Fluid history related to the early Eocene-middle Miocene convergent system of the Northern Apennines (Italy). Constraints from structural and isotopic studies

The late Eocene-middle Miocene erosive plate boundary between the European and the Adriatic plates is exhumed in the Northem Apennines of Italy. The fossil fault zone is 500 m thick and the outcropping portion exposes the :first 5 km of its depth. At this plate boundary basai and frontal tectonic erosion incorporated unlithified, fluid-rich sediments into the fault zone. The deformation and nature of the material along the plate boundary define a fossil subduction channel. Here we couple a detailed structural analysis of the Apennine subduction channel, focusing, in particular, on calcite veins, with a stable isotope analysis to characterize the fluid regime along an active subduction channel. The 13C and 180 composition of calcite vein and host rock samples within the fault zone indicates that there is a deep metamorphic source of fluids migrating upward along the subduction channel, in addition to locally derived fluid components. Dewatering of subducting turbidites contributes significantly only in the shallowest part of the channel. Structural observations indicate fluid flow along and across the subduction channel. At deep levels fluid flow is associated with discrete deformation events on shear faults offset by dilational jogs :filled with implosion breccias. At intennediate levels deformation is stili cyclic and associated with repeated crack-and-seal events. At the shallowest levels deformation occurred, while portions of the subducting material were stili unlithi:fied. Here the deformation was quasicontinuous, without associated vein development. Both isotope and structural analyses indicate that this erosive subduction channel behaved as a weak: fault with a vertical maximum principal stres

Low Coseismic Friction on the Tohoku-Oki Fault Determined from Temperature Measurements

The frictional resistance on a fault during slip controls earthquake dynamics. Friction dissipates heat during an earthquake; therefore, the fault temperature after an earthquake provides insight into the level of friction. The Japan Trench Fast Drilling Project (Integrated Ocean Drilling Program Expedition 343 and 343T) installed a borehole temperature observatory 16 months after the March 2011 moment magnitude 9.0 Tohoku-Oki earthquake across the fault where slip was ~50 meters near the trench. After 9 months of operation, the complete sensor string was recovered. A 0.31°C temperature anomaly at the plate boundary fault corresponds to 27 megajoules per square meter of dissipated energy during the earthquake. The resulting apparent friction coefficient of 0.08 is considerably smaller than static values for most rocks

Fluid history related to the early Eocene-middle Miocene convergent system of the Northern Apennines (Italy): Constraints from structural and isotopic studies

The late Eocene-middle Miocene erosive plate boundary between the European and Adriatic plates is exhumed in the Northern Apennines of Italy. The fossil fault zone is 500 m-thick and the outcropping portion exposes the first 5 km of its depth extent. At this plate boundary basal and frontal tectonic erosion incorporated unlithified, fluid-rich sediments into the fault zone. The deformation and nature of the material along the plate boundary define a fossil subduction channel. Here we couple a detailed structural analysis of the Apennine subduction channel, focusing in particular on calcite veins, with a stable isotope analysis to characterize the fluid regime along an active subduction channel.The 13C and 18O composition of calcite vein and host rock samples within the fault zone indicates that there is a deep metamorphic source of fluids migrating upwards along the subduction channel, in addition to locally derived fluid components. Dewatering of subducting turbidites only contributes significantly in the shallowest part of the channel. Structural observations indicate fluid flow along and across the subduction channel. At deep levels, fluid flow is associated with discrete deformation events on shear faults offset by dilational jogs filled with implosion breccias. At intermediate levels, deformation is still cyclic and associated with repeated crack-and-seal events. At the shallowest levels, deformation occurred while portions of the subducting material were still unlithified. Here the deformation is quasi-continuous without associated vein development. Both isotope and structural analyses indicate that this erosive subduction channel behaved as a weak fault with a vertical maximum principal stress

RETRIEVAL OF TROPOSPHERIC ASH CLOUDS OF MT. ETNA FROM AVHRR DATA

This paper focuses on three eruptiveevents of the Mt. Etna volcano: July 22nd 1998,April 26th 2000 and the recent eruption of July-August 2001. Such eruptions may be a severethreat to aircraft safety, as in the April 2000event. From the AVHRR visible images theheight of the top of the clouds is estimated,using geometrical methods, knowing bothNOAA satellite and Sun positions. The resultsare then compared with information derivedfrom radio-sounding data etc.. The volcanic ashparticles with diameters of 1-10 mm are notdetectable by aircraft radar but they may beremotely sensed using thermal infrared data.The well-known algorithm, based on theAVHRR channel 4 and channel 5 brightnesstemperatures difference [Prata, 1989; Schneideret al. 1994], is here applied to highlight the ashclouds of Mt. Etna volcano. Even though it wastypically used to detect and follow the volcanicclouds of stratospheric eruptions, here it is succesfullytested for tropospheric plume too.Some good results of this technique are presentedtogether with some basic problems. Thiswork points out that it could be useful to preparea procedure to monitor Mt. Etna eruption cloudsanalysing TIR data. Such a procedure shouldautomatically alert (in real time, using the newMeteosat Second Generation satellite) and indicatethe cloud direction on the basis of atmosphericradio-sounded and/or predicted data

Does subduction of mass transport deposits (MTDs) control seismic behavior of shallow–level megathrusts at convergent margins?

We present a critical appraisal of the role of subducted, medium (10–1000 km2) to giant (≥1000 km2) and heterogeneous, mud-rich mass transport deposits (MTDs) in seismic behavior and mechanisms of shallow earthquakes along subduction plate interfaces (or subduction channels) at convergent margins. Our observations from exhumed ancient subduction complexes around the world show that incorporation of mud-rich MTDs with a “chaotic” internal fabric (i.e., sedimentary mélanges or olistostromes) into subduction zones strongly modifies the structural architecture of a subduction plate interface and the physical properties of subducted material. The size and distribution of subducted MTDs with respect to the thickness of a subduction plate interface are critical factors influencing seismic behavior at convergent margins. Heterogeneous fabric and compositions of subducted MTDs may diminish the effectiveness of seismic ruptures considerably through the redistribution of overpressured fluids and accumulated strain. This phenomenon possibly favors the slow end-member of the spectrum of fault slip behavior (e.g., Slow Slip Events, Very Low Frequency Earthquakes, Non-Volcanic Tremors, creeping) compared to regular earthquakes, particularly in the shallow parts (T < 250 °C) of a subduction plate interface