ALBERT

Description: Ozone (O3) is an important atmospheric oxidant, a greenhouse gas, and a hazard to human health and agriculture. Here we describe airborne in situ measurements and model simulations of O3 and its precursors during tropical and extratropical field campaigns over South America and Europe, respectively. Using the measurements, net ozone formation/destruction tendencies are calculated and compared to 3-D chemistry–transport model simulations. In general, observation-based net ozone tendencies are positive in the continental boundary layer and the upper troposphere at altitudes above  ∼  6 km in both environments. On the other hand, in the marine boundary layer and the middle troposphere, from the top of the boundary layer to about 6–8 km altitude, net O3 destruction prevails. The ozone tendencies are controlled by ambient concentrations of nitrogen oxides (NOx). In regions with net ozone destruction the available NOx is below the threshold value at which production and destruction of O3 balance. While threshold NO values increase with altitude, in the upper troposphere NOx concentrations are generally higher due to the integral effect of convective precursor transport from the boundary layer, downward transport from the stratosphere and NOx produced by lightning. Two case studies indicate that in fresh convective outflow of electrified thunderstorms net ozone production is enhanced by a factor 5–6 compared to the undisturbed upper tropospheric background. The chemistry–transport model MATCH-MPIC generally reproduces the pattern of observation-based net ozone tendencies but mostly underestimates the magnitude of the net tendency (for both net ozone production and destruction).

Description: G20 should initiate a global Ocean governance process and call for Ocean Economy dialogues, strategies and regional cooperation to ensure that investment and growth in ocean use become sustainable and reach their full potential.The ocean is the largest and a most critical ecosystem on Earth, with many interactions between the ocean Sustainable Development Goal (SDG14) and other SDGs. It is one of the most biologically diverse and highly productive system on the planet, and potentially the largest provider of food, materials, energy, and ecosystem services. However, past and current maritime sectors’ uses of the ocean continue to be unsustainable. Increasing demand for resources, technological advances, overfishing, climate change, pollution, biodiversity and habitat loss, along with inadequate stewardship and law enforcement, are contributing to the ocean’s decline.As a standing agenda item for the G20, and with associated good governance, a sustainable Ocean Economy can improve the health and productivity of ocean ecosystems, and reverse the current cycle of deline. Better governance, appreciation of the economic value of the ocean and ‘Blue Economy’ strategies can reduce conflicts among uses, ensure financial sustainability, ecosystem integrity and prosperity, and promote long-term national growth and employment in maritime industries.

Description: Discriminating between a creeping and a locked status of active faults is of central relevance to characterize potential rupture scenarios of future earthquakes and the associated seismic hazard for nearby population centres. In this respect, highly similar earthquakes that repeatedly activate the same patch of an active fault portion are an important diagnostic tool to identify and possibly even quantify the amount of fault creep. Here, we present a refined hypocentre catalogue for the Marmara region in northwestern Turkey, where a magnitude M up to 7.4 earthquake is expected in the near future. Based on waveform cross-correlation for selected spatial seismicity clusters, we identify two magnitude M ∼ 2.8 repeater pairs. These repeaters were identified as being indicative of fault creep based on the selection criteria applied to the waveforms. They are located below the western part of the Marmara section of the North Anatolian Fault Zone and are the largest reported repeaters for the larger Marmara region. While the eastern portion of the Marmara seismic gap has been identified to be locked, only sparse information on the deformation status has been reported for its western part. Our findings indicate that the western Marmara section deforms aseismically to a substantial extent, which reduces the probability for this region to host a nucleation point for the pending Marmara earthquake. This is of relevance, since a nucleation of the Marmara event in the west and subsequent eastward rupture propagation towards the Istanbul metropolitan region would result in a substantially higher seismic hazard and resulting risk than if the earthquake would nucleate in the east and thus propagate westward away from the population centre Istanbul.

Description: We studied spatiotemporal b-value variations along the North Anatolian Fault Zone (NAFZ) in northwestern Turkey with a focus on the combined 1999 Izmit and Düzce rupture and the eastern Sea of Marmara. We used a local seismicity catalog of the Izmit-Düzce region covering a time span from 2.5 years prior to the Izmit until 14 months after the Düzce mainshock and a four-year hypocenter catalog in the eastern Sea of Marmara. We consistently calculated moment magnitudes to ensure a homogeneous dataset and applied strict quality criteria. This allows studying variations of b-values throughout the region and at different stages of the seismic cycle. With a standard gridding technique b-value maps, depth sections and time series were calculated which reveal a very heterogeneous b-value distribution in the study area. The variety of b-value observations cannot be interpreted unambiguously, given that the b-value most likely depends on a combination of fault-zone characteristics like local stress conditions, heterogeneity of the crust and damage distribution. By presenting a comprehensive set of possible interpretations we point out that a biased discussion of the results towards stress or another individual parameter may lead to erroneous conclusions. Furthermore, the applied data discretization scheme influences the appearance of the final b-value distribution leading to potential misinterpretations.

Description: In this paper, we introduce two spatially adaptive covariance filtering methods and evaluate their effect on scatterer separation and height estimation from tomographic SAR. The first one was previously introduced for polarimetric data and uses pixel similarities based on Riemannian distances between covariance matrices. The second one is a new method extending the previous one to patch-based similarities. We show the importance of spatial adaptivity in covariance estimation by comparing the 3D reconstructions obtained with our nonlocal filters and the boxcar filter. Our experiments on simulated and L-band experimental data show the ability of the non-local filters to improve the height estimation and scatterer separation in layover areas thanks to their smoothing and edge preserving properties.

Description: In this study we analyze the nano- and picoseismicity recorded during the Fatigue Hydraulic Fracturing (FHF) in situ experiment performed in Äspö Hard Rock Laboratory, Sweden. The fracturing experiment composed of six fractures driven by three different water injection schemes (continuous, progressive and pulse pressurization) was performed during the year 2015 inside a 28 m long, horizontal borehole located at 410 m depth. The fracturing process was monitored with two different seismic networks covering a wide frequency band between 0.01 Hz and 100000 Hz, including broadband seismometers, geophones, high frequency accelerometers and acoustic emission sensors. The combined seismic network allowed for detection and detailed analysis of nearly 200 seismic events with moment magnitudes MW 〈 -4 that occurred solely during the hydraulic fracturing stages. We relocated the seismic catalog using double-difference technique and calculated the source parameters (seismic moment, source size, stress drop, focal mechanism and seismic moment tensor). The derived physical characteristics of induced seismicity are compared with the stimulation parameters as well as with the geomechanical parameters of the site.