A snapshot of the Northern Apennines (Italy) seismicity, merging catalogue and new seismic data

In this paper we present the seismicity analysis of a small sector of the Northern Apennines in 27 terms of spatio-temporal distribution, merging data from the Italian seismic bulletin with new 28 data collected by temporal seismic networks. Our attention is focused on the region enclosed 29 between Toscana, Umbria, Marche and Emilia-Romagna. This area is mainly characterized by a 30 diffuse seismicity, partly clustered in small sequences (Mw < 4.7). Improved seismicity locations, 31 together with stress field analysis allows to characterize the manner of seismogenic stress release 32 in the area. Two regions of significantly different seismic release behavior could be 33 distinguished: (i) the inner/western part (Tuscan side) of the study area, where seismicity is 34 clustered at shallow depths (<18 km) and where strong earthquakes occurred in the past, (ii) the 35 outer(eastern) part (Marche side), where the seismicity is diffuse across all of the crustal volume, 36 reaching depths of down to 30 km. 37 Along the Apenninic chain, seismicity is nearly absent inside well defined zones. In our opinion, 38 these peculiarities of seismicity release could be related to the heterogeneity of crustal volume 39 and to the transition between Tyrrhenian and Adriatic domains

Outline of a joint research project by ENEL-INGV for the study of the microseismicity in the Larderello geothermal area

The Larderello geothermal field is located ca. 100 km southeast of Florence, in the northern part of a volcanic zone that extends along the Italian Tyrrhenian coast. Geophysical investigations in the area suggest a crustal thinning and an injection of hot material from the upper mantle into the crust

Gamma-Spektrometrie zur digitalen Bodenkartierung auf Feld- und Landschaftsskala

Die feldskalige Variation von Bodeneigenschaften wird zunehmend durch geophysikalische Sensor-Erkundung abgebildet (Bodenradar, elektrische Leitfähigkeit/Widerstand). Dabei gewinnt auch die Anwendung Gamma-spektrometrischer Verfahren an Bedeutung. Sowohl boden- als auch luftgestützte kontinuierliche Messungen der natürlichen Radionuklide sind als gute Proxies für Oberbodeneigenschaften bekannt, müssen jedoch auf ihre Anwendbarkeit und Übertragbarkeit innerhalb einer Skala (z.B. Feld) und über Skalengrenzen hinweg (regionale Ansätze) getestet werden. Es soll die Frage beantwortet werden, ob Bodeneigenschaften und ihre räumliche Verteilung innerhalb der Nordostdeutschen Jungmoränenlandschaft bei vergleichbarem geologischem Ausgangsgestein durch die Gamma-Spektrometrie abgebildet und quanifiziert werden können. Zwei Landschaftsausschnitte in der Uckermark (Kraatz, 10 km² und Dedelow, 12 km²) wurden im Herbst 2014 durch eine Hubschrauberbefliegung kartiert. Innerhalb dieser beiden Gebiete wurde jeweils ein Feld (25 ha) annähernd zeitgleich mit einem Traktor-gestützten Messsystem befahren und durch Bodenuntersuchungen an 120 Referenzpunkten begleitet. Auf der Feldskala wurden die boden- und luftgestützten Gamma-spektrometrischen Verteilungskarten für die Gesamtzählraten, K, U und Th mit den punktspezifischen Bodeninformationen in Beziehung gesetzt. Für die Gebietsskala wurden vorhandene Bodenkartenwerke mit den Hubschrauber-spektrometrischen Karten verglichen. Karten unterschiedlicher Rasterzellgrößen wurden auf ihre räumliche Beziehung zu Bodentextureigenschaften an den Referenzpunkten und deren Gültigkeit bzw. Übertragbarkeit auf andere Felder untersucht. Auf der Feldskala waren die bodengestützten Gamma-Informationen in ihrer Genauigkeit an den Referenzpunkten den luftgestützten Informationen überlegen (größerer räumlicher Footprint der Hubschraubermessung). Unabhängig davon sind luftgestützte Gamma-spektroskopische Kartierungen das Mittel der Wahl, um räumliche Muster größerer Landschaftsausschnitte zu kartieren

