

Neuronal growth cones are guided to their targets by attractive and repulsive guidance cues. In mammals, netrin-1 is a bifunctional cue, attracting some axons and repelling others. Deleted in colorectal cancer (Dcc) is a receptor for netrin-1 that mediates its chemoattractive effect on commissural axons, but the signalling mechanisms that transduce this effect are poorly understood. Here we show that Dcc activates mitogen-activated protein kinase (MAPK) signalling, by means of extracellular signal-regulated kinase (ERK)-1 and -2, on netrin-1 binding in both transfected cells and commissural neurons. This activation is associated with recruitment of ERK-1/2 to a Dcc receptor complex. Inhibition of ERK-1/2 antagonizes netrin-dependent axon outgrowth and orientation. Thus, activation of MAPK signalling through Dcc contributes to netrin signalling in axon growth and guidance.     

Evidence from the AD 2000 Izu islands earthquake swarm that stressing rate governs seismicity

Magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat. Such 'swarm' seismicity also migrates with time, and often exhibits a 'dog-bone'-shaped distribution. The largest earthquakes in swarms produce aftershocks that obey an Omori-type (exponential) temporal decay, but the duration of the aftershock sequences is drastically reduced, relative to normal earthquake activity. Here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion. A 1,000-fold increase in seismicity rate and a 1,000-fold decrease in aftershock duration occurred during the two-month-long dyke intrusion. We find that the seismicity rate is proportional to the calculated stressing rate, and that the duration of aftershock sequences is inversely proportional to the stressing rate. This behaviour is in accord with a laboratory-based rate/state constitutive law, suggesting an explanation for the occurrence of earthquake swarms. Any sustained increase in stressing rate--whether due to an intrusion, extrusion or creep event--should produce such seismological behaviour.