Revelation of Potentially Seismic Dangerous Tectonic Structures in a View of Modern Geodynamics of the Eastern Caucasus (Azerbaijan)

The stress state of the earth’s crust in the Eastern Caucasus, located in the zone of collision junction of the North Caucasian, South Caucasian, and Central Iranian continental massifs, is a consequence of the inclusion of the Arabian indenter into the buffer structures of the southern framing of Eurasia at the continental stage of alpine tectogenesis. This evidenced from the results of geophysical observations of the structure and seismic-geodynamic activity of the region’s crust. The latter, at the neotectonic stage, was presented as underthrust of the South Caucasian microplate under the southern structures of Eurasia. The analysis and correlation of historical and recent seismic events indicate the confinement of most earthquake foci to the nodes of intersection of active faults with various orientations or to the planes of deep tectonic ruptures and lateral displacements along unstable contacts of material complexes of various competencies. The focal mechanisms of seismic events reveal various rupture types, but in general, the earthquake foci are confined to the nodes of intersection of faults of the general Caucasian and anti-Caucasian directions. Based on the observed weak seismicity, active areas of deep faults were identified, which are accepted as potential source zones.

Small-scale topography explains patterns and dynamics of dissolved organic carbon exports from the riparian zone of a temperate, forested catchment

Export of dissolved organic carbon (DOC) from riparian zones (RZs) is an important component of temperate catchment carbon budgets, but export mechanisms are still poorly understood. Here we show that DOC export is predominantly controlled by the microtopography of the RZ (lateral variability) and by riparian groundwater level dynamics (temporal variability). From February 2017 until July 2019 we studied topography, DOC quality and water fluxes and pathways in the RZ of a small forested catchment and the receiving stream in central Germany. The chemical classification of the riparian groundwater and surface water samples (n=66) by Fourier transform ion cyclotron resonance mass spectrometry revealed a cluster of plant-derived, aromatic and oxygen-rich DOC with high concentrations (DOCI) and a cluster of microbially processed, saturated and heteroatom-enriched DOC with lower concentrations (DOCII). The two DOC clusters were connected to locations with distinctly different values of the high-resolution topographic wetness index (TWIHR; at 1 m resolution) within the study area. Numerical water flow modeling using the integrated surface–subsurface model HydroGeoSphere revealed that surface runoff from high-TWIHR zones associated with the DOCI cluster (DOCI source zones) dominated overall discharge generation and therefore DOC export. Although corresponding to only 15 % of the area in the studied RZ, the DOCI source zones contributed 1.5 times the DOC export of the remaining 85 % of the area associated with DOCII source zones. Accordingly, DOC quality in stream water sampled under five event flow conditions (n=73) was closely reflecting the DOCI quality. Our results suggest that DOC export by surface runoff along dynamically evolving surface flow networks can play a dominant role for DOC exports from RZs with overall low topographic relief and should consequently be considered in catchment-scale DOC export models. We propose that proxies of spatial heterogeneity such as the TWIHR can help to delineate the most active source zones and provide a mechanistic basis for improved model conceptualization of DOC exports.

Probabilistic seismic hazard analysis for Northern Tanzania Divergence Region and the adjoining areas

This paper presents the seismic hazard levels for the Northern Tanzania Divergence (NTD) and adjoining areas by using area seismic source zones. The 15 source zones were considered based on the major geological and tectonic features, faulting style, and seismicity trends. For each source, earthquake recurrence parameters were computed by using the earthquake catalogue with events compiled from 1956 to 2011. The peak ground accelerations (PGA) and spectral accelerations (SA) at 0.2 and 2.0 second, respectively, were computed for a 10% probability of exceedance in 50 years at sites defined by a 0.1° x 0.1° grid. The recurrence parameters of 15 zones and attenuation relations developed by Akkar et al. (2014) and Chiou and Youngs (2014) were integrated in a logic tree. Obtained results that are presented as hazard maps show strong spatial variations ranging from 60 to 330 cm/s/s for PGA, from 100 to 650 cm/s/s at 0.2 sec and from 6 to 27 cm/s/s at 2 sec for 475 years mean return period and 5% damping. Hazard levels depict the general tectonic setting of the study area with the western (Eyasi-Wembere) and central (Natron-Manyara-Balangida) rift segments having relatively high PGA values compared with the eastern Pangani rift. This work provides indications of seismic hazards to policymakers and planners during planning and guidelines for earthquake-resistant design engineers. Keywords: Homogeneous Earthquakes Catalogue; GMPE; PSHA; NTD

The construction of Minor Statistical Output Areas in Iceland

This paper describes the construction of Minor Statistical Output Areas (MSOAs) in Iceland in preparation for the 2021 Population and Housing Census. It explains how these areas were generated by a partitioning algorithm in the densely populated areas, using pre-existing planning zones as the building blocks or source zones. Approximately a fifth of the MSOAs were constructed manually in the sparsely populated areas by grouping together smaller municipalities and splitting larger localities from the surrounding rural areas.

Patterns and dynamics of dissolved organic carbon exports from a riparian zone of a temperate, forested catchment

Export of dissolved organic carbon (DOC) from riparian zones (RZs) is an important, but poorly understood component of temperate catchment carbon budgets. This paper delineates explicit DOC source zones within the RZ of a small forested catchment in central Germany, and identifies and quantifies their dominant DOC export mechanism at high spatio-temporal resolution. Stream water DOC samples from differing hydrological situations were compared to riparian DOC groundwater and surface water samples and classified chemically (via Fourier-transform ion cyclotron resonance mass spectrometry) and spatially via a small-scale topographic analysis of the RZ at a resolution of 1 m. Explicit water fluxes from the resulting riparian DOC source zones were then simulated by a physically-based, fully-integrated numerical flow model (HydroGeoSphere). Chemical classification revealed two distinct DOC pools (DOCI and DOCII) in the RZ. The comparison of stream and riparian water samples indicated a predominant export of DOCI during wet conditions and high groundwater levels. The two DOC pools were spatially separated and mapped using a threshold value in high-resolution topographical wetness index (TWIHR). Hydrological modelling revealed that surface runoff from DOCI source zones with high TWIHR values dominated overall discharge generation and therefore DOC export. Although corresponding to only 15 % of the area in the studied RZ, the high TWIHR zones provided in total 1.5 times the load of DOC from the remaining 85 % of the area associated with the DOCII pool. Our results suggest that surface DOC export can play a dominant role for DOC export in RZs with overall low topographic relief and should be considered in DOC export models. We propose that proxies of spatial heterogeneity (here: TWIHR) can delineate the most active riparian source zones and provide a meaningful basis for improved model conceptualization of surficial DOC export.