Deep crustal earthquakes in North Tanzania, East Africa: Interplay between tectonic and magmatic processes in an incipient rift

International audienceIn this study, we explore the origin of lower crustal seismicity and the factors controlling rift propagation using seismological data recorded within the youngest part of the East African Rift System, the North Tanzanian Divergence (NTD). Most earthquakes below Lake Manyara occur at depth ranging between 20 and 40 km and have a swarm-like distribution. Focal mechanisms of 26 events indicate a combination of strike-slip and normal faulting involving Archaean basement structures and forming a relay zone. The derived local stress regime is transtensive and the minimum principal stress is oriented N110°E. Crustal seismic tomography reveals low-velocity anomalies below the rifted basins in the NTD, interpreted as localized thermomechanical perturbations promoting fluid release and subsequent seismicity in the lower crust. SKS splitting analysis in the NTD indicates seismic anisotropy beneath 17 stations most likely due to aligned magma lenses and/or dikes beneath the rift and to the lithospheric fabrics. Our results favor a strain pattern intermediate between purely mechanical and purely magmatic. We suggest that melt products arising from a large asthenospheric thermal anomaly enhance lithospheric weakening and facilitate faulting and creeping on critically oriented inherited structures of the Precambrian lower crust. Although the crust is unlikely weakened at a point comparable to other parts of the East African Rift System, this deep-seated thermomechanical process is efficient enough to allow slow rift propagation within the eastern Tanzanian cratonic edge

Application of Surface wave methods for seismic site characterization

Surface-wave dispersion analysis is widely used in geophysics to infer a shear wave velocity model of the subsoil for a wide variety of applications. A shear-wave velocity model is obtained from the solution of an inverse problem based on the surface wave dispersive propagation in vertically heterogeneous media. The analysis can be based either on active source measurements or on seismic noise recordings. This paper discusses the most typical choices for collection and interpretation of experimental data, providing a state of the art on the different steps involved in surface wave surveys. In particular, the different strategies for processing experimental data and to solve the inverse problem are presented, along with their advantages and disadvantages. Also, some issues related to the characteristics of passive surface wave data and their use in H/V spectral ratio technique are discussed as additional information to be used independently or in conjunction with dispersion analysis. Finally, some recommendations for the use of surface wave methods are presented, while also outlining future trends in the research of this topic

Airborne Electromagnetic and Radiometric Peat Thickness Mapping of a Bog in Northwest Germany (Ahlen-Falkenberger Moor)

Knowledge on peat volumes is essential to estimate carbon stocks accurately and to facilitate appropriate peatland management. This study used airborne electromagnetic and radiometric data to estimate the volume of a bog. Airborne methods provide an alternative to ground-based methods, which are labor intensive and unfeasible to capture large-scale (&gt;10 km2) spatial information. An airborne geophysical survey conducted in 2004 covered large parts of the Ahlen-Falkenberger Moor, an Atlantic peat bog (39 km2) close to the German North Sea coast. The lateral extent of the bog was derived from low radiometric and elevated surface data. The vertical extent resulted from smooth resistivity models derived from 1D inversion of airborne electromagnetic data, in combination with a steepest gradient approach, which indicated the base of the less resistive peat. Relative peat thicknesses were also derived from decreasing radiation over peatlands. The scaling factor (&micro;a = 0.28 m&minus;1) required to transform the exposure rates (negative log-values) to thicknesses was calculated using the electromagnetic results as reference. The mean difference of combined airborne results and peat thicknesses of about 100 boreholes is very small (0.0 &plusmn; 1.1 m). Although locally some (5%) deviations (&gt;2 m) from the borehole results do occur, the approach presented here enables fast peat volume mapping of large areas without an imperative necessity of borehole data