Syn-metamorphic nappe complex in the Rhodope Massif. Structure and kinematics

Mylonitic gneisses of the Bulgarian and Greek Rhodope were deformed under medium pressure-type metamorphism. The kinematic information contained in these gneisses shows that shear-deformation occurred during development of a nappe complex. Lithologies and metamorphic histories allow a lower (footwall) and an upper (hanging wall) terrane to be distinguished that define a crustal-scale duplex. As oceanic crust is involved, collision between two continental units with subsequent crustal thickening is inferred. The blocks would be Moesia to the north, and the Lower-Rhodope promontory to the south, which collided in the Mesozoic to early Cenozoic. The nappe complex is characterized by south to southwestward (foreland directed) piling-up and is associated with both coeval and subsequent extension. The late extension is associated with the establishment of a high temperature-low pressure metamorphic gradient and plutonism that predates, but makes a transition to, the lithospheric extension of the Aegean Arc.     

Assessing catch shares' effects evidence from Federal United States and associated British Columbian fisheries

What are the effects of transitioning traditionally managed fisheries to incentive-based catch shares fisheries? In a study of all major United States federal catch share fisheries and associated shared stock fisheries in British Columbia, catch shares result in environmental improvements, economic improvements, and a mixture of changes in social performance, relative to the race for fish under traditional management. Environmentally, compliance with total allowable catch increases and discards decrease. Economically, vessel yields rise, total revenues grow, and long-term stock increases are encouraged. Socially, safety increases, some port areas modestly consolidate, needed processing capacity often reduces, and labor markets shift from part time jobs to full time jobs with similar total employment. Newer catch shares address many social concerns through careful design.     

Large debris avalanches and associated eruptions in the Holocene eruptive history of Shiveluch Volcano, Kamchatka, Russia

 Shiveluch Volcano, located in the Central Kamchatka Depression, has experienced multiple flank failures during its lifetime, most recently in 1964. The overlapping deposits of at least 13 large Holocene debris avalanches cover an area of approximately 200 km² of the southern sector of the volcano. Deposits of two debris avalanches associated with flank extrusive domes are, in addition, located on its western slope. The maximum travel distance of individual Holocene avalanches exceeds 20 km, and their volumes reach ∼3 km³. The deposits of most avalanches typically have a hummocky surface, are poorly sorted and graded, and contain angular heterogeneous rock fragments of various sizes surrounded by coarse to fine matrix. The deposits differ in color, indicating different sources on the edifice. Tephrochronological and radiocarbon dating of the avalanches shows that the first large Holocene avalanches were emplaced approximately 4530–4350 BC. From ∼2490 BC at least 13 avalanches occurred after intervals of 30–900 years. Six large avalanches were emplaced between 120 and 970 AD, with recurrence intervals of 30–340 years. All the debris avalanches were followed by eruptions that produced various types of pyroclastic deposits. Features of some surge deposits suggest that they might have originated as a result of directed blasts triggered by rockslides. Most avalanche deposits are composed of fresh andesitic rocks of extrusive domes, so the avalanches might have resulted from the high magma supply rate and the repetitive formation of the domes. No trace of the 1854 summit failure mentioned in historical records has been found beyond 8 km from the crater; perhaps witnesses exaggerated or misinterpreted the events. Received: 18 August 1997 / Accepted: 19 December 1997     

Numerical Modeling of the Ston-Slano (Croatia) Aftershock Sequence

The rate of aftershock occurrence after the M6 Ston-Slano (Croatia) earthquake is modeled as the Epidemic Type Aftershock Sequence (ETAS). Increase of the modeled cumulative number of aftershocks with time was fitted to observations by the least-squares criterion using the combined grid-search and Monte-Carlo approach. This enabled not only the estimation of the most probable ETAS parameters, but also the determination of their confidence limits, as well as the estimation of the bias between them. It has been found that the bias is significant for some of the parameter pairs, regardless of the threshold magnitude assumed. Residual analyses revealed that all strong aftershocks (M _L 4.5) occurred during the periods of normal to high aftershock activity. There were two periods of quiescence in the sequence, both of which were followed by a strong aftershock.     

Comparison of the FORT approximation of the coupling ray theory with the Fourier pseudospectral method

The standard ray theory (RT) for inhomogeneous anisotropic media does not work properly or even fails when applied to S-wave propagation in inhomogeneous weakly anisotropic media or in the vicinity of shear-wave singularities. In both cases, the two shear waves propagate with similar phase velocities. The coupling ray theory was proposed to avoid this problem. In it, amplitudes of the two S waves are computed by solving two coupled, frequency-dependent differential equations along a common S-wave ray. In this paper, we test the recently developed approximation of coupling ray theory (CRT) based on the common S-wave rays obtained by first-order ray tracing (FORT). As a reference, we use the Fourier pseudospectral method (FM), which does not suffer from the limitations of the ray method and yields very accurate results. We study the behaviour of shear waves in weakly anisotropic media as well as in the vicinity of intersection, kiss or conical singularities. By comparing CRT and RT results with results of the FM, we demonstrate the clear superiority of CRT over RT in the mentioned regions as well as the dangers of using RT there.     

Mean sea level trends around the English Channel over the 20th century and their wider context

This paper provides estimates of rates of change in mean sea level around the English Channel, based on an extensive new hourly sea level data set for the south coast of the UK, derived from data archaeology. Mean sea level trends are found to vary by between 0.8 and 2.3 mm/yr around the Channel. The rates of mean sea level change are calculated by removing the coherent part of the sea level variability from the time series of annual mean sea level before fitting linear trends. The improvement in accuracy gained by using this approach is assessed by comparing trends with those calculated using the more traditional method, in which linear trends are fitted directly to the original records. Removal of the coherent part of the sea level variability allows more precise trends to be calculated from records spanning 30 years. With the traditional approach 50 years is required to obtain the same level of accuracy. Rates of vertical land movement are approximated by subtracting the mean sea level trends from the most recent regional estimate of change in sea level due to oceanographic processes only. These estimated rates are compared to measurements from geological data and advanced geodetic techniques. There is good agreement around most of the UK. However, the rates estimated from the sea level records imply that the geological data suggest too much submergence along the western and central parts of the UK south coast. Lastly, the paper evaluates whether the high rates of mean sea level rise of the last decade are unusual compared to trends observed at other periods in the historical record and finds that they are not.